Would PHr's help me solve a mystery?
Discussion
About 6 months ago we decided to get one of the ultimate PH barges: a BMW 750 with that amazing v12 engine sat up front. Yes, we are insane. 
About 4 months ago it ceased to work. No notice, just didn't start one day. We were in the middle of trying to figure out what was wrong when I crashed the TVR (aquaplaning is not fun
). Now the TVR is being repaired, (yay! 
) we need to carry on trying to sort the BMW.
The problem seems to be there is no spark getting to the plugs. We have checked the following:
Crank sensors (replaced and no effect)
Coils (there are 2, replaced with known working ones)
Hooked up to a professional diagnostics machine and computer says 'yes everything is fine, what are you bothering me for?'
Checked and replaced various relays
Engine turns over
Injectors are firing
Fuel is getting to where it needs to be.
Immobiliser out of synch - someone suggested turning the ignition on for >30 secs to see if it resynchs, still nothing.
It was just when all this heavy rain started, so there is a strong possibility water got into the box containing the ECUs. However, nothing came up on the diagnostics to say they were buggered, and everything else controlled by the ECU appears to work. The other odd thing is that if it was a bit of the ECU then both of them would have gone in the same place at the same time (2 banks of 6, 1 ECU each).
So at this point in time we are a bit stuck as to what to look at next. We believe we have checked out the stuff that is the most likely cause, a mechanic pal has taken a good look and is a bit stumped too. It is just a damn big hunk of useless German tin at the moment sat on the drive so any suggestions, no matter how odd, are most welcome.
I really don't want to scrap the damnable thing, but it is looking a likely prospect at the moment. I also don't want to spend a fortune at a BMW garage for a car that is worth relatively bugger all.
I put this in General Gassing rather than BMW specific forums to get a wider audience in case there is a genius who can help us solve this. If someone does come up with the solution, I will buy them a real pint!
Trace
About 4 months ago it ceased to work. No notice, just didn't start one day. We were in the middle of trying to figure out what was wrong when I crashed the TVR (aquaplaning is not fun
). Now the TVR is being repaired, (yay! ) we need to carry on trying to sort the BMW.The problem seems to be there is no spark getting to the plugs. We have checked the following:
Crank sensors (replaced and no effect)
Coils (there are 2, replaced with known working ones)
Hooked up to a professional diagnostics machine and computer says 'yes everything is fine, what are you bothering me for?'
Checked and replaced various relays
Engine turns over
Injectors are firing
Fuel is getting to where it needs to be.
Immobiliser out of synch - someone suggested turning the ignition on for >30 secs to see if it resynchs, still nothing.
It was just when all this heavy rain started, so there is a strong possibility water got into the box containing the ECUs. However, nothing came up on the diagnostics to say they were buggered, and everything else controlled by the ECU appears to work. The other odd thing is that if it was a bit of the ECU then both of them would have gone in the same place at the same time (2 banks of 6, 1 ECU each).
So at this point in time we are a bit stuck as to what to look at next. We believe we have checked out the stuff that is the most likely cause, a mechanic pal has taken a good look and is a bit stumped too. It is just a damn big hunk of useless German tin at the moment sat on the drive so any suggestions, no matter how odd, are most welcome.
I really don't want to scrap the damnable thing, but it is looking a likely prospect at the moment. I also don't want to spend a fortune at a BMW garage for a car that is worth relatively bugger all. I put this in General Gassing rather than BMW specific forums to get a wider audience in case there is a genius who can help us solve this. If someone does come up with the solution, I will buy them a real pint!
Trace
Nothing really usefull to add on the no spark issue, but if you are getting fuel, then don't waste anymore time with cam/crank sensors, as the PCM will use this as a trigger for the injectors and the coils.
ETA: unlikely to be an immobiliser problem either, as to protect the cats, the PCM will shut down fuel injection rather than the spark
ETA: unlikely to be an immobiliser problem either, as to protect the cats, the PCM will shut down fuel injection rather than the spark
Raize said:
It's NOT just fouled plugs / bad gaps?
We are fairly sure that it isn't because it was running fine one day then just wouldn't start the next. We have also taken 1 plug from each bank and there is just no spark to either bank (we have done the earthing thing, to try to see if there is a spark).To get all the plugs out it is a fairly massive job as they are an absolute pig to get to!
We have also tried running an earth directly from both coils, still no spark.
The only thing we think we could check but need it up on a ramp to do is the earthing strap. Our mech mate is getting his trailer fixed and will test his trailer by picking up the behemoth!
Trace
I once had a similar thing happen on a Fiat: It just died one day, no spark from the plugs.
Dealership diagnostics said everthing was working OK (it was still under warranty).
It turned out to be a broken wire to the coil packs, so although the ECU was sending the signal to fire the plugs no power was getting to them to generate a spark. (At least that's what the dealership told me).
Dealership diagnostics said everthing was working OK (it was still under warranty).
It turned out to be a broken wire to the coil packs, so although the ECU was sending the signal to fire the plugs no power was getting to them to generate a spark. (At least that's what the dealership told me).
