91 535i DME? No start, stumped.

[UberXY]

I'm embarrassed to come to the Internet and say that my 91 535i won't start, but it won't and I'm stumped.

i was driving along in town, car running and starting fine, when I started getting an irregular miss at idle, and finally the engine cut off at a stop light. Would not restart with starter (healthy recent battery), but I was on a hill and it did bump start. Drove home on freeway and car ran normally. Pulled in driveway, engine died at idle, has not restarted since.

so here's what I have done.

1. Replaced CPS, no change. Replaced fuel regulator, no change.

2. Fuel: bench tested relay, works fine. Jumpered fuel relay socket and fuel pump comes on and fuel is being pumped to regulator; however still no start. However, when I plug in the relay and turn on the ignition, the pump does not turn on and of course no fuel to the regulator.

3. Spark: DME relay socket is getting power. Bench tested DME relay, works fine. Tested all fuses front and rear. Pulled distrubutor cap and rotor, look fine. Pulled a plug and grounded it, no spark.

so, I know the fuel pump works and is delivering fuel to the rail when jumped. But with relay in, fuel pump not on. And no spark. Just for fun I replaced the General Module with a spare, no start.

DME? Unfortunately I haven't located my spare one yet.

Any thoughts? And test suggestions?

thanks!

[Layne]

You need to disconnect the fuel return line after the regulator (so the pump has to work against the pressure of the regulator) and observe the flow at this point with the relay jumpered. I don't know the exact flow spec, should be something like a liter in 30 seconds, ie; blasting like a garden hose. It's possible to get good flow with no pressure (input side disconnected) but not get good flow when under pressure.

The FP relay only engages when the engine is rotating, not just with the key on.

Have you tried a stomp test? There aren't many useful codes for the M30 but it would probably give a lean mixture code if the fuel pump is going out.

A bad DME is possible, but not extremely likely. If you have a spare, try it.

[shogun]

fuel pump details, capacity against counterpressure.... http://www.bimmerboard.com/forums/posts/1256230/

[UberXY]

Ok, thanks. You confirmed what I thought about when the fuel pump relay gets power.

removed return line from regulator and there is flow, but very weak. So I just ordered a fuel pump and we will see what happens. Sure is gonna be easier to replace the FP than that %^~*}+{+ CPS.

[whiskychaser]

Pull a plug. If it is wet with fuel then concentrate on the spark side for now. I'm not familiar with the M30 but if it has an HT lead from the coil to the distributor, disconnect it and see if you get a spark off that when you crank. If not, you may have a duff coil or bad connections to it. If that doesn't help, check if the DME relay is actually being energised. Wiring diagrams are here and I think page 1210.2 would be a good place to start:
http://www.wedophones.com/BMWManualsLead.htm

Edit: Just noticed you have low flow on the return. It is the flow side up to the regulator which needs the pressure. A new fuel pump won't make it spark

[UberXY]

Thanks Whisky. I jumpered the DME socket and when doing so could hear a click from the general area of the intake, maybe TPS? But still no start. I'll have a look at the coil today.

[UberXY]

Two other things

only code from stomp was 1223: temperature sensor. No CEL.

12 volts present at coil.

[Layne]

Edit: Just noticed you have low flow on the return. It is the flow side up to the regulator which needs the pressure.

If you disconnect the supply line, the pump produces no pressure. It's easy for a weak pump to move a lot of volume. If you disconnect the return side, the pump has to work exactly as hard as it does when the engine runs to maintain 45-ish psi. If the volume is sparse on the return side, the pump is definitively bad (assuming it's being supplied with 12v).

[whiskychaser]

If you disconnect the supply line, the pump produces no pressure. It's easy for a weak pump to move a lot of volume. If you disconnect the return side, the pump has to work exactly as hard as it does when the engine runs to maintain 45-ish psi. If the volume is sparse on the return side, the pump is definitively bad (assuming it's being supplied with 12v).

What I was getting at is that it is pressure on the flow side which is important. The return is only going to be the difference between what the pump can deliver and the pressure regulator setting. And that is an unknown. TBF, if the FP relay is jumpered and the engine off, I'd expect you to hear fuel flowing through the system though. I just find it very odd to get a fuel pump fail and no spark at the same time.

OP, you get 12v on one side of the coil with the ignition on. The spark is generated when the other side is grounded by the DME. You can check that when cranking the engine too. But don't go leaning on the HT wires

[Layne]

What I was getting at is that it is pressure on the flow side which is important. The return is only going to be the difference between what the pump can deliver and the pressure regulator setting. And that is an unknown. TBF, if the FP relay is jumpered and the engine off, I'd expect you to hear fuel flowing through the system though.

But you aren't measuring pressure (although that's a good idea too, it's a completely different thing than flow). Considering that the engine isn't running for this test, the flow is 100% equal throughout all hoses of the system.

