Strange hot start problem

[LilSki]

OK after figuring out my noise issues and getting the car dialed in I have come across an intermittent problem on hot starts. The car will start fine all day long when it is cold. It turns over about 4 or 5 times and comes to life on high idle according to my IAC settings. The car warms up just fine and will drive fine with no glitches at all.

The problem shows up if I shut the car off when hot and say wait 20 minutes. The car will start but won't rev out and idles around 300 RPM. I can feather it up to about 1000 but that is it and the car dies shortly after. If I try again it usually fires right back up on high idle and settles back down to standard idle around 800 RPM and runs and drives great. Usually if it does this I shut the car off and start it again and everything is fine.

Sometimes however it will not start fine no matter how many times I try it. To fix it I have to pull the 5vref off the ignition module and it will start in base time. Then once it is running I can plug the 5vref back in and it idles up and runs perfect.

I initially had the 5vref connected during cranking and have since changed over to a relay that cuts out during cranking as per the manual. I can tell the relay is working properly but it has had zero affect on my starting problem.

I have also tried 3 different modules and they all act the same. I have also tried changing the max cranking speed with no change.

I have not been able to capture a log of this happening unfortunately but will try again tonight and will post my MSQ later.

My config is:
85 TA
305 with TBI conversion
7 pin HEI
MS2 2.890 w/HEI mod

[LilSki]

Here is my current MSQ file as of this morning. I had it screw up on me this morning with the laptop connected but stupid me forgot to start the log. I will try again tonight and tomorrow.

I will note I did change the cranking and afterstart next pulse tolerance since the screw up this morning. It was 50% for cranking and 75% on afterstart. The normal running is unchanged at 10. changing to 25 and 40 seems to have made the hot start more consistent so I will see tonight and tomorrow.

[LilSki]

I was able to get a datalog of it screwing up. The first part is normal except for a short signal loss on the tach. The middle part is when I got home, shut it off, and then restarted it and it screwed up. The 3rd part is me shutting it off and it starting fine.

[Matt Cramer]

How exactly is the bypass pin on the HEI module wired up?

[LilSki]

Originally it was simply getting its 5v right off the TPS with a connector that I could disconnect to get base time. Now it is setup with the relay in line. It comes off the TPS and goes over to the relay which it then goes to the module. The relay is grounded to the body with the 12v line going to the fuse block where I can choose it to be on or off during cranking. I currently have it set to off during cranking. The 5v wire along with the rest of my wires off the MS are 18ga wires.

I may have found something in the dwell settings but it has only been one day. I was using the default voltage/duration settings and I changed the -2 volt setting to 2.0 duration from 0.9. My theory is that when the battery is fully charged the voltage drop while cranking is around -2 so maybe there wasn't enough dwell to fire while cranking reliably. Again this is just a theory and can easily be set back to 0.9.

[Matt Cramer]

Try using a spare output port to drive the relay and only turn it on when the RPM goes over 600.

[LilSki]

That sounds like it could work. The dwell setting change seems to have fixed it as of today but I will give it a few days until I change anything else.

Does it matter what port I use? Can I use pin 30 since I am using a stepper IAC? Otherwise I have pin 3 and 4 free as I am using 5 and 6 for flyback returns.

Thanks for the help!

[Matt Cramer]

Pin 30 is fine if it's not being used for anything else.

[LilSki]

OK that sounds good. It does seem as though the dwell settings were the primary cause to my problem though. As of this morning it has yet to screw up. The more I think about it the more it makes sense. When it was screwing up it was as if I had unplugged the coil but the computer was still getting a signal and still sending fuel into the motor. This caused it to diesel which is what it sounded like. That is why when I unplugged the 5vref it used the dwell in the module and by the time I went to plug it back in the voltage was back to normal and the dwell settings worked.

I still like the idea of using pin 30 as I would like to have more control over when the timing it engaged.

Thanks again