Fuel pump/starting problem for the electricians and experts

[azale]

When I tested the sensors side by side the new one showed >1000 ohms while the old one showed >500,000 ohms.

I did not check the 'groove' but I will look at that before I sleep. When I put it on it didn't look like there were any options to rotate it.

I think the battery is too dead to turn the engine over now. I pulled all the plugs and turned it over for a while. I smelled gas but the smell was NOT overpowering. It was definitely there. The spark wasn't there for the most part but while I was holding the plug to a bolt, I saw a spark jump to the bolt but I couldn't replicate it. The the starter started clicking loudly because I think the battery could only power the solenoid.

I checked three pins. 26 good. 48 good when key in ignition. 54 BAD! nothing. what does this mean?

I hope I didn't fry my starter. I will put a better charger on it tonight.

[DanDombrowski]

Ok, I gotta clarify something here. >500,000 ohms resistance is not a resistance. Its an open circuit.

[azale]

I finally got a chance to look at the Bentley diagrams and now I have an important question for stevebuk.

. . . check with the multi-meter that you are getting a continuous 12 volt supply to pin 26 and when the ignition is on at pins 48 and 54.

The Bentley Manual (130-27, DME 3.3.1 1993+ 525i) says pin 48 is output to the A/C compressor control. Why did you think/How did you know mine would have voltage there? 54 is input from terminal 87 on the Main relay and I will look into that tonight.

Javier- I didn't see a groove but I did see a marking on the old sensor. I didn't check to see if it was pulsing correctly when I replaced it. I had the intake manifold off and I didn't want to suck in any dirt. I guess I should have checked for pulsing from the DME harness post haste. If it isn't pulsing, through pins 16 & 43, I'll remove it and see if I can unscrew/rotate it at all. I hope that is the answer.

Now that I have the proper diagram (I hope) for all the DME pins, I'll check all the vitals tonight.

DanDombrowskiThe (anologue) ohm meter needle moved to about 600,000 ohms (from infinity) So it may be an open circuit but it's 'less open' than when the wires aren't touching anything.

Thanks for sticking with me guys. I know electrical problems are probably not a few of your favorite things but I need all the help you can give me. This helps me prove to my friends (and if this takes any longer, my wife), what I've been telling them since I bought it: that BMWs are worth it to own and repair. I can't thank you enough.

[Javier]

either it is the one for your car or it is not, only one position, but if the screw is removed, you can rotate and hold it in place wile someone else try starting the engine. As you know, the sensor looks like a metal can, in the top of the can there is a wire going out, in the side, there is a bracket with a hole to fix it to the engine, and in the bottom of the can, there is a line, that protrudes slightly from the can bottom surface (I'll try to post a picture tonight). This line, should have an specific alignment with the tooth on the wheel near the damper.

I do agree to check for pulsing before sticking your head under the engine to check it, if no signal there, and being the sensor new and within resistance parameters, I would say it is not the one for your car. You can verify by loosing the sensor from its place and comparing the relative position of the bracket and the groove, against the old one.


Javier

Javier- I didn't see a groove but I did see a marking on the old sensor. I didn't check to see if it was pulsing correctly when I replaced it. I had the intake manifold off and I didn't want to suck in any dirt. I guess I should have checked for pulsing from the DME harness post haste. If it isn't pulsing, through pins 16 & 43, I'll remove it and see if I can unscrew/rotate it at all. I hope that is the answer.

Now that I have the proper diagram (I hope) for all the DME pins, I'll check all the vitals tonight.[/QUOTE]

[stevebuk]

I used the pin numberings given here

http://www.carsoft.ru/avtorepair/bmw....10/index.html

when I was checking mine, I don't know if they're different to the Bentley manual?

(My problem was with my 520i not my 525i don't know if the pin numbering is slightly different?)

[azale]

The car started tonight!

The battery was fully charged. I tested the CPS and it *was* giving off pulses (thanks anyway Javier). Then I checked for spark and definitely got it. I put it all together and cranked the engine-Nothing. Then I jumped the fuel pump and it the beast purred like a kitten. Then I immediately put the fuel pump fuse back but the engine died. no power is getting to the fuel pump. I tried jumping the fuel pump before I replaced the CPS and it didn't run so we are headed in the right direction.

I can jump the pump at the relay too, so there must be a problem at the relay (which is brand new for those of you just joining the conversation). Looking at the wiring diagram, the relay coil is supposed to get voltage from the main relay, and pin 1 on the DME (either supplies voltage or opens up a ground [bentley 160-6]). I am definitely getting power from the main relay; the socket for fuel pump relay pin 85 (which should go to DME pin 1) acts as a ground (12 volts strong between the relay coil sockets). Last factoid: When the engine is off, I get about 50,000 ohms between fuel relay sockets 86 and 85 (not the relay, just the sockets it plugs into).

So experts I need your help:
What does pin 1 on the DME do for me: negative voltage or ground?
How do I test it? Then what do I do when it fails the test (it probably will)?
Did the CPS ruin something in the DME?
Is there a short between the relay sockets, bleeding out precious amperage for my fuel pump relay?
Should I just put a wire in there, instead of the fuel pump relay, and pray that I never get in an accident (oh yeah and don't leave the key in the on position when the engine isn't runnning)?

stevebuk-carsoft pin numbers are not correct for my car. There are all sorts of sockets missing, and unused sockets in use.

