TBI problems

[chrispbrown27]

Ok, a few weeks back on my 1987 Chevy V10 I redid the intake gasket and the valve cover gaskets trying to chase down a vacuum leak. Got it all back together and she wouldn't start. If I pour gas down the throttle body bores she will fire and run til the fuel is burnt up. I have been troubleshooting this since then. I have changed the fuel pump/sending unit, I can hear the pump kick on when the key is turned on, replaced the ICM, pickup coil, ignition coil, fuel filter, I have pulse at the injectors (tested with a noid light and I can hear and feel them pulse while cranking), I have continuity to the negative on the battery to grounds on the rear passenger head and front of the intake, I have 12 volts on one side of the harness at the injectors for each side.....what am I missing here?

 

[1987 GMC Jimmy]

Ok, a few weeks back on my 1987 Chevy V10 I redid the intake gasket and the valve cover gaskets trying to chase down a vacuum leak. Got it all back together and she wouldn't start. If I pour gas down the throttle body bores she will fire and run til the fuel is burnt up. I have been troubleshooting this since then. I have changed the fuel pump/sending unit, I can hear the pump kick on when the key is turned on, replaced the ICM, pickup coil, ignition coil, fuel filter, I have pulse at the injectors (tested with a noid light and I can hear and feel them pulse while cranking), I have continuity to the negative on the battery to grounds on the rear passenger head and front of the intake, I have 12 volts on one side of the harness at the injectors for each side.....what am I missing here?

It seems like everything is okay with the ignition stuff because your injectors are pulsing. Plus it's firing off with fuel being poured into the base. You hear the pump so the pump relay is fine. I'd pull the main line and see if it pumps fuel when you cycle the key. If you get fuel, I'd do a fuel pressure test to see if you're getting below or above the requisite pressure. If it's below, you're not gonna get enough momentum for the injectors to spray. If there's too much, it'll send it back to the tank. I'd also see if there's any leakage behind the TBI to make sure the regulator diaphragm is not split. My money's on insufficient fuel pressure. I'll go out on a limb and say your ignition system checks out and therefore the electronic aspect of your fuel system is okay. Also, I didn't hear fuel filter. May be worth popping on a new one if you haven't in a while. Autozone will let you borrow a fuel pressure tester kit. Remote chance there's a TPS undervolt but I'd say keep that in your back pocket for the moment, or you can probe the wires and/or unplug the sensor and see if it runs if you want to rule it out.

 

[chrispbrown27]

I did change the fuel filter when I changed the fuel pump and sending unit. I tested the tps a while back and it was fine, but I also have unplugged it a couple of times recently and it still won't start. I am leaning toward fuel pressure myself. I am wondering if possibly a fuel line has collapsed internally since I can't see anything externally wrong with any of the soft lines.
I forgot to mention that I also changed the oil sensor by the distributor to rule that out too.

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[1987 GMC Jimmy]

I did change the fuel filter when I changed the fuel pump and sending unit. I tested the tps a while back and it was fine, but I also have unplugged it a couple of times recently and it still won't start. I am leaning toward fuel pressure myself. I am wondering if possibly a fuel line has collapsed internally since I can't see anything externally wrong with any of the soft lines.
I forgot to mention that I also changed the oil sensor by the distributor to rule that out too.

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You've done everything that I can think of. There's a little something I can think of that I'm gonna buy in the next few months to ease diagnostics a little. I'm thinking the pump is doing too much or too little and/or the FPR is messed up. Have you rebuilt the TBI before? It's only a thirty dollar kit. The fitting that I screenshot screws in behind the TBI and the line screws into it.

 

[chrispbrown27]

Yes, I rebuilt the throttle body when I tore the intake down. What is the fpr?

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[chrispbrown27]

Fuel pressure regulator... Got it. I was thinking maybe something had fallen down into the throttle body while I was putting it back together, so I might pick up another kit and do it again... It's easy enough.

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[1987 GMC Jimmy]

Fuel pressure regulator... Got it. I was thinking maybe something had fallen down into the throttle body while I was putting it back together, so I might pick up another kit and do it again... It's easy enough.

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I mean, the rest of the stuff is just o rings and screens. You might save a buck by getting the diagraphm itself if that's what you want to replace.

 

[yevgenievich]

Easiest first check to see if you are even getting fuel by pulling the line. Then inspect the fpr.

 

[Rusty Nail]

Ground strap on the back of the cylinder head?

How did this all start, exactly? "Chasing down a vacuum leak"? So you pulled the intake manifold? What does that have to do with the valve cover?

 

[chrispbrown27]

The truck ran but it idled high. I tested with starter fluid and there was a surge when I sprayed it behind the throttle body. I figured it couldn't hurt to change the intake gasket and while I was at it I might as well change the valve cover gaskets too. After getting it all put back together it would not start. Gas down the bores and she fires and runs til the gas is gone.
I rebuilt the throttle body today and still the same issue.

 

[1987 GMC Jimmy]

Did you pull the line to see if you were getting fuel?

 

[chrispbrown27]

Yes plenty of fuel.

 

[87ChevyR10]

Maybe the injectors themselves are shot? Have you or someone else looked at them while cranking to see if they spray?

I don't know if it matters, but what if you have the injectors installed backwards and the terminals are connecting wrong? Just a thought.

 

[1987 GMC Jimmy]

I've read that there's no polarity therefore no polarity to reverse on TBI injectors. After two new FPR diaphragms, the problem has got to be the injectors themselves or maybe too high fuel pressure, and it's sending the fuel back through the return. I don't know what the quality is on replacement injectors, but I'd do a fuel pressure test to see what's going on. It wouldn't be the first time a replacement fuel pump was screwed up, anyways. Are you sure it's not like a 454 electric fuel pump or something? Those operate at higher pressure. I know that's a silly question, but you only have a couple options at this point.

 

[chrispbrown27]

As far as I know there is not polarity on the injectors and you can not install them backwards because there is a little pin on them that has to sit in a slot on the injector pods. Otherwise you crack the injector pod and get to search for a new throttle body...ask me how I know this.
The injector do click when they are pulsed with a 12 volt source. I actually have three sets (like I said ask me how I know that the parts of the throttle body crack easily). One isn't in great condition but the other two sets I have tested and as far as I can tell function as they should. Originally I was told that you could test the injectors with a 9 volt battery and I found out that it takes a 12 volt source to get them to cycle.
I have ordered an AC Delco ignition control module and I am going to try it out. The one I put on it was a house brand and I know that they can be picky about brands sometimes. I noticed that the voltage at the injectors was only around 5 volts, so I am wandering if the off brand icm isn't the issue. If this doesn't do it I guess she is going to sit until I can afford to pay someone to figure it out.