88-98 FAQ's "Is your truck running weird? Check here it could help" - Page 2 - The 1947 - Present Chevrolet & GMC Truck Message Board Network

ChevyTech · 02-05-2012, 11:16 AM

Axle ratio by RPO codes.
http://67-72chevytrucks.com/vboard/s...ight=RPO+codes

http://67-72chevytrucks.com/vboard/s...67&postcount=3

Monitoring open or closed loop status on OBD1 vehicles:
http://67-72chevytrucks.com/vboard/s...4&postcount=13

Heated O2 senor upgrade & heated air intake.
http://67-72chevytrucks.com/vboard/s...3&postcount=12

http://67-72chevytrucks.com/vboard/s...=heated+sensor

Mismatched injector on 1987 4.3L light duty truck engines.
http://67-72chevytrucks.com/vboard/s...87&postcount=4

These two long threads cover most problems that can happen with the TBI fuel system trucks.
4 page thread on TBI diagnosis.
http://67-72chevytrucks.com/vboard/s...d.php?t=348308

3 Page thread that EGR fixed.
http://67-72chevytrucks.com/vboard/s...d.php?t=347247

Stalling - Code 54 – Thread covers Fuel relay & oil switch for fuel pump.
http://67-72chevytrucks.com/vboard/s...d.php?t=495054

No fuel – burnt fusible link – code 54
http://67-72chevytrucks.com/vboard/s...d.php?t=460116

Checking OBD1 computer codes without a scan tool.
http://67-72chevytrucks.com/vboard/s...5&postcount=11

V8 Vortec distributor installation & code 1345
Thanks to bwood
http://67-72chevytrucks.com/vboard/s...ighlight=P1345

scotts62 · 02-05-2012, 11:52 AM

Wow, good ones there, thanks chevytech

ChevyTech · 02-13-2012, 05:33 PM

Thank you Scott!
Here’s another one:
V8 Vortec distributor installation & code 1345
Thanks to bwood
http://67-72chevytrucks.com/vboard/s...ighlight=P1345

Drewkimble48 · 04-11-2014, 07:31 PM

I have found 2 websites that could be helpful at times and kind of gives a break down on a lot of different components.

www.aa1car.com

www.2carpros.com

butternut1972 · 02-12-2013, 10:04 PM

Great info chevytech. I have a question for you, I have a 98 W/5.7, 4WD, 1/2 ton. The problem is it stumbles at higher speeds when climbing an incline. Example-Driving on the highway at 70 and start to go up a hill it wants to stumble/shake as its trying to downshift. This happens whether I'm pulling or not. Your help is appreciated.

dragginmetal · 04-27-2013, 10:47 AM

1998 k3500 7.4
wiring diagrams
http://67-72chevytrucks.com/vboard/s...d.php?t=577359

Enginebuilder · 06-05-2013, 07:25 PM

Testing of the 88-95 EGR system:
http://67-72chevytrucks.com/vboard/s...d.php?t=583327

FrankieD · 10-10-2013, 01:21 PM

I didn't see this any where. So a a few years ago I replaced the 350 in my 95 K2500 PU with a 350 from a 88 K1500 Suburban after I got it all together and drove it the Trans didn't shift right and before the swap I had no problems with the trans so I started swapping all the electronics and sensors from the 95 350 and still no good. I only had one more thing that I could change and that was the Knock Sensor which I didn't think could have anything to do with the trans. After changing it the trans shifted fine turned out the part number of the sensors were one number different. Hope this helps somebody doing the same swap.

Dirty South 504 · 12-09-2013, 12:05 AM

I have a 95 c 1500, 350 5.7 TBI I am having problems with the truck starting sometimes.Engine wants to turn over,but doesn't until I pump the gas pedal a few times then the engine starts and runs.Fuel or electric issue? Or both?

dragginmetal · 01-12-2014, 09:31 AM

Identifying Drop Spindles & How to cut Coil Springs.
http://67-72chevytrucks.com/vboard/s...21#post6466621

oldmans88 · 03-29-2014, 09:21 PM

Just got my 1988 Chevy Silverado 350 auto tranny 196000 miles. Seems to run good but in drive with brake on, oil pressure drops to almost 0. I am the 4th owner, 2 older men and an older woman.