I might be able to use DME wiring diagrams specifically related to the fuel pump or DME pin 1, if anybody has those.

[stevebuk]

It's a wonderful feeling when you get the engine to run! That really is major progress.

I'm not going to quote any pin numbers as they're obviously different on your car!

This is from memory but I hope it helps - the engine management unit provides an earth (negative) connection to switch the fuel pump relay, you seem to be getting the positive supply to the relay coil which is good. If you're bridging the switched contacts on the relay to make the pump run then the wiring from the relay to the pump is good and the problem looks like the engine management unit isn't earthing the relay coil. I think there's an impact switch (can't remember where it's located) that stops the fuel pump after a crash but without looking at the wiring diagram I don't know whether it controls the engine management unit or the supply to the pump. Perhaps someone with access to the manual can chime in. You also need to check that there is a connection between the non positive side of the relay and the engine management unit connector.

The engine management unit should switch the fuel pump relay briefly when you turn on the ignition to prime the fuel supply, it then switches off the relay until the engine is running - does anyone know which signal is used for the management unit to determine the engine is running?

Sorry about the timing of my replies - time difference between the UK and US!

[azale]

According to my diagrams, the fuel pump uses the crankshaft sensor to determine if the engine is running. Unfortunately, 1. I know it's working and 2. the DME still doesn't run it to prime the fuel rail pressure before the first crank. I can't find anything about an impact switch but I have seen a crash control relay. I tested it to see if it was working a while ago and it was working fine, but according to the wiring diagrams I looked at, it just did stuff with the hazard lights.

There is no resistance between DME harness socket 1 and fuel pump relay socket 85. There are about 5000 ohms resistance between fuel pump relay socket 85 and ground when the harness is connected to the DME. There is about .5 milliamps going from fuel pump relay socket 86 to 85.

I'm trying to think of problems I may have caused when I repaired the sensor, or else problems the sensor may have caused. I hope my DME isn't ruined; did I mention it still hasn't given me a code?

Either way, I'm not too far from installing a small switch in my car to run the fuel pump when the key is in the ignition. I will also serve as a great anti-theft device. And it's tons cheaper than a new DME.

If you guys think of anything else let me know. I will install the switch next Tuesday or Wednesday if the is in the DME.

[Javier]

Let's follow some plan:

1.- I do not understand what do you mean "Then I immediately put the fuel pump fuse back", if you remove the fuel pump fuse, how did you get it running, the normal way to test the pump is to bypass (bridge) the power contact at the pump relay 30/87, but you need the fuse in place to run the pump. So please check fuse carefully, also measure with an ohm meter the fuel pump fuse F23. You can test the pump by connecting with a jumping wire, socket pins corresponding to FP relay pins 30 and 87. This will confirm proper operation of all FP circuit but the FP relay. Start the car with jumper in place, this will also confirm every thing is OK but the FP relay operation.


2.- Check your FP relay, you can apply Battery + to pin 86 and ground to pin 85 and feel it clicking. At the same time, connect the ohm meter to pins 30 and 87 and see the power contact closing (I mean, when you apply voltage to coil terminals 86/85, meter should read 0 ohms from terminals 30 to 87, and open circuit when coil is de energized.

3.- You already confirmed you get 12 Vdc at pin 86 of the FP relay, but have not confirmed DME is connecting to ground pin 85 (ground and - Battery are the same). You can confirm it feeling for the click in the FP relay at the specific moments it should energize, but first, discard a damaged relay per 2. If it turns out to be that DME is not activating the relay properly, have the DME fixed. May be it is only that relay pins 86 and 85 were accidentally connected, and output transistor actuating FP relay got fried (I doubt it as it must probably fail short circuiting causing the FP relay be permanently energized. Only huge amount of energy (a sustained short circuit in FP) would damage to open the transistor or the printed circuit board pads. In any case, you can take a look inside DME from pin 1, looking for evidences of such damage.

Do not risk your safety bypassing the FP relay

Javier

[azale]

I think I failed to communicate what I checked.

I was jumping the fuel pump from the fuse, not the relay. I was installing the fuse quickly in hopes that the relay had snapped after the car was running.

I checked and double checked the old relay (it was fine) and I replaced it anyway. I have also checked and double checked the new relay.

Regarding your third point:

There is no resistance between DME harness socket 1 and fuel pump relay socket 85. There are about 5000 ohms resistance between fuel pump relay socket 85 and ground when the harness is connected to the DME. There is about .5 milliamps going from fuel pump relay socket 86 to 85.

When the relay should be activating, the is 5000 ohms resistance at the DME. I assume that isn't a good ground. And I assume .5 milliamps isn't enough to trip the relay.

Can you think of any other sensor that would cause the DME to inhibit the fuel pump from priming the pressure in the rail after you turn the key? I assume if my CPS were the only problem, the pump would still run for few seconds when I turned the key to run right? Well, its definitely not doing that.

Do you know of a fast and cheap place that can repair my DME?
What about a $50 used DME on eBay? Too hard to match?

I don't think a manual switch for the fuel pump is as unsafe as sky-diving but I've never seen any statistics either.