Bad module or false triggering?

[Blazer79]

Hello. This is my first post in here.

I just finished my first Megasquirt install. It's a MS-II with 3.0 board bought assembled from DIYAutoTune. It's on a 1986 Iroc with a Chevy 350 engine controlling both fuel and a HEI distributor with a 7 module pin. The distributor has an Accel coil, if that changes anything.

The thing is I got it to crank and start, well sort of. It starts and dies almost immediately. I followed the instructions to adjust after startup enrichment etc, but never got it to change.

Then I noticed that sometimes, right before dying, RPMs would go crazy high. You can see in the attached log that at 295 secs it shows about 5200rpms, which of course the engine didn't do and then the engine dies. At 395 secs rpms are at 9616, then dies. Other times, I'm cranking it and only see 0 RPMs.

Can someone with more experience tell me if these are symptoms of a dying ignition module or simply false triggering? Should I run to the store and buy a new module? Or start tweaking R56 and R52?

Any ideas welcome. Thanks!

[johnTransam]

If you are using a low impedance GM TBI, then most likely the injector are causing significant interference with the tach/ignition signal. See my post "Won't run need help troubleshooting".
John

[Bernard Fife]

Or maybe not. I ran a 4bbl Holley TBI with very low impedance injectors (very similar to the GM injectors) on my 406 for years, and never had any noise issues with the 7 and 8-pin HEI's I was running at the time. That doesn't mean others haven't had problems, just that it's certainly not always the case, and not a guaranteed answer.

Lance.

[Blazer79]

It's a TPI engine with 8 high-impedance 24# injectors. Sorry I didn't specify that.

Do you think I might have the same issues as you?

[Bernard Fife]

B79,

If this was mine, I would look at the next pulse tolerances for cranking, afterstart, and normal running: http://www.megamanual.com/mt29.htm#ib And possibly the tach signal masking as well, if adjusting the tolerances doesn't help.

Also, make sure the coil and module (and MegaSquirt, of course) are well-grounded.

I have had some aftermarket 7-pin modules not work correctly, but all the ones I have used from GM or Accel worked great for me.

Lance.

[HavocFiat]

Hello. This is my first post in here.

I just finished my first Megasquirt install. It's a MS-II with 3.0 board bought assembled from DIYAutoTune. It's on a 1986 Iroc with a Chevy 350 engine controlling both fuel and a HEI distributor with a 7 module pin. The distributor has an Accel coil, if that changes anything.

The thing is I got it to crank and start, well sort of. It starts and dies almost immediately. I followed the instructions to adjust after startup enrichment etc, but never got it to change.

Then I noticed that sometimes, right before dying, RPMs would go crazy high. You can see in the attached log that at 295 secs it shows about 5200rpms, which of course the engine didn't do and then the engine dies. At 395 secs rpms are at 9616, then dies. Other times, I'm cranking it and only see 0 RPMs.

Can someone with more experience tell me if these are symptoms of a dying ignition module or simply false triggering? Should I run to the store and buy a new module? Or start tweaking R56 and R52?

Any ideas welcome. Thanks!

I had the same issue with my HEI setup, my timing was way off. Once set, idled no issue

[Blazer79]

Hello everyone and thanks for your replies.

Unfortunately, more than 3 months later, I'm still having the same issue. Haven't been able to start my Camaro. I already changed the ignition module. Couldn't find a GM module locally, so got an aftermarket one. I also changed the VR sensor in the distributor, hoping this was causing the false readings. I also tweaked the next pulse tolerances for cranking, afterstart, and normal as Lance suggested. But the problem remains.

This are my specs:
1986 Camaro Iroc-Z
Chevy 350 with original TPI setup.
MSII v3.0 firmware updated to 2.905
Bought assembled from DIYAutoTune.
HEI dist. with 7 pin module.
Already replaced new module and new VR sensor in dist.
Maximum Dwell Duration is set to 3.5ms
24# High impedance injectors (3.024 g/s injector flow rate)

I've really contained myself from posting here every attempt at starting it that I made, thinking I was doing something stupid. But really, I've carefully checked the 3 wires that go from the dist to the megasquirt for continuity. All grounds end on a bolt on the TPI fuel rail. There's another ground on the interior of the car, near the MS, but mostly for relays. Everything looks fine. I also checked timing with a timing light today while my wife cranked it. It's set at 0.

This is the diagram I followed for the dist:


Would I be better off changing the MS to VR mode instead, and using an MSD ignition I have from my Blazer?

Attached my latest datalog and current .msq file.

Any help greatly appreciated.

[Blazer79]

I just wanted you guys to know that I swapped back to the previous ignition module. I found it wet. Dried it with a lamp. Installed it and engine now runs without the misterious 0-18,000rpms I was gettinng. This "new" module I removed had no brand on it, but came in a Wells box. It has part No. DR124 on the box. The one I reinstalled is a Standard Motor Products one. Engine still runs rough, and will die if I don't depress the gas pedal about 20% or so.

I am still intrigued however, why did I previously get this erratic behavior with this module too?

Old VR sensor + Standard Motor Products ignition module = Erratic RPMs
Old VR sensor + new Wells DR124 ignition module = Erratic RPMs
New VR sensor + new Wells DR124 ignition module = Erratic RPMs
New VR sensor + Standard Motor Products ignition module = RPMs looking good

The only possibility I can see is if I plugged one or both of the connectors to the ignition module backwards. I checked and it is possible. So be careful with this. Follow the wires from ECM through harness and make sure they end at the correct terminal on the module.

Now I'll try to get a descent idle tomorrow.

[Blazer79]

Well my problems continue. The old module is acting up again. So I'm converting my MS to VR sensor so I can use my ignition box instead of the problematic modules. I'm outside US, so shipping a new module would take about a week.

I understand how to convert to VR and how to hook up the ignition box. My question is, how do I set timing? I'd like to crank it and not have it advance timing while I check timing with a lamp. With the HEI setup, disconnecting the relay that won't turn on ESC until finishing cranking was the solution, but there is no such relay in the MSD diagrams. Do I simply disconnect the white wire that goes to the MSD box (pin #36)?