Poor engine operation when cold--- 95 Blazer 4.3.

NCGATOR

MEMBER
1995 CHEVROLET BLAZER
189,000 MILES

Head gaskets were replaced due to coolant in oil. It did not overheat.

Upon reassembly, a no start condition was encountered. This was solved by installing a used ECM and having it reprogrammed by the Chev dealer. Along the way, the Crank Sensor and the Cam Sensor were replaced.

Currently, after overnight cool down, it runs poorly until normal temperature is reached. During the warmup period, the "check engine light" flashes continuously. When warm, the engine smooths out and the light stays on solid. P0305 is set. Compression was verified at 150 +/- 10 when reassembled. New plug wires were installed. #5 plug was switched with #1, resulting code still P0305. An adjustable spark tester verifies spark at 30,000 on #5 when warm.

Code scanner read coolant temp at 51C when cold and 89C when warm.

Will test #5 spark tomorrow morning with engine cold.

I suspect injector or poppet problem. Can the spyder system be tested if removed from the engine? If so, who can test it?

In the meantime, any suggestions will be welcomed.

5 Replies

HMAC300

MECHANIC
48,601 POSTS

Misfires can be a few things, of course ignition stuff should be checked out first. Then check maf forlow voltage via freeze frame. If you suspect a poppet problem then try running pro style injector cleaner through it. It goes right to the fuel rail and you take out pump relay so only the can stuff cleans the injectors. Have apro do this though as it's a kit to h ook up to your vehicle. Normally the poppet problem would not allow the vehicle to start. Also check for a vacuum leak because when theengine warms it may be richening the fuel load to take care of the vacuum leak. The computer will do that if the O2 sees something like a lean condition. You can use choke cleaner to aid in finding the leak. But make sure air filter is on when doing this and becareful as it's explosive

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Thursday, June 20th, 2013 AT 4:56 PM

NCGATOR

MEMBER
2 POSTS

I think you're assuming I have sophisticated test equipment that I don't have. I don't think I can do "freeze frame".

Your point about vacuum reminded me. We did put a vacuum gauge on the engine when cold and found that during the aforementioned warmup that vacuum did fluctuate in the 10 - 12 range. However, when the engine smoothed out, vacuum was rock solid at 18. Could the computer control fuel to that extent?

What about my question regarding testing spyder?

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Friday, June 21st, 2013 AT 3:20 AM

HMAC300

MECHANIC
48,601 POSTS

Re read my first reply I didn't know choke cleaner was a huge cost for test equipment. If you can't do a freeze frame then have a pro do it. But with the vacuum readings you are getting cold i'd say you have a vacuum leak someplace and yes the computer can richen the mix somewhat after it takes over when warm.

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Friday, June 21st, 2013 AT 6:48 AM

KEN L

MASTER CERTIFIED MECHANIC
47,513 POSTS

Nice work on the injector cleaner to help the problem hmac300. Did you check the fuel pressure regulator? If the diaphragm is blown it with cause #5 to run rich. If that doesn't work replace the injector spider and or the pressure regulator, Gm had big problems with these. The check engine light flashing until warm. Sounds like the comp might be bad, or you have a ground wire not connected. Please check and get back you us. Thanks for the donation :)

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Friday, June 21st, 2013 AT 10:39 AM

HMAC300

MECHANIC
48,601 POSTS

Normally the spider when bad would not let the vehicle start and it's about $400 for a spider but this really sounds as if it's a vacuum leak more than anything especially since engine being cold computer is running in open loop and when it starts closed loop it runs better. So the computer is richening the fuel load to compensate for the vacuum leaking.