E30 Race Car Won't Rev-Out

[E30 325i Rag-Top 2915]

Having issues with the E30 race car not running properly, pulls well up to about 4,000rpm then it misses badly, almost like hitting the limiter. Started doing it last time it was raced at Taupo, usually about six or seven laps in, when it was really hot. Then at the track day on Sunday it was doing it all the time, wouldn't go over 4,000 revs at all and then got worse through the day.

I have replaced the AFM, no difference, and the coil, swapped plugs over all to no avail.

Checked the dizzy cap, found the centre electrode had disintegrated - put in a new cap and rotor still no difference, pulled better but still missed at the same point.

Test the fuel pressure and it seemed good, about 7 bar bit it did seem the FPR was opening at only 1.5 bar so swapped in a 3bar one. This made it pull even better and revved out slightly higher, but still get the same issue just now at about 4,500rpm.

Checked the igniter as its an L-jet and that looks all good. Fuel is fresh, filter is new.

Any ideas as to what is doing it, or what to check??

Edited September 1, 2013 by E30 325i Rag-Top

[OP6 27]

Had a similar problem with a PFL 320i a few years ago, took it to a mate and he rotated the distributor a few degrees and suddenly it became a rocketship, - well, went better than a 320 should.

[hotwire 352]

Jon, Does it miss over 4k under no load too - eg stationary? Have you swapped the ECU?

BTW, I thought you were running Motronic in your car?

[E30-323ti 66]

Also check the HT leads.

One (or 2) may be cracked near the sparkplug due to the heat from the zorst, and arching out to the head.

[E30 325i Rag-Top 2915]

Yup, even does it when sitting still under no load.

I haven't got a spare ECU so that is one thing I haven't swapped over, so could be in that area.

First engine was motronic, then swapped it over to an L-Jet to get the adjustability on the timing.

Is there anything "inside" the dizzy that craps out, or just the cap and rotor usually?

Starting to really piss me off now...

[Nobimmer 694]

I had the same issue on my old m20. The leads were shot and 2 were arcing, also coil was stuffed.

Got fuel pressure up there?

[hotwire 352]

Yup, even does it when sitting still under no load.

I haven't got a spare ECU so that is one thing I haven't swapped over, so could be in that area.

First engine was motronic, then swapped it over to an L-Jet to get the adjustability on the timing.

Is there anything "inside" the dizzy that craps out, or just the cap and rotor usually?

Starting to really piss me off now...

Duh, remember now the wiring issues you had when you converted to Ljet.

Could be an HT lead, though if a major breakdown, the coil - dizzy lead the only likely one.

Have you checked fuel flow? Can still have pressure but crap flow rate.

Usually only the cap & rotor in the dizzy.

You "checked" the ign module - tested or visually??

Is the ECU still mounted in the factory position, if so - checked for water ingress? Been there on mine when screen was leaking

[harvgray 12]

Try another set of plug leads John. Don't use aftermarket cheap ones. Nothing wrong with a good set of the original leads. cheers Harv

[Nobimmer 694]

Hey Jon, I think I actually have a set of brand new 'boyracer blue' leads at the workshop to suit M20. I'll be there tonight, txt me and remind me at 7. 0211272738

[E30 325i Rag-Top 2915]

Cheers Ashkan, or Eisnberg, or Snoop Lion or whatever your handle is, I will give you a text later!

Where is your workshop? I am in town tonight for a fashion show..

[Nobimmer 694]

In the ghetto, Beachaven. Just make sure you don't come over wearing anything frilly, the locals don't take too kindly to that sorta sh*t.

[hybrid 1039]

This is just a another thought to the fire.

Dylan's m3 suffered from something like this when you gave it a bit of herbs. It would hit would would seem like a rev limiter after flooring it up to 6krpm (or there abouts)

It wouldnt do it if you slowly increased revs however as soon as you floored it up around 6-8krpm it would limit to 6k rpm.

It turned out to be a rubber intake hose that would collapse under load. Thats why every time you opened the bonnet it would all look fine.

[E30 325i Rag-Top 2915]

Swapped and checked loads more stuff, still to no avail, same problem..

