You guys are the best when it comes to TPI, so a question. I bought a 1987 Callaway TT Corvette with a TPI. Drove the car from STL to CHI and car ran fine. Then after changing the trans fluid the car would only run for 2 secs and die. The car would run with the MAF disconnected, and runs with the EST disconnected

-Fuel Pressure is at 43lbs
-Replaced cap
-Replaced rotor
-repalced TPS
-replaced ign module
-repalced pickup coil
-replaced IAC
-replaced ECM
-replaced MAF(2X)
-checked injector resist.
-checked to make sure 9th inj was not flooding engine
-TPS counts are ok

If I disconnect the intercooler the car will start and then I can reconnect and it runs.

HELP!

Thanks in advance...

Lee "LGAFF"

 

By the way, depressing the throttle when the car initially starts does not help the car run....I was thinking maybe the throttle may clogged somewhere, but then wouldn't opening the TB blades via the gas pedal provide the engine with the needed air?

 

wow that's a lot of parts replacing. I am confused on the order of events though. Are you saying that the only thing you touched was the trans pan and then the problem started immediately after that?

...and that's when you started replacing parts?

You said it seems MAF related, so you tried other MAFs, but did you ever test or replace the MAF relays ?
I take it there are no DTC codes?

 

Sorry forgot that from the laundry list, yes, replaced both the relays...No codes

 

Do you think disconnecting the Intercooler causes it to go into limp home? I picked up a TECH 1 put I am not sure what I need to be looking for when cranking..


normal IAC counts?
BLM counts
Injector pulse width

What are normal cranking #s

 

So with the MAF connected, but the EST disconnected it will start and run ok?

or with the EST connected, but the MAF disconnected it will start and run ok?

 

Yes disconnecting one or the other allows the car to start, I Assume that limp home mode


Yes, I changed the 4+3 trans fluid dropped it down and thats all she wrote

 

I don't know since I haven't seen your car. Is the intercooler between your MAF and the Throttle-body? or is just before the MAF ?
You might want to check for obstructions in your piping.
When you say you disconnected the MAF do you mean the wires only? or taking the entire unit out of your air piping?

Those numbers will be different based on the engine coolant temp when you are cranking.

 

I mean unplug the EST and MAF wiring

The intercooler is just before the throttle body:

 

Well the ECM recognizes MAF failure or ignition control failure.
If it starts up and runs without misfires in that mode, then that eliminates most mechanical problems, and suggests an electrical problem, most likely a sensor, but that normally sets a DTC code.

If you unplug your O2 sensor do you get a similar result of it running? like with the MAF disconnected

 

Have not tried that one yet.......the car its sitting outside while I finish my ZR-1 project so not on a lift

 

LT-5 build

 

That's pretty packed under there.
Looks like your MAF right after the air-filter.

You said you replaced the MAF a couple of times, so that eliminates some of the possibilities. When your ECM sees the MAF output it doesn't want to run.
It would seem that the MAF output is being skewed severely.

If you can watch your MAF grams/sec output at idle (if you can keep it running that long), that might be revealing of the problem.
If the MAF output is too low, or zero, then you could very well have good sized vacuum leak.
With all that plumbing in there it could be a lot of things from a loose connection to a crack.
You could try plugging all of your normal vacuum lines to include the PCV and brake booster to try to narrow things down a bit, and point towards your turbo plumbing or something else.

 

I will try it tomorrow, as you state hard to tell when it dies after a sec or so.....whats normal?

 

It is possible for a vacuum leak to keep you from running long enough to set a DTC code.
When you force open-loop or limp mode a vacuum leak will not normally set a code by itself. You would just a code for whatever was forcing the limp mode.

One thing you might try is removing your ICs and connecting a flex-tube straight from your TB to your MAF and seeing if the problem goes away, - pointing to a leak in your turbo plumbing.

edit: I meant mounting the MAF right in front of the TB. Hope that wasn't confusing.

Another test could be removing your air filter, disconnecting your MAF and with the car running block the air entry to the MAF with your hand. With other vacuum lines blocked CCP, brake booster, and PCV, it should kill the engine pretty quickly when you block off the air. If the engine can still run then it points to a large vacuum leak.

 

I think 6 grams is about right for a stock idle.
I would expect to see no lower than 4 grams/sec.

If it won't idle then you might want to try the other tests.

 

Thanks for the help, I have worked on the LT-5 so you would think I would be an expert on vac leaks......but I guess I never thought of it with this as a problem, but you are right with that amount of tubing might not be able to build enough vac to overcome the leak

 

On a MAF car it's more a matter of the un-measured air goofing up the fueling calculation.
A low MAF output (due to un-measured air) would call for less fuel, probably to the point of the lower limit of injector pulsewidth capability. I'd assume you have some good sized injectors on there.

In limp mode the commanded AFR is very rich, which would explain why you would be able to run with the vacuum leak.

I don't know if that's definitely it, but it seems logical at this point.

 

Well I checked the hoses for the turbos, but nothing......there was one I really could not see....its under the front crossmember and is blocked by the AC dryer/Compressor and belt tensioner......BINGO!

Runs like a charm now

Thanks for the help

 

Good news!
I'm glad it was relatively easy.