95' 350TBI wont stay running

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The short and sweet:

Symptoms: Truck starts, idles around 1500 RPM, then dies between 15-30 seconds.

Parts replaced: Rebuilt throttle body, IAC, PCV, Vacuum lines, Fuel pump, Fuel filter, spark plugs.

I have a 1995 k3500 with a 350. I purchased this truck about 4 years ago with several issues. It sat up until a couple months ago when I started digging into it. This truck was a plow truck in vermont but has just 50k original and traceable miles. It was pretty rough. It needed all new brake lines along with rebuilt calibers, the clutch was "slipping" (I discovered the throw out bearing was just stuck on the guide tube) and it had a no start problem. When I first bought it, it ran just fine. Started, idled, and would stay running. However, the first week I got it home, it all of a sudden would not restart. Life carried on and another vehicle I have took center stage, so this truck just sat.

Flash forward to a couple months ago. I yanked the truck up to the shop and got to work. Pulled the trans, sandblasted the frame and under the cab, threw a new clutch in, reassembled and set out on getting it running. I first rebuilt the throttle body, including the fuel pressure regulator. I tore it down, dunked it in the ultrasonic cleaner, and reassmbled with an AC Delco kit. I kept the original fuel injectors but I did clean them with an injector tester. They also ohm out good at 1.3 ohms. I also installed a new delphi IAC. The original TPS is retained. I also replaced the PCV valve, cleaned and lubricated the EGR valve, replaced all vacuum lines, and new fuel filter.

I pulled all the plugs, squirted some oil into the each cylinder, and bared the engine over. Then installed new plugs and got preparred for a starting attempt. At first, it fired right up with a high idle and then died. I then could not get it to restart unless I allowed the fuel pump to prime the full 10 seconds. It would then restart, run ok, then die shortly after. I was suspect of the fuel pump, so checked pressure and found to be anywhere from 9-11 psi in the short time it was running. I replaced the fuel pump and in-tank filter. This did not solve the problem.

I would appreciate any guidance the community has to offer. I would like to replace all sensors (TPS, MAPS, O2, Knock, Coolant) eventually, but I do not want to do it until i can get the engine running right to avoid creating another issue.

Thanks,
Seth
 

scott2093

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Any codes stored?
Could be ignition related. Another member here had a similar issue that turned out to be the pick up coil in the distributor acting up intermittently.
Are the injectors working when cranking?
You could check for spark....
 
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Thanks Scott. I have spark when cranking and the fuel injects do spray at that time as well. I used an inline spark tester between the coil and the cap while it was cranking to verify this. When the engine dies, the fuel pump does not continue to run.
 

someotherguy

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Check your CTS with an ohmmeter. There's a chart of resistance values in the service manual where you can compare the reading to what you should expect based on the temp. If it's gone full failure mode it will falsely read so cold that it will richen the fuel mixture to the point of fuel-fouling the spark plugs.

Last time I worked with one that had gone bad in such extreme fashion, it would start, run at high idle for a short while, then start choking down as the plugs would begin to foul. With the air cleaner off, you could hear the sucking sound of the IAC opening all the way in an attempt to keep the engine from stalling, then moments later, stalled and wouldn't re-start until the plugs had dried out.

Richard
 
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Richard, thanks for your reply. That sounds pretty similar to what I am experiencing. I'll ring it out and see what I get.
 

someotherguy

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Richard, thanks for your reply. That sounds pretty similar to what I am experiencing. I'll ring it out and see what I get.
Really high resistance equals a very cold reading. The sensor can fail, but also a truck that has been sitting for extended periods could be subject to corrosion in the ground for the circuit. This especially can be the case when you get rodent activity with mouse pee all over the top of the engine. Check the grounds at/near the thermostat housing while you're in there.

Here's a post with a chart of those resistance readings, 6th one down in this thread: https://www.chevytalk.org/fusionbb/showtopic.php?tid/176155

Richard
 
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Well the sensor ohmed out at .6 Mega ohm. I swapped it out and the truck certainly starts easier and runs smoother, BUT it still just dies after about 20 seconds of running. It does this exactly everytime.

Unfortunately I am headed back out to sea this week so this will have to wait till spring to continue diagnosing. Gonna bring the GM manuals with me to read up on these trucks.
 

someotherguy

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Interesting.. well next step would be to see what's "missing" when it stalls and won't re-start. Is it missing spark, or fuel? If it's got spark while cranking, check to see if the injectors are spraying. If they're not, of course check fuel pressure.

If you've got no spark, AND/OR fuel pressure but no injector spray, most likely suspect is the ignition module - followed by the wiring harness to it (they can get brittle) - and finally the pickup coil in the distributor. My money would be on the module.

Richard
 
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