Engine dies after 10 minutes

[John1]

4.1 Buick v6, Megasquirt II 2.891. Engine is basically a stock rebuild with a mild cam, 24# injectors, converted Holley single plane intake, 1999 dodge 318 two barrel throttle body on a mopar adaptor, 7 pin HEI. Engine will fire right up, idle well for about 10 minutes then shut off. It may restart, if so it will idle up to about 3000 rpm, then die within a few seconds. If it doesn't restart, it will fire while cranking but as soon as the rpm climbs to a running speed it will die. If allowed to cool, it will repeat the above symptons. If I shut it off and hot start it before any symptoms begin, it starts right up and idles at a normal speed. First question is how big of a datalog can I post? I've got a couple from cold start but they run 10 plus minutes before any symptons show up. If they are to large I will try to catch it just before it dies, so the datalog is a more manageable size. All the ignition components are new, and the engine ran on a carb without a hitch for a couple of hours before making the switch to injection. I have scoped the ignition input and it is steady and looks good after the engine dies while it's still losing RPM. I have recleaned the board, and using a lighted magnifier can't find anything obvious, including solder joints. Also, when I first got it running on the fuel injection it would run fine until it came out of WUE, I found a similar post and increased the normal next pulse tolerance and have seemd to solve that problem. Any ideas?

Thanks, John

[Matt Cramer]

Check if your injector drivers are overheating. Also, could you post a data log of the problem and a copy of your MSQ?

[John1]

Here is a datalog of the last couple of minutes before the engine dies. I also logged 2 or 3 start attempts after it died. It looks like the IAC goes wide open as the ecu tries to maintain rpm when it dies. It restarts with a wide open IAC and the rpm climbs high then closes down and it dies. On the last restart I tried to keep it running with the throttle, but it shut off anyway. The injector drivers are both at about 88 degrees F with an infrared. It seems unlikely that both drivers would shut down at exactly the same time. I'll scope the injectors next to see if I'm losing pulse. Thanks for any help.

John

[trakkies]

I'm not using an IAC, but thought it was a simple cold start device - not closed loop which maintains a constant idle?

[Matt Cramer]

The data log shows the IAC going from the cranking position when starting to a run position - it's not trying to catch a stalling idle.

What is suspect here is that the RPM drops very abruptly to zero. I wonder if your HEI module is dying and starts going on the fritz at a particular temperature?

[John1]

Hi Matt,
Replaced the HEI module already, no change in operation. I scoped the HEI input to the ecu with a Fluke 98. The signal is steady all the way though the stall, the input continue looks good as the engine coasts down to a stop. It sure does seem temp related, I'll test tonight with a hair dryer and see if the failure will happen sooner.

Thanks, John

[John1]

Matt,
Replaced module a second time from a different source, and decided to also replace the capacitor since it was the only old part in the distributor. Problem solved, don't know if it was the module or the capacitor, don't really care either. It runs and I'm able to drive it, now it's time to tune.

Thanks for the help, John