What's at fault - EDIS, Coil Packs or Wiring?

[pb3]

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

[zsilinszkyz]

Can you check the PIP and IDM at the same time? If there's no missing pulse on the PIP, the VR part is fine.

Zoltan

[pb3]

Hi Zoltan, that is a good point and a much easier signal to monitor. I could probe the ECU side along with the tacho wire to confirm, just need to do it all again. I take it you would still strongly suspect the speed signal side of things?

[pb3]

An Update:
Today I finally got around to retesting my ignition system, by re-scoping and this time monitoring both the IDM signal and the PIP signal directly off the EDIS-8 connector.

This time I have no doubt that it is an EDIS/coil pack issue, it can be clearly seen from the trace (see below) that the IDM is reporting miss fires, as can be observed by the tacho and from hearing the engine. This problem only occurs above 5100 RPM regardless if it is loaded or not.

The orange (top) signal is the IDM, blue (bottom) is the PIP signal


So now I am sure the VR side is fine I need to try a new EDIS-8, although I thought they were bullet proof, then may be the coil packs!

Regarding the coil packs I am using some Accel ones, does anybody have anything to say about them?

[vinister]

I just bought and EDIS 4 Accel coilpack. Either my stock one was toast, or the Accel one is very very very good. The car feels better everywhere, makes more power, is smoother, etc etc.

I have the same problem as you with a miss in my EDIS. Mine happens at idle, but the troubleshooting is the same. The RPM signal into MS is good, no dropouts, so I can only assume the VR is fine. Testing with a timing light, I can visually see it is missing sparks at idle, causing the engine to stumble. It's completely random, and doesn't seem repetitive. Its like yours, it will drop one spark, then keep going like nothing happened. I replaced the coil thinking it was the cause, since my old one was from the original EDIS setup likely from 1990.

My problem only shows up after the car has been running for 10 minutes, whether it is warm or cold. I really think this is down to our EDIS modules themselves. I'll be trying a new EDIS this week, I'll let you know if it fixes it for me.

[gofastant]

I'm having a very hard time getting my car to idle. Just lots of stumble and wet plugs. I need to change the injectors before I start blaming the EDIS. I suspect whether or not they were damaged during the melted piston incident. I tested the spark and both coils put out a consistent 22 kilovolts. This is just atmospheric testing so I don't know if it's adequate. I used the same gap tool this guy uses http://www.surespark.com/

[Minami Kotaro]

Glad to know I'm not the only person who thinks this:

I just bought and EDIS 4 Accel coilpack. Either my stock one was toast, or the Accel one is very very very good. The car feels better everywhere, makes more power, is smoother, etc etc.

Same deal with me. The Ford coil had a very weak, yellow spark. The Accel coil has a violently powerful blue spark and the car runs much better with it. I'll probably try an MSD EDIS coil, too, just for the heck of it.

I really think this is down to our EDIS modules themselves. I'll be trying a new EDIS this week, I'll let you know if it fixes it for me.

I have two EDIS4 modules that are the same part number. One of them has massive RPM spikes at high RPM/boost and the other doesn't. Some of the companies that make the modules must not be much into quality control.

[pb3]

This is beginning to drive me mad. I replaced my EDIS-8 with a 'new' second hand unit and it has made it worse! I now get misfires from approx 4000 RPM on, under acceleration I now hear pops and bangs and the guy following me said he saw 2ft flames out the back! Also the tacho drops out as before! So there must be a lot of different EDIS-8 units out there with different filmware versions and hardware revisions so I just need one that works or may be I just have two faulty units, or my VR side is still an issue! More digging...