Fuel issue?

[85 Jimmy]

Ok, I know there is a section for this but it'll get more traffic in here.

This is on my TPI 350.

So Saturday I cranked my truck and let it run for about 20 minutes then drove it around my backyard and then parked it in the yard. Sunday I went to start it and it cranked and ran but when I was moving it around it acted like it ran out of gas, so I left it. The tank was close to empty so I figured that was the reason it died. Monday I put 5 gallons in it and attempted to crank it and it would do anything. Checked the fuel rail for fuel and there is fuel while the pump is pumping and while you crank the engine, but it doesn't hold the pressure in the rail. So I pulled the plugs and the plugs are not wet, so it seems that the injectors aren't squirting, but if you smell the exhaust while you're cranking it, it smells like gas. I would pull the injectors to see if they're pumping, but since it's a TPI I'd have to pull the upper plenum off. And I did check the fuses and all my fuses are good, I also checked the fuel pump relay, and it's good.

I did check for spark, and it has great spark, and it'll run on brake cleaner, starter fluid, etc as long as I'm squirting it in the throttle body.

There is an inline filter in the fuel line, so I don't think I got trash in my injectors.

What's my next option? Pulling the plenum and checking my injectors? could bad gas cause it to not run at all? I'd think if it was bad gas it would still run, but it would run like garbage...

 

[4X4HIGH]

Next would be to use a noid light to check for injector wiring signal. I'm going to suspect that's where your issue is at since you say you can spray stuff into the throttle body and keep it running.

 

[85 Jimmy]

Next would be to use a noid light to check for injector wiring signal. I'm going to suspect that's where your issue is at since you say you can spray stuff into the throttle body and keep it running.

Can I check it with a test light or multimeter? I don't have a noid light, although if I need it to test it I'll get one.

 

[85 Jimmy]

I guess I should say I already did check with a test light. I have a street and performance harness, so I don't know if the colors are the same, but on the #1 injector I pulled the plug and the red wire has constant power and with the test light on the blue wire the test light blinks as you're cranking it... If that helps at all

 

[4X4HIGH]

Yes you can check with a test light but a noid light is cheap and should be in your tool box anyways. I just checked e-bay and you can buy a 9 piece noid light kit for $20 shipped. I'll bet if you go to your local auto parts store you can buy just the noid light you need for around $10.

 

[dyeager535]

Honestly I think any meter will work, it is said that the digital meters don't respond fast enough, but as long as you see SOME voltage fluctuation, it's no different than using a light.

I think I'd put a fuel pressure gauge on the fitting. Hello autozone!

Not sure how long they should hold pressure after the pump shuts off, but the prime function isn't every time you turn the key on/off, so GM must have expected it to hold pressure for at least a few seconds without the pump running. My suspicion is that your in-tank fuel hose split.

I will say that if you have spark, pretty unlikely your injectors aren't being commanded to fire...the ECM relies on the distributor pulse to determine whether the injectors should fire or not (engine rotating or not), *normally* a no spark condition from a faulty ignition component, leads to no injector firing.

You can make a noid light out of a dash bulb. Bend the legs straight, tape/solder a piece of wire to each leg, wrap in electrical tape to prevent a short, tin the probe wire ends if you wish, done.

 

[4X4HIGH]

I guess I should say I already did check with a test light. I have a street and performance harness, so I don't know if the colors are the same, but on the #1 injector I pulled the plug and the red wire has constant power and with the test light on the blue wire the test light blinks as you're cranking it... If that helps at all

Check ALL of the injector harnesses, just because 1 works doesn't mean the other 7 do.

 

[85 Jimmy]

Check ALL of the injector harnesses, just because 1 works doesn't mean the other 7 do.

I just did that real quick yesterday before work while I had an extra set of hands.

Is that the correct way to do it with a test light and just to make sure, one wire should blink while cranking and the other should be a constant hot with the key on?

 

[4X4HIGH]

Honestly I think any meter will work, it is said that the digital meters don't respond fast enough, but as long as you see SOME voltage fluctuation, it's no different than using a light.

I think I'd put a fuel pressure gauge on the fitting. Hello autozone!

Not sure how long they should hold pressure after the pump shuts off, but the prime function isn't every time you turn the key on/off, so GM must have expected it to hold pressure for at least a few seconds without the pump running.

I will say that if you have spark, pretty unlikely your injectors aren't being commanded to fire...the ECM relies on the distributor pulse to determine whether the injectors should fire or not (engine rotating or not), *normally* a no spark condition from a faulty ignition component, leads to no injector firing.

