Fuel pump/starting problem for the electricians and experts

[azale]

This is my first post here but I’ve been searching for an answer to this problem for at least 1 week, 2 hours/day all over the internet. Other people have had the problem but there are no answers . . . are you ready?

We just bought a 1994 525i with 191,000, in great shape, meticulously maintained by an engineer. My wife drives 15 minutes to church and it sits for about 15 minutes. She then tries to start it again and it turns over (sounds like good compression) but it doesn’t fire up. A quick diagnosis: no fuel pump noise, bad fuel pump. I buy a used fuel pump off eBay while I’m waiting for my dad to loan me his volt meter. The volt meter says no power is going to the pump (fuse 23). Because I don’t know which relay is for the fuel pump I checked every relay under the hood and only 2 refuse to snap: one large relay with about 8 pins in the driver side fuse box (across from the crash alarm relay, separated by the LKM I think), and a five pin relay by the ECU – yes, the DME or the main relay. I buy a new DME and still no power to the fuel pump. I finally find the fuel pump relay by testing for resistance to the hot side of fuel pump fuse, and replace that relay (even though it was snapping). Still nothing.

Jumped the fuel pump relay with fuse 23 in its proper place and guess what I hear . . . the fuel pump in the trunk and the injectors (I think) in the engine compartment) which makes sense according to the wiring diagrams (the fuel pump relay runs both). All the contacts in the relay plug are working fine: 30 is hot all the time, 87 grounds out after going through fuse 23, the fuel pump, and the injectors. When the key is turned, 86 is hot and is sending 12 volts through contact 85 which grounds out without a problem. Still, with the relay in place no power goes to the fuse.

When I turn the engine to try to start the car *and* jump the relay, the pump runs fine but the engine still won’t start. I don’t smell a lot of gas coming out of the exhaust but I’m afraid I will flood the engine if I keep running the pump/injectors w/o the relay.

This “power-to-the-relay-no-power-to-the-fuse-unless-I-jump-it” is giving me nightmares. I just doesn’t make any sense.

There are no error codes (when I read the codes, the light blinks for .5 sec, off for 2.5, on for 2.5 and off for 2.5 in a continuous cycle).

I’ve heard it could be the crankshaft position sensor but I also heard that would give me a code.

Any ideas? What is that big relay opposite the crash alarm relay? Tonight I will test the sensor if I can find it and check for spark and fuel pressure. I have TIS disks coming in the mail. I need an answer before I run out of money. Any help is much appreciated.

[632 Regal]

Good details in your post, you will have to wait for the electrical department to come back from lunch...lol. Bet you get an answer here.

Lake orion huh? Thats just east of me.

[ryan roopnarine]

did you ever replace the DME relay in all of this?

[azale]

yes, I replaced the DME with a new unit $17, fuel pump relay was $15.

I also replaced the fuse in my dad's volt meter when measuring the amps going through the relay . . . there are at least five amps moving through just fine

Bavarian BMW in Utica/Shelby Township want $114 to look at it but I have to tow it there.
The crankshaft sensor will be $95 if I need it.

[DanDombrowski]

I read somewhere a writeup on checking fuel pressure by doing that, and the guy ran the fuel into a 2 liter bottle. If you've ever sprayed a part with throttle body cleaner (or brake cleaner) and had the excess run into a plastic cup, you'll see why this makes me wary. Not saying its dangerous, but I think petroleum based products don't like plastic so much. In any event, mabye drain the gas into a glass bottle when you check for fuel?

Now, as far as your electrical problem...

When the key is turned, 86 is hot and is sending 12 volts through contact 85 which grounds out without a problem.

I don't like the way this sounds. I might be misinterpreting what you're saying, but nothing at 12V should short directly to ground.

You said you replaced the DME for $17, I assume you mean the DME relay. I've never really had a need to run a test to see if the DME had power by checking voltage, I guess if you're checking current running to it that would tell you (if you have the multimeter connected correctly). I would check for spark by pulling a spark plug. If the DME doesn't have power (or doesn't have all of its info, i.e. no cps, etc) it won't fire the plugs and injectors, right? Someone else can back me up or refute that one.

I would think that if the CPS were bad, or another sensor was keeping the DME from wanting the engine to run, you would get a check engine light. You never know though, the PO could have removed the bulb.

Have a check at the fuel flow rate, but I don't think thats it. If you look at the procedure for replacing the fuel filter, it says "pull the fuel pump fuse and let the car run till it stalls". You would think that if the system has pressure when you shut the engine off, and then go to restart it (without the fuel pump turning on), it should at least run and then die (not sure on that one either).

Also, check for spark and let us know whats up with that. Thats about the extent of my electrical expertise I can give you for now.

[azale]

The contacts I was referencing were specifically for the fuel pump relay (although the DME relay plug tests correctly as well, the only difference there is where the DME relay contacts 87 go, there are 2 87s, five prongs in all)

on the fuel pump relay, contact 86 comes from the DME relay or some type of switch (see here http://www.carsoft.ru/avtorepair/bmw....10/index.html) and 85 goes to the actual DME control unit. I just tested that contact 85 was grounded (I assume after it goes through the DME control unit.

The check engine light is definitely working but I may be reading the codes incorrectly, please see my first post. Also, when I press the reset button under the tach and trun the key and then release the button one line says "CODE.NR 0000" which I assume means no codes??

Tonight I will revert to the troubleshooting I use on my 1980 johne deere snowmobile but I fear the problem is deep inside the electronics.

[stevebuk]

Sounds like you should check the crank position sensor.

I currently have the same problem with my 520i, it was intermitent but now will not fire, cranks fine, fuel pump runs etc.

I've followed the cps cable from the sensor to up near the thermostat housing and behind the oil filter housing but then the cable disappears beneath the inlet manifold / near the alternator and so far I can't locate the connector. Perhaps it's easier from underneath the car?? Or maybe it's easier to check the signal at the ECU plug? anyone know the pin number?

[azale]

Does your fuel pump run when your turn the key? Mine doesn't.

Can you give me a clue where the CPS is? front of engine I hear. high/low? left right? Have you tested your sensor for resistance? everyone says look for 600 to 800 ohms, more than that and you need to get a new one.

Garlic, No, it doesn't ever start (for 2 weeks now, I'm afraid the battery is going to give out soon. BTW I removed the interior lighting fuse but I don't think that should affect anything.

[DanDombrowski]

The fuel pump should run for a few seconds when you turn the key on, then shut off.

I read over those diagrams, I don't think 85 goes to ground. I think its saying that when it has power (12V) from 86 AND 85, then it routes power from the battery to 87, which is the fuel pump. So 85 should not go to ground, but I could be wrong.

See if you can actually test one of the leads for the DME for voltage to see if its turning on, and do a fuel pressure/flow check.

[stevebuk]

I can't hear the pump when I turn on the ignition but I can if I bridge the relay connection - under normal conditions it runs very briefly to prime the system but then switches off until the engine fires.

CPS is about 10 o'clock at the side of the crankshaft pulley close to the teeth of the pulley, there's a picture on this forum somewhere but can't locate it at the moment. If there aren't any pulses from the CPS the car will not start so it's the logical thing to check after the fuel pump - just wish I could find the connector!!