bufmatmuslepants · 07-23-2014, 06:48 AM

Stumble only at idle yet normal power everywhere else? Black smoke from the exhaust when you stab the throttle after idling for a few seconds? Do the paper on the exhaust pipe trick, if it gets sucked in, most likely an exhaust valve not sealing, could be a burnt valve, stuck open from carbon, or in my case, a bad mechanic lashed the exhaust valve too tight. The low rpm does not allow the cylinder to build enough pressure to ignite the fuel, at higher rpm the increased piston speed moving the air faster builds enough pressure before it can leak out the exhaust valve to ignite the fuel, hence only the stumble at idle.

http://67-72chevytrucks.com/vboard/s...d.php?t=635082

Drewkimble48 · 11-05-2014, 09:04 PM

For you TBI guys, I found a great website that shows you how to test sensors and breaks down what things to check for certain symptons your vehicle is having.

http://www.tbiparts.com/techinfo.html

Big Ugly · 11-23-2015, 04:11 PM

I am having a few things going on with my 96 Sierra SLE 5.7L 1500 ECSB. First, my gas mileage has dropped off considerably in this past year. I was getting 15 around town, 19 on highway now it is 12.5 city, 17 highway. I have a slight stumble at idle when the engine is 'hot' (more on that later) but no engine codes are thrown for O2 sensors. My scan tool picks up nothing.

The 2nd thing weird is that the temp gauge reads at 120*. I have switched both temp sensors, but nothing is making a difference. Is there any way to test the actual temp of my truck if the gauge is off?

Any help will be most welcome.
Posted via Mobile Device

ChevyTech · 04-24-2016, 11:01 AM

TBI (Throttle Body Injection) powered trucks, common problems.
In one spot, as short as I could make this post.

It is common for the gasket under the TBI unit to leak vacuum causing idle issues.
The throttle shaft can wear the housing creating a vacuum leak on the driver’s side of the TBI unit.

Testing the fuel pressure is a good idea if the idle is erratic or poor. I wish they would have put fuel pressure test ports on these trucks. The fuel filter, fuel pump, fuel pressure regulator (broken spring) and the rubber that connects the fuel pump to the sending unit are all possible causes of low fuel pressure. Low fuel pressure on these TBI trucks shows up as a poor erratic idle, and slow – hard starting, and just because it runs ok on the the freeway under heavy throttle you should not think it has good fuel pressure.

On these distributors the housing/upper bushing area gets so worn out that the shaft will move sideways so far that the points on the pickup coil pole piece get hit by the reluctor points on the shaft. When this happens the ECM receives compromised signal for RPM and timing issues. These distributors can also have problems because of loss of magnetism needed for the pickup coil to work, which cause more problems at low RPMs. If the magnetic material is cracked in pieces you should replace the shaft or the entire distributor.

Distributor modules are a common failure part. They can fail as they heat up. They can fail causing a no start, because of no spark. They can cause the injectors to not get triggered by the ECM even if there is spark. Or they can fail causing all kinds of poor running conditions. Many parts stores can test them. Make SURE you use heat sink compound under the module when you install it, or heat made in the module can't get dissipated and will destroy the module. Many replacement modules fail VERY quickly.

A bad TPS can make it so that the ECM does not know the correct throttle position and the ECM will not move the IAC. A TPS that shows wide open throttle can cause a lack of fuel for starting the engine because the system goes into the clear flood mode and cuts the fuel injected.

Coolant sensor failure on the sensor the the computer uses to set the mixture can cause the mixture the engine gets to be wrong. The most common problem it causes is a mixture that is too rich.

EGR valves can get carbon chunks holding them open. They can also drag on one side of the plunger and catch, sticking open at times. The EGR solenoids can also leak vacuum to the EGR valve at idle. If there is ever vacuum getting to the EGR at idle, unplug the electrical connecter to rule out an electrical problem, and if there is still vacuum getting to the EGR valve at idle replace the EGR solenoid. The solenoids can suck dirt in and stick.

The most common EGR system on the light duty TBI trucks is a “Negative Back-pressure” EGR system in which the EGR valve itself modulates the EGR opening. This system is very picky about the EGR valve operation and low quality replacement EGR valves can cause drive-ability problems that people are unable to find the cause of.

A common condition caused bad a bad EGR valve is a hesitation, or flat spot, at light throttle acceleration.