- - - Updated - - -

Edit: I missed the part where he said no spark. You're right, two failures at once is uncommon. Either he botched the spark test (easy to do, trying to hold a plug on a grounded surface while also cranking the engine). Or he botched the fuel pump test, OR he changed the CPS for another bad one or there's some other reason the DME isn't getting a good engine rotation signal.

[Pete745]

I have the same problem, did you get it fixed?

[whiskychaser]

Either he botched the spark test (easy to do, trying to hold a plug on a grounded surface while also cranking the engine). Or he botched the fuel pump test, OR he changed the CPS for another bad one or there's some other reason the DME isn't getting a good engine rotation signal.

Have to agree. I'd want take a plug out and see if it was wet with fuel. But before even doing that, I'd use a strobe to check for spark. If there was none at the plug lead, I'd go further back and check it where the HT lead enters the distributor cap and then at the coil itself. We know there is 12v at the + side of the coil, so if there is a pulsing ground on the other side when the engine is cranked, the coil is duff. If not the DME isn't triggering it for some reason. I'm thinking coil because OP was able to bump start it but it would not start on the key. If none of that traces a fault on the spark side, I'd be getting the fuel pressure gauge out

[UberXY]

New coil, no start. Waiting for FP.

Put Fluke on new CPS: 553 ohms, which I recall is correct. Put strobe on plug 1, nothing. Also on HT lead, nothing.

[whiskychaser]

CPS resistance looks right. Might be a red herring but did you check the air gap? Are you getting a ground at the coil negative terminal when you crank?

[UberXY]

Ok gang here is the update.

1. New fuel pump, CPS, coil, rotor, fuel regulator.
2. Fuel and DME relay bench tested ok, no start when sockets were jumpered.
3. Battery recent and good.

still no start. I'm running out of things to replace. Starter cranks great. No spark, 12 v at coil. CPS 550 ohms on 1 and 2.

last time I drove the car I made it home at 70 mph. Pulled in driveway, bad idle, stalled, never started again. Stomp test only shows 1223. Prior to this, the last thing I did under the bonnet was replace the temp sensor on the radiator a few weeks ago.

any more thoughts?

[Layne]

You're sure about the no spark? And you tested it straight off the coil (eliminating the distributor as a possible cause)?

Could be that the coil negative wire going back to the DME was somehow damaged.

Has anyone played with the OBC? If someone sets a code on it, the car will not start. Someone will correct me if I'm wrong, but I believe the starter still cranks in this case, it just won't start. That doesn't explain your bad idle though before the no-start.

Check if your engine harness connects with a 20 or 25 pin connector (the big round one). There are some differences in the wiring. There are some useless anti-theft functions that you could disable just to eliminate them as a possibility.

[UberXY]

One concern I might mention is that when I hook up a voltmeter to pin 1 of the socket where the CPS plugs into, I get a reading of 1.2v where I understand I should be getting a reading of 5v to power the CPS. Ring any bells here?

as for OBC code messing about, no.

[whiskychaser]

I think you should have 5V on the black wire from pin 47 of the DME. With the CPS unplugged, check you are getting that when you put your other meter lead on a good ground

[ross1]

No spark and no fuel, along with your description of how it died is screaming crank position sensor to me. I know you replaced it but perhaps have defective one. OE part or some e-bay cheapie?

[cirrusblau]

I see you changed the rotor, but how about the distributor cap? Doesn't it have posts that the rotor make contact? Maybe they're worn out?

[ross1]

I see you changed the rotor, but how about the distributor cap? Doesn't it have posts that the rotor make contact? Maybe they're worn out?

OR the button could have fallen out but still does not account for no fuel

[UberXY]

Ok, it runs again.

the very first thing I did to fix the no start was replace the CPS. I bench tested the new one at 540 ohms, installed it with spec clearance, no start. Then I started looking at all the other possibilities until there was nothing left to do.

So, I bought a second new CPS, installed it, and the car started right up, runs fine.

Cars. They are a pain in the ass but we still love them.

[zkd]

good job, glad you solved it.

[whiskychaser]

Good to hear you have it sorted. If it is any consolation, check out conclusions draw here:

''Lessons Learned:
Hall Effect sensors are CRAP. (car is only 55k miles)
Hall Effect sensors resistance tests mean NOTHING.
Hall Effect sensors are not completely dead.
Hall Effect sensors are disposable items.
Hall Effect sensors are not "lifetime" like sometimes advertised by BMW.
Never trust anything "lifetime" advertised by BMW.
Hall Effect sensors are more precise, give a better ignition, and are more expensive''

https://www.bimmerforums.com/forum/s...-wizardly-help

[ross1]

Do us all a favor and call out the brand of that defective CPS.