Need help diagnosing problem on uncle's 1996 Silverado - The 1947 - Present Chevrolet & GMC Truck Message Board Network

67ss&99ss · 01-02-2010, 11:09 PM

I went to my uncle's house today to pick up a few spare parts for my 69 C/10. While there, we drove his truck, a 1996 3500 Silverado, 454 automatic. When I first got in the truck, it started great, and we drove about 10 miles to see a friend for an hour or so. Got back in the truck, and it acted like it did not want to start. I got it to start by pressing and holding the accelerator to the floor. The truck idled rough, very rich and did not want to stay running below 2,000 rpm. I was able to get it back to his house by fortunately. It never ran hot and no check engine light, or service engine soon light came on.

I tried the following to repair it with no success.

Disconnected the battery then, removed the mass air flow sensor and cleaned it with an aerosol mass air flow cleaner. Removed throttle body, then removed the throttle position sensor and the idle air control sensor from the throttle body. I cleaned the TB with an aerosol TB cleaner and a tooth brush and let it dry. I replaced the throttle position sensor and idle air control sensor, then reinstalled the TB and MAF. Then reconnected the battery(about 30 minutes disconnected). Tried starting the truck again and the only way it would start was by holding the accelerator to the floor. The truck still had all the same problems. It was running so rich my eyes were burning.

The only other things left that I can think of that would cause this problem would be a MAP sensor or oxygen sensor. Could an ignition coil or ignition module be the culprit? Any ideas?

BigBlocksRule · 01-03-2010, 10:43 AM

Intake coolant temp sensor, right on the front of the intake. When it goes out, the engine thinks it's suuuuper cold and pumps fuel like nobody's business to try to heat it up. Been there, done that, now carry a spare. Easy way to check is get a new one (cheap), unplug the old one and plug into the new one, laying on the intake, no need to thread it in yet. If that's it, problem corrected. If not, you haven't wasted a lot of time or money. You can't just unplug the old one to test, you need a new one as it has to be plugged in to give feedback to the computer.

**bwood** · 01-03-2010, 11:29 AM

X2 on the ECT. When they fail completly, the ECM thinks its -30 or something like that and dumps fuel to compensate for the super cold air to prevent a lean condition. If you search for posts on this subject by forum member ChevyTech, he has posted a chart many times with the resistance values for the ECT in relationship to the temp for testing with an ohm meter. If it goes long enough, it should set a code for O2 rich codes and a failed ECT as the ECM also measures the air temp through the Inlet Air Temp sensor just before or in the MAF.

**Boog** · 01-03-2010, 11:38 AM

Coolant temp sensor.

67ss&99ss · 01-03-2010, 08:56 PM

Quote:

Originally Posted by bwood

If it goes long enough, it should set a code for O2 rich codes and a failed ECT as the ECM also measures the air temp through the Inlet Air Temp sensor just before or in the MAF.

would driving 10 miles with the problems be enough to set off the light?

could the coolant temp sensor be defective if the temperature gauge in the is operating normally? I kept a close eye on it driving it home and it never deviated from what it normally read. the gauge moved to operating temperature and stayed there.

I found a picture of a similar truck with the same engine. In the picture with the yellow circle, is this the sensor?

BigBlocksRule · 01-03-2010, 09:16 PM

There are two separate coolant temp sensors, one for the gauge (in the head most of the time) and one for the computer - that's the one in the front of the intake manifold.

67ss&99ss · 01-03-2010, 09:42 PM

Quote:

Originally Posted by BigBlocksRule

There are two separate coolant temp sensors, one for the gauge (in the head most of the time) and one for the computer - that's the one in the front of the intake manifold.

thanks. i will try the coolant temperature sensor tomorrow and let you all know if it fixed the problem.

60ratrod · 01-03-2010, 09:53 PM

i know chevytech posted a bunch of numerical values in a post that i did some months ago when i what having runability issues after my truck went into overdrive. that was for testing the coolant temp sensor with a multimeter.

60ratrod · 01-03-2010, 10:24 PM

actually it was b-wood that posted it and it was a link to another thread. chevytech is the one that put the table up in post number nine of this link:
http://www.67-72chevytrucks.com/vboa...d.php?t=355350

63chevyll · 01-03-2010, 10:28 PM

sounds like a CTS, but the EGR valve (stuck open)can do similar things, but would normaly set a code and a check engine light.

Keep us posted

ChevyTech · 01-03-2010, 10:49 PM

Here are specs for testing the coolant temp sensor the computer uses to determine how much fuel to inject.

To test the coolant sensor, unplug the wire connector and test the resistance across the two terminals of the SENSOR with an ohm meter.

If you see any coolant leaking out the terminals replace it.

