'92 350 with mild street cam, 5spd manual box, custom-tuned TPI with true dual exhaust, O2 only on left bank. Engine starts immediately, idles smoothly. Stumbles to rev, gets shaky like it's missing when revved. Drives semi-normally in first gear, but shift to second and get muffled backfires that sound like they are in the exhaust and no power (literally can't handle more than first gear only).

Left side exhaust is hot and flowing fine, right side is cold, weak and smells of raw fuel. I've removed exhaust flow restrictions on both sides.

NO OBD CODES FROM ECM.
It last ran fairly normally about six months ago on a 10-mile trip to a body shop for some paint/body restoration work unrelated to the engine. Ran fine even for a couple miles at highway speeds. Shop called me after completing work on it saying the battery was dead and it would no longer start, no further explanation. Total dicks about it. Car had to be towed home. The battery had to be replaced and the engine was in crank/no-start condition. Replaced ignition module and it started right up but now runs poorly as described. All other replacement parts listed were done BEFORE this occurred.

Stuff I've recently done:

Compression checked both sides, all good 165+
New ignition module
New dist. cap & rotor
New plug wires
Cleaned & gapped plugs
Replaced all fuel injectors
Verified firing order on each plug wire
Verified spark ignition with tester
Verified fuel injector harness wiring is good
Fuel tank drained and refilled with fresh 92 octane
Checked for vacuum leaks, replaced bad hoses/plugs/elbows where found

I've been up and down everything I can think of that could have been damaged or disconnected but I haven't found anything out of the ordinary on it at all.

What's unchanged: Ignition coil, MAP sensor, distributor, engine internals, air temp sensor, timing

Would an ignition coil or MAP do this? Doesn't seem to me like it would.

Community insight appreciated.

 

Verify timing with esc disconnected is at 6 btdc. Check fuel pressure via mechanical gauge on schrader valve, should be 38-43.5psi. Verify all sensor data is accurate via live data stream comparison with reference values in factory service manual. Smoke test intake manifold.

 

Someone might bring up that not all ICMs are created equal...but let's concentrate on the cold right bank. I'm not for certain that a busted fuel pressure regulator diaphragm could introduce so much unmetered fuel that it would cause the entire right bank to not fire. Being that it dumps near the 6-8 cylinder runner those would be affected more than 2-4 cylinder. With that said, check the vacuum line for any fuel before you dive into checking fuel pressure.

 

Exactly. Any one of the sensors could cause the problems you're experiencing.

 

I agree with another new icm, they seem to go bad often and never trust anew one either. I would then check all other sensors on laptop .

 

Fuel pressure verified, I have a gage on the fuel rail with an adjustable regulator. No fuel in vacuum line either.

 

What ign module did you put in it?
did you check the pickup coil? The reluctor wheel in good shape? Not rusty, broken or cracked around the rivits?

 

This can definitely make the car run like crap.

 

Aftermarket cam needs more timing. im running 14° ish. about 1/2" before the last advance mark. Est will cause hard starts cold but will even out after a few seconds. Id advance the timing a bit and see how it does. Make sure engine is warm.
Goodluck to you brother ✊

 

Looks OK I think.


Ignition module is of unknown origin, spare I had in the garage. Unlikely to be from Amazon or eBay though.

 

GM H.O.T. cam, not aftermarket and the timing has not been changed since it was built.

 

Pickup coil Needs ohm tested, the ign module doesn't look to be a GM part. May want to look in to testing that too. Id be putting in a GM/delphi unit if it was me. Or buy a nos GM distributor, big bux but 100% worth it.

 

This is what you want to be looking at when doing a visual inspection.



GM Small Cap HEI Distributor Magnet Cracks.

 

Anything that affects the engine timing is going to be a major can of worms. This has NO timing marks anymore. Since the balancer is not visible due to its extreme placement in the engine bay, the marks were painted on the flywheel ring gear to set the timing from beneath when the car was restomodded 23 years ago, but have long since worn away. Tampering with the distributor in any way that affects timing would mean having to determine that all over again from scratch. So, that's one thing I just can't touch on a hunch.

I can, however, ohm out the pickup coil without too much trouble. What should it test at?

 

you can find tdc and upgrade to a timing mark. Would be a overall improvement

 

I'd be really curious to see a photo of this extreme balancer location. If you can't set your timing with a timing light, I think that's probably a prerequisite problem you need to solve.

 

Did the body shop do any welding on the vehicle?

 

Great question - can't say for sure. It was placed on a straightening rack to get the hood to open/close/align properly, but I don't think any welding was done or would have been necessary.

 

I had a thought the other night that maybe the TPS could have something to do with this, so I set up my scanner connection and checked it. 0.56 base voltage, full sweep up to WOT. I had the same part in a different car so I was ready to swap it out to test, but its behavior was normal.

I don't think the IAC could cause this so I'm leaving that alone.