87 TBI troubles, please help

[AyWoSch Motors]

I've been working on my boss's 1987 V20 wood truck, and I cant get that pain in the ass to run reliably.

So far I've replaced fuel pump, fuel pump relay, all the rubber fuel lines, the map sensor, and changed out the pressure regulator that was off a truck that was running great. I also disassembled and cleaned the whole TBI and put on a new gasket set.
And unrelated I also replaced plugs, plug wires, rotor, distributor cap, and ignition module.

The day after I replaced all that, it started up first try, and ran great. I let it run for like 15 minutes idling, then I took it for a good 2-3 mile drive, no problem. Then a week later I tried it, and nothing happened. And I still can get it running.

So I can hear the pump pumping, I can hear the relay turning on and off, the pressure seems to be regulating as it should.
If you bottle feed it, it runs fine. And want is really weird, is that sometimes after bottle feeding it, itll stay running for a couple minutes then die. One time when it did that, I ran around under the hood and watched the injectors spraying as they should, then they just shut off like a switch and about 2 seconds later it stopped running.
I'm at a lost, can't figure it out to save my life.
I have a couple TBIs at home, but never had trouble with them like this one. I'm also unfamiliar with squarebodys with TBI. All mine have carbs, never messed around with an 87 before.

All I can think of, is either the brand new pump we just bought is defective, or the injectors are on their way out.

Please help, any insight would be greatly appreciated. I'm about to loose my mind with this stupid thing.

 

[SirRobyn0]

So the TBI system, think of it as a really simple injection basic injector system. GM started using the ESC system to control spark, some computer controlled carbs, and then TBI. So do you have the ability to hook a fuel pressure gauge to the shrader port on the fuel line near the throttle body? Knowing it has good fuel pressure would be helpful, but we can get around that if you don't have a gauge. Also when there is no fuel coming out of the injectors is there also no spark or does spark continue to be produced?

So here is how the system works, the pick up coil and the ignition control module are connected to the ECU, the ECU uses that information to know when and how fast to fire the fuel injectors. So if you loose both spark and injector pulse at the same time you'd most likely have a bad pick up coil in the distributor. You can test for injector pulse, by removing the injector connector off the fuel injector and connecting a test light (or noid light) from one terminal to the other on the injector connector on the harness side. Crank the truck and it should flash the light. That flashing is called injector pulse.

If you have no spark and no injector pulse it is most likely the pick up coil in the distributor. If you DO have spark, but NO injector pulse then you either have wiring issues, or a defective ECU. Pick up coils and ECU can sometimes be an intermitted failure. If you DO have injector pulse, but NO fuel then it's from lack of pressure for one reason or another, don't forget new parts can sometimes be defective.

If after you look at the injector pulse, you determine that there maybe a wiring issue look really close where the wiring runs into the throttle body and injectors, sometimes there is enough extra wire to catch it and crimp it between the air cleaner (or spacer if equipped) and the throttle body crushing the wiring. I've seen that one a few times.

If you have not flashed codes out of the ECM you should try to, these systems are notorious for not recording errors during cranking, but if there were to be a code stored regarding the camshaft position sensor (pick up coil doubles as that) it could be added confirmation of the problem. If you want / need to know how to do that let me know and I'll do a post on it.

Hopefully that helps, let me know if anything doesn't make sense.

 

[AyWoSch Motors]

So the TBI system, think of it as a really simple injection basic injector system. GM started using the ESC system to control spark, some computer controlled carbs, and then TBI. So do you have the ability to hook a fuel pressure gauge to the shrader port on the fuel line near the throttle body? Knowing it has good fuel pressure would be helpful, but we can get around that if you don't have a gauge. Also when there is no fuel coming out of the injectors is there also no spark or does spark continue to be produced?

So here is how the system works, the pick up coil and the ignition control module are connected to the ECU, the ECU uses that information to know when and how fast to fire the fuel injectors. So if you loose both spark and injector pulse at the same time you'd most likely have a bad pick up coil in the distributor. You can test for injector pulse, by removing the injector connector off the fuel injector and connecting a test light (or noid light) from one terminal to the other on the injector connector on the harness side. Crank the truck and it should flash the light. That flashing is called injector pulse.

