81 528i replaced starter, now engine cranks but won't run

[alabbasi]

All,

I have an odd problem with my 81 528i. I had issues which I thought was the starter (not clicking until the starter got a couple of good thumps).

The starter was replaced yesterday which required the removal of the back intake tube. The gasket did not look to be damaged when everything was put back together.

The Engine will now crank and fire, but only while the starter is engaged. As soon as you let go of the ignition, it will stop running.

For me it sounds like either the fuel pump relay or ignition system cuts out when the starter disengages. I this was one of my Mercedes Benz, I would immediately think that one of the ballast resistors are bad, but I checked and this car does not have any.

Only items in the area which may have been touched are the intake tube that could create a vacuum leak (although I would not expect it to be big enough to prevent the car from running) and the relays. I did remove and inspect the relays and the connections seem to be fine.

I'm now at a loss and would welcome some advice.

[RandyM]

Sounds like you're on the right track.
Bad combo relay?
Ignition switch?
When you disengage starter does it seem like it runs out of fuel(pump shutdown) or immediately quits, (ignition related)
Does the fuel pump turn on when key is turned on? ....starts easily with fuel immediately present? If so I'd first look at ignition switch as culprit.
Then I'd troubleshoot combo relay.

[alabbasi]

Thanks, I picked up another relay from a retired BMW mechanic who has a stash of NOS parts. I'll try it today. Failing that, I'll order a switch.

I also need to check around the AFM as I had to move it around to install new belts.

Thanks again and I'll update shortly.

[Mike W.]

The combo relay is what switches the fuel pump. If the air flow meter is unplugged, it won't get the signal to turn on, but if it dies immediately that's not the problem, it'll run for a little bit off residual pressure. The coil gets increased voltage from the start circuit while the starter is being cranked, so if the circuit from the ignition switch is bad, it would run while being cranked, but not once cranking is stopped. Check for voltage at the coil with the ignition on. Food for thought.

[alabbasi]

I think that i've figured out the issue and also found that this car does have ballast resistors located behind the passenger side headlight behind the windscreen washer bottle.

Part # is 0227900101 but I can't find anywhere that stocks it and I know that Mercedes Benz uses ballast resistors that while they look different, are exactly the same resistance as the ones on the BMW so I'll pull them off my 72 Mercedes Benz 280SEL parts car.


If it does work out, then once again, a Mercedes Benz part will be used to keep a BMW running

[RonDwyer]

Sounds liker the computer and the fuel pump are only running while cranking. This is when i get out the trusty jumpers with alligator clips and start to bypass stuff.

280SEL parts car? That has to be my all time favorite for being a classy cruiser. is it a 4.5?

[alabbasi]

Thanks, the car is now running with one of the ballast bypassed. I've been told that converting to petronix is an option but i'm not too familiar with Petronix and assumed it is only used to convert points setup.

The 280SEL is a 4.5 and it's a parts car for my two 300SEL 6.3's and 300SEL 3.5. The 300SEL is the same body car as a 280SEL but is better appointed and uses air suspension. They do share something in common with the E12 in that they are both designed by Paul Bracq.

I actually met him about 10 years ago at a Mercedes Benz M100 meet in Charleston SC. Really nice guy.

[RonDwyer]

Pertronix is ridiculously easy. Pull out points, install magnet ring, pull points, install pertronix, adjust gap with plastic feeler gauge they provide. Oh, and eliminate the resistors, thrown them away. Welcome to Trantor.

I am interested in a 4.5 diff if you are nearby. I am in Oakland CA. Looking for a nice 280SE 6 to put it in.

[alabbasi]

Ron, this car does not appear to have points as i think the 528i got transistor ignition. I'm in Dallas TX. There is a gentleman by the name of Mike Morris who runs a shop in north Cali called Morris motors. He has a bunch of old MBs and can probably help you with a 3.27:1 diff.

[RonDwyer]

oops,
I mis-spoke on pertroix, it has to be a points distributor to begin with.