What's at fault - EDIS, Coil Packs or Wiring?
Posted: Wed May 14, 2008 5:41 am
I have been running a small block Chevy V8, with MS-II, 2.883 s/w, using an EDIS-8 with twin Accel coil packs for just over 2 years now (that is with continual s/w upgrades). In all that time I have had a persistant problem that I am very slowly getting to the bottom of, I shall explain...
Any engine speed below approx 5100rpm has been fine but going higher (and I have a readline of 7000) causes a notable misfire to occur, this can be felt easily by the car juddering, as the rpm increases this seems to get worse. I have just added my forth new trigger wheel as I had not been happy with previous attempts, and on the assumption that I had a speed/timing sensor issue. But, now after getting hold of a scope I found out something interesting. Another point was that at 5100rpm my tacho, which is driven by pin 2 of the EDIS, the IDM signal, would start to waver and as the rpm inceases completely drop out to zero.
Initially I scoped the VR -/+ pins but this was a little inconclusive as the scope leads were picking up a lot of noise and was harder to see as the revs increased, so decided to scope the tacho signal (IDM) for which a scope trace is shown below. With the scope attached to the VR sensor the engine was revving somewhat wildly without any use input, a little disconcerting. Later I realised it was propable picking up the DC noise of the high pressure fuel pump, as the unscreed portion of the lead lay across the pump!
From this it can be 'clearly' seen (via a blurred photo) that there is a missing pulse (note that the signal has been inverted by the scope to aid triggering). On occassion more than one pulse would be missing but never a whole revs worth or more. So, my conclusion from this is that the trigger wheel/VR sensor side is more than likely to be fine, and I have a coil firing issue, that could be down to the EDIS, the coil packs or may be wiring. My reason for thinking this is that I would expect to see more than one missing pulse in succession if this was down to the trigger wheel, due to the EDIS having to resink with the missing tooth, also I would expect the misfire to be a little more consistant, as a missing pulse seems never to occur every rev.
So armed with the above knowledge what would be your conclusion to the cause of this problem?
Soon I will try two spare coil packs that I have access to, then may be replace the EDIS-8, but I will leave the trigger wheel and VR sensor alone for now me thinks!
Cheers, Phil
Any engine speed below approx 5100rpm has been fine but going higher (and I have a readline of 7000) causes a notable misfire to occur, this can be felt easily by the car juddering, as the rpm increases this seems to get worse. I have just added my forth new trigger wheel as I had not been happy with previous attempts, and on the assumption that I had a speed/timing sensor issue. But, now after getting hold of a scope I found out something interesting. Another point was that at 5100rpm my tacho, which is driven by pin 2 of the EDIS, the IDM signal, would start to waver and as the rpm inceases completely drop out to zero.
Initially I scoped the VR -/+ pins but this was a little inconclusive as the scope leads were picking up a lot of noise and was harder to see as the revs increased, so decided to scope the tacho signal (IDM) for which a scope trace is shown below. With the scope attached to the VR sensor the engine was revving somewhat wildly without any use input, a little disconcerting. Later I realised it was propable picking up the DC noise of the high pressure fuel pump, as the unscreed portion of the lead lay across the pump!
From this it can be 'clearly' seen (via a blurred photo) that there is a missing pulse (note that the signal has been inverted by the scope to aid triggering). On occassion more than one pulse would be missing but never a whole revs worth or more. So, my conclusion from this is that the trigger wheel/VR sensor side is more than likely to be fine, and I have a coil firing issue, that could be down to the EDIS, the coil packs or may be wiring. My reason for thinking this is that I would expect to see more than one missing pulse in succession if this was down to the trigger wheel, due to the EDIS having to resink with the missing tooth, also I would expect the misfire to be a little more consistant, as a missing pulse seems never to occur every rev.
So armed with the above knowledge what would be your conclusion to the cause of this problem?
Soon I will try two spare coil packs that I have access to, then may be replace the EDIS-8, but I will leave the trigger wheel and VR sensor alone for now me thinks!
Cheers, Phil
