Car won't start - not CPS or Fuel pump

[DesktopDave]

I didn't have trouble with the ECU.  I could jump the relay socket and get the pump to work, but still no start.  I wonder if you have a bad transistor?  You took apart the ECU and didn't find anything wrong IIRC.  Maybe a bad wire?  With cars this old, you have to check everything.  A multimeter is your best friend.

[sports.racer]

Now comes the issue---when I use my test lamp on pin 85 of either the Main relay or the Fuel pump relay I don't get a light!
What I think is happening is that there isn't a ground available at the other end of the brown wires connecting to pin 85 of these two relays. If true, could that mean that the DME is faulty as pin 85 from both relays go to DME pins(pin 27 for the MAIN and pin 1 for the Fuel relay)?

Don't know if you've gotten past this yet but, if the ignition key is on then you won't see 12 volts or your test light at relay pin 85 or DME pin 27 because it supplies a ground.

If you turn off the key and then try those pins you should see 12 volts or your test light should come on.

Also, the Idle Speed Actuator will buzz when the key is own and the main relay is closed. If that thing buzzes then the main relay is working.

Recently played this game on a 87 635csi which basically the same circuits and it was his crank position sensor connector had come loose.

[Jimmy Lewis]

I didn't have trouble with the ECU.  I could jump the relay socket and get the pump to work, but still no start.  I wonder if you have a bad transistor?  You took apart the ECU and didn't find anything wrong IIRC.  Maybe a bad wire?  With cars this old, you have to check everything.  A multimeter is your best friend.

That is because the pump is running and building up pressure, but with the bad CPS the injectors don't pulse and the pressure is just bled black to the return by the reg. I convinced myself it had to be the CPS when I checked fuel pressure at the rail and knew I had spark, all 4 injectors wouldn't fail at the same time and it didn't hit a lick. Obviously this doesn't mean yours is bad but it is definitely something to look further into if you are experiencing these similar problems.

[Cobra Jet]

1) the slight buzzing you are hearing if at or near the back of the intake - that IS the ICV - it has a slight "bzzzz" to it when the key is turned to on.  If you don't hear a bzzzz, the ICV is faulty (easiest way to determine if the ICV is working or not - besides actually testing it w/ a multimeter).

2) As I and others have stated in my prior thread and the responses in this one - if the CPS is BAD, for some reason and I do not know why, the DME will NOT throw any fault code....  I don't know if this is a programming error or fault within the M42 175 DME, but when my CPS was bad, I was getting frustrated because I was not getting a fault code for it - and this was after attempting and diagnosing MANY other ignition/fuel related components (as you saw, my original thread was quite long w/ tons of info).  If the CPS is faulty, the signal is not there (or is too weak) to start the fuel/spark process that gets relayed back to the DME...  therefore it's a dead no start event every time you turn the key.  There have been numerous documented (posted) statements by many other M42 owners saying the same - bad CPS = DME spits out 1444 no fault code.

Get another CP (crank positioning) sensor - remove your original and install the other component, if the car starts - that was your problem all along.

A member on here had an extra and shipped it to me to use as a "test", since I was at the end of diagnosing nearly every viable component.  Once the test CPS arrived, I removed the old, installed the used CPS and BINGO - the car started instantly.  I then ordered a brand new CPS and sent the test CPS back to the M42 Member.

If someone can lend you a used CPS, try it - if not, purchase a new CPS and try it.

My bet is, the CPS is faulty, even if you have tested it... more than once...

I've also heard from other members on this site (and others) that if your DME was faulty or bad, you would not get any CEL on the dash upon turning the key nor would you be able to extract any codes...  I think this was also said in my original thread (you may want to re-read there), as I too *had* thought maybe it was my DME...  However, DME failure is not as common as most want to believe...  most other sensors and/or components fail BEFORE the DME fails - and sometimes this could make the owner (and incompetent shops) think it's a bad DME when it is not.

It seems like you have tested nearly everything there is to test based on what you have stated in my original thread and within this one, and there's really not much more you can test at this point.  If the car was running fine one day and it failed to start the next (or within the same day), that's the typical symptoms of a shot CPS - pull the original CPS and try another...

[lindol]

Sorry I haven't written anything in the last 2 days, but we've had bucketloads of rain here and as I'm working outside I didn't wan't to be out there in it.

First, thank you CobraJet for your advise, I too suspected the CPS except I decided to try one last thing before pulling it off of the car today.

As I mentioned in an earlier comment I had removed the fuel pump and applied 12V to it directly to verify that it worked. After that I didn't really give it another thought, but then I found another thread that recommended using a rubber mallet to hit the top of the pump while cranking to see if it will make any difference. Well...this was the trick wasn't it? As I cranked and softly rapped on the top of the pump the car suddenly came alive, but as soon as I stopped rapping on it it would die. A few more attempts to verify what I was seeing and I actually made the pump continue operating on it's own! I was so pleased about this I had to bring my wife out and show her the new trick to start the car, she found this to be highly amusing and suggested we not get a new pump as it's more fun to use a mallet to start it, haha!:D:D
I find it interesting that a pump will work on the bench and convince you it's OK, then once it's back in the tank it goes back to misbehaving.

This exercise while genuinely frustrating at times, has had a few extra benifits as I figured out,

• how to make my own fault code display, mentioned in an earlier comment,
• I figured out why my brake warning light was going on and off all the time as the bulb holder was too loose in the instrument panel,
• I found my car isn't chipped - but still surprisingly quick in that case,
• and electrical tape on the wiring harnesses makes a sticky mess when you unwind it!

Only thing to do now is get a new fuel pump!

[lindol]

Hi all,
Finally received my fuel pump from ebay germany, quite a big savings over the local aftermarket suppliers or BMW as it's not the entire assembly, only the pump, a new filter for the pump and a short piece of rubber tubing and 2 clamps. Just replace all the pump bits from the old pump assy with the new and carefully put it back in the tank. Problem solved!

[DesktopDave]

Glad to hear it.  Those fuel pumps are quite the PITA for our cars, aren't they?

[romeomike]

A happy ending in about three weeks time -- congratulations!

[lindol]

Indeed, thanks to everyone who put their ideas forward to help me get my head around this problem!

[Shaunster]

I know that this a little late, but I have had the exact same problem in the past, and what it was is the little power connectors that you slide onto the top of the pump where not making a complete connection. When I went over some speed bumps or drove over a bumpy road the fuel pump would cutout, especially if I was going into a car part and stopping right after it.

I would come back to the car several hours later and it would not start.
Might be something to check should you have this issue again.