M42club.com - Home of the BMW E30/E36 318i/iS
DISCUSSION => Electrical => Topic started by: mk2vr6 on December 28, 2009, 05:13:41 PM
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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?
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Hello - Check out this thread over in engine and drive line section ( dvmotorsports - Dead cylinder ) it might be helpful for you. GL
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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.
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My bet would be bad CPS...Had the same problem a few weeks back..
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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?
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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.
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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??
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bueller?
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hmm that is odd
try bypassing those relays
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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
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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..
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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.
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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.
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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.
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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.
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CPS is as close as I can possibly get it to the trigger wheel without grinding down the bracket that holds it, which would be just ridiculous.
It has to be something else, it measured at 814 ohms at the plug. The fuel pump fuse (7.5A as stated in the manual) is good. I will try replacing the new relay with the old one JIC, but if that's not it, I think it might be time to just suck it up and tow it to the stealership. I have to be back to school in less than a week and I don't know what else to do.
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CPS is as close as I can possibly get it to the trigger wheel without grinding down the bracket that holds it, which would be just ridiculous.
It has to be something else, it measured at 814 ohms at the plug. The fuel pump fuse (7.5A as stated in the manual) is good. I will try replacing the new relay with the old one JIC, but if that's not it, I think it might be time to just suck it up and tow it to the stealership. I have to be back to school in less than a week and I don't know what else to do.
814 ohms seems too high for the crank sensor. What did your original sensor ohm out at ?
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814 ohms seems too high for the crank sensor. What did your original sensor ohm out at ?
Original came in at 498.
I read that it shouldn't be below 550. I didn't hear about an upper range.
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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.
When the DME gets a signal from the CPS, it powers up the FP relay. It's a safety feature...so that a non-running engine won't receive fuel. In most cases that's a good thing, but in our cars it makes the CPS a critical part. If the DME doesn't sense the crank trigger signal, the car will not start. It also won't set a code!
I still suspect your relay is dead or even the wrong part...they have diode & resistor relays that'll fit but not function properly. Either that or the CPS isn't right or you have the cam & crank sensors swapped...
Closer to the trigger wheel is best from what I've heard. At least you know the fuel pump is OK! That's the expensive one...
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When the DME gets a signal from the CPS, it powers up the FP relay. It's a safety feature...so that a non-running engine won't receive fuel. In most cases that's a good thing, but in our cars it makes the CPS a critical part. If the DME doesn't sense the crank trigger signal, the car will not start. It also won't set a code!
I still suspect your relay is dead or even the wrong part...they have diode & resistor relays that'll fit but not function properly. Either that or the CPS isn't right or you have the cam & crank sensors swapped...
Closer to the trigger wheel is best from what I've heard. At least you know the fuel pump is OK! That's the expensive one...
Amen on the fuel pump!
I put in the old relay just to check as well as the new one, the PN off the new one matches up as best as I can tell.
I can say for certain the CPS/CMS are ok and in the correct spots.
The only thing I guess I'm not positive about is whether the CPS is good. I measured it at the plug so I know it works but maybe 814 is too high?
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1) extra crank ps = 500 ohms
2) crank ps in good running car = 525 ohms
I copied this from the other thread when I thought I had sensor problems.
My old (extra) was 500 ohms.
My new one was 525. I remember testing it right out of the box.
I'm not saying yours is no good it just seems high .Is there anyone else on this board who has testing there crank PS and can post???
When you turn your key on do you hear the relay click ?
Good luck
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I figured I'd update this thread because this experience provided a bit of valuable info.
First off, I need multimeter lessons.
Secondly, my first hunch was right.
I just got the car back from the dealer (ouch.), it was the fuel pump.
The replacement pump that I purchased at autozone (Airtek IIRC) was faulty. My replacement/soldering job was fine, dealer reported that the pump did receive power, but it wouldn't pump, leading me down the CPS/relay road.
I could have sworn I used the multimeter to measure the plug properly, but reality states otherwise.
So to sum up:
1. New fuel pumps aren't always good.
2. 814 Ohms isn't too high of a reading for a new crank sensor as my car runs perfectly now.
3. Learn to use a multimeter to measure things other than resistance.
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I'm glad you got it sorted. Sorry I wasn't 100% on the troubleshooting...I'll file that away for future reference.
Good lessons; I'll be doing some of the same myself with the low speed coolant fan...car's overheating a bit now & again.