The TBI trucks from 1987 to 1995 are the OBD1 system and the computer trouble codes can be read without a scan tool. All you need is a paper clip.

You must unplug the set timing connector (wire) to set the ignition timing on these trucks, and if you don't the timing will be wrong. This will set a trouble code.

As these trucks age head gaskets leaking between the cylinders is a problem. As the head gasket fails, often the first symptom is pinging, and sometimes it causes a trouble code caused by high knock counts.

The none-roller lifters used in these engine along with the changes in motor oil removing ZDDP has shown up in the number of flat cam lobes on high miles engines.

Trying a different brand of gas is another thing you can try. It has been my experience that the TBI trucks do not idle as well on ethanol fuel and as they raised the ethanol content this was noticed by many people.

With a search you should be able to find discussion on all these topics in old threads.

T_RAV · 08-09-2016, 09:22 PM

Hey guys, I have a 97 Sierra 4.3L V6. It idles just fine and under acceleration runs just fine but, at a steady pace, no matter the speed, it kicks/bucks/jerks and has actually backfired once. Always has since the day I bought it. I did notice when I was doing a tune up recently, there is a small chip in the base of the platic distributor where the cap seals to it....could this be my problem? I bought a distributor from a local junk yard but haven't put it on yet.

Any suggestions?

98extracab · 10-29-2016, 03:12 AM

Quote:

Originally Posted by ChevyTech

TBI (Throttle Body Injection) powered trucks, common problems.
In one spot, as short as I could make this post.

It is common for the gasket under the TBI unit to leak vacuum causing idle issues.
The throttle shaft can wear the housing creating a vacuum leak on the driver’s side of the TBI unit.

Testing the fuel pressure is a good idea if the idle is erratic or poor. I wish they would have put fuel pressure test ports on these trucks. The fuel filter, fuel pump, fuel pressure regulator (broken spring) and the rubber that connects the fuel pump to the sending unit are all possible causes of low fuel pressure. Low fuel pressure on these TBI trucks shows up as a poor erratic idle, and slow – hard starting, and just because it runs ok on the the freeway under heavy throttle you should not think it has good fuel pressure.

On these distributors the housing/upper bushing area gets so worn out that the shaft will move sideways so far that the points on the pickup coil pole piece get hit by the reluctor points on the shaft. When this happens the ECM receives compromised signal for RPM and timing issues. These distributors can also have problems because of loss of magnetism needed for the pickup coil to work, which cause more problems at low RPMs. If the magnetic material is cracked in pieces you should replace the shaft or the entire distributor.

Distributor modules are a common failure part. They can fail as they heat up. They can fail causing a no start, because of no spark. They can cause the injectors to not get triggered by the ECM even if there is spark. Or they can fail causing all kinds of poor running conditions. Many parts stores can test them. Make SURE you use heat sink compound under the module when you install it, or heat made in the module can't get dissipated and will destroy the module. Many replacement modules fail VERY quickly.

A bad TPS can make it so that the ECM does not know the correct throttle position and the ECM will not move the IAC. A TPS that shows wide open throttle can cause a lack of fuel for starting the engine because the system goes into the clear flood mode and cuts the fuel injected.

Coolant sensor failure on the sensor the the computer uses to set the mixture can cause the mixture the engine gets to be wrong. The most common problem it causes is a mixture that is too rich.

EGR valves can get carbon chunks holding them open. They can also drag on one side of the plunger and catch, sticking open at times. The EGR solenoids can also leak vacuum to the EGR valve at idle. If there is ever vacuum getting to the EGR at idle, unplug the electrical connecter to rule out an electrical problem, and if there is still vacuum getting to the EGR valve at idle replace the EGR solenoid. The solenoids can suck dirt in and stick.

The most common EGR system on the light duty TBI trucks is a “Negative Back-pressure” EGR system in which the EGR valve itself modulates the EGR opening. This system is very picky about the EGR valve operation and low quality replacement EGR valves can cause drive-ability problems that people are unable to find the cause of.

A common condition caused bad a bad EGR valve is a hesitation, or flat spot, at light throttle acceleration.

The TBI trucks from 1987 to 1995 are the OBD1 system and the computer trouble codes can be read without a scan tool. All you need is a paper clip.

You must unplug the set timing connector (wire) to set the ignition timing on these trucks, and if you don't the timing will be wrong. This will set a trouble code.