Changed out ECU, tried new coolant temp sensor, new external fuel pump, new ignitor.

I am starting to think that it could be the lift pump in the fuel tank, as it sounds like the "miss" you get when you run low on fuel and come out of the hair-pin at Hamptons, that and the fact that the new FPR made it go a few revs higher up before coughing and spluttering.

With no load (ie. revving it out of gear) gets up to five and a half six before missing. When driving and accelerating gets to the same point each time, about four and half thousand.

All making me thing poor fuel flow?? I have changed the filter in case that was blocked, checked all the lines, replaced the external pump. Even pulled out the lift pump and checked the mesh filter wasn't clogged with crap. No changed.

I did notice it was hard to get the lift pump to lock back into the tank - had to push it down really hard (could be due to the big dent in the bottom of the tank from getting it stuck half on half off a trailer) could that be the issue -the pump is "squashed" against the bottom of the tank - restricting the flow at higher revs?

[ashmill 68]

Swapped and checked loads more stuff, still to no avail, same problem..

Changed out ECU, tried new coolant temp sensor, new external fuel pump, new ignitor.

I am starting to think that it could be the lift pump in the fuel tank, as it sounds like the "miss" you get when you run low on fuel and come out of the hair-pin at Hamptons, that and the fact that the new FPR made it go a few revs higher up before coughing and spluttering.

With no load (ie. revving it out of gear) gets up to five and a half six before missing. When driving and accelerating gets to the same point each time, about four and half thousand.

All making me thing poor fuel flow?? I have changed the filter in case that was blocked, checked all the lines, replaced the external pump. Even pulled out the lift pump and checked the mesh filter wasn't clogged with crap. No changed.

I did notice it was hard to get the lift pump to lock back into the tank - had to push it down really hard (could be due to the big dent in the bottom of the tank from getting it stuck half on half off a trailer) could that be the issue -the pump is "squashed" against the bottom of the tank - restricting the flow at higher revs?

Have heard of that one before - pull the lift pump out, get a big piece of 4 x 2 and a big hammer and beat the crap out of the dent in the tank - should sort that bit out. Can't remember if you said the fuel pressure regulator was ok?????

[E30 325i Rag-Top 2915]

Smacking it with a lump of 4 x 2 is very tempting right now... might not fix the problem but will make me feel better !!

I think that is the way to go, but I am a little relctuant to start whacking the fuel tank right now, with my luck I'll end up splitting it and burning the house down!!

[yng_750 247]

Strange that it does it on and off load as fuel use etc varies vastly, only way to check for flow issues would be to plumb in a pressure gauge and see if pressure drops off, i used a mechanical oil pressure gauge from supercheap, came with a t junction that fit into the fuel line, not good for it long term but a little fuel doesnt hurt.

could well be that fuel tank dent, at worst that will stop you getting to the last of your fuel so better whack it out.

Sounds like an AFM issue to me so make sure the new one is actually good.

Have you checked ignition timing etc as it may start detonating and back itself off (maybe not sure about those old ecus)

[Allanw 1051]

Since it's getting onto grasping at straws time, is the battery and earths etc in OK condition?

Granted, it was on an old aircooled VW, but I had one I jump started with a flat battery - the battery was drawing so much current on charge, that it wouldn't rev past about 3500 due to spark break down. It was worse under laod, bt did it with no load. All Idid was fit a new battery, and away it went!

[Nobimmer 694]

Have you tried turning it off and on again? Seems to fix most things.

[*Glenn* 854]

I did notice it was hard to get the lift pump to lock back into the tank - had to push it down really hard (could be due to the big dent in the bottom of the tank from getting it stuck half on half off a trailer) could that be the issue -the pump is "squashed" against the bottom of the tank - restricting the flow at higher revs?

I'd be sorting this out first and trying it again

[E30 325i Rag-Top 2915]

Have you tried turning it off and on again? Seems to fix most things.

Nice one.. I have tried both a soft and hard re-boot and a "bounce" as well, no joy.

Have also tried randomly changing random parts, hope, prayer, shouting and swearing.

Now having to resort to gauges and diagnostics and stuff..

Glad you have got your sense of humour back now your engine is going, have you joined the series yet though??