The Infamous No Fuel - No Spark

[Jean]

FYI.. Brand new M50 CPS measure 901 ohms

What's the brand or part number on it?

I am going to post my finding in about an hour.

[rs4pro3]

Well that is closer to the manuals, the range on the e36 bently is for it to be within 1152 to 1408 ohms

[JGood]

I had a hunch that it was the crankshaft position sensor. I checked the resistance on it per Bentley and found it to be 549 ohms. Since this is less than the spec found in the Bentley (1280 ohms), I said voila.... problem solved. So I went to the dealer and bought a new CPS. To my surprise, the new one read 545 ohms. What the heck... I installed the new one anyway. Unfortunately this did not solve the problem. Subsequent to this, I read the Mar 02 Roundel article on CPS and the author said most 1 sensor (CPS) DME systems should have a resistance value of 540 ohms. This was my experience so I'm not sure why the Bentley is wrong on this.

http://forums.bimmerforums.com/forum/archive/index.php/t-41233.html

[JGood]

Yes, about 500 ohms is correct despite what Bentley says. I checked resistance on a new crank rpm sensor at the dealer when mine was suspect and it measured about 500 ohms as well.

http://forums.roadfly.com/forums/bmw/bmw-5-series-e34/384850-1.html

[Rocla]

This same problem often occurs when you install later m20 motronic to pre -88 car. Later cars AFAIK don't have this problem.

I have no right solution for it, I've just allways cut the wire from ecu to relay and ground the relay. That naturally makes fuel pump run allways when key is turned.

EDIT: some harnesaes have smaller green wire on other pin of engine harness socket, older car lack a splice for that wire on car side socket, make sure that the engine harness smaller green wire has sam +12 on ignition shwitched as the bigger green wire has.

[Jean]

Just checked mine and it's right at 540ohms (confirmed with TWO digital multi meters)

[RobertK]

Yes, both multi meters gave the same read on the bad sensor and the good one. Regardless the new one is 400 ohms higher than the old one.

540 is a good read out for a M20 CPS from what I've read in the various manuals.

[rs4pro3]

i just looked over your x20/c101 adapter. pull e36 x20 p7. (e30/e36 immobilization does not work well together.)
cheers, jason

Well that ended up being the problem, Robert disconnected that wire and the engine fired right up. So for anyone else doing an m50 swap into a pre 88 e30, do not send 12-volt to pin 7 of the e36 x20 plug.

[FredK]

Sweet! Mucho props to Swap Doctor, Jason89i! :mrgreen:

[Jean]

What were the "bad" and "good" values?

Yes, both multi meters gave the same read on the bad sensor and the good one. Regardless the new one is 400 ohms higher than the old one.

540 is a good read out for a M20 CPS from what I've read in the various manuals.

I measured 540 on a m50 cps, not m20 for the record. So is it confirmed, both bentleys are wrong?

[RobertK]

What were the "bad" and "good" values?



I measured 540 on a m50 cps, not m20 for the record. So is it confirmed, both bentleys are wrong?

I believe so.. turns out the CPS that my friend picked up for me was for a M52 anyway.

So yeah.. IT LIVES!! All that for one little wire.

Just in time for chemo tomorrow. Hopefully, if I don't get too sick from this round I can get it to the exhaust shop on Friday.

Thanks to everyone who chipped in.. especially Jason89i, you're a life saver! Atleast now we have the answer to this issue documented.

EDIT: JGood this might be the same problem you're having since your car is pre-88 as well.

[JGood]

EDIT: JGood this might be the same problem you're having since your car is pre-88 as well.

My car lives as well :)

More info to come when I verify a few more things...

I believe my problem had to do with corrosion of connectors. DOH!

[RobertK]

My car lives as well :)

More info to come when I verify a few more things...

I believe my problem had to do with corrosion of connectors. DOH!

Awesome to hear!

[Stevie30]

Great! No more Ole Smoky.

[mattdk318i]

Great! No more Ole Smoky.

amen, though last time wasnt so bad. Because i wasnt in the drop top