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Backfire through Intake/Stalling on "Cold" Starts

Old 01-19-2019, 10:31 AM
  #1  
Junior Member
Thread Starter
 
Join Date: Jun 2018
Posts: 33
Car: 1988 Iroc-Z
Engine: 350 TPI L98
Transmission: 700R4 Auto.
Backfire through Intake/Stalling on "Cold" Starts

Hello there,

I am having issues with my 88 Iroc-Z 350 TPI.

Every time I start it after sitting ("cold engine") no matter what the temperature is outside, the engine will run a few seconds and stall out. I have to restart the car between 7-10 times before it will run. As I am doing this I must rev up the engine (to prevent it from stalling). While I rev up the engine there is significant backfiring through the intake which can be felt by resting your hand on the snorkel/air breather.

After the car eventually gets running there are no issues (despite my idle issues in park/neutral but that's another thread I have which I haven't gotten to the bottom of). I can drive it all day beautiful. And will start no problem for the rest of the day until it is left to sit lets say.... 4 hours or so. Then the process repeats. So i know its happening on a "cold" engine, and is most likely a lean condition upon start up?

I have a new distributor cap & rotor, wires, plugs, IAC, TPS, MAF, Coolant temperature sensor, fuel pump, fuel sending unit, fuel filter and no vacuum leaks I checked everywhere. I have put a vacuum gauge on it and it holds steady 20 inches of vacuum. Good compression. NO ENGINE LIGHT.

Any help would be appreciated.

Thank you.

Last edited by BlksIrocZ; 01-19-2019 at 10:34 AM.
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Old 02-03-2019, 04:59 PM
  #2  
Junior Member
 
Join Date: Apr 2010
Location: Waxahachie, TX
Posts: 50
Car: 92 Firebird Convertible
Engine: 383 - First Fuel Injection TPI
Transmission: 700R4
Axle/Gears: 3:23
Re: Backfire through Intake/Stalling on "Cold" Starts

I unfortunately experience the same cold start problem at times. I have had an occasional "backfire" issue during a hot weather start but it is intermittent which is frustrating.
I am surprised though that you haven't gotten a response as yet.
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Old 02-03-2019, 05:15 PM
  #3  
Junior Member
Thread Starter
 
Join Date: Jun 2018
Posts: 33
Car: 1988 Iroc-Z
Engine: 350 TPI L98
Transmission: 700R4 Auto.
Re: Backfire through Intake/Stalling on "Cold" Starts

Originally Posted by gw082008 View Post
I unfortunately experience the same cold start problem at times. I have had an occasional "backfire" issue during a hot weather start but it is intermittent which is frustrating.
I am surprised though that you haven't gotten a response as yet.
No responses unfortunately no. However I will not abandon my posts if I find the issue and resolve it I will post back here. In the spring I plan on going all out to find the problem. I am going to check for timing chain slack, EGR function more thoroughly, Individual injector pulse, Smoke test the intake for leaks, even a back pressure check. I will HAVE TOO!!!! find the problem after those checks since thats the only things I have not tried yet.

I notice you have FIRST FUEL INJECTION system. Did you tune after installing it? Maybe your problem has something to with that? Just a suggestion.
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Old 02-04-2019, 11:00 AM
  #4  
Junior Member
 
Join Date: Apr 2010
Location: Waxahachie, TX
Posts: 50
Car: 92 Firebird Convertible
Engine: 383 - First Fuel Injection TPI
Transmission: 700R4
Axle/Gears: 3:23
Re: Backfire through Intake/Stalling on "Cold" Starts

I use the EBL P4 system and Tuner Pro for tuning.
I had thought I had pretty much solved the "cold start and die issue" but it's reappeared.
I admit to "tinkering" with my tune and perhaps made an unintended change. I'm now in the process of rechecking settings.
The "backfiring" problem seemed to occur during hot weather after the engine was shut off for only a short time - drive 5-10 miles stop for 10-15 minutes - then have the restart issue which occasionally mimics either too much timing or a hydro-lock condition - but only intermittently and would not do this with every restart. Frustrating!
I suspect a leaking fuel injector although when I check the fuel pressure gauge I have installed it does not indicate a great loss. The frustrating part is after looking at the gauge it usually starts normally.
When removing the gas cap I do seem to have excessive pressure. I cleaned the fuel tank relief valve a couple of years ago and perhaps I need to do this again.
I - like you need to find the time to find the problem so good luck!
Hopefully other members will provide some suggestions!
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Old 02-04-2019, 11:24 AM
  #5  
Junior Member
Thread Starter
 
Join Date: Jun 2018
Posts: 33
Car: 1988 Iroc-Z
Engine: 350 TPI L98
Transmission: 700R4 Auto.
Re: Backfire through Intake/Stalling on "Cold" Starts

Check your coolant temperature sensor they can cause issues and seem to go unchecked with no suspicion towards them.
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