Fuel Pump vs CPS

[Sir Montalbon]

Background
I started the car from cold and it was running fine. As the temp gauge got a little above blue, I came to a stop sign. As I went to accelerate, the check engine light came on, the car lost all power and it barely had enough power to get from the stop sign to the side of the road.

The car sat there overnight. The next morning, while it was cold, the car cranked right up. I got about 1/2mi before the same symptoms showed up again. Parked it and got it towed home.

I let it sit about a week, then tried to crank it again. This time the car turned over for about 30sec before just barely cranking up and immediately dying.

EDIT: See post 16 for latest info

[darrenforeal]

If the CPS resistance is anything like the M50 the bentley is wrong. Specs on the CPS should be around 500ohms not 1200ohms. So, try to see what the correct reading is for the CPS on the M60B30. I wouldn't trust the bentley on this one because it was wrong about the M50 CPS reading. Also, fwtw a bad CPS usually will read 0 or something ridiculous in the millions or something of the like.

[Sparke34]

According to multiple posts here Bentley is wrong about the CPS spec. It's supposed to be 550 or so.

It sounds to me like a fuel pump going bad except for the no power issue.

GL

[hammy35]

I had to crank the car to get voltage at the fuse #23. If you're getting voltage, but no pressure - my money is on the pump.

[MBman]

I almost feel like an expert since I am dealing with similar on mine:D, I doubt it is the CPS - ohms are OK for it , it can give some intermitant problems, but my money is on the pump or relay

[bolloc]

I almost feel like an expert since I am dealing with similar on mine:D, I doubt it is the CPS - ohms are OK for it , it can give some intermitant problems, but my money is on the pump or relay

Yup I would listen to you, you have done a helluva diagnostic job on your car, its welcoming to see someone who actually follows through and actually do diagnostics on their engines' components.

[cornflakecwl]

Sounds similar to what happened on mine... replaced the fuel pump and been fine ever since. New battery resolved the other random no crank issues that I THOUGHT was cps.

[bolloc]

Sounds similar to what happened on mine... replaced the fuel pump and been fine ever since. New battery resolved the other random no crank issues that I THOUGHT was cps.

When you engage the starter the engine should turn over, aka cranks. Miche mentioned in an earlier post there seems to be some confusion about this, he attributed it to being a non native English speaker, it seems though it is actually a common mistake many people seem to make. I would be surprised to find a faulty cps could be the cause of a cranking failure, if it were, it would have to be something programmed into the cps to tell it not to crank.

[cornflakecwl]

When you engage the starter the engine should turn over, aka cranks. Miche mentioned in an earlier post there seems to be some confusion about this, he attributed it to being a non native English speaker, it seems though it is actually a common mistake many people seem to make. I would be surprised to find a faulty cps could be the cause of a cranking failure, if it were, it would have to be something programmed into the cps to tell it not to crank.
Valid point, at the time I hadn't really diagnosed the issue but that makes sense now. Regardless, I won't have to push start a black car with no a/c in 90 degree weather next summer every 5th time I try to start it! :) (althought the A/C is going to be fixed by then)

[Sir Montalbon]

Thanks for the help and replies so far guys. They bring up a new question...

Does the key need to be in positon III, aka the "crank" position (as opppsed to position II, aka "run") for the relay to send power to the fuse box and then to the pump?

I ask b/c I was under the impressoin that with the key in postion II (no cranking, just accessories, ac, etc), that the pump is powered and begins to pressurize the fuel system. But some say that you need to be actively cranking the car (positon III) for power to be sent to the fuel pump fuse (#23) and then the pump.

Basically, help me understand the "power up" order of the diffrent systems related to the DME and its various signals.

[E34ührer]

IIRC, the fuel pump should have power in position II.

[93FIM5]

Not sure the set up on a 530i but for my E36 325i I did the following when I had a similar issue.

- First check the fuse to the fuel pump if its blown well yea.

- Check to see if you are getting voltage at the fuel pump when the car is switched on, err the position you crank from but not while cranking.

- If you get voltage at the fuel pump connector you have a bad pump pretty simple. You can hear the pump running or if you want a visual disconnect the feed line to the fuel rail and spill a bunch of gas.

