midface

1995 LS 400
Hi guys...I'm kinda new here. I used to participate in the forum years ago when I bought my car but have since had a computer crash and lost everything. So I am starting over!
My import mechanic (these guys are pretty good) can't figure out why my 95 LS400 misfires when he puts the engine cover on and I am trying to help by coming here.

He just put in a new timing belt/water pump housing(it was leaking and caused the belt to slip)new spark plug wires. At idle it runs fine ( a little higher than it did) . Under load it misfires when the engine cover is on.

Take the engine cover off and it runs like a raped ape. He had it up 100 MPH....Puts the engine cover back on and it misses like crazy while under load.
I have searched here and the web and can't seem to find a direct answer or solution.
Any suggestions or tips? My car has been there for 3 weeks and I need it back as it is my only ride. I am also going through a divorce and can't just go buy another car.
Can anybody help us out?
Thank you for any replies!
Midface

oldskewel

iTrader: (1)

My '91 does not have an engine cover, so I'm not really sure here, and this may be obvious, but ...

I'd check to see if any wires are touched at all when the cover goes on. If a plug wire is broken, it may connect when the cover is off, and then if bent slightly when the cover goes on, the circuit is broken.

An intermediate test ... try putting the cover on with screws missing and/or loose to see if you can narrow it down that way. If it really is night and day when the misfire appears, it should be easy to narrow it down.

Nishy

Possible that the cover is recirculating heat back onto the engine and that excess heat is screwing with the ignition coils. Kinda weird that it would do that with a stock engine cover though

dicer

Easy fix. Just don't put the cover on.
If so then the heat idea would be one thing the other is the disturbed wire or hose.

AkumaUCF10

The coils on this are just like the earlier 1uz, there are 2 and they sit off to the side un covered, therefore the covers being on should not affect the coil or cause it to heat soak.

My bet is on one of the wires being disturbed when the cover is on. most likely a connector or connection. You could always test for continuity when contorting the spark plug wires, or just replace them. Chek all the plugs on the wiring harness and vacuum lines

midface

I suggested this and the owner and mechanic said there was too many exposed parts. I think the mechanic is flustered and the owner is trying to keep me happy.....
I will suggest the putting the cover on with a few missing bolts/loose bolts and go from there.
Anybody else?

dicer

Just tell the owner to look at a 1991 and he will see those same parts exposed all the time. The cover is on there for looking cute and nothing else.

AkumaUCF10

Honestly sounds like you need to take it to someone who knows these cars better. Like I understand shop loyalty, but it seems like the mechanic is in over his head, esp given the fact that the vehicle owner is on the internet doing the research and not him. This should be a simple issue related to wiring, my bet is the plug wires, I could be wrong but its a really easy thing to rule out by just swapping the wires to new ones and seeing what happens. A good mechanic would be willing to give it a shot to rule that out. The fact that he hasn't tried it yet is a little bit baffling. Take it somewhere new or have them try new plug wires.

RA40

iTrader: (6)

Were the caps and rotors changed with all this? The cover doesn't really contact anything other than the ignition wires at the front. Make sure that any parts of the wiring harness and vacuum tubes around the intake plenum are clear and in good shape.