91 K1500 5.7 Cold Start TReMoRs!

[knjwells]

I just posted last night with a few other issues with this truck and I appreciate everyone's time and help. But the major issue I am having with this vehicle now needs more attention this time of year than ever.

My truck (1991 K1500 Chevy 4WD Auto 5.7 EFI) runs very strong with no intake or exhaust leaks, no "ticks" or "pings" from the motor, and it'll sit you back in the seat when you gun it... but when it's been sitting cold overnight or even during my 8 hour shift at work it has the hardest time getting started. By saying that I don't mean it cranks and cranks and gets no where. It will fire right up within 4-5 crank revolutions... everytime. But when it's cold it stutters, shakes, spits, and let's out lil backfires and dies. It'll then fire right back up the same way and when the initial burst of fuel has ignited and it starts doing it again. I'll give it a little gas to raise the rpms a bit and it'll do better, but it's still not solid. It gets a little better as the motor gets warmer (better enough that I don't have to nurse it along) and then it runs perfectly. It does this exact same thing every time I start it cold.

I have replaced the following parts due to other issues and invite you to view the post I left last eve to see the other issues if needed.... distributor (+ cap & rotor, etc.), iac, and thermostat. I have been told it may be the TPS -or- Coolant Temp. Sensor?

Any suggestion would be greatly appreciated. Thanks again for your time either way.

[2000CAYukon]

The ECT Sensor may be reporting the wrong temp making cold starts difficult. If you access to a scan tool, you should look at the temp being reported during cold starts.

If you let it sit overnight and then disconnect the ECT (in the intake near the tstat housing) and it starts better, the ECT is bad. Disconnecting the ECT sensor tells the ECM that the engine is very cold.

//2000CAYukon

[knjwells]

Originally Posted by 2000CAYukon

The ECT Sensor may be reporting the wrong temp making cold starts difficult. If you access to a scan tool, you should look at the temp being reported during cold starts.

If you let it sit overnight and then disconnect the ECT (in the intake near the tstat housing) and it starts better, the ECT is bad. Disconnecting the ECT sensor tells the ECM that the engine is very cold.

//2000CAYukon

I disconnected it after sitting frigid all night and it made no change at all. What else might it be? I am lost. Thanks for your time.

[knjwells]

I disconnected it after sitting frigid all night and it made no change at all. What else might it be? I am lost. Thanks for your time.

[dewaynep]

I was dealing with a similar situation on a 1994. When you start it cold, once it is running, press on the brake 2 or 3 times. My truc will start great, but when it's cold out a seal in the brake booster must leak and cause a pretty big vacuum leak. Now that I now what mine is, I just hit the brake 2 or 3 times after starting the truck and it idles smooth as glass. I am going to replace the booster as soon as it gets warmer than 10degrees here.

[knjwells]

I tried that this morning and it did not change anything... except for the rusted brake line "breakthrough" I experienced. The pressure from me pushing on the pedal just so happened to be too much for a rusted area in my rear brake line. The pedal fell to the floor and I spent the evening repairing the line. I do appreciate your attempt to help.

Anyone else know what it might be? Thanks again for your time.