Misfire when changing to right lane

[adam quantrill]

This is a strange one - the 400SX has developed a misfire - and it seems to be brought on when changing lane to the right. So - just when you need power for an overtake, the engine splutters for about 1-2 seconds!

I tested this on the way home today on some open road, just cruising then changing lanes causes the splutter.

Anyone else had this? It feels like either fuel or ignition cutting briefly. What's more, it's worse when the engine is warm.

[wedgeinald]

Weird you should say that I have a similar issue on my 280i...

Mainly when exiting a roundabout (i.e. turning left-ish) feels electrical to me, only very short lived, and recovers quickly but is kinda embarrasing.

Pulls like a train most of the time, problem mainly shows on med-high throttle, might be a vacum issue too? Its always free revving in "neutral", (i.e. drop the clutch and it revs off no problem)

Had a Similar issue on an old V12 Jag that turend out to be a "bad earth" on the engine.

If you trace yours please let me know, and I'll do likewise.

[adam quantrill]

Yes I was thinking possibly a bad earth too - when shifting the car to the right the engine will lurch over to the left, pulling on any earth straps.

[Pothole]

no idea if this is hogwash as I'm not familiar with the cars, but if the ignition is on the steering column could you be straining a connection when turning the wheel? (guess it should happen on slow speed manoeuvres too, though)

[adam quantrill]

Yes, I will check all this out stationery in my driveway on idle - much easier then.

[jeff m]

If it were a Formula one style lane change I would say you need baffles in your fuel tank(s)

Back to reality...possibly a lean miss. Sudden fuel need that your fuel pump cannot supply, fuel filtre/pump.
The change of lane info could possibly be driving style, maybe some empty road testing!

[adam quantrill]

Well the car could put up with my driving style previously.... ;^)

Maybe the fuel swishing about might affect the pickup if one pipe if a bit bloked from one of the tanks?


I have access to a fuel pressure gauge so that will be tried, too. Mind you the way it gets though fuel I don't think it's running lean!!!

[adam quantrill]

Update on this:

checked on drive, no effect when yanking the wheel over.

Fiddled around with the ignition leads so they didn't run quite so parallel.

Took for a spin, seems a bit better, but car probably wasn't as hot as before.

So - another thought is crosstalk in the ignition leads, as I move the car right they shift about slightly. Will try spacing them out better. Unfortunately the later style leads are really thick and don't go into the clips (or if they do, they pop out again). I might make some spacers up with engineering plastic.

[gifdy]

I had the symptoms on my S. It turned out one of the connections to the cut-out switch ( the one that cuts the engine in an accident ) had come out and was earthing on the chassis as I turned right. I'd be amazed if it was the same thing, but worth checking ?

[Barkychoc]

From Haynes Range Rover Manual

[wedgeinald]

gifdy said:

I had the symptoms on my S. It turned out one of the connections to the cut-out switch ( the one that cuts the engine in an accident ) had come out and was earthing on the chassis as I turned right. I'd be amazed if it was the same thing, but worth checking ?

I don't think my wedge has such a switch...but just in case where is it fitted on the S?

[adam quantrill]

Yeah I happen to have the RR manual in front of me right now because I'm trying to find out how to extract the engine and gearbox from one. It's a 4.3l engine and quite a beast (or it was when it was running). Sometimes it's quite hard to enforce the even spacing between the wires without adding extra spacers.

AFAIK wedges don't have cutout switches usually, but it's worth checking too.

Edited by adam quantrill on Thursday 28th April 08:55

[Grady]

IIRC - the wiring plan for a 280 indicates that the cut-off switch was a USA only fitment, or maybe it was in the Bible, or maybe I'm wrong. Grady

[350zwelgje]

wedgeinald said:

I don't think my wedge has such a switch...but just in case where is it fitted on the S?

Think an S has a cut-out switch in the boot somewhere.

Rob

[wedgeinald]

Thanks guys didn't think the 280i had such "modern" devices, but always worth a check in case.

[adam quantrill]

New development - since changing the plugs, the misfiring has cleared up considerably. I might even say, it's gone (tempting fate here).

The old plugs were sooty and the noses seemed a lot shorter than the ones I put in. I wonder if they were the best ones for the job? The ones I just took out were B7EC-S. I've heard if the noses are too short then the plugs run too cool.

Edited by adam quantrill on Tuesday 3rd May 20:41

[gifdy]

350zwelgje said:

wedgeinald said:

I don't think my wedge has such a switch...but just in case where is it fitted on the S?

Think an S has a cut-out switch in the boot somewhere.

Rob

Doesn't look like that was the problem, but for reference my S has it fitted to the front left bulkhead in the engine bay