Another E30 no start issue!

markdas · 10-05-2010, 03:48 AM

Hi guys,

I know this is very well discussed on all BMW forums....but....we can't find the solution to our no start issue!

We have a BMW Lemons Race car in Houston......its an 87 E30 but it has a 1991 E30 engine (similar for sure). We totally stripped it out and most of the wiring too. We have run and raced the car once already, then swapped the engine and it has been running well since.....until Sunday! It refuses to start....again. We have frequently had to do the ECU reset thing....key in position 1 and disconnect the battery for 15 mins......it usually works but not this time.

We have 12v at the pins 30 and 87 on the main relay and also 30 and 87 on the fuel relay. If I link these out, I can force the in tank fuel pump to run but not the main fuel pump - no volts at the pump. Hot wiring the main pump makes it run but we have no spark!

We do have 12v on the coil LT terminal and the centre pin of the coil itself.

I've changed the crank sensor....

We have 2 ECU's and have tried both.

Following the excellent guides available we have tried to link out the DME relays (force them closed) and checked the various voltages on the ECU main cable....all seem good except no volts on the #37 line? Is this important???

It feels like there is a key bit of info not being sent to or from the ECU to power up the fuel pump and allow spark....but its not obvious! We did have a short through one of the earths on the car wiring loom that goes to the inside of the car from the large round multi pin connector.....the 1991 engine loom was not compatible with the 1987 car harness!!! but I have re-made that wire and checked all earths etc...

It needs a cleverer man than me and my team mates put together, so hopefully someone can suggest what we are missing?

Thanks

Mark

JhwShark · JhwShark's Garage

Mark,

Please post a link to the wiring diagram...I may be able to help.

You indicated that you have tried the "substitution test" with the extra ECU's, correct?? Did you try this with the FP relay or at least jumped the pin slots sending direct voltage to the devices (it sounds that you did bridge the pin slots)?? How about the position sensors or temp sensors (you did check the crankPS, but others, I do not remember the sensor config's)??

If so, deep dive through the diagrams is what I would need...odds are something in the swap and rewires. I have rewired many looms...it is either sensor or wire if not ECU or relays.

Jon

markdas · 10-06-2010, 04:06 AM

Hi jon, thanks for the input.....

Okay here goes....out of the blue......we got it started at 10.30pm last night......why.....we're not sure!

I did go back and check the resistance on the CPS and the spare CPS that we tried to start the engine with.....both about 540 ohms which depressed me no end as I think thats about spot on?

We double checked the 12v to the main relay and to the FP relay....all good.....good continuity to the FP wires to the fuse box and to the pump. Linking the main and fuel relay forced the in-tank pump to run but nothing at the main pump (which I think is important - now).

We changed ECU's for the one we took apart and ran a wire to monitor voltage on pin 37 (I guess we read somewhere that this pin should have 12v and it did?

We had no spark at #1 plug for 2 days......I also checked the king lead for spark and same thing.

NOTE: Out wipers stopped work ages ago, so we hard wired them in to a new switch in the car......they had also stopped working recently??? I removed the large black relay in the fuse box a while ago as they ran without it anyway.....

No, I am not sure at what point but we had almost all the wiring laid out, we changed back to the original CPS that used to work on the car and we had been messing around with the OCM relay, the connectors for the pulse #6 lead and the CPS (any idea why those 2 are interchangeable)??? Oh, and I put the wiper relay back in again and the wipers worked?

We tried the engine and we got spark at king lead, but not at #1 plug? Changed the distributer cap and leads over and she fired up! For laughs we put the old dist cap and leads back on....and it still worked? Changed the pulse sensor #6 and CPS connections over and it didn't work.....

Took the wiper relay out and it still works.........

So - Yayyyy its working again......but I am not at all sure if I mended it, or there is something lurking in there that will do this again and spoil a race day perhaps???

I'd still like to remove all remaining bunches of wires from the car and end up with the bare minimum in there......not weight saving just ease of use and removing all the crap that could cause this!

We don't have the OBC plugged in anymore with no ill effects to date......

I think I am learning more about this E30 but man its been a round about route to an unclear solution!!!

Mark

JhwShark · JhwShark's Garage

Do you still have a Ballast resistor in the start circuit that could be problematic...if it is cracked and with temp changes an open can occur which would yield no spark out but voltage will still be at the dist...?? I've heard of this from a few over the years. Some change out the coil to rid the Ballast.

Just thinking of all possibilities...

markdas · 10-11-2010, 04:34 AM

Morning all,

Another update.....she's still fighting us!

It has been running, we had good spark etc last week, then over the weekend, it was running and decided to stumble and then stall, no re-start!

We had 12v at the coil and good spark, if I link out the ful pump relay, it made the in tank pump run, but nothing to the main pump.....

Forcing 12v onto the main pump and all is well, she starts and runs.....so we run a new wire in from the fuse box to the pump direct and and put a new earth onto the pump to the chasis.....all was well until late last night when she failed to start again.......I haven't done any checks yet!

We have a new coil on there, so I am assuming the ballast idea has been taken care of?

I have a brand new main relay and FP relay?

Im getting voltage at both relays.......it there something going on in the fuse box? I have continuity from the FP relay to the 101 connector (green and purple wire in and it changes to the purple and red from 101 to the fuse box one side of the fuse, then back to green and purple from the other side all the way to the rear of the car, where it splits and feeds the in tank pump).....one odd thing is that I check have continuity with a couple of other wires in that 101 connector when testing the purple and red wire)???

It feels like we are going to have to run an independant 12v to the pump....but it just doesn't feel like the correct solution??? Am I over looking something here???

Thanks

Mark

markdas · 10-12-2010, 04:37 AM

Further update!

Once again, we get a no start condition....this time no spark and no fuel pump!

Linking the relays gave us fuel but no spark still.....

Changed the CPS and the ECU (again) also ran wire to pin 37 and no volts on it! We put 12v onto pin 37 and the relays fire up.....but no spark!

We do the 15 minute disconnect reset.......no spark!

Then we realise that the fancy fuel pump cut off switch that we thought we disconnected, is still attached to on of the 4 small wires that go to the ECU from the speedo loom......a small gauge lightwiehgt wire, that seems to disable the main and fuel pump relays and stops a spark being initiated.....what the hell!

so we got her running again and im going to take that damn switch out!!!

Mark