PROBLEM WITH INTERMITTENT "MISSING"
Sorry this is so long, I wanted to give as many details as possible.
4.9L NON-Northstar, in a 93 Eldorado
Missing in Cyl 3 and also 4. INTERMITTANT. Driving down the highway at
70mph+ it runs like a top -about 90% of the time. Sometimes in city driving,
runs great (10% of the time). Sometimes feels like just ONE cylinder
missing, other times, like both are missing. Sometimes I can start it and it
will run like a top for 5, 10, even 30 minutes (I call this a "Good start").
Other times I start it and it it's running rough
from the get-go (I call this a "bad start"). If it is running good, 2
minutes later it could be missing. if it's missing, 2 minutes later it could
be running great. But it does seem to run good almost all the time when
cruising 70mph and up, and tends to run bad almost all the time when
cruising around 25mph.
When it's missing, the RPM needle jumps up and down spastically. The needle
gets crazier the worse the engine is running.
I was able to access the computer thru the climate controls, and there's no
codes that could possibly be related to engine missing (had a TPS error,
replaced TPS and that error is gone).
In that computer access, I was able to disable injectors, when I
disabled Cyl 3, there was no difference in the idle (indicating Cyl 3 was
currently not firing). One time when it was REALLY running bad, neither Cyl
3 or Cyl 4 were firing.
WHAT HAS BEEN REPLACED:
- All 8 Injectors with rebuilt from Linder Technical Services (highly
recommended by CadillacForums.com, voltage/flow tested, flow matched to
+/-8%, and guaranteed)
- All plug Wires
- All Spark Plugs
- Distributor and cap (not the coil)
- Battery and battery connections (also inspected all grounds, all were
- Alternator was tested by a reputable shop and tested out fine
I'm about 95% sure this is electrical. since it seems to me that if
mechanical, it would miss 100% of the time (ie. Valves or bad cylinder,
Tonight I think I confirmed it being electrical.. I was driving with windows
down, car was in it's "bad running" missing on at least 1 cylinder. I then
put up both windows at the same time, and the instant that they were fully
up (and I was still pushing the switches up)... the car STALLED, engine to
WHOA... did that really happen? I let off the switches and RPMs back to
normal! Then I again just tapped BOTH window controls up, RPMs to "0", I let
off, engine running again. I could repeat it.
Then I had a stop, turned it off, started it back up, now the car is on one
of the "good" starts (ie. no missing!) so I tried the windows again... car
KEPT RUNNING, the only thing was the lights dimmed pretty badly. But the
RPMs didn't go to "0".
A while down the road, car started missing again, so I tried the windows and
BAM, RPM's to "0".
For what it's worth, I pulled up Battery Voltage and it never wavered or
changed even when I did the window switches.
So it seems when it's acting up, the window switches kill the engine. If
it's running good, they only dim the lights.
Any ideas on where to start looking for this problem? People on
CadillacForums are suggesting I replace the Coil next. I have no problem
doing that but I don't want to keep throwing money at non-problems. If I
have to spend the money on a new computer and that fixes it, then I'll
spend the money!