5.3 swap won't stay running can anyone help

[Bulldog88]

I did a 5.3 swap on a 88 Chevy Truck, I got everything hooked up, correct fuel pressure, and it turns on for a second and shuts off, I don't know what's going on, I had the ecm checked out and everything is good, vats deleted, emissions are there so I don't know what to do

['68 Newtricks]

Can you check for codes?

[chev3600]

Does the fuel pump stay running after you let off the key? Seems like a remember reading about a similar issue, had some wires swapped around.

[Bulldog88]

I have not checked for codes my service light is not on, but I guess I can hook up a scanner to it, the fuel pump comes on when I switch the key to the on position, fuel pressure will stay about 58-60 psi when it starts, fuel pump is on a relay,

[BR3W CITY]

Still scan, codes can be set to "not report" which won't throw the MIL, but it will actually store the code.

Try unplugging your MAF and see if it wants to idle.
Can you give it some throttle and try to "save it", or does it die no matter what?

[Bulldog88]

It dies, don't matter if I hold the pedal down, it will just die, it is electronic throttle body and pedal, blue and green ecm, 2004 5.3

[ls1nova71]

I'd double check the VATS. Things can happen and it not get turned off.

[Bulldog88]

I had the ecm checked out again, and the vats double checked and it seems to be cleared,

[JMac11]

Check All grounds, test a ground to the PCM. Mine still acts as if there is a need to directly ground PCM with a spider web of grounds

[Hart_Rod]

Originally Posted by ls1nova71

I'd double check the VATS. Things can happen and it not get turned off.

Winner Winner Chicken Dinner!

[Bulldog88]

I ran direct ground to the pcm grounds, which is two ground to each side and still nothing, now time to scan it for codes

[Dustytrix]

If vats has for sure been deleted, although it sounds like vats, check grds again. Make sure you have 2 grds to main coil plug on each side. Also injectors can be full of varnish, if you didnt clean them they will be.

[Bulldog88]

So I cleaned all the injectors, they pulse like there suppose to, I scanned it and is giving me code 2135 throttle position sensor, so then I swapped out throttle bodies, using two others that I have, and still nothing, I also swapped out the pedal control box, and getting same results, I'm started taking the harness apart tonight, just to chase down the wires to the throttle and make sure there not damaged in some way, also found out that SPEARTECH HARNESS ARE A JOKE they charged 680 dollars to do a harness using black electrical tape on their connections and splices, I have done better work myself, good thing I didn't pay for that

[62chevy302]

do you have access to a scan tool tool that reads data? if so look for rpm,if it don't see rpm it will quit firing injectors. you can spray carb cleaner in the throttle body to see if it keeps running. if its not vats sounds like its losing crank signal

[Bulldog88]

Got back to working on this project, the only way I can keep this motor running is by spraying either gas or carburetor cleaner at the throttle body, also changed out crank sensor, anybody have an idea

[BR3W CITY]

You get around to trying the MAF yet? It can provide bad readings that won't throw a MIL, but can cause fairly drastic bad-running conditions.

[Bulldog88]

Even unplugging the maf still nothing, change pedals also and nothing, if I spray fuel into the throttle body it will stay running, but even if I have someone smashing the gas pedal, after I quit spraying it the pedal has no response and it dies

[BR3W CITY]

Did Speartech do the flash also? You said you had the "ECM checked out" by which I assume you meant you had the tune looked at again.

I didn't see you actually post up what check engine light code its throwing. Your changing all sorts of parts, but what is the car telling you? You'll keep chasing the problem if we can't narrow down what area(s) are causing the major issues.

A tuner or anyone with HPT can watch the live data or do a log and look at the MAP, cylinder volumes, spark timing etc and look for anomalies. If you have a rare problem, or something being caused by an issue in the harness itself, that will be the shortest route to finding.

[TooTall]

it really sounds like the VATS are still active, that's exactly what it does

I recently had one that did the same. But it ended up being a bad tune file. I had all of the VATS removed, but still had the same issue. I flashed an original GM tune back on it and started over again . . . problem solved

Seeing how it's starting, injectors are good, coils are getting power, meaning the grounds are good. No sky high idle means the MAP is good too.

Put a pressure gauge on the fuel rail, it will be pinned at 58 for prime and start up.