I've got an 85 LG4 w / quadrajet. The problem is that it will cut-out under load, as when climbing a mild hill at around 3K RPMs. There is also a popping sound during deceleration from high RPMs.

The backfire is very muffled, more like a popping sound.

My only real mod is hedman hedders via Y-pipe. I've still got the stock cat and muffler on the car.

An interesting fact is that the car runs better with the o2 sensor disconnected. I was checking it out, found it disconnected, and then ran slighlty worse (rough) after hooking it back up.

I've got new plugs and wires on the car. I've set the IAB with a dwell meter. Unfortunately, I don't seem to have a timing tab. I thought that no timing tab was unusual, but I did a search and found that it wasn't totally uncommon.


diagnosis?

 

Well, I'll try to help out on the timing tab issue, anyway. It's directly behind the water pump at about the 12 o'clock position relative to the balancer (not over at 2 o'clock like may SBC's). When setting timing you want to disconnect the timing wire first so you are reading true base timing. THis is a 4-wire plug coming out the back of the distributor and down to the wiring harness that goes over the tranny bellhousing. Stock spec on an LG-4 is 0* BTDC but they can ALL be set to at least 4* BTDC, sometimes more, if using a stock computer chip for more power with not detrimetal effects.

Popping under load could be ignition, could be lack of fuel delivery, could be an exhaust leak. ANy more info you could give would probably be helpful.

 

Fuel delivery might be an issue. The car had some steel fuel line replaced with rubber fuel line. And, because the rubber can't 'turn' as sharply as steel without kinking, the rubber fuel line is significantly longer than the original.

thanks

 

I found the cause of the problem... My baro sensor (the one one the passenger side) was hooked up to manifold vacuum. In fact, my baro and vac sensor (MAP equivalent) were sharing the same vacuum port on the back of the carb, split via a t-connector. And, the tube to the vac sensor was 100% clogged.

I had seen the code 32 for quite a while, but had assumed that it was related to egr. But I only recently started getting the code 34 on the vac sensor. Then I did some searches on both, found that they were identical in appearance, often confused, etc.

Anyway, I disconnected the baro, ran a fresh vac line to the vac sensor, and the car runs MUCH better.

Many thanks to the thirdgen.org knowledge base...

 

What exactly do you mean when you say "baro sensor?" Is this a barometer sensor or what?

 

The baro sensor gauges atmospheric pressure, and adjusts timing accordingly. It advances timing at higher altitudes.