If you have no spark and no injector pulse it is most likely the pick up coil in the distributor. If you DO have spark, but NO injector pulse then you either have wiring issues, or a defective ECU. Pick up coils and ECU can sometimes be an intermitted failure. If you DO have injector pulse, but NO fuel then it's from lack of pressure for one reason or another, don't forget new parts can sometimes be defective.

If after you look at the injector pulse, you determine that there maybe a wiring issue look really close where the wiring runs into the throttle body and injectors, sometimes there is enough extra wire to catch it and crimp it between the air cleaner (or spacer if equipped) and the throttle body crushing the wiring. I've seen that one a few times.

If you have not flashed codes out of the ECM you should try to, these systems are notorious for not recording errors during cranking, but if there were to be a code stored regarding the camshaft position sensor (pick up coil doubles as that) it could be added confirmation of the problem. If you want / need to know how to do that let me know and I'll do a post on it.

Hopefully that helps, let me know if anything doesn't make sense.

Well thank you. That seems like it will be very helpful.

I did take a paper clip and jump the A and B terminals and no trouble codes came up, just the check code.

And it will run without the injectors not firing if you pour a little down the throat with a water bottle of gas, so it has spark without the injectors turning on.
And I do not have a fuel pressure gauge to test the pressure. All I can say for the fuel pump, is when i turn the key,i can hear it turn on and off. And if I can get it run for a moment at all, after it dies, I can hear the pump whirring for a couple seconds, so I'd say its coming on and off like it shouldn't, but your right, could be defective, who knows.
I do have a test light though. So your saying, if I unplug the injector, and hook up the test light, I should see it lighting up as it cranks? And if not, that would mean either bad fuel pressure, a faulty ECM, or possibly a bad injector?
Is it possible for the injectors to be bad?
I did check to see if we had a crimped or cut wire there somewhere, all looks healthy. Plus,it does run here and there.
There are a few wires there in the engine bay that are not hooked to anything, but I don't think that's related. I have no clue the history on this truck, my boss bought it from some guy at the flea market.

 

[SirRobyn0]

Well thank you. That seems like it will be very helpful.

I did take a paper clip and jump the A and B terminals and no trouble codes came up, just the check code.

And it will run without the injectors not firing if you pour a little down the throat with a water bottle of gas, so it has spark without the injectors turning on.
And I do not have a fuel pressure gauge to test the pressure. All I can say for the fuel pump, is when i turn the key,i can hear it turn on and off. And if I can get it run for a moment at all, after it dies, I can hear the pump whirring for a couple seconds, so I'd say its coming on and off like it shouldn't, but your right, could be defective, who knows.
I do have a test light though. So your saying, if I unplug the injector, and hook up the test light, I should see it lighting up as it cranks? And if not, that would mean either bad fuel pressure, a faulty ECM, or possibly a bad injector?
Is it possible for the injectors to be bad?
I did check to see if we had a crimped or cut wire there somewhere, all looks healthy. Plus,it does run here and there.
There are a few wires there in the engine bay that are not hooked to anything, but I don't think that's related. I have no clue the history on this truck, my boss bought it from some guy at the flea market.

Sure it's possible the injectors are bad but it would run really bad when you get it running. Injectors are rarely intermittent.

Yes, you can check pulse to both injectors, disconnect the wiring from the injector and hook your test light across the connectors on the wiring harness side. crank the engine you should see it flash, if it flashes then it almost has to be lack of fuel pressure. If it does not flash and you do have spark then I'd be looking at wiring and ECM. Maybe possibly distributor, but typically if you loose the pick up coil you'll loose both injector pulse and spark, since you have spark that seems unlikely.

 

[SirRobyn0]

I should probably ask, does the truck ever stall out while driving? Or run bad? I have assumed no, but thought I should check

 

[AyWoSch Motors]

I should probably ask, does the truck ever stall out while driving? Or run bad? I have assumed no, but thought I should check

Before all this started happening, it was very hard to start, very hard to keep running, and very very easy to stall.
It ran pretty smooth considering, and once it was warmed up, itd stay running all day.

