1987 c20 New fuel pump, injectors not injecting

[nitrousluvr]

Fuel pump died, installed new fuel pump and grinded chassis clean for a nice clean ground. Started right up but stalled on me. Understandable cause I have a ton of broken vacuum hoses I needed to address after I had this fuel problem finished. Thought I finished this fuel problem, left town for a week for work, came back and no fuel is coming out of the injectors even though the fuel pump is priming. The fuel filter was already replaced. Chasing my tail around this cause ECM B fuse is good, relay is good, new fuel pump, new fuel filter, clean ground for fuel pump. Could the injectors be bad? Should I use a test light for the wiring harness for the injectors? What should I do if i’m not getting power to the injectors?

Thanks. Electrical isn’t my forte and I’m almost certain this is something electrical. Had to pull the transmission to fix some freeze plugs before the fuel pump died, so I’m getting kind of sick of this truck even more since I only drove it probably 15 miles since I bought it.

 

[Redfish]

What about the pressure regulator? I know they can go bad but I don't know what direction they fail.

Also, have you checked the oil pressure switch at the back of the engine? It's sort of hidden against the firewall. It looks like a pressure sending unit but it is actually a pressure switch and it is tied into the fuel circuit. It should provide power to the pump if the relay isn't working.

 

[WP29P4A]

If it worked before you pulled the transmission and not after, there is a good chance you inadvertently disturbed some wires or a ground on the dual tank valve (pollick valve) or the oil pressure switch Redfish mentioned on the back of engine while removing bolts for trans. A through inspection of wiring close to trans would be where I would start.

 

[JoeR Jr]

Do a quick check to see if you have spark. If the ignition module or pickup coil went bad you wouldn't get an injector pulse.
In order for the PCM to fire those injectors, it needs to see a 5V pulse from the module on the purple/white wire from the distributor, so it might not be a fuel pressure problem.
Joe

 

[bucket]

Do a quick check to see if you have spark. If the ignition module or pickup coil went bad you wouldn't get an injector pulse.
In order for the PCM to fire those injectors, it needs to see a 5V pulse from the module on the purple/white wire from the distributor, so it might not be a fuel pressure problem.
Joe

Yep, exactly! My vote goes to a failed ignition module.

 

[nitrousluvr]

Rebuilt the TBI, so it’s not the fuel pressure regulator. Don’t think it’s the ICM or pickup coil. I just checked the injectors with a test light. Two of the wires makes the light come on, I don’t know if there’s supposed to be pulsing but it’s not. WP might be right though, it was able to start before I installed the transmission. I’ll check over everything else you guys mentioned. Thanks

 

[nitrousluvr]

If the ICM or pickup coil would be bad, would I still be able to get a test light from the injector harness but it wouldn’t be pulsating? I don’t know if this helps but I also got spark, shot some brake clean into the intake and then the truck started for a few seconds

 

[bucket]

You can make an injector test light easily with a 194 bulb and socket. Just insert it into the injector connector, the light should pulse while cranking.

I can't remember for sure, but I think it switches the ground side of the injector connector.

 

[nitrousluvr]

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Replaced what looks like the original ICM. Still no progress. There’s an electrical connector near the bell housing that was unplugged and don’t know where it goes to. Also, would a real ugly slow sounding starter trip the oil pressure switch into thinkings there’s no oil pressure and cut the fuel? I got an extra GM starter in my garage but I’m probably overthinking this.

 

[nitrousluvr]

I’m going to test the injectors again and check if it’s pulsating with the new ICM

 

[bucket]

A lack of oil pressure will not cut power to the fuel pump circuit. However, the presence of oil pressure will provide power to the fuel pump in the event of a pump relay failure, when the system is operating properly. If the oil sender is unplugged, obviously that feature won't work.

 

[Redfish]

A lack of oil pressure will not cut power to the fuel pump circuit. However, the presence of oil pressure will provide power to the fuel pump in the event of a pump relay failure, when the system is operating properly. If the oil sender is unplugged, obviously that feature won't work.

I am looking at a circuit diagram and I think you may be correct on this and I may be...I may be... wrong. I cannot see what is triggering the coil to pull in the fuel pump relay so I am still not completely certain.

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[bucket]

I am looking at a circuit diagram and I think you may be correct on this and I may be...I may be... wrong. I cannot see what is triggering the coil to pull in the fuel pump relay so I am still not completely certain.

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The ecm controls the fuel pump, which is also where the prime feature comes from. The oil pressure switch also sends 12v to the pump as a backup. So if a fuel injected GM vehicle doesn't have a prime and it has an extended crank time, it is often just because the pump relay has failed. Also to note, that diagram shows a fuel module that was used on certain trucks, but not used on others.

The whole "no oil pressure, no fuel pump" thing is old timer folklore and internet misconception. I never knew how the rumor got started to begin with, until a discussion here a few years ago. It apparently stems from Monzas and Vegas and such. Even though they were carbureted, they had an electric fuel pump that obviously needed controlled some how, so they received power solely from an oil pressure switch.

 

[Redfish]

@bucket your term "internet misconception" is exactly where I got my apparently incorrect information. When I first got this truck the oil pressure gauge didn't work. The sending unit under the engine and next to the oil filter was brand new so I assumed the issue was with the other "sending unit". The internet and the forums were evenly split about which sending unit was for the gauge and which "controlled" the fuel circuit. I ended up replacing both.

After I looked at the diagram I posted I am sure that you are correct and I repeated bad information. My apologies to the forum. I will go back and edit my earlier posts.

 

[bucket]

@bucket your term "internet misconception" is exactly where I got my apparently incorrect information. When I first got this truck the oil pressure gauge didn't work. The sending unit under the engine and next to the oil filter was brand new so I assumed the issue was with the other "sending unit". The internet and the forums were evenly split about which sending unit was for the gauge and which "controlled" the fuel circuit. I ended up replacing both.

After I looked at the diagram I posted I am sure that you are correct and I repeated bad information. My apologies to the forum. I will go back and edit my earlier posts.

Lol, the "which sender is which" thing still confuses me. It's all over the place. Either GM switched it up from time to time, or there's a bunch of trucks that have been engine swapped and the locations got swapped too.