56rat

I have a LS1 in my chevelle with the PCM located on the firewall above where the heater lines go through. If I drive on really hot days ( 90+ Degrees ) for an extended period of time the car will start cutting and acting like it's running out of fuel. No throttle response and keeps stumbling until the engine dies. If I try to start it right away it will just crank and will not start up. If I let the car sit for ~15 minutes and try again it will start right back up and I can drive another 5 miles or so and it'll do the same thing again. I thought for sure it was a fuel filter / pressure / pump issue so I installed a digital fuel pressure gauge off the rail and watch the gauge closely when the car starts to act up. The rails do not lose fuel pressure. Pressure will stay all the way up until the engine dies. If I drive the car on a 70 degree day it will run for hours without a single problem. Engine temps are good, oil pressure is good, no check engine lights and no codes. The only think I can think of is the actual PCM against the firewall is getting so incredibly hot from the fans, headers and overall engine bay temp blowing against it that it actually has some type of thermal protect built in and shuts down. I have no idea if this is accurate or not but for the life of me I can't figure out what is causing the stalling and why it only does it on hot days. Before I go relocating my PCM I wanted a few opinions.. Nothing else seems to make any sense up to this point of what is actually happening and what is causing the engine to stumble and shut off. Any suggestions or ideas I'm all for them. Thanks!

ls1nova71

iTrader: (4)

I have never seen that happen before and I have done several swaps with the PCM in the engine bay. Sounds like maybe its trying to vapor lock or something. Are any of your fuel lines near the exhaust? Maybe try putting some insulation over the PCM to test if its heat doing it?

56rat

Thank you for the reply. This has never happened until this summer and I've owned the car for years. The only thing I changed was the position of the ECM and a new fuel pump. I don't think it's the fuel pump due to my fuel pressure staying up while it starts to sputter and die. I could be wrong though and it could be vapor locking. I guess I will keep messing with my setup and possibly add a couple in line fuel coolers and see if it helps. Also, None of my lines are near exhaust. I have the speedway filter/regulator/return combo near the back of the car with the single -6 going up to the engine. Thank you for the reply.

sowbelle

I don't know about vapor locking. Wouldn't that show up with fuel pressure dropping?

what about the coils? I say this because a coil can stop working in the heat but all eight?
I would try the idea above. Also, Relays can do the same thing because they are a coil also. Check power to the pcm when this happens.

56rat

There is power to the PCM when this happens. I can be parked on the side of the road with my laptop connected to HP tuners and the connection is good. I can watch the injector rate at cranking, spark, etc and it all seems to be responding correctly but the car will just turn over and over but will not start. This is seriously so frustrating to try and diagnose.. I wouldn't have fuel pressure if the pump was overheated or if the fuel pump relay were tripped. It sure acts like it's starving for fuel. Let the car sit 15 minutes, it'll fire up and will be good to go until it does it again. One of those newly acquired car gremlins I guess.

my406cid

Are u speed density or maf? What is your intake air temp on these days? This may very well be a kit temp issue.

my406cid

Iat issue. Sorry on wifes tablet,spell check on.

56rat

Speed Density. Car has a big front mount intercooler and I'm mostly just cruising when it happens.

1dirtyZ

iTrader: (1)

I really doubt it is a pcm issue ,

in our neck of the woods we have the lumina and caprice that you guys stateside don't get , and on those models the pcm is located on the frame rail right next to the header/ exhaust manifold from the factory with only a flat piece of insulation between the two . and it gets really hot over here

I know this sounds weird , but check your grounds ( pcm grounds , engine ground to chassis , and batt ground).

start with the cheapest easiest tests first

Old Geezer

iTrader: (3)

A cold towel over the PCM, when this happens... Starts?

Angledriven

have you figured it out my car is doing the exact same thing.

56rat

sorry for the slow delay. My life has been crazy lately.. moving into a new home in 2 weeks and trying to tie up loose ends with the construction. FUN FUN!

As far as my car. No, i'm still chasing this gremlin. I don't think the PCM has a fail safe related to heat. I can't seem to replicate the problem unless i'm driving on a hot day.. I think my problem lies somewhere else and I am not sure where. At least I have a new 2000+ dollar fuel system that doesn't do me a bit of good.

Sad thing is, I doubt I will have many more 90+ degree days this year so I might not be able to replicate the problem until next year. When I do replicate the problem it's always on a hot and miserable day while i'm stuck on the side of a road not sure where to turn or what to check. Every time this happens I feel useless because HP tuners thinks everything is fine and it's not like I can easily work on a hot motor on a 100 degree day. I just have to sit there sweating my *** off until I let the car sit 30 minutes and drive away until it happens again.

I took the car to a local performance shop to have them look over the car. They specialize in LS swaps. They have went through all the grounds, wiring, etc and it looks good and they are not sure what could be causing the car to die like it is. They noticed my alternator wasn't wired the best way, which was causing my fuel pressure to bounce up and down so they fixed this, but nothing else jumped out to them. The most frustrating thing about this is the fact the car ran perfect before I added the blower. There are only so many things involved with adding a supercharger and I have traced my steps and i'm at a complete loss. It's as if the ECM just stops firing the injectors and coils, even though it thinks it is. I would understand the ECM being the problem if I couldn't connect to it. I can connect fine and as far as the ECM is concerned everything is working like it should. It shows RPM during cranking and shows it's spitting out fuel and spark even though it's not..

This really is the most frustrating car problem I've ever dealt with because it always happens at the hottest part of the day. I am 98% confident the car is not producing spark or firing the injectors.. The car would thump, sputter, attempt to fire if it were. As the car dies and i'm coasting I put it in neutral and start it and it just turns over, not a single attempt to light. I don't smell any fuel vapor and it acts like I have all 8 coils unplugged.

Angledriven: if you make any progress please come chime in. I'm at a loss right now.

ls1nova71

iTrader: (4)

I think I would try another PCM Keep it in the car and when it happens just swap it out, if it starts then you know its the problem. Maybe the circuit board inside is swelling with heat and making a connection come apart? Just thinking out loud.

tfi racing

iTrader: (2)

Try a heat gun on it,keeps tabs on the temp with a cheapo IR gun you don't want to over-do it and permanently fry your pcm.Or if you still can get it out on a 90' day this year,run it till it quits and blast it with propane or other canned gas to cool it down rapidly.

jimmyg

Get rid of pronto filter/reg get a wix . Same thing happened to me I changed out filter and it was fine.

ls1_chevelle

iTrader: (9)

sounds like the engine is overheating and going into limp. I had a water temp gauge not read correctly but when logging with HP tuners the GM sensor was 240f and car was in limp mode.

bczee

iTrader: (12)

If this started to happen after you made changes. I would focus on those area of changes.. There may be no problem with what you did or moved physically.

But maybe on moving the PCM and harness.. it has developed a bad connection in the harness or connector now and heat or vibration is exposing them now. Check the grounds (as suggested) and the PCM Connector, Pin's and wire junctions.

BC