Backfire through TBI

[RI95Tahoe]

1995 Suburban 5.7L Automatic 4WD.

Truck was running rich (could smell fuel in the exhaust), had to feather it to get it to drive (anything over 1/4 throttle would cause it to sputter and backfire both exhaust and intake).

Done so far:

Replaced fuel regulator (old one had a small tear in it)
Replaced TPS (tested and it was bad)

Full tune-up (plugs, cap, rotor, wires)
Note: Old plugs were burned one one side of electrode but clean on other side

Test coolant temp sensor and tested within Ohm limits

Checked spray pattern with stobe light -- good spray

Timing is at 0 deg with computer disconnected

Disconnected EGR valve and plugged line (no changes)

I do have a code for the IAC, which truck does idle high when you cold start it and returns to normal once warmed up

So....I'm at a point where the truck idles great, no issues when I rev it up in park (revs smoothly up and down), but as soon as I attempt to drive it it cuts out then backfires through intake. Will idle in gear without an issue.

Any insight would be appreciated. Really can't afford to keep throwing parts into it.

 

[UrbanSuburban]

Wow, its been a long time since I did any thing with OBD1 and it looks like you are covering a great deal of bases. The best advice for this vehicle is to use a good scan tool, which means either a Tech 2 or a High end Snapon, scantools of that vintage especially for GM did not give you much to work with. From what you are describing, it may come down to replacing the ecm, which was great deal easier than the ones today.

 

[RI95Tahoe]

I usually don't have this much of an issue, all I've mostly owned is early 90s Tahoes and Burbs, but this has been a challenge. Hopefully will get to check out the ECM this weekend.

 

[exp500]

Ohm test the coil and ICM. Did the reluctor look rusty falling apart when you had cap off? In all of my TBI trucks only replaced one ecm and later determined the relutor was the cause. ( I had parts trucks). When timing light on it does timing stay rock steady( unplugged)? Backfiring most always Ignition first, then mechanical. Are your Injector lead wires( clip ons) twisted all the way? Use fingers and move EGR valve, should move smoothly, and watch for full return to closed. Sometimes can check them running without burning fingers too bad. For egr to backfire, has to be really too far rich and EGR stuck way far open.

 

[OR VietVet]

Needs a compression test and check for vacuum leaks. Plus, you said it ran rich. Needs oil change for all the oil mixed with fuel. Also, check the pickup coil wires for a rub thru at the insulation and any of the other recommendations.

 

[Fless]

The OP was last seen almost 2 years ago.

 

[OR VietVet]

Good catch.

 

[wjburken]

Looks like a classic case of TYF thread Archeology.