Sudden Loss of Power?

[bhanse4]

I picked up a 89 325is a few weeks ago and had a new problem creep up that I don't know where to start with. I am crusing on the freeway at 75 and all of a sudden car loses all power and the tach takes a nose dive for about a second and then it comes back to life. It has been doing it more regularly lately and it is getting quite annoying because the car jerks quite a bit when it happens. Where do I start? I am new to the e30's and not as familiar with all the sensors. Thanks guys

[jlevie]

The tach taking a nose dive with a loss of power says that the DME stopped providing that signal to the cluster. Which in turn means one of:

1) The DME is loosing power (bad main relay, damaged wiring)
2) The DME is loosing the timing reference signal (bad CPS, bad harmonic balancer)
3) Bad DME

[E30_fiend]

^^^^^^
What he said

[jmc1590]

I agree as well. The same thing happened to my 528e while driving cross country. The problem will continue to get worse until you are stuck on the side of the road wondering why it won't start! In my case a replacement ECU fixed it in 5 minutes flat. (After the fact, I found that the solder joints on the voltage regulators had cracked, providing contact until they warmed up, at which point they separated!)

I've also had a CPS up and die on me, but the symptoms were completely different.

James

[bhanse4]

Thanks for the help guys. Now it looks like its time to track down a dme and relay. The cps looks like has been replaced pretty recently so the PO of the car might have been trying to track down the same problem.

[jlevie]

With the engine idling, take a look at the harmonic balancer. Its rim looks to be wobbling, you may have a cause. The rim of the harmonic balancer (where the teeth are) should be running perfectly true.