erwalker

I have an '82 U.S. model and have had a problem since I bought the car 2 years and can't seem to find the cause. Engine runs smooth until it hits 3500 rpm. At 3500 (not always but perhaps 40% of the time), the engine breaks up, misses and you can feel the car buck. Rev counter bounces up and down until I let off the gas and the car slows down. I have changed/checked the following:

1) Replaced green wire
2) Changed rotor (cap appears fine - no tracking)
3) Cleaned all the grounds (except grd on rt side under horizontal tube for headlamps) including engine ground.
4) Removed, cleaned and balanced injectors (yes, hoses replaced too!).
5) Replaced spark plugs (standard plugs, not platinum)
6) Cleaned multi-wire connector at hot post.
7) Cleaned all connections/fuses on fuse panel.
8) Cleaned connection at ignition unit near hot post.
9) Cleaned connections at ECU in passenger footwell.
10) Checked operation and cleaned connections at WOT switch
11) Checked plug wires in darkness to confirm there were no "fireflies". Wires appear new but were not replaced.
12) Cleaned connections at coil (coil not replaced).
13) Checked vacuum advance and retard on dist. and confirmed smooth operation.
14) Checked and adjusted timing - 22 degrees at 3000 rpm.
15) All vacuum hoses replaced.
16) AFM connections cleaned. Flap works smoothly but AFM not tested.
17) Fuel filter replaced. Fuel pump replaced (due to leak at seam).
18) Compression checked and 165 +/- 10 on all 8 cylinders.

It there anything I am missing, short of replacing some of the electronic units with known good units? I am thinking the coil should be replaced, just for peace of mind. The engine starts to miss and buck only at 3500 rpm, no more or less so I am trying to figure out what in the 16 valve cars happens electronically at 3500 rpm that might explain this. Happens when motor is both hot and cold (not stone cold but after 4 or 5 minute warmup).
Any help would be appreciated.
Ernie

Fabio421

Does it only do it under load or also when you sit and rev the engine?

mark kibort

coil wire connection both low voltage and high voltage contacts and insulation.

hacker-pschorr

I've run into a similar situation that turned out to be the ignition module, mounted on the passenger side inner fender below the jumper terminal.

They do fail and contrary to popular belief a failed ignition module doesn't mean the car is 100% dead.

erwalker

Happens both under load and no load. Bad coil seems like a possible cause. Also, I have not checked for a plugged cat but I would think a plugged cat would do this consistently, not just sometimes and also affect the running at various rpm's, not just at 3500 on the nose.

Lizard928

I am with Erik on this one,

Swap out the ICM and see if problem remains.

GlenL

I'd throw wires at it. Just the wires, though, to keep costs down.

At this point, a new cap would be a decent try.

I'll concur with the group on having an electrical problem. What does a timing light show when going through that RPM band? If the timing jumps around more than a few degrees then do the ICM for sure.

Also, I'm reminded of a few years back when there was a batch of bad green wires. The connections were swapped and gave odd results.

erwalker

Timing light appears fine but I have only reved up to 3000 rpm to adjust timing. I'll try it up to 4g tonight and see what happens. Green wire should be ok - just got that from Roger within the last month. Cap and wires are on the list of things to replace but I'm going to change the coil and see what that does. I want to go step by step and see what exactly fixes the problem vs. changing a whole bunch of stuff then never knowing what exactly cured the problem.

PorKen

The fuel pump relay on L-Jet cars is also the rev limiter. Try bridging it, and see if the problem stops.

hacker-pschorr

Really? Mine will soar to 7,000rpm
What is the limit supposed to be?

PorKen

6300±200?

Maybe you have a regular 57 relay in that spot, instead?

Daniel Dudley

The Air fuel meter on those cars has a flap valve that opens with the flow of air into the engine. It moves a pickup along a potentiometer to signal the ECU how much fuel to meter. Sometimes the potentiometer wears at certain cruising RPMs, due to constant hovering of the pickup around that area. A way to test this is to cruise that RPM, and see if there is a cutout at a specific range of rpm that is constant and repeatable. If you take the black cover off the AFM, you will see the pc board potentiometer, and it will be quite clear if there is a worn spot along the arc of the arm swing. Some people will try to rebend the arm to contact the PC board on a different arc radius. Some will just replace the unit with a known good unit.

I am not saying this is your problem, but it does come up from time to time. Good luck with your repair.

kikitup

Any fix on this yet?
Thanks

erwalker

Sorry, but I have not yet been able to checking out the car yet - weekends seem to be the only time I can muster up the time to work on her. Hopefully saturday or sunday I will be able to get back to it. But I will let you all know what I find. Thx, Ernie

vbatla

When checking the plug wires at night, try lightly spraying water on them.