Tune-up Issues


Created: 9/5/2004

Last updated: 


Author/source: Rich Acuti via DML


 
----- Original Message -----
From: "cruznmd" <racuti1@delorean.com>
To: <dmcnews@yahoogroups.com>
Sent: Sunday, September 05, 2004 10:12 AM
Subject: Ignition issue- RESOLVED (long)

I'm posting this because a few folks have related that are interested
in my results because they have a similar problem. To recap:

Symptom(s):  Car started well, idled acceptably. All fuel pressures
nominal by Bosch fuel pressure test rig. All fuel components
replaced. Car stuttered heavily under load (A/C on, pulling away from
dead-stop, hard accel), surged when maintaining steady speed, and
experienced a power fall-off when the accelerator pedal is pressed
more than 1/3 of the way down. The power curve "drops off" and the
car decelerates. The engine sound changed drastically, as if
misfiring.

I'm sorry to say that there wasn't one particular "smoking gun" to
this problem. It was a many-layered thing. Here are the items that
caused a noticible improvement as I fixed them:

As David Titlebaum says "Just because it's new, doesn't means it's
working correctly".

1. My "new" plug wires were SHOT. 2 read "infinite" or "open" on my
Fluke multimeter. The others 4 read 9k ohms or more. The normal
resistance for new, plain old store-bought 7mm wires is around 1.5k
ohms. My new hi-po wires read 350 ohms/ft. 8mm, silicone.

2. My "new" cap and rotor had HEAVY carbon scoring. Uncleanable. Most
likely due to my plugs being overgapped and failing plug wires.
Replaced with Bosch plugs of the correct part #, correctly gapped and
new cap and rotor.

3. Grounds: I replaced the black ground cable that runs from inside
the coil box to the frame. I cleaned the ground cable behind the
parcel shelf wall, passenger side. Also, the ignition ECU grounds the
coil via the white/slate wire. Inside the coil box this wire goes
from the coil to the yellow plug, pin 3. The pins were -green- and
didn't contact well. I cleaned these up and crimped the female closed
a bit. I then checked the white/slate junction in the relay
compartment. Pics available upon request.

4. Coil: I have experimented with; Accel, OEM Bosch(blue), 18kv Bosch
(red), MSD Blaster 2.
Of these, (oddly) the red, 18kv Bosch and the Accel coils run the
worst. For me, they cause a less acceptable idle and performance is
not as good under load. If I had to hazard an educated guess, I say
it's because the -internal- resistances are not OEM spec. They are
higher. I believe to function correctly, they might need a longer
dwell time to build the proper field in the coil prior to discharge.
As we all know, dwell is neither readable, nor adjustable on our
cars. The MSD has the same internal resistance as the OEM coil. It
idled well and had good performance. The biggest difference I noted
between MSD and the OEM coil was easier starting, a slightly better
idle and slightly more horsepower. I'm probably not making full use
of the MSD coil because I haven't matched it with other hi-po
ignition components except the wires.

I don't guarantee that my problems are your problems but I make the
following recommendations:

1. Clean the aforementioned grounds. Use contact cleaner from Radio
Shack (spray can) and emery paper, then coat lightly with brand: CRC
di-electric grease. Verify that all spade connections are in good
repair and tight. Many of mine broke off due to wire-fatigue.
(especially white/slate)

2. No matter how recently you've done a tune-up, inspect or replace
your ignition components. I can't stress the word QUALITY enough. I
tried to cheap out, and it caused me trouble in a couple of areas.
Bosch, Bougicord, etc. DMCH's Nology and John Hervey's hi-po wires
are also good (just my opinion).

3. Ensure coil compatibility. Some of you who wrote me also have the
red, 18kv Bosch coil. I recommend experimenting with the OEM coil,
but if you have to have a "firecracker", get the Nology kit or MSD or
Pertronix. I would stay away from Accel and I don't think I trust the
red 18kv Bosch coil anymore. Whatever you do, try to get a coil with
the same internal resistance as "old blue".

My power curve is back to normal. No surging, no power drop off. I
can push the pedal anywhere I like and the car keeps on going. A/C on
or off. I had to fix -all- of these things to get it that way.

I hope this helps,

Rich A.
#5335



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