1990 Chevy 4x4 low speed miss - The 1947 - Present Chevrolet & GMC Truck Message Board Network

Free88 · 07-14-2009, 11:12 AM

Truck starts good but idles a little rough for about a minute than smooths out. Runs rough until about 40 mph. Over 40 it runs well with no roughness at all. Had the throttle body gasket changed and it made no difference. Does not idle fast.

ChevLoRay · 07-14-2009, 01:09 PM

Somebody will pick up on this and make some suggestions, but there are a boatload of posts from within the past month that deal with rough idle, etc., and may offer you some good tips for troubleshooting. I'll check out some links and throw one your way.

ChevLoRay · 07-14-2009, 01:11 PM

Check this post. Go down towards the bottom and there is a reply from ChevyTech that has some info that may help.

http://67-72chevytrucks.com/vboard/s...d.php?t=348308

Free88 · 07-14-2009, 03:03 PM

Thanks.

ChevyTech · 07-14-2009, 08:26 PM

It sounds to me like weak ignition or a distributor issue.

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.

Around 1989-1990 the distributor shafts didn't have the groove in the shaft to direct oil "back" down into the engine. Oil will get into the pickup coil and can damage the coil windings. Any of the distributors can do this if they get very worn.

If there is oil coming up the shaft and getting out onto the pickup coil – replace the distributor.

These distributors can also have problems because of loss of magnetism needed for the pickup coil to work.

Free88 · 07-14-2009, 08:27 PM

Does anyone have a part number for this spring. We don't have a Chevy dealer where I live and I have to call a dealer and don't really want to stay on long distance hold while they look up the part. Thanks

ChevyTech · 07-14-2009, 08:30 PM

Quote:

Originally Posted by Free88

Does anyone have a part number for this spring. We don't have a Chevy dealer where I live and I have to call a dealer and don't really want to stay on long distance hold while they look up the part. Thanks

Are you referring to a fuel pressure regulator spring?

Free88 · 08-01-2009, 08:36 PM

ChevyTech, today while crawling around under my truck to see where the noise was coming from I noticed that the sensor in the exhaust pipe had no wires coming from it. I checked all over for a while but could not find one. I looked in the manual and it showed a purple wire in the schematic number 412 going to connector D7 on the ecm. I can not locate this wire and was wondering if you had any idea as to where this may be located. It looks like a two wire connector on the O2 sensor but only shows one wire in the schematic. Thanks

ChevyTech · 08-02-2009, 10:30 AM

It should be a one wire sensor on your 1990 truck and the wire should be Purple.

On that truck the O2 sensor should have a single wire to a connector the in several inches from the actual sensor.

I can’t remember which years have the sensor in which positions. It may be that the exhaust system on your truck is from something else. Look at the driver side exhaust manifold and make sure there is not oxygen sensor there also, close to the outlet.

The single wire O2 sensors have to be very close to the engine to stay warm enough to function well.

Free88 · 08-02-2009, 10:59 AM

Good morning. There is a sensor on the drivers side exhaust manifold and this one was in the exhaust manifold. I am going out to check and see what sensor is in the exhaust manifold on the drivers side. The sensor I took out has 4 wires on it.

ChevyTech · 08-02-2009, 11:18 AM

That is a four wire heated sensor which is NOT for your truck.

07-14-2009, 11:12 AM	#1
Free88 Registered User Join Date: Jan 2004 Location: Northwestern Ontario Canada Posts: 359	1990 Chevy 4x4 low speed miss Truck starts good but idles a little rough for about a minute than smooths out. Runs rough until about 40 mph. Over 40 it runs well with no roughness at all. Had the throttle body gasket changed and it made no difference. Does not idle fast. __________________ 1986 Silverado Short box fleet side. project 2005 VW Tiguan 4 Motion 1997 Blazer S10 4x4 1990 Chevy Silverado K1500 Extended long box

07-14-2009, 01:09 PM	#2
ChevLoRay Old Skool Club Join Date: Jun 2001 Location: Benton, AR "The Heart of Arkansas" Posts: 10,880	Re: 1990 Chevy 4x4 low speed miss Somebody will pick up on this and make some suggestions, but there are a boatload of posts from within the past month that deal with rough idle, etc., and may offer you some good tips for troubleshooting. I'll check out some links and throw one your way. __________________ 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.

