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Hi all,

    I have a 1987 525e (Motronic) which after spending two weeks in America, i come back to my car and she refuse to fire. I've done what i can and im out of ideas so really hoping someone can help! Also, worth mentioning that on the day that i got back and i realised the car refused to fire up i went to the petrol station and got £12 worth of fuel and some carb cleaner to assist a start. SHE STARTED UP! left running fine for 10 minutes but when ignition was switched off she refused to start immediately after (STRANGE, what is going on!?) . 

Problem/Symptoms;

   - No spark to any of the plugs apart from a single spark when coil is engaged at Pos3
   - I believe im getting fuel as plugs are wet 

 

The facts; (strange results shown in RED)


   - Engine turns over by the key, top of engine moves (in time) with bottom
   - Brand new distributor cap and rotor arm

   - Brand new ignition coil
   - Swapped out CPS with one i had from 520i e28 (same hardwired one facing front harmonic balancer)
   - Swapped out main fuel relay with one from 520i

   - Swapped out MAF from 520i (i know it's trivial but, meh) 
   - Checked for 12v heading towards the coil between 15+ and 0. (12v upon pos3, 10v when cranking

   - Although coil is new, Resistance across posts all check out fine
   - Spark plugs are 2 months old
   - Continuity between both ends of main HT lead (coil tower to distributor) 
   - Battery charged fully externally inside the house

   - DME socket where relay fits;
      - Tab30 suppose to have 12v, shows 0v 
      - Tab85 suppose to have 0v, shows 0v
      - Tab 86 suppose to have 12v, shows 0v
      - Tab 87 and 87 suppose to both show 12v, shows 12v
      - Tab 87 and 87 suppose to both show 0v, shows 12v with ignition off

   - Checked for click from DME relay, it clicks just fine and i get the engine hum 

 

Questions that i am asking myself;

   - If my 520i M20 uses Jetronic fuel injection, and my 525e M20 uses motronic, why do they both have the same hard wired (no clip, needed cutting and soldering) crankshaft position sensors? 
   - Why do i only get one spark when ignition is turned on, but none whilst cranking?
   - Does p.d towards the coil normalling drop from 12v to 10v when cranking? 
   - Why did she start ONCE but refused to start immediately after?
   - Is my ECU fried? and if so.... why? only sat for 2 weeks...

Any help is very much appreciated!! 

Regards,
Darren (From Brighton) 

 

Edited by dazh90

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The cps on the front of the engine does nothing it's a service thing

Crank positioning is done by two sensors on the bell housing.

Check the no start guide in e28 section.

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Motronic and jetronic are quite different things like afm, relays etc may not be the same.

Culprits might be the bell housing sensors or the dme relay.

Is the battery good? Might it be flooded?

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Duncan, hey! 

   Thank you very much for getting back to me. I thought that sensor didnt look like it was supposed to be changed, but changed it because i've never had a problem with CPS on an M20 in the past and assumed it was there. I've heard about the sensors on the bell housing, will i have easy access to the bell housing ones to change them from underneigh? 

Would you suggest me changing them before i go ANY further with anything else? think i have missed anything from what i have said above? 
 

 

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You can check the resistance and continuity from above. Two plugs on the back of the engine. Though the same m20 the moronic is the same as the 535i

Have a browse of my no start guide as I say.

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Yup, read your entire guide yesterday (hence hearing about these crank sensors). I'll get me some new sensors as soon as i can!

    What do you think about the results i found at the DME plug? They are off from the values in your guide.... :unsure:

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On these, it's also worth fitting new DME and fuel pump relays as a matter of course. Also clean up the engine earth strap (remove it to do it) and true eath point for the engine loom. ECU's like to fail as well. Motronic 1.1 is a horrid old system really. It's worth converting to the later 1.3 system, vastly better.

