Fuel pump/starting problem for the electricians and experts

[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!!

[Garlic Breath]

Sorry I misunderstood your message. I didn't realize that you couldn't start the car at all after the short trip to church. Didn't mean to muddy the water. Good Luck!

[azale]

stevebuk, maybe we do have the same problem. http://www.carsoft.ru/avtorepair/bmw....10/index.html says that pins 78, 79 and 82 are for the crankshaft sensor and pin 52 may be important as well. But I don't know where that plug is. Is it the DME harness inside the passenger-side box? And what are we looking for resistance/votage between + and - or resistance to the ground? I'll mess around with it tonight.

Dan, I've tested leads to the DME successfully and it should be/is switching. I'll still check the pressure flow.

garlic, thanks for your help anyway.

[ryan roopnarine]

look at the front of the cylinder head. the cps sensor body is attached down near where timing marks would normally be. a wire runs up and along the front of the cylinder head. a plastic "retainer" held on with circlip type fastners is on the front of the cyl head too, the cable runs under there. follow it back under the intake manifold . the connector you are trying to get to may or may not be resting in a mounting bracket.

[stevebuk]

If you use a jumper lead to connect the fuel pump relay pins 30 & 87 (6 and 2) on the socket the pump should run continuously, if the car still doesn't star it will point to a different problem. You should hear the fuel hissing through the pressure regulator in the injector rail and near the wheel arch under the fuel filler.

I'm going to have another look under the inlet manifold tomorrow to see if I can locate the CPS connector, the CPS produces pulses around 0.5v if it's working.

[Kalevera]

Azale:

First, welcome. Congrats on the car, they're lots of fun.

Now, for some criticism. I'll be nice, but it still needs to be said:

Despite the diagnosis of fuses and relays, you still haven't determined to which necessary element of engine operation the problem can be attributed. An engine (even a VaNOS M50) requires fuel, air, and a spark to work. The first thing to do would be to determine if the fuel is being delivered. Playing around with relays is nice, but it doesn't help much. You can strain your ears as much as you want, but it still won't tell you much. Heck, the gas tank could have a dent in it, thereby messing with the fuel level sender -- car thinks it has gas, you think it has gas, but it doesn't. Listening won't tell you that. Get a fuel pressure gauge on the rail and see if you have fuel with the key in the run position. No fuel? Hey, you've just narrowed the scope of possible malfunctioning elements by 50%.

Do that and then tell us what you've got. People saying, "I think it's the CPS" based on what you've told us already (unless I missed some critical element, which is possible) is just a waste of your time. Randomly replacing parts is an even bigger waste of time (and money).

By the way, how do you know that the car is in great shape?

best, whit

[azale]

Lowell: Thank you, I do like the car: almost as much as my wife does.

Thank you for being kind with the criticism, I get enough rejection from my BMW right now.

For a little more background: I had it towed to my friend's garage. I live in an apt and my dad's garage already had a disabled vehicle. Because I never heard the pump, I assumed it would be an easy fix with minimal tools--a job that could easily be performed inside my buddy’s garage. Because of the lack of tools, I have been looking for an easy fix, and everyone online is talking about the DME relay, the fuel pump relay, and the crankshaft sensor. When I checked the fuel pump relay, things didn’t add up so that caught my attention.

Now, I am following the bottom-up approach. Using minimal tools, I broke the seal on the fuel rail and gas squirted out all over the place. Fuel in rail and pressurized – check. Plenty of air is coming out of the tailpipe so air must be getting in there. Air – check.

The next tests were performed with no help, while the battery was losing power. I pulled one plug: it was dry and it didn’t look like it was sparking (from inside the car), but the plug wasn’t touching a grounded bolt (which I have been told to do). Then I checked for voltage going into the coil and didn’t get any, but it is possible that when I taped the connections to the frame I wasn’t getting a good connection.

I will check tomorrow with some help but I assume there is no spark and it’s possible that the injectors aren’t pushing fuel. The gas tank has no significant dents .

I say good shape, you may say the car looks great, almost no rust, the interior is in great shape, strong engine, smooth shifting, new timing chain, new tires, new suspension, new steering linkages, and I could perform open-heart surgery in the engine compartment if I had a willing patient.

Stevebuk, I looked for the CPS connector with about as much luck.

Does anyone know what pins in the DME harness are for the CPS? I read they were 78, 79, and 82 was ground. Well, my harness doesn’t even have wiring in socket 79. The way things are going with this job, I’m not surprised.

[Kalevera]

Excellent. Now we're getting somewhere.

Checking for spark on the M50 is a bit tougher than the earlier engines because it uses coil packs. Why was the timing chain changed? My thinking here is that the engine may be out of time -- I've never heard of anyone doing a timing chain on an M50, esp TU, without extenuating circumstances.

Before monkeying around with anything else: pull all of the coil packs and inspect them for leaking ("caramel candy") insulation. Once they leak, they're bad -- they'll fry out the DME (not the relay -- the final stage inside the DME itself).

The M50TU has two sensors of import that relate to timing: a crank and a cam position sensor. The crank sensor is located on the top header side of the vibration dampener and reads the ring gear. Cam is on the side of the head tucked behind the VaNOS solenoid.

Please don't be frustrated; we'll get it worked out for you. I didn't mean to come off as a jerk in the earlier post -- I was impressed with the information, just believe that there're better ways to approach the diagnosis.

best, whit