If the terminals in the connector are corroded replace the “pigtail”.

Temperature sensor approximate resistance specifications:

177 ohms @ 212 deg. F. or 100 deg. C.
241 ohms @ 194 deg. F. or 90 deg. C.
332 ohms @ 176 deg. F. or 80 deg. C.
467 ohms @ 158 deg. F. or 70 deg. C.
667 ohms @ 140 deg. F. or 60 deg. C.
973 ohms @ 122 deg. F. or 50 deg. C.
1188 ohms @ 113 deg. F. or 45 deg. C.
1459 ohms @ 104 deg. F. or 40 deg. C.
1802 ohms @ 95 deg. F. or 35 deg. C.
2238 ohms @ 86 deg. F. or 30 deg. C.
2796 ohms @ 77 deg. F. or 25 deg. C.
3520 ohms @ 68 deg. F. or 20 deg. C.
4450 ohms @ 59 deg. F. or 15 deg. C.
5670 ohms @ 50 deg. F. or 10 deg. C.
7280 ohms @ 41 deg. F. or 5 deg. C.
9420 ohms @ 32 deg. F. or 0 deg. C.
12300 ohms @ 23 deg. F. or -5 deg. C.
16180 ohms @ 14 deg. F. or -10 deg. C.
21450 ohms @ 5 deg. F. or -15 deg. C.
28680 ohms @ -4 deg. F. or -20 deg. C.
52700 ohms @ -22 deg. F. or -30 deg. C.
100700 ohms @ -40 deg. F. or - 40 deg. C.

Being your truck is a 1996 it should be an OBD2 system which is much better at catching problems that the OBD1 systems. I would check it for trouble codes with a scan tool.

You could also test the fuel pressure during and after the fuel pump prime to see if the pressure is bleeding off, when the pump stops, which would happen if the fuel system is leaking fuel into the engine.

BigBlocksRule · 01-03-2010, 11:12 PM

Remember, try a new one plugged in first without removing the old one. Might save a few steps. At any rate, throw a spare in your glove box for just-in-case, it might make a big difference if this happens in the middle of nowhere sometime.

67ss&99ss · 01-22-2010, 11:27 PM

I got the truck fixed today for my uncle. It was the coolant temp sensor in the intake. Thanks to those that posted for the help.

ChevLoRay · 01-22-2010, 11:32 PM

I'm sending a big THANKS to those who contributed information for this poster. Too many times, it seems that when we're trying to work out an issue it becomes frustrating and seemingly endless. Having a good network of knowledgeable people is a great thing about this forum.

**bwood** · 01-23-2010, 01:10 AM

Good work, thanks for the update.

BigBlocksRule · 01-23-2010, 05:38 AM

Glad it worked out.
As much time as I have to spend with my woman, it's good to come on here and have a chance to be right once in a while

Have him buy a spare and throw it in the glove box so if this happens again, he can make it home without burning twice as much fuel as normal.

01-02-2010, 11:09 PM	#1
67ss&99ss Andy Join Date: Feb 2009 Location: Cleveland, GA Posts: 224	Need help diagnosing problem on uncle's 1996 Silverado I went to my uncle's house today to pick up a few spare parts for my 69 C/10. While there, we drove his truck, a 1996 3500 Silverado, 454 automatic. When I first got in the truck, it started great, and we drove about 10 miles to see a friend for an hour or so. Got back in the truck, and it acted like it did not want to start. I got it to start by pressing and holding the accelerator to the floor. The truck idled rough, very rich and did not want to stay running below 2,000 rpm. I was able to get it back to his house by fortunately. It never ran hot and no check engine light, or service engine soon light came on. I tried the following to repair it with no success. Disconnected the battery then, removed the mass air flow sensor and cleaned it with an aerosol mass air flow cleaner. Removed throttle body, then removed the throttle position sensor and the idle air control sensor from the throttle body. I cleaned the TB with an aerosol TB cleaner and a tooth brush and let it dry. I replaced the throttle position sensor and idle air control sensor, then reinstalled the TB and MAF. Then reconnected the battery(about 30 minutes disconnected). Tried starting the truck again and the only way it would start was by holding the accelerator to the floor. The truck still had all the same problems. It was running so rich my eyes were burning. The only other things left that I can think of that would cause this problem would be a MAP sensor or oxygen sensor. Could an ignition coil or ignition module be the culprit? Any ideas? __________________ 1967 Camaro SS 406\|522hp/514ft lbs\|M20 Muncie\|3.73s\|Posi 1969 CST/10 383\|Aisin AR5 5 speed 1972 K5 350\|Turbo 350 4x4 2005 Duramax 2500HD 4x4

01-03-2010, 10:43 AM	#2
BigBlocksRule Registered User Join Date: Jun 2008 Location: Lubbock, TX Posts: 2,047	Re: Need help diagnosing problem on uncle's 1996 Silverado Intake coolant temp sensor, right on the front of the intake. When it goes out, the engine thinks it's suuuuper cold and pumps fuel like nobody's business to try to heat it up. Been there, done that, now carry a spare. Easy way to check is get a new one (cheap), unplug the old one and plug into the new one, laying on the intake, no need to thread it in yet. If that's it, problem corrected. If not, you haven't wasted a lot of time or money. You can't just unplug the old one to test, you need a new one as it has to be plugged in to give feedback to the computer.