- If you dont have voltage at the connector for the pump check the main relay and the fuel pump relay to see if they are working, there will be an audible click if they are working correctly you can check them pretty easily with some jumper leads.

- If the relays are good check the relay sockets for the correct voltage.

- If all the above checks out then jumper the relay sockets and check to see if you are getting power at the fuel pump.

- If you can jumper the sockets and the fuel pump pumps but still no start move on from the fuel system and check spark.

- To check spark you are going to need to pull a coil and either use the old screw driver method (Be very careful!) or use a plug pulled from the engine.

- If no spark and the CPS is reading below ~510-540 ohms I would say replace your CPS, that was my issue. The DME doesnt see the engine cranking so it doesnt initialize the pump or fire the plugs.

- If the CPS is within spec there are a couple things on the DME you can check but you will need a pinout of the DME connector for that.

Good luck.

[Sir Montalbon]

Not sure the set up on a 530i but for my E36 325i I did the following when I had a similar issue.

- First check the fuse to the fuel pump if its blown well yea.

- Check to see if you are getting voltage at the fuel pump when the car is switched on, err the position you crank from but not while cranking.

- If you get voltage at the fuel pump connector you have a bad pump pretty simple. You can hear the pump running or if you want a visual disconnect the feed line to the fuel rail and spill a bunch of gas.

- If you dont have voltage at the connector for the pump check the main relay and the fuel pump relay to see if they are working, there will be an audible click if they are working correctly you can check them pretty easily with some jumper leads.

- If the relays are good check the relay sockets for the correct voltage.

- If all the above checks out then jumper the relay sockets and check to see if you are getting power at the fuel pump.

- If you can jumper the sockets and the fuel pump pumps but still no start move on from the fuel system and check spark.

- To check spark you are going to need to pull a coil and either use the old screw driver method (Be very careful!) or use a plug pulled from the engine.

- If no spark and the CPS is reading below ~510-540 ohms I would say replace your CPS, that was my issue. The DME doesnt see the engine cranking so it doesnt initialize the pump or fire the plugs.

- If the CPS is within spec there are a couple things on the DME you can check but you will need a pinout of the DME connector for that.

Good luck.
93FIM5, those instructions are pretty much everything I've been researching on No Start Conditions boiled down to 10 bullet points. Thanks, I'll use this tomorrow.


So, I have discovered that I was chasing the wrong relay. Cornflake says it best....Oh LAWDY!!!! Searching google and our forums, the almost overwhelming consensus was it was the orange relay, or the white one, so long as it had the green/violet wire. This was confirmed with the ETM and I found the green/violet wire only on my orange relay. This was incorrect. Turns out, the most inaccessible relay, the blue one, also has a green/violet wire. I also noticed that this wire was the same gauge as the matching end at the fuel pump. The green/violet wire leading to the orange relay was much smaller. A quick continuity check to fuse #23 confirmed I had found the correct relay.

So, just wanted to put that out for future searchers. 1995 6/95 530i fuse pump relay is blue and the hardest one to get to. You'll know when you get in there :stickoutt

Thanks again for all the help. I'm sure I'll have an update tomorrow.

And a big shot out to TGreene for offering to mail me some test CPS's, totally unsolicited. This place is full of good people.

[bolloc]

And a big shot out to TGreene for offering to mail me some test CPS's, totally unsolicited. This place is full of good people.

Yes it is.

[DUDMD]

The fuel pump doesn't power on unless the car is cranking/running. So when you were testing for power at the pump, unless you had someone cranking the engine, the test gave you wrong results. Have someone crank the car while you check the voltage at teh pump.

[Sir Montalbon]

I finally got some more time with the car. Here is where I am at...


