TBI issue

[cods]

Hi y'all. very new to this forums, but I've run out of options. have an '87 r10 w/ 350 tbi. bought the truck and it ran long enough to get it home. now it won't stay running. I have gone through multiple different parts to get it running includin: new egr, distrib., ignition coil, ignition module, fuel pump, fuel pump relays, and probably more that I'm forgetting. I have fuel coming to throttle body when cranking, I have spark. just no fuel spraying into throttle body. will start and run off of gas or ether. please help with some possible diagnoses, I'm still learning about TBI. thanks a ton.

 

[Georgeb]

Check for injector pulses. Any trouble codes? Check the fuel pressure when cranking. Blown fuses?

 

[cods]

Check for injector pulses. Any trouble codes? Check the fuel pressure when cranking. Blown fuses?

no codes or blown fuses. don't think the injectors are pulsing though. I'm not sure why they're not. also, how would I check fuel pressure?

 

[cooter55]

If the injectors are good, you should hear them cycling - a fast ticking sound. Dirt and crud in the fuel line will mess up injectors real fast.
Check your wire from the coil to the ECM(similar to tach signal) If the ECM is not getting a signal that you have ignition voltage, the pump will run for a couple of seconds and then the ECM will shut it off.
Another issue could be a broken spring or bad diaphragm in the throttle body pressure regulator.

 

[jmbcary44]

if they're just stuck or dirty they really aren't that hard to take out and soak to clean, if you get a TBI rebuild kit ( I think mine was like 30 bucks) it usually has new filters plus you could just rebuild it with the gaskets and what not. fairly simple process. However I have a 91 so im sure my TBI is a bit different.

I have read about this issue quite a lot however on different forums and while cycling I may not have an answer for I always seem to read in the end there was an EGR issue or PCV or one of the vacuum lines going into the TBI.

just .02

 

[cods]

If the injectors are good, you should hear them cycling - a fast ticking sound. Dirt and crud in the fuel line will mess up injectors real fast.
Check your wire from the coil to the ECM(similar to tach signal) If the ECM is not getting a signal that you have ignition voltage, the pump will run for a couple of seconds and then the ECM will shut it off.
Another issue could be a broken spring or bad diaphragm in the throttle body pressure regulator.

sorry I haven't responded to this post in a while, I've been pretty busy but I'm ready to get my damn c10 back on the road. I narrowed it down to, my injectors not getting power through my wiring. noid light did not flash and proved so. how do i know if my wiring is bad or my whole ecm is?

 

[cods]

if they're just stuck or dirty they really aren't that hard to take out and soak to clean, if you get a TBI rebuild kit ( I think mine was like 30 bucks) it usually has new filters plus you could just rebuild it with the gaskets and what not. fairly simple process. However I have a 91 so im sure my TBI is a bit different.

I have read about this issue quite a lot however on different forums and while cycling I may not have an answer for I always seem to read in the end there was an EGR issue or PCV or one of the vacuum lines going into the TBI.

just .02

& do you really think that dirty or stuck injectors could cause them not to spray? by the way, your 91 tbi is the exact same as my 87 tbi. all tbi is basically the same across the board as far as setup. just different power flow and wires to ecm.

 

[jmbcary44]

I definitely think if they were clogged enough it could cause poor flow but with back pressure I would still think something would be coming out or I guess it could just go into the return line. I don't think it would ever flood from back pressure like a carb or something could possibly do.

If and when the issue is fixed I do believe new injectors are fairly affordable also for our TBIs and there actually some sites floating around that specialize in selling performance ones or rebuilding the ones you already have which could also just be an overall benefit. I read somewhere on here to about 454 injectors also but I think psi may have to be bumped up.

hopefully someone with more experience on this will speak up as I will admit I am fairly new to TBI also, I have had my 91 for about 4 months

 

[cods]

I definitely think if they were clogged enough it could cause poor flow but with back pressure I would still think something would be coming out or I guess it could just go into the return line. I don't think it would ever flood from back pressure like a carb or something could possibly do.

If and when the issue is fixed I do believe new injectors are fairly affordable also for our TBIs and there actually some sites floating around that specialize in selling performance ones or rebuilding the ones you already have which could also just be an overall benefit. I read somewhere on here to about 454 injectors also but I think psi may have to be bumped up.

hopefully someone with more experience on this will speak up as I will admit I am fairly new to TBI also, I have had my 91 for about 4 months

I agree that I think they would atleast spray poorly even when clogged. because when the injectors have the wrong pressure and get backed up, they still spray. UPDATE on mine though. I checked my injector wiring with a noid light and they are not getting power so I either have bad wiring or a bad ecm. I doubt its the whole ecm that's bad. where my wiring connects in the firewall, it is all corroded as well. any suggestions on where to get new wiring without spending an arm and a leg?

 

[yevgenievich]

I agree that I think they would atleast spray poorly even when clogged. because when the injectors have the wrong pressure and get backed up, they still spray. UPDATE on mine though. I checked my injector wiring with a noid light and they are not getting power so I either have bad wiring or a bad ecm. I doubt its the whole ecm that's bad. where my wiring connects in the firewall, it is all corroded as well. any suggestions on where to get new wiring without spending an arm and a leg?

A part out or junk yard would have the harness. Injectors should take a constant 12v and a switching ground from ecm. You can check if supplying constant 12v on the cotrect wire makes it run.

 

[cods]

this is where all of the harness wires go. this thing is completely corroded to all hell though. I checked at half a dozen junkyards today and could not find a harness. does anyone know which of the wires is the main ground? or the name of this part so I can look up a diagram?

 

[yevgenievich]

this is where all of the harness wires go. this thing is completely corroded to all hell though. I checked at half a dozen junkyards today and could not find a harness. does anyone know which of the wires is the main ground? or the name of this part so I can look up a diagram?

That does not look bad. Also wiring for tbi comes through the firewall near the hvac box and the distributer. Verify if you in fact have no 12v at the injectors and try to apply 12v with a jumper.

 

[cooter55]

A safer way to test the injector is to use a 9 volt battery, hook up positive to positive on the injector and momentarily touch the ground to ground. do not leave connected because you could toast an injector coil. You should hear if cycle or click.

I would also put a fuel pressure gauge in line to the TBI and verify that the pump is supplying 11-13 PSI. Also, if the ECM loses an ignition signal it will shut off the fuel pump. It will turn over all day long but no fuel will go to the TBI.

 

[jmbcary44]

A safer way to test the injector is to use a 9 volt battery, hook up positive to positive on the injector and momentarily touch the ground to ground. do not leave connected because you could toast an injector coil. You should hear if cycle or click.

I would also put a fuel pressure gauge in line to the TBI and verify that the pump is supplying 11-13 PSI. Also, if the ECM loses an ignition signal it will shut off the fuel pump. It will turn over all day long but no fuel will go to the TBI.

That's a good trick. Hey for my own knowledge because I wanted to add a gauge too do you recommend one that is complete inline before the TBI or one that actually screw into the input and just has the line on the other side? I guess I need to take mine apart and see what size that connection is

 

[foamypirate]

That's a good trick. Hey for my own knowledge because I wanted to add a gauge too do you recommend one that is complete inline before the TBI or one that actually screw into the input and just has the line on the other side? I guess I need to take mine apart and see what size that connection is

Get one for after the fuel filter. I bought one of the RVMorse ones that goes by the TBI unit, and it doesn't fit for ****, you have to bend your fuel line all ghetto and leave your ignition coil bolted on with just a single bolt. It was a waste of money.