Get the pin data for that model and start by checking the coil packs are getting an ignition fed battery voltage supply with the ignition on. If not find out why (fuses/relays/wiring broke/multiplug fault)
Now look for switch signals at the coil packs on cranking (you need an led test lamp for this or if you are ok with an automotive multimeter set to Hz). If you aren't getting them use the pin data to check for the same at the ecu end. If it's ok then the wiring is faulty if not the drivers for the coils are fubared you'll need to send the ecu off to be tested.
Now look for switch signals at the coil packs on cranking (you need an led test lamp for this or if you are ok with an automotive multimeter set to Hz). If you aren't getting them use the pin data to check for the same at the ecu end. If it's ok then the wiring is faulty if not the drivers for the coils are fubared you'll need to send the ecu off to be tested.
sounds stupid but does it have much fuel in it. I had an Audi s2 that stopped on me, fuel light wasn't on but it was low, There was fuel in the tank as I pulled the pump out to test it. I spent hours working on it till I decided to pour 5 litres of fuel into the tank and the b
h started first time.
h started first time.Thanks for the suggestions chaps
It's a 97 by the way.
Trace
Puddenchucker said:
It turned out to be a broken wire to the coil packs, so although the ECU was sending the signal to fire the plugs no power was getting to them to generate a spark. (At least that's what the dealership told me).
We have not specifically checked this wiring but as there are 2 coil packs doing the same thing, I can only assume it would be an unlikely cause. Will check though. We started to disassemble the radiator cowling to get access to the distributors but it started getting too dark to see and began to rain quite hard so we gave up at this point and have not looked since. StuartGGray said:
Flat battery.
Tried to start it using our mechs booster pack thingy and jump from his BMW. Same result: turns over, but doesn't start.wolf1 said:
Get the pin data for that model and start by checking the coil packs are getting an ignition fed battery voltage supply with the ignition on. If not find out why (fuses/relays/wiring broke/multiplug fault)
Now look for switch signals at the coil packs on cranking (you need an led test lamp for this or if you are ok with an automotive multimeter set to Hz). If you aren't getting them use the pin data to check for the same at the ecu end. If it's ok then the wiring is faulty if not the drivers for the coils are fubared you'll need to send the ecu off to be tested.
Thank you for this. I will pass this on to our mech as this is beyond my capability. Hitting things with hammers is about my level. Now look for switch signals at the coil packs on cranking (you need an led test lamp for this or if you are ok with an automotive multimeter set to Hz). If you aren't getting them use the pin data to check for the same at the ecu end. If it's ok then the wiring is faulty if not the drivers for the coils are fubared you'll need to send the ecu off to be tested.
james7 said:
Not sure of the year of your car but I have seen other bmws with similar faults caused by the DME relay.
If it has one its often worth changing or having as a spare. Sometimes a tap with a screwdriver etc can make it work for a while.
DME relays were the first thing we tried. Brand new from BMW. No luck. If it has one its often worth changing or having as a spare. Sometimes a tap with a screwdriver etc can make it work for a while.
It's a 97 by the way.MM said:
sounds stupid but does it have much fuel in it. I had an Audi s2 that stopped on me, fuel light wasn't on but it was low, There was fuel in the tank as I pulled the pump out to test it. I spent hours working on it till I decided to pour 5 litres of fuel into the tank and the bh started first time.
It was low but the fuel light wasn't on but, like you, we stuck another 5 litres in. Diagnostics show there is about 18 litres in the tank. Also the injectors are firing petrol into the cylinders as they should be. Just no spark to light the darn stuff! h started first time.Trace
My Corrado did something similar,
Cut out at a junction, was getting fuel, spark plugs fine, coil fine, etc.
I threatened to scrap it, took battery off. Put it back on and it started.
All because I told it I was selling it.
Maybe it doesn't want you to driver after hearing about the TVR?
Cars have feelings too...
Cut out at a junction, was getting fuel, spark plugs fine, coil fine, etc.
I threatened to scrap it, took battery off. Put it back on and it started.
All because I told it I was selling it.
Maybe it doesn't want you to driver after hearing about the TVR?
Cars have feelings too...
TerzoNeil said:
earth strap from engine to body possible corroded try another cable from block to negative of battery
The earthing strap was our next thing to look at but we need to get it on to our mates ramp. However would using a jump lead work?16v stretch said:
My Corrado did something similar,
Cut out at a junction, was getting fuel, spark plugs fine, coil fine, etc.
I threatened to scrap it, took battery off. Put it back on and it started.
All because I told it I was selling it.
Maybe it doesn't want you to driver after hearing about the TVR?
Cars have feelings too...
Cut out at a junction, was getting fuel, spark plugs fine, coil fine, etc.
I threatened to scrap it, took battery off. Put it back on and it started.
All because I told it I was selling it.
Maybe it doesn't want you to driver after hearing about the TVR?
Cars have feelings too...
To be fair, I crashed the TVR after the 750 died. Anyhoo, the 750 is his car, not mine.
Trace
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