Strange timing issue - 1991 s10 4.3L

[Timearley89]

Hi all,

I can't seem to get this truck running properly for the life of me. I need to get it fixed tonight, if at all possible.

When the timing is set to 0 on the balancer, the starter turns the engine, but about every second to 2 seconds, the lights dim and it stops turning, almost as if the engine is "pushing back". I can get it to run (kind of) if I advance the timing by turning the distr. housing, but when it runs it runs very rough, and dies after it slowly seems to lower rpm until stalling.

I've tried turning the distributor 180 degrees, rewired the spark plug wires to the proper firing order (165432) several times, replaced the fuel pump, fuel filter, cleaned the IAC, cleaned the tbi assembly and injectors, and replaced the battery.

When I try to start it (even with advanced timing) without the 4-wire connector plugged into the distributor, it just cranks over and over, and doesn't fire (I get the impression this is abnormal). I also adjusted the timing away from zero a bit and almost always seemed to get some backfiring through the throttle body when the pdeal is depressed, usually once it slows down to a low idle speed, before stalling.

It seems to be acting like it has very retarded timing via the ECM, right? Or could the timing issue be due to a worn internal component somehow causing the timing to need more advance?

I haven't worked with TBI before, and although I believe I understand the concept fairly well, there could be something I'm overlooking that wears out somewhere to cause timing to need to be bumped up to compensate at idle.

At this point I'm out of ideas, except for advancing the timing as far as I can before things start breaking to see if it will keep running enough to drive it to work. Thanks for any help you can give.

[Palf70Step]

I have not had to do mine in many years, but I believe there is some wire you must disconnect first before you adjust the timing. Far as I know there is no adjustments with a 4.3 distributor. Everything is changed at/by the computer.

[Timearley89]

Thanks for the reply. I did read about that wire, but have been unable to find any wires that match the description. So I've been setting the timing up at dead TDC on #1, then removing ecm fuses for a few minutes, then replacing and trying to crank, expecting the computer to dial the timing in, as is designed.

I did find one thing though: the FPR spring is broken, and thus is applying less pressure to the fuel system through the diaphram, but could a lean condition cause a need for advance? If so, a new regulator kit may fix my issue, combined with adjusting the tps.

What do you think, does it sound feasible, like it could cause these types of problems?

[ChevyTech]

You MUST unplug the set timing wire to check or set the timing. If you don't the timing will be of between 12 and 22 degrees.

The wire should be a tan wire with black stripe inside the cab on the passenger side of the firewall within 6 inches of where the main computer harness come through the firewall.

If the fuel pressure regulator spring is broken the pressure will be low which can cause backfiring which could be interpreted as a timing issue.

[Timearley89]

I didn't realize disconnection of the set timing wire was so critical, thank you. I thought of it as something the ecm would reset anyway, instead of a "hard coded" signal to the ecm.

That means that a fuel pressure regulator kit and a proper timing setup *should fix my issues. I'll try that in a few hours once the part is shipped over.