07-14-2009, 01:11 PM	#3
ChevLoRay Old Skool Club Join Date: Jun 2001 Location: Benton, AR "The Heart of Arkansas" Posts: 10,880	Re: 1990 Chevy 4x4 low speed miss Check this post. Go down towards the bottom and there is a reply from ChevyTech that has some info that may help. http://67-72chevytrucks.com/vboard/s...d.php?t=348308 __________________ 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. Last edited by ChevLoRay; 07-14-2009 at 01:12 PM.

07-14-2009, 03:03 PM	#4
Free88 Registered User Join Date: Jan 2004 Location: Northwestern Ontario Canada Posts: 359	Re: 1990 Chevy 4x4 low speed miss Thanks. __________________ 1986 Silverado Short box fleet side. project 2005 VW Tiguan 4 Motion 1997 Blazer S10 4x4 1990 Chevy Silverado K1500 Extended long box

07-14-2009, 08:26 PM	#5
ChevyTech Registered User Join Date: May 2004 Location: Minnesota Posts: 4,620	Re: 1990 Chevy 4x4 low speed miss It sounds to me like weak ignition or a distributor issue. 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. Around 1989-1990 the distributor shafts didn't have the groove in the shaft to direct oil "back" down into the engine. Oil will get into the pickup coil and can damage the coil windings. Any of the distributors can do this if they get very worn. If there is oil coming up the shaft and getting out onto the pickup coil – replace the distributor. These distributors can also have problems because of loss of magnetism needed for the pickup coil to work.

07-14-2009, 08:27 PM	#6
Free88 Registered User Join Date: Jan 2004 Location: Northwestern Ontario Canada Posts: 359	Re: 1990 Chevy 4x4 low speed miss Does anyone have a part number for this spring. We don't have a Chevy dealer where I live and I have to call a dealer and don't really want to stay on long distance hold while they look up the part. Thanks __________________ 1986 Silverado Short box fleet side. project 2005 VW Tiguan 4 Motion 1997 Blazer S10 4x4 1990 Chevy Silverado K1500 Extended long box

08-01-2009, 08:36 PM	#8
Free88 Registered User Join Date: Jan 2004 Location: Northwestern Ontario Canada Posts: 359	Re: 1990 Chevy 4x4 low speed miss ChevyTech, today while crawling around under my truck to see where the noise was coming from I noticed that the sensor in the exhaust pipe had no wires coming from it. I checked all over for a while but could not find one. I looked in the manual and it showed a purple wire in the schematic number 412 going to connector D7 on the ecm. I can not locate this wire and was wondering if you had any idea as to where this may be located. It looks like a two wire connector on the O2 sensor but only shows one wire in the schematic. Thanks __________________ 1986 Silverado Short box fleet side. project 2005 VW Tiguan 4 Motion 1997 Blazer S10 4x4 1990 Chevy Silverado K1500 Extended long box

08-02-2009, 10:30 AM	#9
ChevyTech Registered User Join Date: May 2004 Location: Minnesota Posts: 4,620	Re: 1990 Chevy 4x4 low speed miss It should be a one wire sensor on your 1990 truck and the wire should be Purple. On that truck the O2 sensor should have a single wire to a connector the in several inches from the actual sensor. I can’t remember which years have the sensor in which positions. It may be that the exhaust system on your truck is from something else. Look at the driver side exhaust manifold and make sure there is not oxygen sensor there also, close to the outlet. The single wire O2 sensors have to be very close to the engine to stay warm enough to function well. Last edited by ChevyTech; 08-02-2009 at 10:45 AM. Reason: Add more

08-02-2009, 10:59 AM	#10
Free88 Registered User Join Date: Jan 2004 Location: Northwestern Ontario Canada Posts: 359	Re: 1990 Chevy 4x4 low speed miss Good morning. There is a sensor on the drivers side exhaust manifold and this one was in the exhaust manifold. I am going out to check and see what sensor is in the exhaust manifold on the drivers side. The sensor I took out has 4 wires on it. Attached Images __________________ 1986 Silverado Short box fleet side. project 2005 VW Tiguan 4 Motion 1997 Blazer S10 4x4 1990 Chevy Silverado K1500 Extended long box

08-02-2009, 11:18 AM	#11
ChevyTech Registered User Join Date: May 2004 Location: Minnesota Posts: 4,620	Re: 1990 Chevy 4x4 low speed miss That is a four wire heated sensor which is NOT for your truck.



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