Going nuts: electrical problem shutting down fuel alim.

[ludovic]

Any input much appreciated, I am going nuts with this...

So I got my car back from the paint job last xmas. Happy as ever, car runs fine for a while.

Then in march, when stopped at traffic lights the mpg gauge goes down to zero and back in half second...

No fuel/no power at all during that time.

I am thinking first my fuel pumps is dying or my afm needs to be cleaned...

I have my mechanic replace the fuel pump and adjust the afm and the car runs fine for another 150miles then starts doing it again.

But this times the car does it even when driving causing a total loss of power while accelerating, this repeat itself several times a minute.

At last the car won't even let me drive back home and I have to pull over as the car now stalls and stalls again after those brutal loss of power.

I pick it up a few hours later and painfully manage to return to my parking. I check the fuse box and see the fuel pump fuse is too low on ampers, I immediatly replace it with the correct one and go for a test drive...of 20 meters as the car goes bad again.

So the car stays put for a few weeks as I can deal with it immediatly.

A few weeks later, I finally get the time to drop it again at my mechanics (15 miles drive city and motorway), the car starts immediatly and runs smooth like butter the whole time!!!

Anyway the mechanics changes the fuel pump relay and I am awaiting to get it back next week...but I fear this is not the cause of my problem.

Anybody ever experienced such a thing ??

Could the wiring of the fuel pump have melted causing a short circuit even though the wrong fuse was lower than the one normally used even though the wrong fuse never melted and everything seemed to work that way for more than a year and a half with no problems.

I did not replace or installed any electrical device since last summer my parrot asteroid, that works fine.

Here is a link to a vid of my problem:



Any help would be immense as I don't know s* about electrical 'things'...

Many thanx guys!

Ludo

[jlevie]

The behavior of the MPG gauge makes me think of a failing CPS, bad engine harness, or even a failing DME. Does the tach react along with the econometer?

[ludovic]

Thanx for your answer ! I will have my mechanic check the cps tomorrow.

Hope it's not the dme or engine harness quite pricey!!

To me the rpm drop a bit when it occurs but it's not going down brutally to 0 like the econometer does. Even at iddle the tach goes down to 500rpm.

I replaced already distributor + rotor / sparks / tps / icv / cleaned and adjusted afm...

[jlevie]

The reaction of the tach and MPG gauges strongly suggests that the DME is loosing power/ground or timing data. In the first case the CEL should briefly illuminate during an event as the DME restarts. In the second case the only symptoms will be the loss of power and the reaction of the tach and MPG gauge.

Since this kind of fault is intermittent it can be difficult to diagnose. I fought a similar problem on a race car for over a year. Everything in the engine management system was replaced at least twice with supposedly known good used parts (or new OE parts), to no avail. Finally I rented a battery operated digital storage scope, connected it to the CPS input pins at the DME (with the backshell removed), and had a passenger monitor the scope and freeze the data when an event occurred. The waveform distortion was obvious. So I ordered a new engine harness from BMW and that fixed the problem. I have the four used harnesses that all had problems hanging on the wall of my shop. The only reason I've kept them is as a source of connectors.

[ludovic]

Jim,

Many thanx for the input! That reduces the list of suspects!

I will try to swap the harness if the replaced relays and if needed the cps aren't doing any good to the car.

[ludovic]

My mechanic still did not manage to test the CPS - he hurted himself this week.

Anyway, I was wondering if the culprit could be too the C191 connector as the temp gauge is also droping at the same time as the economoter in my vid?

any help much appreciated!

Thanks ludo

Ludo

[jlevie]

There could be more than one problem here. The loss of power and MPG behavior suggests a problem with the engine management system. The temp gauge is independent of the engine management system and only relies on the cluster, wiring, and sensor.

Attack the engine management system problem first. Then look into the temp gauge.