E30 325i wont go above 4000RPM!!!

[onthames]

First post, so forgive me if I fk something up.
I have an 88' UK spec E30 325i.
Here are the symptoms of the problem:
When I first take the car out, and put my foot to the floor in say 2nd/3rd, its fine, can hit redline.
Then, after a few runs, it'll refuse to go above 4k, or sometimes 5k (seems to depend on how long I've been driving).
However, when it refuses to go above 4k, this is when I'm keeping the throttle wide open. If I go to 50% I can get it past the limit I'm facing.
BUT, in 5th gear, I cannot get past 4k RPM no matter how light I am on the gas. Just wont go.
So, in short, first few runs no problems, then the car starts to stop accelerating when I'm revving high. I tried pulling over today and giving it a break for 10 mins and trying again, this let me get to around 4.5k whereas the run before the break I couldn't get above 4k.

Replaced fuel pump and filter because I thought it might be that. No luck.

Anyone faced this problem? I feel like its temp related or theres a problem with fuel delivery. But I recently replaced the intank pump and the filter under the car.

Video of it happening.
https://streamable.com/e/n20q9g

Edit: I should add, apart from this, the car runs and idles perfectly. No problems whatsoever and no noises once it hits it's limit, just seems to try and then gets stopped by something, then try again, then stop again, no odd noises while this is happening

Edited by onthames on Thursday 17th June 22:07

[onthames]

helix402 said:

I once fixed an E30 with a similar problem, it had water in the DME due to a screen leak.

What like a leak in one of the screenwash valves? Cos I had one leak recently... Could be that.

[onthames]

I see, I'll check tomorrow. Well the car runs perfect apart from this issue do I suspect ecu is fine but never know

[onthames]

Disconnected boot from maf and blew smoke in at 2psi, no leaks as far as I can tell.

[onthames]

Will try that. I did find a missing relay when cleaning all the connectors near the rubber boot. Any idea what should be here? if anything.

[onthames]

helix402 said:

I suspect the missing relay is for an option your car doesn’t have, such as a cat. Re the white relay-I can’t remember if it’s DME or fuel pump, I can remember that they are renowned for failing (won’t be the cause of your 4K fault IMHO). As the relay is original in the interests of reliability I would recommend replacing it with a brand new gen BMW one.

I think its the O2 sensor heater relay. I'm not sure if it is causing my problem but I think there should be a relay there... Will put one in and see if problem goes away, unlikely it will but would be a cheap fix!

[onthames]

I'm trying to figure out the problem before I start replacing bits and bobs as could get costly pretty quickly.
The main thing I'm trying to work off is that this starts to happen after about 15 mins of driving. So, in that time, what changes? I'm pretty new to this (this is the 1st car I've ever worked on!) but the only thing I can think of would be temperature, pressures and richness?
Which leads me to believe it may be a sensor issue?

Any thoughts on that theory? Or am I using too much logic for this old old engine!

[onthames]

sunbeam alpine said:

One very simple thing to try is running without the fuel filler cap. If the tank isn't venting properly, fuel can't get out. Produces these kind of symptoms.

Am I okay to drive with it like that to test?
not sure if e30s have flapper valves

Edited by onthames on Friday 18th June 23:21

[onthames]

Gonna try it today. Also gonna test the "blue temp sensor" with my multimeter following a guide on e30zone. Will report back

[onthames]

Touring442 said:

I'd suspect the flap in the air flow meter could be binding.The throttle position sensor sits on the underside of the throttle body and over time oil leaks in - but whilst you can remove it, open it up and clean it out I don't think that's it.

It sounds like a fuel delivery thing or the ignition timing isn't advancing - that's an ECU or crank sensor fault. No cam sensor on the M20.

So should I take the afm off and clean the flap/wiggle it? What's the process you'd do

[onthames]

Afm flap fine. Moves with ease and doesn't bind. Clean in there too.

[onthames]

sunbeam alpine said:

One very simple thing to try is running without the fuel filler cap. If the tank isn't venting properly, fuel can't get out. Produces these kind of symptoms.

Didn't help

[onthames]

buggalugs said:

Are you able to check fuel rail pressure when the problem is occurring? Can’t remember how easy it is to get O2 sensor data on those, if you even have one.

No O2 sensor on my car I don't think
Also no idea how I'd go about checking fuel rail pressure. Cheers though

[onthames]

Problem is only under load idle rev is fine even when hot

[onthames]

Touring442 said:

A post 9/87 build 325i will have Motronic 1.3 with the crank sensor on the front pulley reading TDC and RPM as opposed to the older system with two separate sensors on the flywheel. There will be a C101 plug for diagnostics - what can be read from it is debatable.

For what they cost, I'd replace the fuel pressure regulator. Make sure the vacuum pipe isn't leaking as well.

Will replace.

Touring442 said:

So it won't go over 100 mph in 5th? They were geared up at around 25mph/1000.

Struggles at around 90 yeah. Sometimes lower depending on how long I've been driving. This is on track of course


Cars currently in the bodyshop guys having full M-tech 2 kit fitted + painted so gonna be a couple weeks before I try any of this stuff. Will update the thread then and thanks for all the help. Hopefully its something harmless and nothing serious is damaged (like an ECU!)

[onthames]

Am changing fuel tank. Will update

[onthames]

E-bmw said:

Why?

I believe the car drives fine for a bit because over 20 or so mins flakes of rust etc from tank get sucked onto the sock filter on bottom of in-tank pump. Which is why restarting the car causes the problem to go away and then come back (turns off the pump, dropping the gunk off the sock)
Tank needs replacing anyway, rust inside and is original and too much faff to clean inside, cheaper to get a new one.

[onthames]

Fixed. I took the cover off the afm and cleaned all contacts with electrical contact spray and bent the arm ever so slightly to make contact with a new area of the carbon rail