Running issue related to alternator

[r lane]

A 92 Turbo with Electromotive twin plug. Performance has gradually degraded over the past few months but comes and goes. One minute it will improve if you unplug one of the coil packs and then later will degrade while running on one set of coils but improve if you plug the coil pack back in. Is Nuts. My post is about what is needed from the alternator. I am seeing 13.6-7 V at the battery and 13.4-5 V back at the DME. The erratic pattern feels like a ground but the engine ground strap is intact and running a jumper cable between the engine and chassis doesn't change anything, so don't think I have a ground issue. New AGM battery. So back to the alternator. Appreciate anyone's experience with running issues related to the alternator. Thanks, Bob

[brighton911]

Are those voltages with the engine running ? If so, while a tad low, (should be about 14 V while running), it is certainly enough to satisfy DME demands (or Electromotive).

[Dpmulvan]

Sounds like a coil going bad

[spoke]

[QUOTE=r lane;12562470]I am seeing 13.6-7 V at the battery and 13.4-5 V back at the DME.

So you have 0.2V difference between the battery at the front of the car and the DME at the rear? That does not seem to be much difference. Maybe a tad low but should be ok. Now if the voltage is jumping around during operation, then I'd be concerned.

[ant7]

Make sure the wiring; and the insulation on the wires going to the alternator are in good condition, there may be an intermittent short going on somewhere.
Just a thought.
Ant.

[r lane]

My worry here primarily after a conversation with Richard Clewett was that the amount of voltage wasn't sufficient. After cleaning up some power and ground wiring the drop became what I thought negligible. Also Went from 14 gauge power wire to the relay board to a 12 gauge and maybe I reduced the drop a tenth of a volt. The alternator for that car is expensive and the thought of going to the trouble and expense and winding up with the same voltage numbers made me tremble. Header temps were all over the place as well. Pulled the intercooler and plumbing so I could access stuff and began checking the plug wires, which you might check first if you could get to them. The upper 1,2 and 3 complete resistance. Wire set is 4 years old. Excessive resistance on others, so am getting a set of wires. Will try a set from Magnicore. Will post when back together. Thanks much for the response. Bob

[unclebilly]

How do you know it isn’t a fuel issue? You could have a flakey fuel pump (there are 2), a flakey fuel pump relay (there are 2), or a bad overboost relay which was the issue on my hotrod 86 930S.

[unclebilly]

It could also be the rubber air intake elbow collapsing under boost… I chased this issue for a year before I found a thread here.

When does it act up?

At idle?

Only under boost?

All the time?

Does it run rich (sound like a lawnmower and smoke like a chimney)?