1990 4.3L TBI not firing

[Creatine]

Hi everyone,

I am trying to problem solve my friends truck. I will list everything that I know has been done/tested so far, so you can better assist me in helping him out.

The truck was running fine, up until a starter was swapped out of the truck. Then electrical problems existed ever since. Somehow, the fuel pump was not turning on, so they jumped it with a straight 12V from the fuse panel (no inline fuse). It ran for about 4 days then died (the truck not pump). My friend started school so he parked his truck ever since, and its been over a month now.

He is trying to get it going again, so I started testing a few things. We have compression and spark, I put some gas down the carb and she tried to start each time. I also manually pulled plugs and wires and checked that they were ok. The fuel pump is running (gota love GM FPs) I can hear her going all day. The fuel pressure I am not sure of yet, but will be picking up a local test kit to get back at you on the pressure. Seeing as they did not put a fuse in, I could see that messing it up. There is no fuel spraying out of either of the injectors.

I pulled off the injectors and hooked up my multimeter and got practically 0V coming out of either of them. I was told the best way to test these though is with a NOID light or using a 194 bulb. When I get a chance I will do so.

I don't see what problem from changing just the starter could have caused all this to happen. Maybe the mechanics tried messing with the truck, idk. Before it went to the shop the truck ran mint.

I have seen around the internet of similar problems relating to the PCM, bad grounding, fuses, or not enough fuel pressure. How can I test if the PCM has gone bad. He said he has checked his fuses but thats only his word right now, I will manually check them myself when I visit him again on wednesday (it was dark at the time with no light when I tried last week)

What other steps/tests should I preform?

Thanks,

Kevin

[MT-2500]

Originally Posted by Creatine

Hi everyone,

I am trying to problem solve my friends truck. I will list everything that I know has been done/tested so far, so you can better assist me in helping him out.

The truck was running fine, up until a starter was swapped out of the truck. Then electrical problems existed ever since. Somehow, the fuel pump was not turning on, so they jumped it with a straight 12V from the fuse panel (no inline fuse). It ran for about 4 days then died (the truck not pump). My friend started school so he parked his truck ever since, and its been over a month now.

He is trying to get it going again, so I started testing a few things. We have compression and spark, I put some gas down the carb and she tried to start each time. I also manually pulled plugs and wires and checked that they were ok. The fuel pump is running (gota love GM FPs) I can hear her going all day. The fuel pressure I am not sure of yet, but will be picking up a local test kit to get back at you on the pressure. Seeing as they did not put a fuse in, I could see that messing it up. There is no fuel spraying out of either of the injectors.

I pulled off the injectors and hooked up my multimeter and got practically 0V coming out of either of them. I was told the best way to test these though is with a NOID light or using a 194 bulb. When I get a chance I will do so.

I don't see what problem from changing just the starter could have caused all this to happen. Maybe the mechanics tried messing with the truck, idk. Before it went to the shop the truck ran mint.

I have seen around the internet of similar problems relating to the PCM, bad grounding, fuses, or not enough fuel pressure. How can I test if the PCM has gone bad. He said he has checked his fuses but thats only his word right now, I will manually check them myself when I visit him again on wednesday (it was dark at the time with no light when I tried last week)

What other steps/tests should I preform?

Thanks,

Kevin

A lot of them in them years had a 12 volt feed wires from starter solenoid to electrical power with Fusible links at starter solenoid and some had a fusible link connection on firewall and some atalternator.
Start at battery and check cabels both neg and pos.
Check for good 12 volt power to all electricl stuff.
Like fuse box and ign switch.

On checking fuses always check all of the for 12 volts on both sides.

Then check for lose of spark to spark plugs and for good fuel pressure.

Post back if you are losing spark or fuel pressure or 12 volt power.

[Creatine]

I have been tracing back all the wiring, and the injectors were getting power, just not grounding out. None of his lights are working either, but the truck has spark.

Just to test and try and get the truck firing, I tried running the ground wires from the injectors off the main harness to the body. I got a good reading across the injectors now. Still didn't start, his gas was very watery and stale. So were gonna try and flush it out and put some fresh gas in and try again.

Any other suggestions to fix this wiring issue? I've tried to trace the main harness, and see that the main negative terminal goes to the engine block on top, and the computer runs to a ground on the firewall. Theres 2 wires coming off his firewall ground that have weird ends and no connection to them. Someone also said that putting the new starter in may have caused some issues with the electrical, since it started when the new one was put in.

I can't really do much without finding a wiring schem. if anyone has one it would be greatly appreciated. Some redneck had this truck before and has bu chard this harness.

Oh, and is the pcm located on the firewall? I see a little black box mounted near the wiper motor with a few wires coming out but don't know what it is.

[Creatine]

Okay I didn't really think the PCM/ECM is the same, but I found a wiring diagram off the internet, and it helps me see things better since this one is labelled completely. Now I can trace most of the problems, I'll report back to you guys

[Creatine]

Correct me if I'm wrong here, but what I did was wrong. The blue and green wires that I know were ground based on this wiring diragram, ground through the PCM. So If I am bypassing that to just ground in the truck, the PCM won't be controlling the injectors, which is prob why it didnt fire even with the stale gas, am I wrong?

Or should the engine still have fired if everything else is fine? BTw, all fuses are good.

http://www.moates.net/files/6)%20Mis...%20Diagram.gif

[old_master]

Grounding the injectors like you did, will fully open the injectors when the ignition is in the RUN or START position. It may have damaged the injector drivers in the ECM, and, if left energized too long, may have overheated the injectors. Both red wires at the injectors must show battery voltage when the ignition is in the RUN and START positions. The pickup coil in the distributor sends data to the ECM. The ECM uses that data to fire the ignition module, which in turn fires the ignition coil, (all that stuff is working). It also uses that data to send a pulsed ground signal to the injectors to fire them at the proper time. Get the NOID light on the injectors and check for blinking when cranking. If that's OK, check fuel pressure, should be 9psi to 13psi when the pump is running.