88 Chevy Will start but shuts off. At a Lost need Help

[ColoradoChevy13]

I have a 88 C1500 5.7. We just installed a Mild rv cam for a little more torque/hp. It will Fire up it runs for about 3-5 minutes with no issues an then shuts off (as if the key was turned off) , about 10 sec before it shuts off it idles up a little about an extra 300Rpm an then dies. The Injectors Do Keep pumping till loss of pressure after it dies, It will Start right back up an dose this again. We Did not get an Check Engine light either or Code 42 For the Esc system. I Have been Hunting this Issue for the past 8 days an have come to a complete loss.

We were thinking it might be something with the ESC system So we replaced Distributor, Coil, An ESC module on the bracket next to the TBI. All one at a time testing each Component. Plugs are new and so are wires. We have proper fuel Pressure. The Map, ICA An TPS, Temp Sensors (both), Knock sensor along with a new ECM an Prom Chip, This is Basically a all new truck. new block the beginning of 2021. now has 45k truck has 420k

NEED HELP Thanks all

 

[ColoradoChevy13]

Update Still trying to figure this out I ended up replacing the ECM an the Prom Chip thinking it was malfunctioning. Ended up not being that. We have gone back though an checked every wire in the engine bay twice an the second time redoing all splices or connections looking for croded wiring and found nothing. have tried 3 differant sets of sensors for everything an still having the issuse of running good for about 3.5-4 mins an then idels up for about 10 secs then shuts its self off. Any Ideas might come in handy Thanks

 

[Frank Enstein]

What are the cam specs? An "RV" cam generally won't run with a stock TBI chip.

 

[PlayingWithTBI]

Stop changing parts and diagnose your issue(s). You need to put a scanner on it to check stored codes and see what's happening with your sensors' input when this happens. Even though your injectors are spraying when it dies, you need to verify your fuel pressure too. Check for vacuum leaks by spraying brake cleaner (the flammable kind) or an unlit propane torch, around the Throttle Body's base, throttle shaft, vacuum lines, etc. to see if idle changes. Is your EGR valve working properly?

 

[1998_K1500_Sub]

1988 is pretty old. If you can find an old data logger to capture the ECU data, I can guarantee you'll be much better off.

I have an early version of DIACOM from Rinda Tech running on an old laptop, I use it on everything GM up to 1995. I don't know if the later DIACOM versions work with OBDI but they might.

Tools like DIACOM allow one to capture over time the sensor outputs (e.g., IAC, TPS, MAP, IAT, O2), injector operation, EGR, ignition timing as commanded by the ECU, etc., so you can review, after-the-fact, what's happening in those 3-4 minutes up to and when the engine finally dies.

Rinda Technologies Inc. Marine and Industrial Engine Diagnostic Tools

The Official Site of Rinda Technologies, Inc. Designing innovative engine diagnostic tools and software for over 20 Years.

www.rinda.com

 

[1998_K1500_Sub]

Here's a thought:

After your engine's started and running, disconnect the idle air control (IAC) electrical connector and see what happens. This will "freeze" the air bleed through the IAC valve. The RPM might rise some over time as the engine warms, but that's OK (as long as it doesn't go crazy, if so turn it off, hook up the IAC and try this experiment again with the engine now warmer).

It will be interesting to see if it dies.

Report back what you find.

 

[ColoradoChevy13]

What are the cam specs? An "RV" cam generally won't run with a stock TBI chip.

Im not sure right off hand it was out of the old 5.7 engine block that was in the truck. old block had a crank bearing turn. I ended up getting another engine that was build with what ever Jasper Engines uses for there stage 3 internals. an now that the warranty is up figured id throw the old mild rv cam back in the system, I have the old prom an ecm that was with it an it also dose the same thing. an the New Hypertech prom is set up for a a rv set up, the Tbi System is still the same when it was running it also. old block lasted 310k+ miles with it in there. I havent dont anything else to the system.

 

[ColoradoChevy13]

Here's a thought:

After your engine's started and running, disconnect the idle air control (IAC) electrical connector and see what happens. This will "freeze" the air bleed through the IAC valve. The RPM might rise some over time as the engine warms, but that's OK (as long as it doesn't go crazy, if so turn it off, hook up the IAC and try this experiment again with the engine now warmer).

It will be interesting to see if it dies.

Report back what you find.

I will try that in the morning.

 

[ColoradoChevy13]

Stop changing parts and diagnose your issue(s). You need to put a scanner on it to check stored codes and see what's happening with your sensors' input when this happens. Even though your injectors are spraying when it dies, you need to verify your fuel pressure too. Check for vacuum leaks by spraying brake cleaner (the flammable kind) or an unlit propane torch, around the Throttle Body's base, throttle shaft, vacuum lines, etc. to see if idle changes. Is your EGR valve working properly?

I have tested everything on this including checking for vacuum leaks an test the fuel pressure while idleing an when it dies. The EGR System has been Deleted for about 15 years now. I am getting no codes what so ever. an when running it with scanner there's nothing that stands out. we have even gone to the extent of testing ohms on all the wires an secsors, Iv had my dad who is a master tech of 25 year help do all this. He is just as stumped as I am. everything that we can tell its running great till it shuts off.

 

[evilunclegrimace]

Try powering the fuel pump relay with a fused power wire and see if it will stay running