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.

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.

Re: Backfire through Intake/Stalling on "Cold" Starts
 

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.

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!

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.

Re: Backfire through Intake/Stalling on "Cold" Starts
 

Did you ever figure it out? I'm having the exact same problem.. :doh: I've done Fuel Filter, Coolant Temp Sensor, Plugs & Wires, Ignition Module & Coil. My next step is O2 sensor and then probably MAF, TPS, IAC.. Fuel Pressure Regulator? I unplugged my MAF and started the car and the backfire persisted.

Re: Backfire through Intake/Stalling on "Cold" Starts
 

I posted this in 2018 wow I cant believe it.....its 2022 and unfortunately yes I am still struggling with this issue, however, refuse to get rid of my car...... It has treated me so good for 12 years. I have tried everything except for a leak-down test which I will try out this summer. If you are having the exact same problem O2 sensor would be a waste since the O2 sensor has no function until the engine is at operating temperature(closed-loop) and does not relate to a start stall issue. Please keep me posted also if you resolve your issue.

If you have not checked your injectors try that ohm them when cold and hot see if they are all the same. Heres a good video to test their mechanical function.

Re: Backfire through Intake/Stalling on "Cold" Starts
 

Alright, i'll keep you posted if I solve the problem. Did you ever consider timing?

Re: Backfire through Intake/Stalling on "Cold" Starts
 

I had several issues at the time but the hot start problem I was having was cured by replacing the ICM in the distributor. My 1992 Firebird uses the small cap version which was relatively new. The hot summers here in Texas apparently caused it to fail. I had to replace the starter motor with a smaller high torque version as it being too close to the headers caused it to expand the winding's and lock up (the other cure was to open the hood and let it cool for roughly 20 minutes).
This website is also helpful: https://easyautodiagnostics.com/gm/4...ed-icm-tests-1
I do remember taking that ICM to an auto parts store for testing which indicated it was good - but the module - using my own bench test would not fire a spark plug.
Good Luck!

Re: Backfire through Intake/Stalling on "Cold" Starts
 

timing is good, and once warmed up runs good once in a while might have the odd bog down but all in all no issues once its running but always idles high

Re: Backfire through Intake/Stalling on "Cold" Starts
 

Have you tried advancing the timing? I read on a similar thread that a few other guys advanced their timing past stock and it alleviated the problem. The reason why the backfire goes away once it warms up is likely because the timing automatically advances itself when it gets hot. I quoted this all from another thread, so I did a really poor job of explaining it —I’ll try to find link to it later. But yeah I’d try advancing a few degrees.

Re: Backfire through Intake/Stalling on "Cold" Starts
 

Update: I solved my problem. New MAF Sensor did the trick. ill attach a post with some videos later.

Re: Backfire through Intake/Stalling on "Cold" Starts
 

Been a while still have the problem.. changed intake gaskets also still same issue no resolve.

Re: Backfire through Intake/Stalling on "Cold" Starts
 

Well, one thing you could do is a smoke test to verify you don't have vacuum leaks. Could have a strange one not gasket related. Another thing would be to gather a datalog, see what the ecm is thinking while it's acting up.