Ok, so I've finally gotten to a point in this build so that I can drive the car down the road, but I have a very intermittent problem that has me stumped.

Sometimes, not frequently but often enough, the engine/ECM tries to and often completely cuts off. I say ECM as well because I have an EBL P4 Flash and during the initial idle tuning I experienced the same problem and I could see that something was happening via the WUD. The read outs would start displaying values all over the place - even oil temp which I don't have hooked up!! All while the engine is stumbling as tho its loosing ignition power or running out of gas.

I initially chalked it up to a bad battery that had been in the car sitting without being charged/discharged for a year. It was a new battery when i put it in a year ago. It'll take a charge just fine and the starter doesn't drag, so my next guess is that maybe low battery voltage/alternator undercharging (under drive pulleys) might be the culprit, so I upped the crank pulley size to get 13v at idle.

I thought that did the trick until I took it out for some road tuning today - a run up to the gas station 5mins from my house. Everything was fine - engine ran pretty good considering the tune is way off in left field still - until 2/3 of the way back it starts doing the same thing - engine starts cutting out, WUD values all over the place - then it quit. I tried to restart it several times with no luck other than a brief fire off but then quickly dying again. I made about 20 start attempts and finally got it started - but still trying to die throttling it trying to keep it running. It died and I went thru that whole procedure (start attempts, kinda running while pedaling, stalling, etc., etc) 4 times in the last 1/3 of this little trip.

So I finally get it back in the driveway (fortunately no tow needed!!) and let it sit for maybe 5mins. I tried to restart it and it fires right off! WTF!!!!! No stalling, no stumbling, nothing but steady rumpity rump at 800rpms for over 30mins.

I did a little more fine tuning (no load) up to 3000rpm for another 45mins after that and still no problem.

I'm stumped, I rarely get a hand or second set of eyes to help monitor things to get a diagnosis put together so I can be rid of this irritating problem.

Does anyone have any idea what might be happening and where to start tracking down the problem?

Thanks Guys
D

What ecm? Maybe a bad ecm or power wire to ecm somewhere?

Mine had a very crazy issue that i never did figure out but think it was a wire problem.

I could take and hold my ecm with car running, and if i tilted ecm over car would start to stumble. If i kept tilting it would shut car off but if i brought it back it was fine. Swapped ecms and problem went away for awhile then started doin it again but not quite as bad or as often. Weird. This was 730 ecm

It's a 92 Z28 with a Dynamic EFI EBL P4 Flash ECM.

The problem screams electrical glitch, but I checked all the wiring the first time it did it a long time ago and never found anything out of place. I also tried the hold the ECM in my hand with the engine running and shake it around a little - nothing, and wiggle wires at ECM connectors - nothing

This has been an issue since I installed it or at least shortly after I installed it, but the car sits the vast majority of the time because I don't have much time to tinker with it and when I have had time to work on the car it's been to upgrade practically everything else on the car, not so much trying to alleviate this issue.

So here we are, everything else works as it should except for this. Wouldn't be a big deal if it was just annoying....but it left me in the middle of a two lane country road dead in the water today with no where to pull off!!!

Gotta get it fixed!!!

Check grounds?

As Orr89RocZ posted, definitely check the grounds. These are the EFI harness connections to the engine block.

Further checking of the ECM is to rap on it with your knuckle as the engine is running. If it stumbles or such, then it is likely intermittent. In that case you can ship it to us for a look see.

RBob.

I've checked grounds many times thinking maybe, just maybe I'll find something I've missed the previous 12 times!!!! Yes, I have definately checked grounds lol.

Either I keep missing the one thats almost broken or isn't connected where it should be or it's such a tiny flaw or set of circumstances that it checks out ok when tested (hope this isn't the case cuz it could prove unsolvable)

Hmmmm......maybe.....

What do you think of this??

Sorry, more back story....

....after months of sitting with the engine out of the car being built and a T56 swap the original battery was dead when I finally got everything buttoned up to start it for the first time. It tried charging it but it was toast and puked some battery acid. After replacing the battery I tried to start it and it spun maybe a half turn then just stopped and everything quit working - no starter, fans, lights, fuel pump - everything. After hunting in the harness, I find a large 2pin weather pack connector with 2 12ga orange wires going to and from that connector.

When I boiled that battery acid out, some of it apparently got on that connector, and somehow caused a poor connection inside and it arced which disconnected pretty much everything from the battery. I did fix it immediately.

I'm going to check that connector...but....

Do you think it's possible that from ambient temp to under hood operating temp could cause an already slightly damaged connector to somehow expand somewhat at a certain under hood temp that could also create this intermittent condition????

I have in the past and did today do just as you said RBob by lightly tapping on the case of the ECM with my knuckles, flipping it around every which way, wiggling all the wires in the harness connectors, but nothing. It never faultered.

Head scratcher....

I think that is a place to look at, if all else hasnt panned out

I just worked out an issue just like this.

In the end it was the EST/ICM module which has always been known to work, yet fail and work again while being faulty. Who knows where 40,000 volts is going while it's glitching?

First thing I noticed was arcing in rotor and cap, button spring was failed and button was just hanging, so it was replaced and symptom got a little better.

Work on everything else the same as you are including grounds many times.

Go back and look at new cap and rotor and see very small amounts of arcing again? Further inspection found melted plug from pickup coil to EST, pull distributor to replace pickup coil and find further hot issues of pickup coil copper winding. Replace pickup coil and EST because at this point it has been inside a cap with 40.000 volts flying around.

Problem solved!

EST can be faulty with none of these signs...

HTH!

I have all new MSD ignition - every component including dizzy...

But...

Engine has Moroso solid mounts, they raise the front of the engine about a 1/2 or so higher that stock. That causes the dizzy to be closer to the fire wall and the harness connectors going to the base of the dizzy point toward the rear of the car somewhat.

I'll check to see if maybe those wires are touching the firewall.

BTW...drove the car up and down my 1/2 mile long street today about 4-5 laps.

No problem at all

Except clutch issues, but that's another thread!

Brand new parts don't mean they are good working parts. All parts can come faulty when new.

MSD has casued more issues then most and don't even compare to stock when it comes to reliability...

It was just a thought to help your issue though, not to compare parts.

I've never had an ICM quit then start working again. I've had several just quit tho, even in "new" high end performance parts including MSD. I'm not saying it can't happen and it would be great if it is that or something else not wiring related cuz the fix is fairly cheap and quick

We'll see

I had the same issue with my car a couple of months ago. Found voltage on pin A6 had degraded to low 12V range while everywhere else was 13.6+. ECM shuts off around 11 volts and wouldn't send data either. My datalog showed voltage dropping to ~10 on that circuit at idle or when the fan kicked on, then the data stopped. Ended up making a separate fused circuit with a relay for max voltage. Could be something worth looking into.

So I guess my question would be why would that pin have a lower voltage than any other?

Corroded connection somewhere would be my guess.