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Old 01-12-2019, 05:48 PM   #1
AKChevyman
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Bringing a 91 K1500 back to life

Well it has been a while since I was on here but I am in the middle of bringing a 91 Short bed Silverado 350 w/automatic back to life. I have ran into an issue I can't seem to narrow down and need the wealth of your knowledge to hopefully figure it out. Thanks to the trouble guide on here I already took some steps but still have an issue. The issue is with the TBI I have rebuilt it and replaced the MAP, TPS, Temp sensor and even the ECU. Number one issue is the truck is hard to start. Second once started it will only start for about 30 secs then die. Third is once it engine dies the injectors continue to fire for another 10-15 secs flooding the TB with fuel. Which make restarting it a lot easier but isn't right. Thanks for your help
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My first love
1971 C20
Hugger orange
Getting face lift and heart transplant .30 402 BB /TH400 and GV
Wifes car
1969 Chevelle SS 396 325hp/TH400
Factroy A/C Automatic w/ Floor shift console.
restored.
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Old 01-13-2019, 12:04 PM   #2
Cabnchassis
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Re: Bringing a 91 K1500 back to life

Is this truck new to you or one you drove before it had this issue?

Check fuel pressure if you haven't. Until you know that, the only way to figure this out is by wasting money. Most trucks don't have an easy way to do that, find a thread on how to plumb in a gauge and bite the bullet. It's nothing crazy, just annoying, but critical to diagnosing the issue.

Checked the EGR to make sure the passage isn't choked with soot?

THere are two TPS sensors, one for the dash one for the ECM.

Have you cleaned the IAC pintle? Shouldn't cause this, but it's a maintenance item at some point in the truck's life (if you do this reset the ECM afterwards by cycling the ignition switch several times)

Oxygen sensor will sometimes code out, or throw lean condition code (EGR can cause this too) but most often you won't get any code from the ECM unless it's misfiring.

If you can keep it running long enough, spray all the gaskets and vacuum hoses with starting fluid, if then engine picks up you have a vacuum leak. The intake manifold can leak internally and cause the engine to stutter, but shouldn't kill it consistently in the same way. Starting fluid cannot diagnose an internal manifold gasket failure.

The ECM in these trucks is a very simple unit but has enough control of running conditions to be a big pain in the behind if it isn't getting the diagnostic information it wants, or that information is incorrect. When it resets everything usually gets better...for a minute or two.

What brand is the MAP sensor you used? Sometimes trucks won't tolerate bosch aftermarket replacement parts that have information to relay to the ECM Too often brand new parts store replacement parts are failed due to poor construction upon purchase. Your original parts will be the highest quality available in most cases, avoid changing anything you haven't verified is failed.

The other reason you don't want to change anything until you're sure it's failed, is the more you change the input information the ECM is collecting, the more it changes the operating conditions of the vehicle. Often you'll think you've made improvement but it's just that the ECM reset, and once you shut the truck off or run it long enough it will act up again.

If the ECM gets bad input information it will overfuel to keep operating temperature as low as possible, and the vehicle will run cold until that input is corrected. Low operating temperatures will damage your catalytic converter if you have one.
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Old 01-13-2019, 10:55 PM   #3
AKChevyman
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Re: Bringing a 91 K1500 back to life

Thanks for your reply. I worked on it again today and did track down the culprit. Wasn't getting enough fuel pressure. The little rubber hose in the tank was completely shot. I got this truck as a non runner with no engine. I did drop the tank initially before getting the engine in it to check for bad gas or worse. It was spotless inside. I didn't notice at the time the hose was shot because the tank was bone dry. On initial start up everything was fine a few months back and set the truck on the back burner to work on my 71. I guess that inferior hose had enough time to soak in the gas I had in the tank and go to crap. I dropped the tank today and got a new piece of Fuel injector grade hose and replaced it. I hope it holds up better than what was on there before. I replaced a lot of parts but now I know they are all good and she runs great now just have to rebuild the transmission. Thanks again
__________________
My first love
1971 C20
Hugger orange
Getting face lift and heart transplant .30 402 BB /TH400 and GV
Wifes car
1969 Chevelle SS 396 325hp/TH400
Factroy A/C Automatic w/ Floor shift console.
restored.
AKChevyman is offline   Reply With Quote
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