Misfire, Donny, Help

[graeme]

Trying to trace a misfire. I used to blame it on the rain, but now even after long dry spells it still misfires.

Fully charged battery, alternator ok, so lots of volts.
Cleaned battery terminals and earths
Replaced dizzy and rotor arm
Replaced leads with Magnecor reds (which are a sh*te fit BTW - worse seal than OEM!)
Replaced plugs twice

I haven't tried new crank pos sensor or new coil, just because of cost/hassle.

2 plans next. First, I've got it booked in in 2 weeks for a compression test and a coolant sniff.
Second, I want to try a known-working crank pos sensor before I fork out for a new one, and anything else anyone can recommend which could be suspect.

Rest of the electrics seem ok, although my temp gauge is a bit random and doesn't stay on one figure, but jumps about rapidly 1 or 2 degrees either side which it didn't used to. Brown and blue plugs and a coolant bleed haven't cured the misfire or the dodgy temp display. Might be unrelated.

I'll be at Donny, but I'm skipping the trackday as the car is running like a dog and it looks like I might need the cash! Is there anyone else going to the show but not on track who could lend me their car for a few hours while I swap bits around in the hope of finding a cure? Also, anyone who takes a look and spots the problem won't have to buy a beer all weekend!

Cheers,
Graeme

[Rich H]

Sounds like a job for Robin, but I would be taking a long hard look at the coil pack seeing as there isn't much left. Is it misfiring on one cyclinder specifically or just randomly? Plugs might tell you.

IIRC crank pos and coil are std Rover jobbies, find a scrappy or look on the 'bay.

[graeme]

Hard to tell. It sounds random, but I'm not techy enough to know. Plugs all looked OK to my very untrained eye.

G

[Andy G]

Think Dan (JPS) and Ali (SLS) might both be down for this trip.

Dan is on track and Ali isn't as far as i know - combine that with Robins encyclopedic knowledge and you might be in luck

[fd]

Periodic ?
Under load ?
Off load ?
When cold ?
When hot ?
Revs ?
etc etc . . .

You have to give people something to work with dude

Fd

[graeme]

Hi Fd,

Periodic ? Yes, at idle it sort of comes in waves, juddering the engine off its mounts for a bit, then back to normal 160 'smoothness' in a 10-15 sec cycle.
Under load ? Yes, light load of 2-3k revs is the best way to hear it. Higher revs, I think it's still there, but harder to hear to my untrained ear.
Off load ? Yes, noticable at idle, and lots of popping and banging on overrun, but then I don't think it sparks on overrun, so not sure how relevant that is.
When cold ? Yes.
When hot ? Yes. It runs better warmed up, but so do all engines. The missfire is still there.
Revs ? see above.

Ta.

[fd]

Had it compression tested ?

Sounds Electrical . . . without hearing it . . .

How does it misfire under light load - constantly or in waves ?

Fd

[graeme]

Not yet. Had it booked in for a couple of weeks time here in Sheffield, but just spoken to Ali and he's going to do it on Thursday afternoon.

Under light load I would say the waves go away, but the misfire is random.

[GregR]

Distributor cap?

[graeme]

Replaced dizzy and rotor arm

Distributor cap?

Old one was fine, but replaced it with a brand spanking new one anyway just in case. Same with leads, rotor arm and plugs.

[ninja]

ninja

[ninja]

from the shared bits post

i've got

two rear potenza's (part worn)
two ignition coils
a water temperature guage sender
crank position sensor
camshaft position sensor
a main relay module

all for the S2 (k series engine)

let me know if you need anything

i did have an ECU but that's been "borrowed"

ninja

if any of this cr*p will help i can mail it off to you....?

at a guess useful bits my be crank position sensor, main relay unit and coil pack, just a thought. Mac was very good to butcher his car when i had a similar problem and so i am very happy to help out a fellow SE'er. following my previous problems i purchased a few "spares" (see list above). in my case it turned out to be the coil pack but now i have a little bit of cash tied up in stuff that lives in a box in my hut!!

ninja

[robin]

Hi Fd,

and lots of popping and banging on overrun, but then I don't think it sparks on overrun, so not sure how relevant that is.

There's your clue

If it pops and bangs above 1,500 or so (not sure where 160 ECU cuts fuel/spark back in) then the ECU actually thinks you're still on the throttle when you aren't.

A very good chance this is a flaky TPS or wiring problem. If you replace the TPS you'll need to work out how to recalibrate the TPS (usually an ignition key and pedal dance; again, no idea about the various 160 ECUs).

If it comes in waves during idle it might also be a flaky lambda sensor, but that shouldn't have an effect at wide open throttle, so if you have a misfire at full load, it won't be the lambda, probably

Cheers,
Robin

[Victor Meldrew]

I have a new TPS sitting at home, will bring it to Donny with me if thats a help..

[graeme]

Awesome help from SEers, as always.

Ninja,
Very many thanks for the offer. Might well take that crank pos sensor from you. I've already bid for a new one on ebay ending tonight, but if I don't get that I'll PM you. S2 coil pack won't fit, but I have a lead on a S1 coil (no pun intended) from Stu.

Robin,
Interesting stuff. Lambda and TPS are now on the list of things to check. Could well be onto something there. Thanks! Also, prompted by Fd's questions I gave it a bit of welly last night, and my untrained ear could not really perceive the misfire at big revs under full load, but it does feel a bit sluggish and down on power.

John,
Yes, please bring the TPS to Donny. I'll try to get one to test before then to see if it helps.

Cheers,
Graeme