Misfiring Mi

[pacey205 2]

Right my car has been off the road for a long time with this problem (almost a year and a half now ) and AB Motorsport have been looking at it this week.

 

Basically it misfires between 3.5-4.5K but is fine both above and below this.

 

I have replaced every, abd I mean every, part that may cause this.

 

Leads

Plugs

Distributor + rotor arm

Coil

Ign Amp

CAS

Injectors

TS

ECU

AFM

Loom

etc

 

Engine is fully rebuilt (bar new pistons/liners) and has excellent compression. Fuel pressure etc is OK with a new filter etc.

 

All earths have been checked and checked again. AB motorsport have gone thorugh everything and cannot find anything wrong with it to my dispare but they have suggested that maybe the timing ring on the flywheel could be warped, chipped etc and causing this.

 

It sounds like a possibility and I know of it happening on other cars before, the guy at AB said they had the same problem on an Audi Quattro.

 

So I was just wondering what you guys thought. The plan is to get a flywheel off Andy at AB and swap it over the christmas period but do any of you engine gurus (Miles, Puma etc etc) think that this could be a possibility.

 

Im hoping it is because if it isnt I seriously have no idea what Im going to do. The bllody things cost me a fortune so far and I havent even been able to drive it yet

 

Look forward to hearing your thoughts.

 

Michael

[Anthony 1,000]

Is the misfiring load-dependant? ie will it misfire between 3500-4500rpm even if you rev the engine in neutral, or does it only do it when there's load on the engine?

 

Does it do it just as badly when the engine is stone cold as when it's upto temperature?

 

When you say misfiring, is it like you're getting complete ignition cut (feels like you're hitting a rev limiter / brick wall), does it seem to just be missing on one cylinder, or is it more of a giant flatspot?

 

I'd have personally thought that a dodgy flywheel wouldn't just cause problems in a fairly narrow rev range, but I could be wrong.

[taylorspug 7]

I was also thinking that surely the flywheel would affect the whole rev range and not just one part, have AB had experience of this happening before then?

[maxi 36 1 Cars]

Pacey it was over a year ago I came up and got the car running for you mate! You still havent driven it?!?!?!?

 

I was just about to suggest a fault with the ring gear around the flywheel....In addition, was the flywheel definately put on and torqued up properly ( frim memory they are 50NM)??

 

Whizz the box off and bang another flywheel on, I have loads here if your stuck for one. 2hr job on the floor so with a ramp it will take no time!!

 

Maxi

[jonnie205 1]

i very much doubt it will be the flywheel to be honest. Take the car to owen developments and let them look at it mate. Ab is not a diagnostic centre whereas owens is and they are very very good if not the best in the country. They will get it on a crypton and fault reader and should sort it in no time. Failing that use millins BOSCH centre in witney or Bradleys garage (BTEC Racing) in burford.

[jackherer 543]

an oscilloscope on the tdc sensor should tell you if the timing teeth are ok without taking anything apart.

[pacey205 2]

Anthony - It isnt load dependant it does it whilst stationary as well and dosent seem to matter whether its hot or cold. Its not like a hard misfire it just seems to pop like its missing on one cylinder or something. When driving it just kind of stutters then its alright again.

 

Adam - I know tell me ahout it Its got no MOT or tax at the mo either but Ill prob sort it after christmas. Plan was to get a flywheel off of AB and if it dosent work take it back to them. When I refitted it it was all torqued up to the specs so should be OK.

 

Jonnie - AB took it to theyre diagnostics guy in Warwick who was the one that suggested the timing ring.

 

Jackherer - Have you got any idea what teh signal should look like as my old man will have an oscilloscop somewhere.

 

Ill be picking the car up tomorrow so I can have a better look at things on Saturday

[jackherer 543]

Jackherer - Have you got any idea what teh signal should look like as my old man will have an oscilloscop somewhere

 

something like this:

 

[C_W 3 1 Cars]

Not the same but mine has a mis-fire below 2500rpm and only seems apparent once warm, is fine after that though but admit I've not really looked at it properly.

 

I can't see the flywheel teeth being a problems as surely this would present a problem at ALL revs?

[pug_ham 240 3 Cars]

Might seem like a really stupid suggestion but is the CAS fastened down tight in the gearbox?

 

Graham.

[pacey205 2]

CAS is definately fastened down tight in the gearbox yes.

