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My 1990 has been running rough all of a sudden. Some symptoms have included (last two weeks) high idle, service engine light came on, when started it sounds like it wants to die, when i floor the gas pedal truck turns off, but runs if i drive it light, failed smog test. Thank you


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Location: Oregon
high idle could be from a couple of things, coolant temp sensor reading too cold or it could be a vacuum leak. there may be other things but I would look at those two first. Either one could also affect smog inspection. Why didn't you say what your truck was failed for? High hydrocarbons? High CO? of what does your state look at for to pass?

Fuel pressure and volume could be a possibility. Hows the O2 sensor trims? LT (long term) and ST (short term) fuel trims will tell you how the exhaust gases are being interpreted by your computer and in effect how your computer feeds your engine.

If your service engine light came on you should have your truck scanned to see what the code or codes are and go from there.


   
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Thank you for replying. Ok so i changed the coolant temp and that seems to have fixed the high idling problem. The results for my failed smog insp where high dc and high nox on both modes.would u happen to know why my engine stalls when i floor it? it only happens when my fuel tank is below quarter tank and I believe it started after i changed my fuel filter. Dont know if that might have somtging to do with it? Thanks in advance.

1990 chevy c1500 reg cab
350 5.7L


   
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changing the fuel filter shouldn't cause a problem. you didn't put it on backwards did you? joking but it happens.

High HC (hydrocarbons) is unburned fuel, usually from a lean condition.
High NOX (nitrous oxides) smog from cylinder running too hot or high compression. Egr valves were made to recirculate exhaust gas back into the cylinder mix to help reduce the cylinder temperature and lower NOX. A lean mixture will also make the cylinder temp higher.

Verify your timing is not set too advanced. Remember to turn off computer timing to set actual timing.


   
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Arrow on fuel filter is facing towards engine. Would a fuel pump cause the vehicle to stall. I changed that also?

Ok now to smog…. ill replace or clean egr valve and hopefully thatll take care of that. now how do i check to see if timing is not set to advanced and How do i turn off compuuter and set actual timing. Where is timing located? Sorry not familiar with that. Thank you for info and quick response


   
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disconnect the tan/black wire EST by pass connector usually located behind the junction box cover or near the distributor. Not the four wire to the distributor. this will be a single wire connector. with the wire disconnected and the engine warmed up, set the timing to 0 at idle.


   
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