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New Stumper


the_tow_guy's Avatar
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02-08-18, 01:50 PM   #1 (permalink)  
New Stumper

Okay, so after tearing my hair out for couple of months with my random misfire that's finally fixed and trucks running better than it has in YEARS. This is the wrecker 1994 5.7L Chevy TBI.

The stumper, though, is one that cropped up last year and comes and goes at random. What happens is I crank it up and it fires off goes to idle rpm(more or less) and then immediately dies. Sometimes a second try will duplicate and sometimes it will remain at idle. Applying a little gas pedal usually makes it go away. Have already eliminated the TPS and IAC. When I disconn the TPS, it starts and runs fine even disconn'ed. With the IAC it starts and runs at a fast idle. Most of the other components that might be suspect have very low miles on them, plus don't want to just throw parts since it's not costing me any money like the misfire was. Scanner tells me nothing, since it never does it when I'm hooked up and there's no codes.

Anybody ever run across anything similar?


Measure it with a micrometer; cut it with an ax.

 
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alan73's Avatar
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02-09-18, 04:49 PM   #2 (permalink)  
does it occur when cold or warmed up or both?
would probably check the base idle speed with iac closed the engine should still have enough airflow around throttle plates to idle at a slow speed around 600 rpm if for some reason you do not have minimum idle speed the engine would be more likely to start and die as its completely relying on the iac bypass air to keep it running.

 
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02-09-18, 06:30 PM   #3 (permalink)  
Do you ever get a anti-theft or security light blinking on the dash when it shuts off? I had a 1997 GM product that had a fault with the Passlock anti-theft system, and it would start, then immediately stall.

 
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02-10-18, 05:28 AM   #4 (permalink)  
I had a Ranger about like that. I changed the temp sensor for the computer and it took care of it. It would always die the first time, I never checked for codes on that one. I just replaced the sensor.

There was an odd one, though on a Camry. It was a head ache that turned out to be nothing more than low coolant level. We figured the temp sensor wasn't submerged in liquid.

 
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02-10-18, 08:39 AM   #5 (permalink)  
Does it both warm and cold, perhaps more often when cold although the incidents are so far apart can hardly remember from one to another. Base idle checked during previous troubleshooting for the misfire. IAC has been swapped out during other unrelated troubleshooting.

It's a '94. The only anti-theft device it has is the door locks.

Temp sensor replaced, also during recent troubleshooting. I was really grasping at straws at the time. Also, I've had a CTS go bad before and it resulted in a total crank/no fire (and code set). It sets no codes except for an oddball trans code that's come back time after time for about the last 300,000 miles.

The entire ignition system is essentially brand new from troubleshooting the random misfire. Almost makes me think it's having a random event of dropping the injector pulse. Would be nearly impossible to diagnose if that's it; 99 times out of 100 I'm not at a location where I could troubleshoot it and it's not always immediately repeatable anyway. If I ever get the chance I'll check that, all I need is someone to gaze down the TBI throat while I crank to see if we're getting fuel delivery (fuel pump has checked good and filter is fresh).

Likely to be one of those things I just live with. Did it one time this week, Tuesday or Wednesday


Measure it with a micrometer; cut it with an ax.

 
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02-10-18, 10:56 AM   #6 (permalink)  
Everything runs on voltage/resistance. It could come down to a bad wire or poor connection. Sometimes ya feel like looking for a 1960's something.

 
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02-10-18, 02:03 PM   #7 (permalink)  
I think I would probably just live with it also, at least until it got a lot more consistent since it always starts back up, if the engine has 300k miles on it could be something even mechanical the computer cant compensate for like timing chain wear if it starts to occur more often maybe you will have the chance to do some more testing.

 
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02-10-18, 07:04 PM   #8 (permalink)  
I had a slightly similar situation a few years back with a 94 Buick Park Avenue. Id be driving down the road and it would die. Pull off the road, turn the ignition off and back on and it would crank right up. No trouble codes would set. It got so bad I could shift to neutral, turn the ignition off and back on and crank it back up without ever slowing down. After about 6 months it finally set a code (dont remember what it was now). When I followed the steps to troubleshoot the component, it was good. Turned out the ECM was bad. I replaced it and it never died on me again.

I'd think there's a good chance yours is bad but if it were me I'd obviously wait until I could prove it before replacing it.

Jim

 
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02-11-18, 09:40 AM   #9 (permalink)  
My tow buddy, who's a way better mechanic than I'll ever be, keeps reminding me I'm into uncharted territory with 300k miles on it. I'll post more if anything changes. Not even sure I could FIND an ECM if I needed one.


Measure it with a micrometer; cut it with an ax.

 
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