 

I would have thought that a problem with the timing gear would have posed a problem throughout but then I suppose it is possible that at certain revs its out just enough to play silly buggers, I dunno.

 

Michael

[pacey205 2]

Right just got back from AB Motosport with the old girl, towing back in the dark was NOT fun :S

 

After speaking to Andy at AB he said that when they checked the signal on an oscilloscope the signal did look 'dirty' but it wasnt consistent, so it wasnt missing on a certain tooth but just randomly, whcih is very strange.

 

He said therefore that he dosent reckon its the flywheel but more likely to be some electrical problem where its getting interference from somewhere (brilliant isnt it).

 

He suggested checking the wiring for the fuel pump/ pump earth, and bypassing the pump wiring to rule that out. So I am going to do this (after christmas now I think) and hopefully will make some headway doing this.

 

If not I think its headscratch time again + maybe flywheel swap (although Id rather not if I can avoid it).

 

So thats the state of play. Complete pain in the arse basically as its going to eb one of those faults that is a complete bastard to track down, just as I expected.

 

Michael

[jonnie205 1]

Yes i would try running the engine as a stand alone unit. Run the switched live straight to battery and hard wire fuel pump. Doing this will show up if there is any probs with the chassis harness of the car or fuse box etc. Also check the earth from the 4 pin brown multiplug under dash, i usually earth these on the column. Disconnect rev counter too on the 2 pin bx plug as this may be sending some funny surge back into the coil. I would also disconnect altenator as this may be surging and causing funny things to the main car power circuit.

 

If none of this works and your are sure there is compression accoss the rev range then i would swap the loom again along with the ecu.

[GtiMad 1]

Its the flywheel/ring gear, bet you a night with Butlers mum that I am right.

[pacey205 2]

Well its looking that way actually.

 

Hard wired the fuel pump earlier, ran the switched live straight from the battery, disconnected the rev counter. All made no difference at all. Im going to re-try the switched live tomorrow though as the connection wasnt very good.

 

Michael

[GtiMad 1]

Flywheel flyweel, a weld is broken, ring gear ring gear, bet you a curley wurley.

 

 

 

 

[jackherer 543]

is mattsav making those ring gears that go on to the bottom pulley? if so it would be a way to avoid taking the gearbox off...

[maxi 36 1 Cars]

Flywheel flyweel, a weld is broken, ring gear ring gear, bet you a curley wurley.

 

 

Rich is right, it is flywheel problem!!! Matt had the same problem with one of his prototype bottom pulleys, turned out the welds had broken and at a certain RPM the ring gear would vibrate. This caused an enormous misfire in the rev range....

 

Get the box off, new flywheel on and your away!!! 2hr job on the floor, do it tomorrow!

 

Maxi

[pacey205 2]

Do it tomorrow lmao, Ive not got a flywheel so I need to pick one up before I can do anything anyway.

 

Michael

[pacey205 2]

Well Ive just been out again and tried all the wiring again and theres no difference.

 

One interesting thing though is that when you run the switched live straight to the battery the misfire is actually lower down in the rev range, and it dosent run as nicely either. Figure that one out

 

Im just going to try disconnecting the alternator but to be fair Im not holding out much hope.

 

Bloody cars

 

Michael

Edited January 2, 2006 by pacey205

[M@tt 77]

might be a dumb question

but is the flywheel not just one piece of metal machined? when i had last looked at mine i cant remember noticing any welds or have I misunderstood?

 

also what is meant by ring gear?

 

thanks matt

[pacey205 2]

By ring gear I mean the teeth that teh crank angle sensor takes its signal from. I have no idea whether its welded on or not as I cannot remember (it was a long time ago I last saw it though) and unfortunately non of my pictures are clear enough.

 

 

Ring gear is the one with the larger teeth next to the starter motor teethed edge (not explained very weel)

 

Michael

[M@tt 77]

ah nice one, now i get it

 

cheers

[Man3 0]

I had a problem like this when my coil packed up and i replaced it with a new intermotor one. The car ran fine before the coil packed up so i was pretty certain the new coil was causing the misfire so i went back to the motorfactors and got another replacement coil. I fitted it and still had the same problem with misfiring. In the end i decided to try a Lucas coil from neat and everything was fine. Moral of the story, only use an OE coil. You might well have a lucas/valeo/bosch coil already in which cas ignore everything i've just said!

[pacey205 2]

Yup