Low Voltage, Miss Fire

[Nash]

1990 Eagle Talon TSi AWD
MODs are as follows:
SCM 61
3" Buschur Cold Air Intake
850cc Fuel injector clinic injectors
Walbro 255hp pump, re-wired
Areomotive AFPR
Eprom ECU from a 92 with DSM Chip, 5000 sutter box, 6000 no lift to shift, and some other things I can't remember
Taylor wires
BPR7ES plugs, gapped at .028

I have a low voltage problem, that I'm not even sure if it's a problem, or if all DSMs do this. The problem is when I start the car the voltage is 14.0-14.08, as I drive the car it drops. Depending on how far I drive it will drop any where from 13.5 to 13.0. Just on my way home from work, 15 miles, it went from 14.0 to 13.34. And it will drop under 12 if I really get on it. I put a different alternator in, one that I had that test good. I have checked all the grounds and they all look good, same with all the fuses. Anyone have any ideas on what it could be? Battery?

The other problem is a really bad misfire at anything over 13-14psi. I have tired two sets of wires, new plugs and a different coil pack. Any ideas on this? I'm going to do a boost leak check this weekend, but with the MAFT set up for blow through I didn't think it would cause this bad of a misfire. Could the low voltage problem be causing the misfire?

[SlowWhite]

When i first got my Yellow Top Type 51 battery (my new one) my voltage was at 14.0-14.5 all the time then about a week or so later I started seeing my voltage staying around 13.0-13.5 and would sometimes dip into the 12's.

so I don't think it's your battery or Alternator - my DSM's been driving fine (well until the rear diff went out)

I'd still check the battery anyways just to eliminate that possibility.

Can you describe the miss fire better....

-How long a go did you do the "RE-Wire"? -Possible something a miss there.


Not sure what else it could be since you swapped plugs/Wires/Coil packs already.


although TT Jake came to my house a few months back with a simular issue. Not sure if 1G's have this or not but on the 2G the sensor that is to the left of the coilpack in this picture went out twice on him and was causing the same symptoms. (the one that is infront of the "NEUSPEED" stickers) - it normally bolted on the intake of a 2G.

[Nash]

I'm not sure how to explain the misfire. It's just missing, sounds like a ignition miss to me. I haven't re-wired anything since swapping the coil pack and ignition transitor out for one from a 92. The car just fine after doing that.

That is the ignition transistor, I'm going to be swapping that too as soon as I can find another one to try.

[JustROLLIN]

Voltage while driving should be right around ~13.8 volts. So, you are not too far off on that mark. Check voltage on the battery after it has sat for a while. Voltage should be ~12.6. If its lower, then you likely have an ALT problem, poor grounds, or a wiring restriction. (Likely the ALT)

As for the misfire. I would certainly think that low voltage could cause your misfire. My guess is that not all the voltage necessary is going to the coil. Our cars produce very high amounts of voltage for the spark. My guess is that the boost is just blowing out the spark.

[TheBlizzard]

It should also be mentioned that his timing is something like 10deg advanced which from what I have read numerous times could cause a misfire, depending on the car. However his car did run good like that before the tranny swap and the timing hasn't been changed since he dynoed last I am pretty sure. So its a very puzzling problem. The battery is where I would go next and I think he is going to do the same, maybe that battery is drawing too much from the alternator and cause you to lose spark.

Andy if you PM me with what battery you need I can run down the street and get on for you and we can put it in when you come here to move stuff in. Let me know.

CRAIG

[Nash]

It's not the timing, it's now set at about 4deg, didn't help at all lowering it.

[TheBlizzard]

Originally posted by Nash@May 21 2004, 11:40 AM
It's not the timing, it's now set at about 4deg, didn't help at all lowering it.
Ahhh I see, didn't know you did end up lowering it. Yeah then get that battery and if its not that, who the hell knows.

CRAIG

[TheBlizzard]

You also could have an arcing problem somewhere also.

CRAIG

[JET]

Originally posted by Nash@May 21 2004, 08:41 AM
I'm not sure how to explain the misfire. It's just missing, sounds like a ignition miss to me. I haven't re-wired anything since swapping the coil pack and ignition transitor out for one from a 92. The car just fine after doing that.

That is the ignition transistor, I'm going to be swapping that too as soon as I can find another one to try.
Well, you only need to look in our garage to find another transistor.

I also think it is an ignition misfire. It is a crisp misfire, but not abrupt. It may be fuel though, I have ran into problems on my car that really sounded like ignition and it was fuel related. Although we did mess with the SAFC and it didn't change it. Plug wires and coils were also changed.

[LightningGSX]

The low voltage shouldn't have an effect on spark.The ECU compensates for low voltage by increasing the coil charge time.