You can make a noid light out of a dash bulb. Bend the legs straight, tape/solder a piece of wire to each leg, wrap in electrical tape to prevent a short, tin the probe wire ends if you wish, done.

Don't forget that he could have a shorted out injector harness though which will stop them from firing. I had this EXACT problem with the EXACT same Street & Performance TPI harness years ago and IIRC their harness splits the left and right side injectors and in my case the harness rubbed a hole and shorted 1 side of the injector harness on the back side of the fuel rail near the regulator.

 

[4X4HIGH]

I just did that real quick yesterday before work while I had an extra set of hands.

Is that the correct way to do it with a test light and just to make sure, one wire should blink while cranking and the other should be a constant hot with the key on?

Yes, either a test light or NOID light and there will be a constant hot wire and then the ground is what is signaled to make the connection. A DVOM meter will not work since the reaction happens too quickly for the meter to pick up.

 

[dyeager535]

Is that the correct way to do it with a test light and just to make sure, one wire should blink while cranking and the other should be a constant hot with the key on?

Sorry thought you were dealing with a stock harness. All my stuff is based on stock.

Stock TPI (at least mine) splits the injectors right and left as well. You have two injector drivers at the ECM, and two fuses.

To test, you use a test light BETWEEN the two injector leads. One is constant 12V, the other the ECM grounds. Kill two birds with one stone running the light between the two terminals on the same injector connector.

 

[85 Jimmy]

The Street and Performance harness I'm using does split the injectors into left and right harnesses.

Tomorrow I'll swing by the parts store to see if they have a NOID light and get my wife to turn the key for me.

If all 8 injector harnesses check out, then what? I don't have the cold start injector, mine is supposed to fire all 8 injectors for cold start. How do I check to make sure that's working right?

 

[dyeager535]

If the injectors work, short of an ECM software programming change, cold start is working. Not something that can arbitrarily change, it's "hard coded" into the PROM.

I believe bumping the starter a couple of times for a split second each will provide extra fuel too. Nothing guarantees the injectors are not malfunctioning of course, I ran into a no start condition because of multiple failed injectors...but with good injectors, once running, I can kill at least three cylinders and it won't die. I know Accel had/has some bad injectors, but the ones I had bad were the stock ones from 1988, so just old.

 

[85 Jimmy]

Hmm, I am running Accel injectors.......

So after confirming that the harness is good and each injector is getting a signal my next step is to pull the fuel rail and check the injectors? Is there a way to test them without sending them somewhere?

Just to be clear, this isn't a new swap, I've been running TPI on this engine for 3-4 years.

 

[dyeager535]

Before pulling anything apart, I'd run a pressure check, that's what the fitting on the rail is for. Absolutely pointless to pull it all apart if the problem is in the pump or somewhere else.

 

[85 Jimmy]

that's what the fitting on the rail is for.

I know, I'll have to borrow my buddies fuel pressure gauge.

 

[85 Jimmy]

Alright, I hooked the fuel pressure gauge up and I've got 7psi with the key cycled on and 9 psi while cranking. So that should narrow it down to either a clogged fuel filter or bad pump, correct?

 

[4X4HIGH]

Alright, I hooked the fuel pressure gauge up and I've got 7psi with the key cycled on and 9 psi while cranking. So that should narrow it down to either a clogged fuel filter or bad pump, correct?

TPI requires something like 40-45psi and with the engine running if you pull the vacuum hose off the regulator the psi should go up about 7-8 psi. Sounds like you either have a bad pump or a bad regulator. Also on the TPI systems the regulator should hold the pressure after the engine is shut off so i would bet you have a bad regulator. Pull the hose off the regulator and see if there's fuel in it, if there is then it's definately a bad regulator.

 

[dyeager535]

If you get into the tank, don't waste money on a pump just yet. Split hoses in the tank are a fairly common occurrence.

I don't disagree with regulator problems either, just an FYI on the pump.

Is there any way to hook a gauge up to the fuel filter fitting, without letting fuel flow through? (deadhead vs. flowthrough? Not sure of terminology) I would think that would also tell you pump or regulator...45+ PSI at filter isn't going to be a pump problem.

 

[4X4HIGH]

Dorian is correct, the small hose that connects the pump to the sender sometimes splits and will give all kids of frustrating issues that are hard to find. Like he said, if you deadhead the pump with a pressure gauge that should be enough to let you know without dropping the tank that the hose is fine. If that hose is bad you need to realize that that hose is special hose called SUBMERSIBLE FUEL HOSE and you cannot use the standard fuel hose otherwise the fuel will eat the hose from the outside.