Fuel Pump: Replaced fuel pump relay and installed new fuel filters. Pump has power and makes sound.
Fuel Pressure: During cranking, the gauge bounces about 10x/sec between~49psi and 54psi. Just after cranking (still no start), gauge stays steady at ~54psi. Over the course of the day, pressure slowly declines. The next day, it was at ~35psi, and dropped all the way down to ~10psi when the really cold weather hit. Is this normal? If not, FPR?
Spark: Removed only one spark plug and checked it for spark. I got spark, but it was a rather dull orange color. I have never done this before, and expected a bright blue. Also, the plug was more black than brown and smelled like gas. (don't have pics handy, but can get them up later if it helps)
CPS: Spec is 495 to 605. My CPS reads 488ohms. Out of spec, but just barely. I replaced it anyway with one that TGreene was so gracious to supply for testing purposes. It read 545ohms. Still no start.
So, what next? I'm thinking to check the rest of the spark plugs (and maybe replace), check the coils, check injector operation. If still nothing, maybe MAF?

What do you guys think?

[MBman]

ECU/ coils/ ECU relay/fuel pump relay

[darrenforeal]

from what you said, check your coils

BTW how many volts is your battery reading?

[Sir Montalbon]

BTW how many volts is your battery reading?

My battery had become low due to multiple attempts to start the engine. When I performed the spark test, I had a 1200amp jump pack attached to the battery, so my voltage "should have" been good. I can get a reading this afternoon to see the cranking voltage.


from what you said,check your coils

What is the best way to do this with a non-running engine? I've done some reading, and it seems the best way to test a coil with a non-running engine is to use a multimeter, checking for proper resistance. Is this correct?

Warning: Beginer Mechanic Time, please follow my train of thought and tell me if I'm remotely close
Lastly, the engineer in me has a problem with it being the coils themselves. After reading up on coil test, I ran across a mention of a m60 running on just 4 coils "fairly well, considering". So, this makes me think that just one coil can't be bad. It must be all of them for my car to not run at all. This is fairly unlikely, so it must be a supply-voltage-to-the-coils issue. But I'm getting some spark, which leads me to believe that my supply to the coils is ok. So then, what about the ECU relay? Well, if the ECU relay or the ECU itself were dead, the fuel pump wouldn't come on at all, correct? But the fule pump DOES work. Where would I go from here? :eyecrazy

[darrenforeal]

well... your logic regarding the coils I think is fairly legit. But, testing them insures that they are getting the proper voltage from further up the electrical chain. To me, based upon what you said re: the spark plugs, it seems you aren't get sufficient spark, causing the rich looking look to the sparks. But I don't know if that would cause the no start.

I'll think about it some more. But, in the mean time hopefully someone with more experience will chime in.

[Sir Montalbon]

I'll think about it some more. But, in the mean time hopefully someone with more experience will chime in.

Thanks Darren.

In the mean-mean-time, I have a few more details and rambling thoughts...

The detail I left out is that the car wants to fire up. When I turn the key, it cranks and cranks and cranks, and about every 2 seconds, the engine kinda "hits", like it wants to fire up so bad, but just can't quite do it. I don't mean that it starts to sputter and die. It doesn't even get that far. You just feel that slight little jolt that is usually followed by a VROOM!, only there is not subsequent VROOM!

Which leads me to my next question? Is it possible to flood the engine on one of these cars?

Thanks again for all the help guys!

[darrenforeal]

that description sounds just like a CPS. Did you clean off the actual metal magent of the sensor? This happened to me, the CPS was so gunked up that it wasn't reading where the sprocket really was. cleaned this area all up, and I was back in business.

[jfj707]

that description sounds just like a CPS. Did you clean off the actual metal magent of the sensor? This happened to me, the CPS was so gunked up that it wasn't reading where the sprocket really was. cleaned this area all up, and I was back in business.

Yes - there is a spec'd air gap too.

BTW, the FP dropping like that seems weird, but I don't know too much about testing pressures. You don't have a spare FPR to test, do ya?

[Sir Montalbon]

that description sounds just like a CPS. Did you clean off the actual metal magent of the sensor? This happened to me, the CPS was so gunked up that it wasn't reading where the sprocket really was. cleaned this area all up, and I was back in business.

I too kept thinking CPS when I first started the diagnosis. I didn't clean off my CPS, I replaced it with a new one. As for the air gap, I measured the two side by side, and they looked identical.


Yes - there is a spec'd air gap too.

BTW, the FP dropping like that seems weird, but I don't know too much about testing pressures. You don't have a spare FPR to test, do ya?

