1990 Chevy Silverado Miss Fireing

Tiny
STRENT5
  • MEMBER
  • 1990 CHEVROLET SILVERADO
  • V8
  • 2WD
  • AUTOMATIC
  • 240,000 MILES
My 1990 Chevy pickup has a reman engine in it and has been running fine, but it has lattly started missfireing when cold. Shudders really bad untill wamed up. Once it reaches operating temperature it seams to run fine. But not untill. It also surges a little at 35 to 45 mile per hour after warm. I have changed distributer, idle air controll and throttle position sensor. No check engine lights. Could this be O2 sensor?
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Thursday, November 6th, 2008 AT 7:55 AM

5 Replies

Tiny
RACEFAN966
  • EXPERT
Ok need some information first if you could. How old is the O2 sensor? When was the fuel filter last changed? How dirty is the air filter? I know this sound simple but you would be very supprised as to how often the simple is over looked thinking it must be something else. I would also like you to take a timing light if you have one and check the timing and check the injector spray with it too. To check the injector spray you hook up the timing light like you normaly would and with the air cleaner off you point it to the injector and look at the spray pattern. It should look like a fine mist if you see any droplets or streams then you will need to do some cleaning. Let know what you find with this and give the needed info and we will go from there. You might need to do a seafoam treatment and I will let you how to do that after you get back to me ok.
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Thursday, November 6th, 2008 AT 10:31 AM
Tiny
STRENT5
  • MEMBER
The fuel filter was changed as well as air oil about 1500 miles ago. I did an injector cleaner in the tank with no change. I did the timeing when I changed the distributor, I will look at the fuel injection spray, the O2 sensor has had about 80000 miles on it.
Thats why I was woundering about it. If you watch the temp. Climb you can allmost tell when it will start running smoth, it is right when it gets to about 180 deg. I dont know the programing of this system but it seams strange.
Thanks!
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Thursday, November 6th, 2008 AT 10:47 AM
Tiny
RACEFAN966
  • EXPERT
It could be a temp sensor too. This is the sensor that tells the computer how warm it is and when they go bad they do weird things and usually don't set codes either. Let me know what you find with the injector spray with this timing light first and we will go from there. I will look up what the ohms should be on the sensor today at work and then you test that next.
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Thursday, November 6th, 2008 AT 10:59 AM
Tiny
STRENT5
  • MEMBER
The spray pattern is good
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Friday, November 7th, 2008 AT 9:02 PM
Tiny
RACEFAN966
  • EXPERT
Ok good that means less money to spend gotta love that. Now do you have a manual on this? If you do ohm out the coolant sensor and see if it is in range if you don't know what the specs are let me know I will find them for you. You could also do the seafoam treatment. What I mean is buy some seafoam and get some vacuum line and find a cup you don't care to keep. Pour about 8 oz into the cup and as the truck is running slowly using the vacuum line a smaller vacuum port off the throttle body slowly suck up the seafoam and put the rest of the bottle in the tank.
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Saturday, November 8th, 2008 AT 8:32 AM

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