Problem for all you DME gurus out there

[BigTim]

Hey everyone, I PM'd this to Mark D'Sylva (thanks for the quick reply too Mark) and he suggested I put it up on the board for you guys to consider as well. Any input greatly appreciated!

Firstly, mine is a fairly early 1989 Euro 535i with no cat (leaded fuel map). It's been sitting in my mechanic's workshop for about 5 months now (I am in withdrawal)

The head on my car has been rebuilt and a new slightly warmer cam has been put in (stage one if this means anything to you). The computer is unchanged. The car starts fine and runs great until it warms up - then it starts idling like a rotary engine (large pauses in between firings) and apparently consumes large amounts of fuel, running rich (there was no problem with the old cam, besides the fact it was completely stuffed.)

My mechanic has all the latest Bosche gear and tells me that the problem is with the computer - or more specifically, my computer doesn't like this particular cam. He has tried installing a different computer with similar results. I spoke with him today and I think he is stumped - I have to wait for some Bosche guru from Australia to arrive next week to have a look at it (with some replacement computer in tow at mega $$).

What is interesting is that he plugged his Bosche unit into the computer and ran the car fine for half an hour (problem disappeared). As soon as he disconnected it the car went back to it's sick state. He explained that the Bosche unit took over running the engine while connected, and that my car's computer couldn't do the job. Hmm.

He also tells me that the old computer has had a chip upgrade at some stage, and that his Bosche gear can't read the parameters of this chip.

What I was wanting to ask was - is this crap, or can the computer's performance be affected by a cam upgrade (to this degree)
He tells me that my computer is fairly crude and takes input from only a few sources. Is the computer inflexible in that it can't adjust to the cam upgrade? Or is this where a performance chip like the EAT chip takes over?

Any other suggestions - perhaps a faulty sensor that might cause this engine condition? He mentioned the Bosche unit indicated a fault with the crank position sensor, then told me that the E34 doesn't have one of these anyway? I'm confused.

Thanks everyone.

Tim

[Paul in NZ]

Quentin (in Aussie)has a 535 with a warm cam and a chip and he reckons it is awesome.I cant see how the cam could affect low speed running so much.Brent in NZ has a 535 parts car so perhaps he can lend you his dme to at least take the phantom chip out of the equation........

[BigTim]

Yeah, I reckon it's BS too. Mark D observed that the car should be running leaner anyway with the increased valve duration, not richer, and that it might be the cam timing.

The mechanic had another DME sent over from Oz with a different chip - still no joy. Will send Brent an email tonight.

Quentin (in Aussie)has a 535 with a warm cam and a chip and he reckons it is awesome.I cant see how the cam could affect low speed running so much.Brent in NZ has a 535 parts car so perhaps he can lend you his dme to at least take the phantom chip out of the equation........

[Jeff N.]

Calling JoeS. Didn't your car run like crap with that Schrick till you dicked with the FP?

[632 Regal]

with a bigger cam the vacuum at idle drops and the injectors rely on that vacuum. if you boost the pressure at idle I think your problem will go away. The computer might not like your new bumpstick but will tolerate it a lot better than its running right now.

if raising the fuel pressure doesnt help the idle you may need to have a chip burned with a slightly richer fuel map in addition.

Calling JoeS. Didn't your car run like crap with that Schrick till you dicked with the FP?