I don't have a spare FPR, but I did remove the vacuum hose from it and placed a towel under there. I then tried cranking the car for about 30sec to see if anything came out due to a ruptured diaphragm. Towel was bone dry.

[m60b40]

I'm not sure why you are beating around the bush. OEM CPS if broken will not cause those symptoms. If it breaks your car will not start. It will not stall the car once it's already started.

You have a classical MAF or Fuel Pump failure symptoms.

Take out your MAF, inspect it and clean it. Check resistance. If your fuel pressure tests and amount check out replace the MAF.

For fuel pump, again you are wasting your time. Get a fuel hose $2, 3 way connector $5 and gauge $10 take out fuse, put it on input line screw in gauge in the 3 way you put in between fuel rail check pressure per specifications then check how it reacts to system loads.

Check your FPR for fuel smell on line, unplug it and it should raise PSI on rail 5-10 points.

Make sure it holds pressure after you turn the car off.

If it passes all those tests, replace MAF.

If your idle is uneven you may have air leak OR bad ICV that can cause same symptoms.. and I will assume you checked your cats/fuel filter/air filter.

[darrenforeal]

I'm not sure why you are beating around the bush. OEM CPS if broken will not cause those symptoms. If it breaks your car will not start. It will not stall the car once it's already started.


this is not true. At least on the m50 its not.

[MBman]

ecu?

[m60b40]

this is not true. At least on the m50 its not.

If you have old OEM with full magnet it should not stall 100% on M60. I'm certain it's the same with M50.

[Mark185]

I'm not sure why you are beating around the bush. OEM CPS if broken will not cause those symptoms. If it breaks your car will not start. It will not stall the car once it's already started.

You have a classical MAF or Fuel Pump failure symptoms.

Take out your MAF, inspect it and clean it. Check resistance. If your fuel pressure tests and amount check out replace the MAF.

For fuel pump, again you are wasting your time. Get a fuel hose $2, 3 way connector $5 and gauge $10 take out fuse, put it on input line screw in gauge in the 3 way you put in between fuel rail check pressure per specifications then check how it reacts to system loads.

Check your FPR for fuel smell on line, unplug it and it should raise PSI on rail 5-10 points.

Make sure it holds pressure after you turn the car off.

If it passes all those tests, replace MAF.

If your idle is uneven you may have air leak OR bad ICV that can cause same symptoms.. and I will assume you checked your cats/fuel filter/air filter.

+1 for all of the above except faulty CPS not causing engine to stall. Mine did on my 535i. It was causing intermittent engine stuttering and stalling because it had vibrated loose and was not maintaining a steady gap.

If you have been conducting a lot of engine cranking while troubleshooting, it is very likely you have flooded the engine and sent a lot of gas past the rings into the crankcase. You should consider changing the engine oil. Possibly put some cheap non-synthetic oil in until you sort the problem and then change it again for proper synthetic oil. Oil thinned with gasoline will only make it harder to get the engine to fire. Years ago, I was helping a friend with a no start condition and even after we fixed an ignition problem, his engine would not fire and stay running because the oil was so diluted with gasoline. After changing the oil, it started right up and ran well.

[Sir Montalbon]

Well, the car is running (which I'm ecstatic about!), but I'm not sure how the culprit broke, or affected the starting of the car.

The culprit was a large red 50A Autolite style fuse in the DME box. It is mounted on the top row of the relay slot in the box (clearly visible in the pic). I do know that the fuel pump relay was defective, b/c I began to get power to the fuel pump after replacing it, but either during my dismantling of the DME box or at the same time the fuel pump relay went out, this 50A fuse blew.

http://i24.photobucket.com/albums/c26/cobcobbs/384524495_photobucket_33946_.jpg

The mystery for me is, what does this fuse do? I looked for it in the ETM. Only two 50A fuses were mentinoed: one for secondary air pump, and one for ABS/ATC. Of these two, the ETM says that the only one in the DME box is the secondary air pump fuse, but upon researching what the secondary air pump does, I wouldn't think that it would prevent the car from starting.

Regardless, the car is back to running, and running well at that. Thanks for all the help!