[DMCForum] Loss of Power/Flat acceleration (Long, but worth reading)
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[DMCForum] Loss of Power/Flat acceleration (Long, but worth reading)



I've been getting lots of good advice regarding my problem and I
appreciate it so keep it coming.

Again, this morning for 3/4 of my drive to work the car ran very
well. Foot to the floor and all of that. It didn't start to buck
appreciably until the engine had been at operating temp for a while.

Marc, after the engine compartment is good and hot, the tach flickers
even when parked and idling. It's rock-steady after things cool
appreciably.

Dave S. has rightly advocated the scientific method for sticky
problems so I am trying to take that route.

Problem: Loss of power under load, and skipping idle (both when
engine is hot)

Theories:

Fuel:
I haven't totally ruled out the fuel system but I think I can rule
out clogs because a clog is a clog, hot or cold. Main line pressure
doesn't change hot or cold so I don't think the fuel pump is slowing
down when it warms up. Control pressure is in spec.

Electrical:

Martin, your distributor spring story is very interesting. I will
definitely keep it in mind. We know that electrical circuits hate
heat. Here are some theories, and I need ways to test them:

#1: The ballast resistor, or resistor relay may be faulty. The
resistor regulates voltage to the coil. Too much and the coil
overheats and is ruined. The relay cuts out 1/2 of the resistor
during cranking. If the relay is stuck, (only .5 ohms vs. 1 ohm) then
the coil could overheat during driving. I can measure this with my
ohm meter.

#2: Distributor pick-up coil: Could it be breaking down when it gets
hot? My experience with them is that they work or fail, not in
between. Anyone have experience with them causing something like this?
How could I measure its output when the engine is hot, and running?

#3: Sparkplug wires: Although new, they are not the type that most
owners buy. They are 7mm but maybe they are just a poor quality that
don't like heat. Could I be experiencing cross-fire/misfire? How can
I test for this? I tested all wires with a timing light. The light
flashes but that's a long way from saying that they fire correctly.

#4: Timing advance: The distributor is clean and the timing advances
but is it advancing enough? How can I tell? It shoots off the scale
so how do I measure it?

#5: Vacuum leaks: My fuel injection manual recommended checking for
leaks first. I've installed some silicone vac lines on the fuel evap
canister, the cold start valve and from the dizzy advance to the
solenoid. I found an A/C actuator hose for the center console vent
dangling free. The actuator is physically broken. I plugged the line
with a golf-tee for now. I checked the brake booster lines. I can not
find any other vacuum leaks. I've mostly ruled this out.

#6: Faulty relay: The RPM relay is not clicking on and off when hot.
I removed the cover when everything was good and hot and observed the
relay. It seems fine. Lambda relay: I hear no clicking but that
doesn't prove anything. The dwell meter indicates the freq vavle is
behaving properly. If the lambda ECU were intermittent due to a fault
or a bad relay, the valve would be too. I've mostly ruled this out.

I know this much for sure:

When cool, the tach is perfect. Idle is steady. If I drive on the
freeway, many times the car runs ok for as long as 20 minutes before
things start going wrong. Especially if the ambient air temp is cool.
Once components in the engine compartment are exposed to engine heat
for a while, that's when things degrade. It's very gradual at first,
then it accelerates to the point where profanity comes into use.

What say you?

Rich A.
#5335




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