01-03-2010, 11:29 AM	#3
bwood Registered User Join Date: Jan 2003 Location: Denison, Texas Posts: 1,919	Re: Need help diagnosing problem on uncle's 1996 Silverado X2 on the ECT. When they fail completly, the ECM thinks its -30 or something like that and dumps fuel to compensate for the super cold air to prevent a lean condition. If you search for posts on this subject by forum member ChevyTech, he has posted a chart many times with the resistance values for the ECT in relationship to the temp for testing with an ohm meter. If it goes long enough, it should set a code for O2 rich codes and a failed ECT as the ECM also measures the air temp through the Inlet Air Temp sensor just before or in the MAF. __________________ 1998 GMC Sierra SLE 1/2 ton 2WD 305 Vortec -Gibson Stainless Cat Back Swept Side -SS Wheels 2005 Honda CRF250R 2006 Honda CRF150F Last edited by bwood; 01-03-2010 at 11:32 AM.

01-03-2010, 11:38 AM	#4
Boog laying low Join Date: Mar 2001 Location: Searcy, Ark. USA Posts: 12,959	Re: Need help diagnosing problem on uncle's 1996 Silverado Coolant temp sensor. __________________ Boog 69 Chevy stepside, 358/T350, 4.11 posi, 4.5/4 drop, rallys, poboy driver primer is finer 91 Chevy sportside, Tahoe, Yukon & GMC Crewcab All GM..'nuff said. I stand for the flag and kneel at the cross

01-03-2010, 09:16 PM	#6
BigBlocksRule Registered User Join Date: Jun 2008 Location: Lubbock, TX Posts: 2,047	Re: Need help diagnosing problem on uncle's 1996 Silverado There are two separate coolant temp sensors, one for the gauge (in the head most of the time) and one for the computer - that's the one in the front of the intake manifold.

01-03-2010, 09:53 PM	#8
60ratrod yes, i do Join Date: Jun 2007 Location: Spokane, wa Posts: 2,734	Re: Need help diagnosing problem on uncle's 1996 Silverado i know chevytech posted a bunch of numerical values in a post that i did some months ago when i what having runability issues after my truck went into overdrive. that was for testing the coolant temp sensor with a multimeter. __________________ ERROR 404....... SNAPPY COMEBACK NOT FOUND _______________________________________________________________________________________________ -60 Chevy C10, dead 350/good th350 combo, sitting on a 76 c10 blazer frame, built from 11 different vehicles "the abomination" -07 gmt900 silverado 1500 lt xcab z71, granite blue -81 suzuki gs650g "shelah"- current project -81 kz1000m1 csr "sarge" -next project (just beautification) -07 kawasaki vulcan classic vn900

01-03-2010, 10:24 PM	#9
60ratrod yes, i do Join Date: Jun 2007 Location: Spokane, wa Posts: 2,734	Re: Need help diagnosing problem on uncle's 1996 Silverado actually it was b-wood that posted it and it was a link to another thread. chevytech is the one that put the table up in post number nine of this link: http://www.67-72chevytrucks.com/vboa...d.php?t=355350 __________________ ERROR 404....... SNAPPY COMEBACK NOT FOUND _______________________________________________________________________________________________ -60 Chevy C10, dead 350/good th350 combo, sitting on a 76 c10 blazer frame, built from 11 different vehicles "the abomination" -07 gmt900 silverado 1500 lt xcab z71, granite blue -81 suzuki gs650g "shelah"- current project -81 kz1000m1 csr "sarge" -next project (just beautification) -07 kawasaki vulcan classic vn900

01-03-2010, 10:28 PM	#10
63chevyll gets board easy....... Join Date: Mar 2009 Location: Colorado Springs Posts: 717	Re: Need help diagnosing problem on uncle's 1996 Silverado sounds like a CTS, but the EGR valve (stuck open)can do similar things, but would normaly set a code and a check engine light. Keep us posted Last edited by 63chevyll; 01-03-2010 at 10:28 PM.