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So an update on my quest for spark,

 

Quote

 

8. Engine speed sensor (CPS): With the ignition off we should see 960? +/- 96? between terminals 8 & 27 = Test passed

9. Reference Sensor (CPS): With the ignition off we should see 960? +/- 96? between terminals 25 & 26 = Test failed, no resistance

 

 

So my Reference CPS has failed, but my Speed CPS seems fine. How do i tell them apart? or are they both the same? 

 

2 hours ago, Sir Anthony Regents-Park said:

On these, it's also worth fitting new DME and fuel pump relays as a matter of course. Also clean up the engine earth strap (remove it to do it) and true eath point for the engine loom. ECU's like to fail as well. Motronic 1.1 is a horrid old system really. It's worth converting to the later 1.3 system, vastly better.


How would i go about upgrading to Motronic 1.3? This interests me alot :P

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That's why people avoid calling them CPS's, the engine speed is the Crank position sensor, the "reference mark" is the Cam position sensor.

Both can be initialised as CPS, but it can mean a bit of confusion.

 

A failed cam sensor would match, the cam sensor is used to figure out which cylinder is at TDC for the power sroke and should be sparking, and when a cylinder is at TDC on the exhaust stroke and shouldn't spark.

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They do fail. I have some know good sensors or ecp sell them. (Same part) and the dme and fuel pump relays if needed.

Sent from my iPhone using Tapatalk

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1 hour ago, dazh90 said:

So an update on my quest for spark,

 

 

So my Reference CPS has failed, but my Speed CPS seems fine. How do i tell them apart? or are they both the same? 

 


How would i go about upgrading to Motronic 1.3? This interests me alot :P

 

If it has a standard (non switchable) auto box, you'll need a complete E34 520i or 525i manual loom, ECU, injectors, front crank pulley etc. A fair bit of work but 1.3 was simpler and more reliable. The ECU almost never fails, true relays seem hardier and there is only one crank sensor on the front pulley measuring TDC and speed.

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2 hours ago, duncan-uk said:

They do fail. I have some know good sensors or ecp sell them. (Same part) and the dme and fuel pump relays if needed.

Sent from my iPhone using Tapatalk


You have the part i need matey? I guess i'll only need the one showing no resistance so... a Cam sensor... Can you send me a personal message on here if you do and can sell it to me?

I already have new relays, thanks though :D

.. Also, out of interest, image i've attached, is that the one i would need to get from EuroCarParts if purchased there? 

CamSensor525e.jpg

Edited by dazh90

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** Update on the situation **

 

    So i bought a brand new Camshaft sensor, and she still has no spark. I now have fuel going to all the cylinders which is nice. Both the Camshaft and the Crankshaft show 900+/-96ohms from the DME plug. If anyone is looking at this and wondering how that is tested, refer to Duncan's guide here --> 

I've re-soldered the DME to make sure there were no solder cracks and looked for any obviously blown resistors (as they can be easily changed) but nope... all looked okay and still shows the same symptoms. I have a used DME coming in the next few days (60 notes from a spare parts fella that i know - bargain) so after that is tried, fingers and toes crossed she fires up nicely :) 

Good luck to anyone else who is in the same boat! B)

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Substitution of ECU/DME, has not solved problem.

Gone through Duncan's troubleshooting guide a second time but this time, with a brand new multimeter which is far better. Didn't trust the last one at all. These are the only points worth noting from the most recent run-through of the guide; (See attached image). 
 

 

525ePRob.jpg

 

Any thoughts on this? I DO hear the relay click when it is gently pushed in so it has power but what is going on with the 87's? :unsure: (Tag 87 - Injector and ECU output) 

Odd thing i find is, i get 12v to the COIL? correct me if i am wrong but, if i have tried 3 different coils (one being brand new) and i apply 12v to it, surely as the engine is cranked, the distributor will do it's job and distribute that, now ~30kV to the spark plugs? what is the DME doing other than assuring the coil gets its stable voltage? I assume it's not regulating the ignition pulse, hence the presence of a distributor... <_<

Edited by dazh90

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