'88 GMC Sierra will not start after stalling

[icanfixit]

OK, Sorry for the book but here's my problem:

 

Big Red: 1988 GMC Sierra, Extended Cab 4x4, 350ci/5.7ltr TBI-model 220, w/Automatic Trans. 140K plus miles.

 

The truck sits more than it's been driven the last ten years. Before that is was driven out from Mich. to Phx. Driven all over the SW and Mexico. But other than a bad battery, it always started right up, even after sitting for 6 to 8 months.

 

Recently went out to make a Home Depot run in "Big Red". She fired right up as always. I pulled it from the back yard to the driveway and let it idle like I usually do after having it sit so long. Rinsed it off with a hose and it was running maybe 5- 10 minutes. Just as I was opening the door to turn on the wipers, it flat died. It died quickly like the spark was removed. no sputter, no nothing, it just quit.

 

So I grabbed my Haynes manual and started to troubleshoot. For ease of reading I will list the order of what I have done. Another thing is all of these parts are original. I have changed things like spark plugs, wires, cap, rotor, fuel filter, etc. at maintenance times, but the fuel system has been untouched. As one should, I tried to determine if it was spark or a fuel problem.

 

Confirmed the fuel pump fuse is good.

 

Confirmed the fuel pump relay was operating correctly.

 

Confirmed the fuel pump was running.

 

Removed the fuel feed line from the TBI and fired the fuel pump. Looks like a decent flow but at this point I have no way to check pressure. I am told I need an adaptor that goes inplace of the fuel filter.

 

Checked the fuel filter just to cover the bases, it's clean.

 

As a test, I pour some gas down the TBI. It fires on this gas until it is gone, then nothing.

 

 

 

This tells me it's a fuel problem and not a spark problem.

 

 

 

I checked for any error codes with my cheapy code reader, Code 12 (the all is well code) is all that it flashes out to me. no other codes.

 

After looking at wiring diagrams I 'jumped out' the "fuel pump oil pressure switch", (located behind & below the distributor). From reading and surfing forums I determined this will close once oil pressure has been achieved. From what I can tell this bypasses the ignition switch after the engine is running to keep the fuel pump running. It's a safety to kill the engine is oil pressure is lost. Am I correct?

 

Next was to inspect the TBI. I removed and rebuilt it. I sprayed all the parts down with carb cleaner, and blew out any orifice I could find. I took care to not submurge the injectors but I did spray and blow orifices on them too. They actually 'looked' fairly clean when I removed them. Re-assembled & re-installed but still no change. I did use the old "Fuel Pressure Regulator" spring, as the rebuild kit did not come with one.

 

I read that the 'Ignition Module' in the distributor sends a signal to the 'ECM' to pulse the injectors and the ignition coil. Now it would fire with gas poured down the TBI, so I didn't think this was the problem. In desperation I changed it out anyway, still no fire.

 

I ohmed out the injectors. The are at 0.9 ohms, (digital Fluke meter) I believe this is within range. When I checked for voltage at the injectors, my Fluke meter floats between 1.8 to 2.0 VDC. One injector connected and the other connector to the meter when cranking the engine. I am not sure what signal is being sent to the injectors, so I don't know what this reading is telling me.

 

I talked to a few more people and decided to try a new ECM. Switched the chips from the old ECM to the new, but still no change.

 

Now I am really running out of ideas. So I buy a new set of injectors and "try one". My thinking being if the new one does work, it will fire and run, but would be very rough. It still won't fire up.

 

Now I am reaching...

 

From what I read, the "idle Air Control" just allows air to bypass the throttle plates to control idle speed. But I am not getting any fuel, so it shouldn't matter how much air is being allowed to bypass. Right?

 

 

 

From what I can tell there is something telling the ECM to "not" pulse the injectors, but I have no idea what it is. Or I am way off base in my troubleshooting.

 

 

 

Summation:

 

I have fuel to the TBI, pressure unkown.

 

It just cranks over but does not fire.

 

It will run for as long as the gas holds out when puring some into the TBI.

 

The 'Fuel Pump Pressure Switch' is jumped out during all tests.

 

EDIT I just went out and tried it disconnected & no jumper on the fuel pump oil pressure switch and finally with it connected. Still won't start. Does this switch make on oil pressure rise??