As these trucks age head gaskets leaking between the cylinders is a problem. As the head gasket fails, often the first symptom is pinging, and sometimes it causes a trouble code caused by high knock counts.

The none-roller lifters used in these engine along with the changes in motor oil removing ZDDP has shown up in the number of flat cam lobes on high miles engines.

Trying a different brand of gas is another thing you can try. It has been my experience that the TBI trucks do not idle as well on ethanol fuel and as they raised the ethanol content this was noticed by many people.

With a search you should be able to find discussion on all these topics in old threads.

My friend has a 94 5.7 and at around 1500 rpm or so and deceleration it hesitates/bogs and has a code 43. We had recently changed the motor out because it was knocking and it ran great until about a week after and started having these issues. From what I read on the egr failure it seems more like that. He still has his old egr valve and will be throwing it on since there were no codes when that engine was in. But I was just wanting an input to see if that may be the issue.

Chevyaz · 10-02-2016, 05:28 PM

Ive found out more great information on this thread dam. Very good job. Thanks very much. Brand new to this forum.

Chevyaz · 10-29-2016, 10:28 AM

Thats great information. Good work.

diveplane · 11-14-2016, 12:50 AM

whats the part number for the sensor sends a signal to temp gauge in dash

i think mine is reading wrong temp

i know theres 2 temp sensors in the engine block right v6 vortec 1994,
i have 2 new radiator hoses to replace and thermostat , also want to replace this sensor.

thx in advance.

jchav62 · 07-18-2017, 01:28 PM

I was just asked a question...

What are the different auto transmissions offered for 88-98? (half tons)

I think the first few years were 700r4, up to 1991?
Then 1992 and up were 4L60e's? Were they all the same up to the body style change?

diveplane · 07-27-2017, 11:57 AM

ok need help

i just installed a full brand new exhaust system from y pipe new cat all the way down including new tail pipe, and o2 oxygen sensor.

most cases the check engine lamp stays off, but it comes on off intermittent.
code am getting is a code 44 lean mixture

how can i resolve this one?

its a bosh o2 oxygen i put on , what other o2 units work?, engine is a 1994 v6 vortec 4.3
manual 5 speed.

i tried a reset on computer , code keeps coming back.

diveplane · 12-13-2017, 10:48 PM

bump anyone know what brand of 02 chevy slammed on at the factory?

shifty · 03-29-2019, 08:40 AM

If the sticky is still going to be made, awesome write-up for how to handle air conditioning issues, replacement of compressor, AC not working etc.

http://67-72chevytrucks.com/vboard/s...d.php?t=783964

knifeman1 · 05-15-2019, 08:58 PM

I just got my first late model crew cab project truck. Its an all original 88 TBI 350. The truck seems to run pretty well but at low idle when in gear it struggles and acts like and sometimes dies. I was going to put new fuel pumps in and new sending units and check the little hose. Did they put a pump in each tank or was it one pump outside the tanks? Has anyone had one act like it wants to die when in gear and stopped?

Thanks!

02-05-2012, 11:16 AM	#1
ChevyTech Registered User Join Date: May 2004 Location: Minnesota Posts: 4,620	Re: 88-98 FAQ's "Is your truck running weird? Check here it could help" Axle ratio by RPO codes. http://67-72chevytrucks.com/vboard/s...ight=RPO+codes http://67-72chevytrucks.com/vboard/s...67&postcount=3 Monitoring open or closed loop status on OBD1 vehicles: http://67-72chevytrucks.com/vboard/s...4&postcount=13 Heated O2 senor upgrade & heated air intake. http://67-72chevytrucks.com/vboard/s...3&postcount=12 http://67-72chevytrucks.com/vboard/s...=heated+sensor Mismatched injector on 1987 4.3L light duty truck engines. http://67-72chevytrucks.com/vboard/s...87&postcount=4 These two long threads cover most problems that can happen with the TBI fuel system trucks. 4 page thread on TBI diagnosis. http://67-72chevytrucks.com/vboard/s...d.php?t=348308 3 Page thread that EGR fixed. http://67-72chevytrucks.com/vboard/s...d.php?t=347247 Stalling - Code 54 – Thread covers Fuel relay & oil switch for fuel pump. http://67-72chevytrucks.com/vboard/s...d.php?t=495054 No fuel – burnt fusible link – code 54 http://67-72chevytrucks.com/vboard/s...d.php?t=460116 Checking OBD1 computer codes without a scan tool. http://67-72chevytrucks.com/vboard/s...5&postcount=11 V8 Vortec distributor installation & code 1345 Thanks to bwood http://67-72chevytrucks.com/vboard/s...ighlight=P1345 __________________ For those of you that are wondering why you are not getting replies to your thread: Did you give the model, year, engine, fuel system type, and transmission information? If it is modified from what came stock from the factory, let us know that too. Last edited by scotts62; 11-08-2012 at 10:02 PM.

