Author Topic: Help!! Car won't start! (Read 7031 times)

mk2vr6 · « **on:** December 28, 2009, 05:13:41 PM »

It was fine one day and the next morning it was dead.

It cranks over but won't fire.

I put in a new fuel pump and a new relay because both parts were original and had 150k on them.

I ohmed out the CPS and it came in at 498 (started in the 1100's and came down to this reading), I know this is lower than spec.

I ohmed out the CMS and it came in at 1198, which is also kind of low.

I think the car would start with the CMS the way it is, but not with the CPS if it's faulty. I'm home for break and really need to get this fixed ASAP.

Suggestions?

dj91318is · « **Reply #1 on:** December 28, 2009, 05:47:53 PM »

Hello - Check out this thread over in engine and drive line section ( dvmotorsports - Dead cylinder ) it might be helpful for you. GL

DesktopDave · « **Reply #2 on:** December 28, 2009, 06:20:02 PM »

Stomp test, check for spark & fuel. If the code comes out 1444 then likely it's the CPS. If the CPS is bad the DME won't turn on the fuel pump relay. You're right about both CMS & CPS. The CMS is just used for high-resolution spark advance, the car will run even with it unplugged.

I bought my car not running & it was just a dirty CPS that was too far away from the trigger wheel. The front main seal is really weepy on my '91.

Also a good idea to replace pump & relay. They don't last forever.

Wizard · « **Reply #3 on:** December 28, 2009, 06:50:26 PM »

My bet would be bad CPS...Had the same problem a few weeks back..

mk2vr6 · « **Reply #4 on:** December 28, 2009, 07:02:34 PM »

I did the stomp test earlier, forgot to put it in the original post.

1-4-4-4 = freaking great, thanks motronic!

I think I'm definitely going to order the CPS because 498 is definitely low and from the reading I've done, this could likely be the culprit.

Any opinion on the CMS? IIRC it's 1250 or 1280 +/- 10%, so 1198 is within spec but on the low side. I'd rather not throw parts where they aren't needed.

Any other suggestions? I'm a complete electrical noob.

I know the fuel pump isn't turning on b/c I can't hear it, I'm going to check spark in the morning, b/c it's 20 degrees now and I'm working on the car in the street.

EDIT:
1. from what I've read, it's normal for the CPS to just crap out like this? One day, ok, the next day not, but I had no symptoms of this at all, I drove the car 220 miles one way and around town 3-5 times without a hiccup...is that normal?

2. The relay was purchased from the BMW dealer (boo), it had 5 pins instead of the normal 4 for the fuel pump. Checking online confirmed that it's a "universal" relay so I'm thinking the extra prong doesn't matter? Can anyone confirm?

DesktopDave · « **Reply #5 on:** December 28, 2009, 07:11:15 PM »

Yup, normal for it to just quit, but not when the engine is running. Every time I've heard of it failing it just won't staer the next time.

You can jump the fuel pump relay terminals just to be sure...30 & 87. You'll hear the pump & fuel flowing through the FPR with the key on.

You're right about the extra pin...doesn't matter, they're interchangeable. Pin 30 will flip-flop between 87a and 87 IIRC so it's the same difference. There is even an empty socket to accommodate the universal relay's extra post.

Replacing the CPS isn't fun. You'll have to dismount the A/C bracket. Dumb design, not fun to replace outside in the rain (ask me how I know). Be sure the little plastic bracket is in place middle left or the A/C pulley can trim the CPS lead.

mk2vr6 · « **Reply #6 on:** December 31, 2009, 03:15:47 PM »

UPDATE:

New CPS is in and the car still won't start. (fvck that AC bracket). It's just cranking and cranking.

There is no power going to the fuel pump.

What else could I check?

Main relay?

ECU

How do I check these things?

Anything else??

mk2vr6 · « **Reply #7 on:** January 02, 2010, 09:53:30 PM »

bueller?

fiftytakedowns · « **Reply #8 on:** January 02, 2010, 11:10:01 PM »

hmm that is odd

try bypassing those relays

RED IS 91 · « **Reply #9 on:** January 03, 2010, 06:20:42 AM »

This is one of the best no start threads there is ............ read carefully and good luck.

http://www.m42club.com/forums/showthread.php?t=5462

Wizard · « **Reply #10 on:** January 03, 2010, 08:27:01 AM »

Also check your electrical connection at the fuel pump. After I replaced my fuel pump the pump still would not come on. Ended up being a bad plug or bad wiring within the plug..Just snipped it off and used butt connectors..

DesktopDave · « **Reply #11 on:** January 03, 2010, 09:08:33 AM »

Quote from: RED IS 91;83974

This is one of the best no start threads there is ............ read carefully and good luck.

http://www.m42club.com/forums/showthread.php?t=5462

+1 ^^^

If the stomp test works, your main relay is OK. Might be a short, broken wire, bad ground, loose plug on the pump, bad FP relay or even a bad pump. Pull the fuel pump relay & test it off the battery by jumping terminals 85 & 86. Polarity doesn't matter. Test the relay for continuity when it's energized from 30 to 87.

While the relay is out, jump the FP relay socket with a bit of wire (from pins 30 to 87 IIRC) to see if that gets power to the pump.

If that doesn't do it, run some long jumper wires from the battery to the pump connector to test that. If you can get the pump to start, it is possible that a replacement CPS isn't good. It has happened before. Did you test it for resistance before you installed it? I agree about the A/C bracket, it's a notably bad design. I also suspect that a few are mounted too far from the trigger wheel. The DME won't get a sufficient signal if it's too far off the wheel.

mk2vr6 · « **Reply #12 on:** January 03, 2010, 11:25:43 AM »

The replacement CPS measured at 840 ohms before I put it in. I also cleaned off a ton of oil/sludge from that area. The old CPS was caked with it.

It was weird because the old CPS had extremely brittle wiring which cracked at the junction when I took it off which is why I figured that would fix it.

I tried squeezing the prongs down on the FP just in case, but I checked out the connection w/ the multimeter and there's just no power going to it. I guess it's possible that the plug somehow went bad, but I don't really know how that would happen. If all else fails I will replace the plug.

I'm heading out to pick up a fused wire and a switch to make a jumper now...will report back.

DesktopDave · « **Reply #13 on:** January 03, 2010, 12:43:51 PM »

Sounds good. I know you've replaced everything new but that DME won't turn on the fuel pump relay without a solid signal from the CPS. I've heard about a brand new CPS that failed and seen crap ones that ran perfectly, go figure.

I have a lot of oil on mine too from the weak front main seal. I figured that the sludge that collected was mostly iron off the trigger wheel and it was preventing a clean signal to the DME. Unfortunately it's impossible to test that signal without an oscilloscope.

mk2vr6 · « **Reply #14 on:** January 04, 2010, 01:22:27 PM »

Ok.

The fuel pump does turn on when terminal 30 & 87 are jumped. So that means the wiring and plug are ok.

I am going to reinstall the CPS and see if that helps. Maybe it is too far from the wheel.

Otherwise I am really at a loss, what else could possibly be wrong?

When I turn the key, there is nothing from the fuel pump. Does the ECU need to receive a signal then? Or is it only when cranking. I will check the resistance of the CPS again just to be sure.