 

[SirRobyn0]

Before all this started happening, it was very hard to start, very hard to keep running, and very very easy to stall.
It ran pretty smooth considering, and once it was warmed up, itd stay running all day.

Interesting. I will think on that some. Another one off hand though, is if the coolant temp sensor is stuck reading to hot, it'll still get gas but run bad when cold, possibly to the point of not wanting to start cold at all. You could try looking up resistance specs for the sensor and test it with a multimeter, but the way it would normally be checked would be by looking at the temp on a scanner before starting it and seeing if it is close to outside temps. So in that case you'd be getting enough fuel pressure, you'd have injector pulse, but the pulse width (amount of time the injector is open) would be to short due to the ECM thinking it's already warmed up. No way to test pulse width using a test light, so maybe perform the other tests and then try a new or known good temp sensor.

 

[AyWoSch Motors]

Interesting. I will think on that some. Another one off hand though, is if the coolant temp sensor is stuck reading to hot, it'll still get gas but run bad when cold, possibly to the point of not wanting to start cold at all. You could try looking up resistance specs for the sensor and test it with a multimeter, but the way it would normally be checked would be by looking at the temp on a scanner before starting it and seeing if it is close to outside temps. So in that case you'd be getting enough fuel pressure, you'd have injector pulse, but the pulse width (amount of time the injector is open) would be to short due to the ECM thinking it's already warmed up. No way to test pulse width using a test light, so maybe perform the other tests and then try a new or known good temp sensor.

Hmmm, hadn't thought of that. That's interesting.
I will do some testing. Thank you very much

 

[SirRobyn0]

Your Welcome, hopefully something I've said will help you to get to the cause of the problem!

 

[AyWoSch Motors]

Okay, so am update on this:

Yesterday I took off the injector plug connectors off, put a test light in them, and had someone crank it. They lit up intermittently like they should. So I hooked it up, and gave it a crank, and it fired right up and was idled nicely. After about a minute, it just died randomly. Tried to start it and nothing. Checked the injector plugs again, and no signal no light.
A couple minutes later, just for kicks, I tried to start it again, and it fired right up, then after a second or 2 it just shut off like a switch.
Seems like its getting a intermittent signal from the ECM.
Any new thoughts anybody?
@SirRobyn0

 

[SirRobyn0]

Okay, so am update on this:

Yesterday I took off the injector plug connectors off, put a test light in them, and had someone crank it. They lit up intermittently like they should. So I hooked it up, and gave it a crank, and it fired right up and was idled nicely. After about a minute, it just died randomly. Tried to start it and nothing. Checked the injector plugs again, and no signal no light.
A couple minutes later, just for kicks, I tried to start it again, and it fired right up, then after a second or 2 it just shut off like a switch.
Seems like its getting a intermittent signal from the ECM.
Any new thoughts anybody?
@SirRobyn0

You have spark when there is no injector pulse is that correct? I'll think about this some more too.

 

[AyWoSch Motors]

You have spark when there is no injector pulse is that correct? I'll think about this some more too.

I didn't check that it has spark after the injector pulse went out.

 

[SirRobyn0]

Ok here's another thought for you. There should be some ground wires attached to a stud on the thermostat. These ground wires the computer uses. The injectors are constantly fed power, and the computer completes the circuit creating the pulse though those ground wires at the thermostat.

 

[SirRobyn0]

So in re-reading your first post this started happening after doing the ignition system work, and I reading that correctly? I'm wondering if you got a new module that isn't giving the computer a strong enough RPM signal? If you have a spare I'd swap it out just to see, especially if it was lower cost or off brand module.

Make sure that none of the wiring is damaged where the injector wiring leads to the injectors especially where it passes from the outside to inside the throttle body sometimes it gets rubbed in that little rubber bushing it passes though or someone damages it putting the air cleaner one, some times it take a while for a wire crimped for that to actually become a problem so if one or more of the wires has been flattened even if it didn't break though the insulation it could be a problem. Feel free to post pictures of the wiring and engine it might not tell us anything but maybe we'll spot something.

 

[SirRobyn0]

I didn't check that it has spark after the injector pulse went out.

be good to do that next time if possible.