02-05-2012, 11:52 AM	#2
scotts62 One day... Join Date: Apr 2008 Location: Tuttle, Ok Posts: 9,240	Re: 88-98 FAQ's "Is your truck running weird? Check here it could help" Wow, good ones there, thanks chevytech __________________ Scott 93 crew cab build Project 62

02-13-2012, 05:33 PM	#3
ChevyTech Registered User Join Date: May 2004 Location: Minnesota Posts: 4,620	Re: 88-98 FAQ's "Is your truck running weird? Check here it could help" Thank you Scott! Here’s another one: V8 Vortec distributor installation & code 1345 Thanks to bwood http://67-72chevytrucks.com/vboard/s...ighlight=P1345 __________________ For those of you that are wondering why you are not getting replies to your thread: Did you give the model, year, engine, fuel system type, and transmission information? If it is modified from what came stock from the factory, let us know that too. Last edited by ChevyTech; 02-13-2012 at 05:47 PM.

04-11-2014, 07:31 PM	#4
Drewkimble48 Registered User Join Date: Dec 2013 Location: Addison TX Posts: 142	Re: 88-98 FAQ's "Is your truck running weird? Check here it could help" I have found 2 websites that could be helpful at times and kind of gives a break down on a lot of different components. www.aa1car.com www.2carpros.com

02-12-2013, 10:04 PM	#5
butternut1972 Registered User Join Date: May 2009 Location: longview,wa Posts: 1,094	Re: 88-98 FAQ's "Is your truck running weird? Check here it could help" Great info chevytech. I have a question for you, I have a 98 W/5.7, 4WD, 1/2 ton. The problem is it stumbles at higher speeds when climbing an incline. Example-Driving on the highway at 70 and start to go up a hill it wants to stumble/shake as its trying to downshift. This happens whether I'm pulling or not. Your help is appreciated. __________________ 1972 GMC (PROJECT LONG OVERDUE) 1998 SWB 4WD

04-27-2013, 10:47 AM	#6
dragginmetal here, just not logged in Join Date: Nov 2007 Location: Tx Posts: 1,011	Re: 88-98 FAQ's "Is your truck running weird? Check here it could help" 1998 k3500 7.4 wiring diagrams http://67-72chevytrucks.com/vboard/s...d.php?t=577359 __________________ Mike 88 GMC "GOT BORED" several truck pics a few '88-'98 pics more pics

06-05-2013, 07:25 PM	#7
Enginebuilder Registered User Join Date: Jun 2011 Location: Palmer AK Posts: 68	Re: 88-98 FAQ's "Is your truck running weird? Check here it could help" Testing of the 88-95 EGR system: http://67-72chevytrucks.com/vboard/s...d.php?t=583327 __________________ Enginebuilder (Eric) 1995 K2500 w/5.7 & A/T Alaskan Members Check In http://67-72chevytrucks.com/vboard/s...22#post5094422

10-10-2013, 01:21 PM	#8
FrankieD Registered User Join Date: Jan 2011 Location: Gilberts IL. Posts: 2,488	Re: 88-98 FAQ's "Is your truck running weird? Check here it could help" I didn't see this any where. So a a few years ago I replaced the 350 in my 95 K2500 PU with a 350 from a 88 K1500 Suburban after I got it all together and drove it the Trans didn't shift right and before the swap I had no problems with the trans so I started swapping all the electronics and sensors from the 95 350 and still no good. I only had one more thing that I could change and that was the Knock Sensor which I didn't think could have anything to do with the trans. After changing it the trans shifted fine turned out the part number of the sensors were one number different. Hope this helps somebody doing the same swap. __________________ 94 k2500 EXCab Long Bed 350ci New Toy 95 K2500 Suburban New PlowTruck 454ci Support our Troops @ http://anyairman.com http://www.woundedwarriorproject.org/