 

 

 

So now I ask you people for guidance!! What am I missing?? Does anyone have more detailed wirng diarams or maybe a detailed sequence of operation for the engine starting and running circuits??

 

Help a brotha out!!

[Platonic Solid]

Prior to this incident, when's the last time this truck was run? If it regularly sits for long periods of time without fuel stabilizer (FYI: "Stabil" brand sucks) you should verify that the gas hasn't separated.

[icanfixit]

It's been about 6 months.

 

It did run for almost ten minutes before it died. Would bad gas work one minute and not the next? No sputtering, just instantly quite running.

 

I'll check it out as I am running out of options.

 

Thanks,

 

 

Still open for suggestions!!!

[Platonic Solid]

Yes, bad gas will usually sputter before dying. And Yes, bad gas will work one minute and not the next, though some vehicle motion is usually involved. It's probably not your problem, but it is possible.

[icanfixit]

On another forum they are suspecting low fuel pressure. They tell me the injectors require a minimum pressure to operate. I know the fuel pressure needs to be 9 to 13 psi but does this pertain more towards getting a proper spray pattern/fuel-air mixture, rather then "helping" to open the injectors?

 

Just to see if I was getting gas through the TBI, to the injectors, I removed one injector, removed both electrical connectors, and replaced the TBI top. I turned it over and had gas streaming into the area the injector is supposed to be. And it actually fired on this raw gas being dumped into the TBI.

 

So I guess the gas is good enough at this point.

 

Does anyone know what voltage the injectors are supposed to see??

 

0 VDC = closed

12 VDC = open

 

Or visa-versa?

 

Or something besides 12VDC???

[Corky356]

On another forum they are suspecting low fuel pressure.  They tell me the injectors require a minimum pressure to operate.  I know the fuel pressure needs to be 9 to 13 psi but does this pertain more towards getting a proper spray pattern/fuel-air mixture, rather then "helping" to open the injectors?

 

Just to see if I was getting gas through the TBI, to the injectors, I removed one injector, removed both electrical connectors, and replaced the TBI top.  I turned it over and had gas streaming into the area the injector is supposed to be.  And it actually fired on this raw gas being dumped into the TBI.

 

So I guess the gas is good enough at this point.

 

Does anyone know what voltage the injectors are supposed to see??

 

0 VDC = closed

12 VDC = open

 

Or visa-versa?

 

Or something besides 12VDC???

 

<{POST_SNAPBACK}>

 

 

 

 

This is maybe a wild guess, but if it started on your fuel from the tank with an injector removed, I say put a pressure guage on the fuel line and make sure you have the required pressure: 4.0 to 6.5 PSI according to Chilton manual.

[icanfixit]

I'm getting the same thing on other boards. I'm in the process of obtaining a test gauge now. I'll reply with the result.

 

Thanks!!

[icanfixit]

Sorry for the long delay. I was side tracked with 'Life Responsibilities' and then lost my logon info. But now I can close the loop.

 

After not working on it for a month or so I went back at it and noticed I could hear fluid splashing in the gas tank when I turned the key to [On]. Didn't hear this before. I also noticed my fuel flow to the TBI was much lower than before.

 

My new fuel presure gauge tells me [no fuel pressure]. Removing the fuel pump I find the hose from the pump, to the fuel line, finally ruptured. It was all FAT, Squishy and Expanded, and ripped. Replaced the pump and she started but ran very rough. I put the new injectors back in seeing as how I changed everything else out. Might as well include them too.

 

Now she purrs like a kitten.

 

Thanks to all who helped me out!!

 

No it's time for a radiator change out........

[rem 870 ex mag]

good to hear you figured it out . i have an identical truck to yours. 88 GMC k1500 automatic with the TBI 350. i know this should be a new topic, but i can't post a new one for some reason. does anyone know the stock shift points for this truck? i know it is possible to "estimate" them by running it full out and noting the rpms at shifts, but if anyone knows exact rpms it would be greatly appreciated.

[Mstjr2001]

I have exactly the same symptoms, but my tanks, pumps, sending units, fuel filter, injectors, and selector valve (dual tanks) and everything in between is brand new. I have no fuel pressure to the TBI, but I can hear both pumps turn on. No fuel at block - I disconnected the lines going in and watched while cranking and no fuel is coming???

 

And yes, there is $75 worth of brand new gas in the brand new tank.

 

Ideas?

 

Mark