lloydie

Right, my initial setup - Motec M4 Pro ECU, running AEM Twinfire ignitor and four Chrysler 300M coils. The Twinfire isnt a great product. Im on my third ! Normally they just die at ignition on.
Symptom - cruising along at 2000rpm just fine about 3 weeks ago, tach starts jumping up to 3000, down to zero and back again. Car gets a little jittery but nothing bad. Few hundred yards down the road and BANG - huge backfire from the exhaust and the engine dies. Crawl to the side of the road and turn the engine over - turns over fine, but the tach doesn't 'wobble' as the engine turns over. Got the car recovered back to my house, assumed it was the Twinfire, ripped it all off and stuck the stock coils/ignitor/plug leads on. Car starts and runs fine. Problem solved............or not
Fast forward to this morning. Same deal - cruising along, tach starts jumping around. Stop at a junction and go to pull away, BANG huge backfire and i'm pushing the car to the side of the road. Same problem, turn the engine over no tach 'wobble'. This time i left it for 5 minutes, car starts first time. 10 yds down the road, backfire and stops again!! Left it to cool at the side of the road (didnt know what else to do), then turned it over, starts up first time and i drove it back home. Used my bike to get to work.

Im hoping someone with a little more knowledge can point me in the right direction here as im floundering. The only common thing between the two setups would be the ECU, the CAS and the wiring between the two and the plug where my twinfire or stock ignitor plug in. The CAS is a replacement unit (re-con) and been on the car about 12 months.

Am i right in saying that it could be any of the above ?

Braineack

iTrader: (62)

Gotta be the CAS.

C. Ludwig

I'll agree is sounds like a trigger issue. Easy enough to log/view trigger count when the issue repeats. This will confirm or rule out a trigger issue. Some CDI units emit a lot of electrical noise. This would be something else I would look at. Again, this will show up in trigger count and pattern.

It's a shame you opted for a very good ECU but have to deal with the suspect quality of the AEM CDI. There are better, much more reliable inductive options that are just as powerful (some more so) as this unit.

lloydie

Well the AEM unit is in my garage at the moment so isnt the cause of my woes this time. This mornings 'fail' was purely on OEM ignition components.
As for logging the trigger events on the Motec i dont think i can :( That would be ideal !

lloydie

The latest Motec software does allow for logging of faults relating to trigger events which would be good enough to start with, so ive downloaded it, then i'll grab the log off the ECU tonight. Only issue is that its a logical switch i.e. 1 or 0 to indicate a fault or not, so it will switch to 1 on the first error and then not show any subsequent errors until the ECU is restarted (dont forget its a 90's ECU!!)

C. Ludwig

True. You're looking for a ref or synch error. I thought the M4 would display live data. If so you can watch for the error. Have you always had this problem with this ECU or is something new? If you've always had it, adjusting the trigger threshold may be in order.

lloydie

Pulled the log and sure enough sync error. Sync is the yellow/blue wire to the CAS, so powered up the igntion and got a solid 5v at the wire, then traced the wires back through all the joints to the ECU, shaking/moving them as i went to see if i could get the voltage to dip. 5v held firm. So changed out the CAS. Thing is its not a 'known' good CAS - just one out of a junk yard on my way home. Starts and runs so fingers crossed. Thanks for the help in working it through.

lloydie

Hate it when people never post up the solutions to their problems, so thought i'd revisit this.
It was the CAS - the car ran (and still runs) just fine. Disassembled the old CAS and it was full of very fine dust so maybe that caused its demise ? Wouldnt have helped anyway ! Car made 300bhp and 300ft/lb at the dyno last week so all good

Braineack

iTrader: (62)

woot.