1989 chevy k1500 engine problems?

I am having issues with misfiring and smoking. First, let me tell you what I have had done. I put a new 5.7L 350 crate engine in the truck. It has all new sensors, distributor, cap, coil, and all new connectors. It has new fuel pump and filter. New plugs and wires. New ignition control module. New injectors and rebuilt tbi. All new wiring. New radiator, water pump, and fan clutch. New thermostat. New oil pump and all gaskets. Everything is new except the intake manifold, air cleaner, and ecu. I made sure timing is dead on and valves adjusted per service manual. I start it up for the first time and it purrs like a kitten....for 30 seconds. Then it starts to miss worse and worse as it warms up. Then it starts backfiring, smoking and then it dies. If I let it cool off, it does the same thing...runs good, gets worse, then dies. I checked and there is no stored ecu codes. Any ideas on what could be going on? Maybe a bad rebuild on the crate engine? Faulty part? I am lost as to what it could be.


Also, I forgot to mention that the old engine had headman long tube headers on it and I kept the same setup on the new engine...it also had a newer style heated o2 sensor that I kept on it as well...not sure if that would be the problem.

7 Answers

  • Geo
    Lv 6
    1 month ago
    Favorite Answer

    First I would check all the Vacuum Lines and Fittings. Then I would look at the TBI 'spitters' to make sure they are spitting all the time. Then I would remove the distributor cap and look for any carbon tracking. If all those are fine remove the Spark Plugs and look at them and while they're out do a Compression Test on the cylinders. You can run it at night to see if you have a high tension leak on the Ignition system. Nothing wrong with the Headers, but put the 1 wire 02 sensor on it...like the original setup. 

  • 1 month ago

    Go back and look at the ign module .If it's not a AC DELCO PART then maybe that's the issue What you described is what I've seen with aftermarket modules As they heat up They start to work intermittently If it's a cheap aftermarket one I'd start there first A vac leak won't make it fun crappy AFTER ITS WARM it'll always run shitty even cold .Also check the plugs gap check the coil too .Start at the ignition. its not uncommon a cold vehicle runs okay until it heats up In my experience modules can work intermittently Unlike ford that just crap out I've seen GM trucks do that from a bad or cheap module .In my opinion it's the ignition ,the module ,coil ,even bad gapped plugs I doubt it's a vac leak Which would in most cases run crappy whether hot or cold .You can check for vac leaks when it's running better and not misfiring when hot Matter of fact it'll be easier to find any vac leaks if any of it's running without misfiring Also check the map sensor too It's electrical or all ignition issues Just cause the module is new UNLESS IT'S A DELCO PART anything else is crap EVEN MALLORY ,ACCEL ign.modules are in my opinion junk The best would be a delco part .The aftermarket ,unless you have a mallory dist or Accel dist even then on a.stick motor the delco.part is best also make sure the rotor and cap are not cracked or piss poorly made STOCK ENGINES ARE BEST WITH DELCO PARTS  .I've e

    Used them all and had the best results as far as longevity is with a delco ignition parts The rest are crap for a stock engine 

  • Anonymous
    1 month ago

    You have an electrical problem.

  • Anonymous
    1 month ago


    What an antique computer that must have!

    The mechanical engine (block, pistons, crankshaft, heads, valves, etc) is likely not the problem.

    The problem is something that has wires connected to it.

    Ok so all that stuff you changed, what didn't you change? 

    And newstyle heated oxygen sensor, whose idea was that?

    You likely have a mishmash of unrelated parts that don't belong together.

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  • Anonymous
    1 month ago

    Check for a vacuum leak.  Check fuel pressure.  Check for a good spark.  Check for leaking injectors.  Check for a leaking fuel pressure regulator which is likely the culprit here.

  • Anonymous
    1 month ago

    The engine is fine, you know that because: "it purrs like a kitten....for 30 seconds".

    Something is going sideways after it starts. You're going to need a scan tool that displays live data to see what's really going on. If it were me the first thing I'd do is remove the EGR valve and put a block off plate there just to make sure it's not being caused by a stuck open valve or something pulling it open after the engine starts. Next guess would be a suspect MAP sensor.

  • Anonymous
    1 month ago

    you would have to ask a mechanic

    Source(s): pearl
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