12-09-2013, 12:05 AM	#9
Dirty South 504 Registered User Join Date: Nov 2013 Location: New Orleans,La. Posts: 24	Re: 88-98 FAQ's "Is your truck running weird? Check here it could help" I have a 95 c 1500, 350 5.7 TBI I am having problems with the truck starting sometimes.Engine wants to turn over,but doesn't until I pump the gas pedal a few times then the engine starts and runs.Fuel or electric issue? Or both?

01-12-2014, 09:31 AM	#10
dragginmetal here, just not logged in Join Date: Nov 2007 Location: Tx Posts: 1,011	Re: 88-98 FAQ's "Is your truck running weird? Check here it could help" Identifying Drop Spindles & How to cut Coil Springs. http://67-72chevytrucks.com/vboard/s...21#post6466621 __________________ Mike 88 GMC "GOT BORED" several truck pics a few '88-'98 pics more pics

03-29-2014, 09:21 PM	#11
oldmans88 Registered User Join Date: Mar 2014 Location: Anderson, SC Posts: 1	Re: 88-98 FAQ's "Is your truck running weird? Check here it could help" Just got my 1988 Chevy Silverado 350 auto tranny 196000 miles. Seems to run good but in drive with brake on, oil pressure drops to almost 0. I am the 4th owner, 2 older men and an older woman.

07-23-2014, 06:48 AM	#12
bufmatmuslepants Junior Member Join Date: May 2007 Location: Hampstead, NC Posts: 313	Re: 88-98 FAQ's "Is your truck running weird? Check here it could help" Stumble only at idle yet normal power everywhere else? Black smoke from the exhaust when you stab the throttle after idling for a few seconds? Do the paper on the exhaust pipe trick, if it gets sucked in, most likely an exhaust valve not sealing, could be a burnt valve, stuck open from carbon, or in my case, a bad mechanic lashed the exhaust valve too tight. The low rpm does not allow the cylinder to build enough pressure to ignite the fuel, at higher rpm the increased piston speed moving the air faster builds enough pressure before it can leak out the exhaust valve to ignite the fuel, hence only the stumble at idle. http://67-72chevytrucks.com/vboard/s...d.php?t=635082 __________________ 1979 K10 reg cab short bed 33x12.50s - GONE 1988 4x4 reg cab long bed 337k miles - GONE 1995 Z71 GU6 G80 F44 ext cab short bed 149k 305/70/16s - GONE 1995 NZZ GT4 2dr Tahoe 3" lift 14 bolt sf 155k 305/70/16s - GONE 1994 Z28 M6 1995 Z71 GT4 G80 ext cab short bed 215k GONE 1997 GT4 G80 Yukon 4 door leather, sunroof 168k miles GONE 2003 Avalanche Z71 GT4 G80 165k miles

11-05-2014, 09:04 PM	#13
Drewkimble48 Registered User Join Date: Dec 2013 Location: Addison TX Posts: 142	Re: 88-98 FAQ's "Is your truck running weird? Check here it could help" For you TBI guys, I found a great website that shows you how to test sensors and breaks down what things to check for certain symptons your vehicle is having. http://www.tbiparts.com/techinfo.html

11-23-2015, 04:11 PM	#14
Big Ugly Registered User Join Date: Dec 2013 Location: Gloucester, VA Posts: 1	Re: 88-98 FAQ's "Is your truck running weird? Check here it could help" I am having a few things going on with my 96 Sierra SLE 5.7L 1500 ECSB. First, my gas mileage has dropped off considerably in this past year. I was getting 15 around town, 19 on highway now it is 12.5 city, 17 highway. I have a slight stumble at idle when the engine is 'hot' (more on that later) but no engine codes are thrown for O2 sensors. My scan tool picks up nothing. The 2nd thing weird is that the temp gauge reads at 120. I have switched both temp sensors, but nothing is making a difference. Is there any way to test the actual temp of my truck if the gauge is off? Any help will be most welcome. Posted via Mobile Device*

