Hesitation, won’t rev past 4000 rpm, stalls when warm

[jaquimbayod]

Hi everyone,

I recently bought a 1982 BMW 323i that had been sitting off the road for a few years. Over the past few months I’ve been bringing it back into shape, and during the summer it was running great.

A few weeks ago, however, problems started to appear. While driving on the highway, the car refused to go beyond 4000 rpm and began to hesitate. Eventually it struggled to idle and then died completely. It wouldn’t restart at the time, so I had to leave it parked. After a few hours it started again, and I managed to drive it home, but after about 10 km the same symptoms returned.

Here’s what I’ve done so far:

Replaced the fuel filter and fuel pump

Checked ignition timing (it’s correct)

Replaced the distributor arm

Tested the fuel pump relay

Spark plugs are relatively new

Coil (bobine) is also new

All six injectors are new

At the moment, the car runs fine for a few minutes, but once it warms up and I’ve driven a few kilometers, it starts hesitating again and sometimes struggles to idle.

Has anyone experienced something similar, or have ideas on what else I should check?

Thanks in advance

Julian

[Jeroen]

Hi Julian,

That's annoying! A exhaust gas test would provide some more info but it does sound like a fuel delivery problem. Since you already replaced the fuel pump I am thinking of 2 options, a defective fuel accumulator (the 3rd part underneath the car with the fuel filter and pump) or a defective warm up regulator messing up your mixture. The accumulator you can bypass for testing purposes, to see if the WUR is causing issues you can try with a known good used example perhaps?

Some useful background info here: viewtopic.php?t=18255

[jaquimbayod]

Hi Jeroen,

Thanks for the hint! it does look like the WUR is causing trouble. I checked the heater element, and the resistor appears to be dead. I’ve ordered a new one (32 Ω, since I couldn’t find the original 26 Ω). I went with the 32 Ω option because it should provide a slightly slower warm-up, keeping the mixture a bit richer during cold starts, which is closer to the original behavior.

I’m planning to mount it this weekend and will let you know how it goes.

Thanks again!
Julian

[jaquimbayod]

Dear all,

I finally got the new heating element and installed it in the WUR. However, I discovered that the WUR also has a vacuum leak that I haven’t been able to fix. After reading more about how it works, I understand that it adjusts the control pressure during warm-up. So if the heating element wasn’t working (which was my case), the car would essentially be running rich all the time.

What I don’t understand is why, once the car warmed up and was idling, it started to struggle by running too lean.

To test things, I tried “deactivating” the WUR. I pulled the pin and springs so it can’t open the diaphragm and lower the control pressure. In theory, the car should then stay on the rich side and I shouldn’t get the same symptoms. But I ended up with exactly the same behaviour: it runs normally for a few minutes, and once warm it starts to struggle. It won’t go past 4000 rpm, and the warmer it gets, the worse it runs. Lots of hesitation, eventually stalling.

Any ideas on what this could be? I’m running out of things to check.

Thanks!

Cheers,
Julian

[Jeroen]

If you adjust the mixture on the fuel distributor, does the engine respond at all? I'd first try to get it set up better to run when fully warmed up, just to see if the mixture is the culprit.