01-03-2010, 10:49 PM	#11
ChevyTech Registered User Join Date: May 2004 Location: Minnesota Posts: 4,620	Re: Need help diagnosing problem on uncle's 1996 Silverado Here are specs for testing the coolant temp sensor the computer uses to determine how much fuel to inject. To test the coolant sensor, unplug the wire connector and test the resistance across the two terminals of the SENSOR with an ohm meter. If you see any coolant leaking out the terminals replace it. If the terminals in the connector are corroded replace the “pigtail”. Temperature sensor approximate resistance specifications: 177 ohms @ 212 deg. F. or 100 deg. C. 241 ohms @ 194 deg. F. or 90 deg. C. 332 ohms @ 176 deg. F. or 80 deg. C. 467 ohms @ 158 deg. F. or 70 deg. C. 667 ohms @ 140 deg. F. or 60 deg. C. 973 ohms @ 122 deg. F. or 50 deg. C. 1188 ohms @ 113 deg. F. or 45 deg. C. 1459 ohms @ 104 deg. F. or 40 deg. C. 1802 ohms @ 95 deg. F. or 35 deg. C. 2238 ohms @ 86 deg. F. or 30 deg. C. 2796 ohms @ 77 deg. F. or 25 deg. C. 3520 ohms @ 68 deg. F. or 20 deg. C. 4450 ohms @ 59 deg. F. or 15 deg. C. 5670 ohms @ 50 deg. F. or 10 deg. C. 7280 ohms @ 41 deg. F. or 5 deg. C. 9420 ohms @ 32 deg. F. or 0 deg. C. 12300 ohms @ 23 deg. F. or -5 deg. C. 16180 ohms @ 14 deg. F. or -10 deg. C. 21450 ohms @ 5 deg. F. or -15 deg. C. 28680 ohms @ -4 deg. F. or -20 deg. C. 52700 ohms @ -22 deg. F. or -30 deg. C. 100700 ohms @ -40 deg. F. or - 40 deg. C. Being your truck is a 1996 it should be an OBD2 system which is much better at catching problems that the OBD1 systems. I would check it for trouble codes with a scan tool. You could also test the fuel pressure during and after the fuel pump prime to see if the pressure is bleeding off, when the pump stops, which would happen if the fuel system is leaking fuel into the engine.

01-03-2010, 11:12 PM	#12
BigBlocksRule Registered User Join Date: Jun 2008 Location: Lubbock, TX Posts: 2,047	Re: Need help diagnosing problem on uncle's 1996 Silverado Remember, try a new one plugged in first without removing the old one. Might save a few steps. At any rate, throw a spare in your glove box for just-in-case, it might make a big difference if this happens in the middle of nowhere sometime.

01-22-2010, 11:27 PM	#13
67ss&99ss Andy Join Date: Feb 2009 Location: Cleveland, GA Posts: 224	Re: Need help diagnosing problem on uncle's 1996 Silverado I got the truck fixed today for my uncle. It was the coolant temp sensor in the intake. Thanks to those that posted for the help. __________________ 1967 Camaro SS 406\|522hp/514ft lbs\|M20 Muncie\|3.73s\|Posi 1969 CST/10 383\|Aisin AR5 5 speed 1972 K5 350\|Turbo 350 4x4 2005 Duramax 2500HD 4x4

01-22-2010, 11:32 PM	#14
ChevLoRay Old Skool Club Join Date: Jun 2001 Location: Benton, AR "The Heart of Arkansas" Posts: 10,880	Re: Need help diagnosing problem on uncle's 1996 Silverado I'm sending a big THANKS to those who contributed information for this poster. Too many times, it seems that when we're trying to work out an issue it becomes frustrating and seemingly endless. Having a good network of knowledgeable people is a great thing about this forum. __________________ Member Nr. 2770 '96 GMC Sportside; 4.3/SLT - Daily driven....constantly needs washed. '69 C-10 SWB; 350/TH400 - in limbo The older I get, the better I was.

01-23-2010, 01:10 AM	#15
bwood Registered User Join Date: Jan 2003 Location: Denison, Texas Posts: 1,919	Re: Need help diagnosing problem on uncle's 1996 Silverado Good work, thanks for the update. __________________ 1998 GMC Sierra SLE 1/2 ton 2WD 305 Vortec -Gibson Stainless Cat Back Swept Side -SS Wheels 2005 Honda CRF250R 2006 Honda CRF150F

01-23-2010, 05:38 AM	#16
BigBlocksRule Registered User Join Date: Jun 2008 Location: Lubbock, TX Posts: 2,047	Re: Need help diagnosing problem on uncle's 1996 Silverado Glad it worked out. As much time as I have to spend with my woman, it's good to come on here and have a chance to be right once in a while Have him buy a spare and throw it in the glove box so if this happens again, he can make it home without burning twice as much fuel as normal.



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