04-24-2016, 11:01 AM	#15
ChevyTech Registered User Join Date: May 2004 Location: Minnesota Posts: 4,620	Re: 88-98 FAQ's "Is your truck running weird? Check here it could help" TBI (Throttle Body Injection) powered trucks, common problems. In one spot, as short as I could make this post. It is common for the gasket under the TBI unit to leak vacuum causing idle issues. The throttle shaft can wear the housing creating a vacuum leak on the driver’s side of the TBI unit. Testing the fuel pressure is a good idea if the idle is erratic or poor. I wish they would have put fuel pressure test ports on these trucks. The fuel filter, fuel pump, fuel pressure regulator (broken spring) and the rubber that connects the fuel pump to the sending unit are all possible causes of low fuel pressure. Low fuel pressure on these TBI trucks shows up as a poor erratic idle, and slow – hard starting, and just because it runs ok on the the freeway under heavy throttle you should not think it has good fuel pressure. On these distributors the housing/upper bushing area gets so worn out that the shaft will move sideways so far that the points on the pickup coil pole piece get hit by the reluctor points on the shaft. When this happens the ECM receives compromised signal for RPM and timing issues. These distributors can also have problems because of loss of magnetism needed for the pickup coil to work, which cause more problems at low RPMs. If the magnetic material is cracked in pieces you should replace the shaft or the entire distributor. Distributor modules are a common failure part. They can fail as they heat up. They can fail causing a no start, because of no spark. They can cause the injectors to not get triggered by the ECM even if there is spark. Or they can fail causing all kinds of poor running conditions. Many parts stores can test them. Make SURE you use heat sink compound under the module when you install it, or heat made in the module can't get dissipated and will destroy the module. Many replacement modules fail VERY quickly. A bad TPS can make it so that the ECM does not know the correct throttle position and the ECM will not move the IAC. A TPS that shows wide open throttle can cause a lack of fuel for starting the engine because the system goes into the clear flood mode and cuts the fuel injected. Coolant sensor failure on the sensor the the computer uses to set the mixture can cause the mixture the engine gets to be wrong. The most common problem it causes is a mixture that is too rich. EGR valves can get carbon chunks holding them open. They can also drag on one side of the plunger and catch, sticking open at times. The EGR solenoids can also leak vacuum to the EGR valve at idle. If there is ever vacuum getting to the EGR at idle, unplug the electrical connecter to rule out an electrical problem, and if there is still vacuum getting to the EGR valve at idle replace the EGR solenoid. The solenoids can suck dirt in and stick. The most common EGR system on the light duty TBI trucks is a “Negative Back-pressure” EGR system in which the EGR valve itself modulates the EGR opening. This system is very picky about the EGR valve operation and low quality replacement EGR valves can cause drive-ability problems that people are unable to find the cause of. A common condition caused bad a bad EGR valve is a hesitation, or flat spot, at light throttle acceleration. The TBI trucks from 1987 to 1995 are the OBD1 system and the computer trouble codes can be read without a scan tool. All you need is a paper clip. You must unplug the set timing connector (wire) to set the ignition timing on these trucks, and if you don't the timing will be wrong. This will set a trouble code. As these trucks age head gaskets leaking between the cylinders is a problem. As the head gasket fails, often the first symptom is pinging, and sometimes it causes a trouble code caused by high knock counts. The none-roller lifters used in these engine along with the changes in motor oil removing ZDDP has shown up in the number of flat cam lobes on high miles engines. Trying a different brand of gas is another thing you can try. It has been my experience that the TBI trucks do not idle as well on ethanol fuel and as they raised the ethanol content this was noticed by many people. With a search you should be able to find discussion on all these topics in old threads. __________________ For those of you that are wondering why you are not getting replies to your thread: Did you give the model, year, engine, fuel system type, and transmission information? If it is modified from what came stock from the factory, let us know that too. Last edited by ChevyTech; 04-24-2016 at 11:09 AM.



Register or Log In To remove these advertisements.

08-09-2016, 09:22 PM	#16
T_RAV Registered User Join Date: Aug 2016 Location: Topeka KS Posts: 4	Re: 88-98 FAQ's "Is your truck running weird? Check here it could help" Hey guys, I have a 97 Sierra 4.3L V6. It idles just fine and under acceleration runs just fine but, at a steady pace, no matter the speed, it kicks/bucks/jerks and has actually backfired once. Always has since the day I bought it. I did notice when I was doing a tune up recently, there is a small chip in the base of the platic distributor where the cap seals to it....could this be my problem? I bought a distributor from a local junk yard but haven't put it on yet. Any suggestions?

10-02-2016, 05:28 PM	#18
Chevyaz Registered User Join Date: Oct 2016 Location: Mesa Az Posts: 46	Re: 88-98 FAQ's "Is your truck running weird? Check here it could help" Ive found out more great information on this thread dam. Very good job. Thanks very much. Brand new to this forum.

10-29-2016, 10:28 AM	#19
Chevyaz Registered User Join Date: Oct 2016 Location: Mesa Az Posts: 46	Re: 88-98 FAQ's "Is your truck running weird? Check here it could help" Thats great information. Good work.

11-14-2016, 12:50 AM	#20
diveplane Registered User Join Date: Nov 2016 Location: Tulsa Posts: 418	Re: 88-98 FAQ's "Is your truck running weird? Check here it could help" whats the part number for the sensor sends a signal to temp gauge in dash i think mine is reading wrong temp i know theres 2 temp sensors in the engine block right v6 vortec 1994, i have 2 new radiator hoses to replace and thermostat , also want to replace this sensor. thx in advance.

07-18-2017, 01:28 PM	#21
jchav62 1962 C-10 Join Date: Apr 2005 Location: Las Vegas, New Mexico Posts: 4,978	Re: 88-98 FAQ's "Is your truck running weird? Check here it could help" I was just asked a question... What are the different auto transmissions offered for 88-98? (half tons) I think the first few years were 700r4, up to 1991? Then 1992 and up were 4L60e's? Were they all the same up to the body style change? __________________ Joseph Chavez "See the USA in a Chevrolet!!" ......................_____ .........________//__{\_____ ,,,,,,,/__(O)___//___/__(O)_/ 1962 C10 Shortbed Fleetside 327/th350 GV overdrive 1974 C10 Longbed Fleetside 350/th350 "The Trash Truck" 1999 Chevy 2500 OBS, Longbed 5.7/4L80E 4x4 2015 GMC Sierra SLE 1500 4x4

07-27-2017, 11:57 AM	#22
diveplane Registered User Join Date: Nov 2016 Location: Tulsa Posts: 418	Re: 88-98 FAQ's "Is your truck running weird? Check here it could help" ok need help i just installed a full brand new exhaust system from y pipe new cat all the way down including new tail pipe, and o2 oxygen sensor. most cases the check engine lamp stays off, but it comes on off intermittent. code am getting is a code 44 lean mixture how can i resolve this one? its a bosh o2 oxygen i put on , what other o2 units work?, engine is a 1994 v6 vortec 4.3 manual 5 speed. i tried a reset on computer , code keeps coming back.

12-13-2017, 10:48 PM	#23
diveplane Registered User Join Date: Nov 2016 Location: Tulsa Posts: 418	Re: 88-98 FAQ's "Is your truck running weird? Check here it could help" bump anyone know what brand of 02 chevy slammed on at the factory?

03-29-2019, 08:40 AM	#24
shifty Questionable Join Date: Mar 2005 Location: Atlanta Posts: 13,376	Re: 88-98 FAQ's "Is your truck running weird? Check here it could help" If the sticky is still going to be made, awesome write-up for how to handle air conditioning issues, replacement of compressor, AC not working etc. http://67-72chevytrucks.com/vboard/s...d.php?t=783964 __________________ If I've got anything up for grabs, it'll be here: 7-hole gauge cluster for a 67-72 p/u FREE (link) I can't check the forum daily. If I don't reply to you within 24 hours, drop me a PM! I'm (hopefully) still alive and will reply faster to a PM.

05-15-2019, 08:58 PM	#25
knifeman1 Registered User Join Date: Dec 2011 Location: Franklin TN Posts: 5	Re: 88-98 FAQ's "Is your truck running weird? Check here it could help" I just got my first late model crew cab project truck. Its an all original 88 TBI 350. The truck seems to run pretty well but at low idle when in gear it struggles and acts like and sometimes dies. I was going to put new fuel pumps in and new sending units and check the little hose. Did they put a pump in each tank or was it one pump outside the tanks? Has anyone had one act like it wants to die when in gear and stopped? Thanks!

Register or Log In To remove these advertisements.