Very perplexing no start/spark issue.

[AustinK]

Hey guys. I've been over at bimmerforums for awhile now...since a friend gave me a 1985 635csi that hadn't run in ten years. It's in very good shape considering. I'm no rookie to forums and have been scouring the boards and Internet in general trying to get this car started and make sure I want to keep it and do a full build on it. I've got the motronics articles, I've got the Bentley, manual, I've got the 635 electrical troubleshooting manual. I posted a link below to my bimmerforums thread with all the back story, but in a nutshell here's where I stand.

I'm getting no spark to a plug that's hooked directly to the coil wire.

The coil is brand new, the old one tested bad.

I have a confirmed good DME I got as a loaner from a bimmerforums member.

Speed and reference sensors test good.

I visually inspected the reference pin on the flywheel.

All fuses and relays are good.

The only pin outs on the harness that aren't right are the readings for the TPS, but I don't believe that affects spark at the most basic point.

I was hoping to wait and start my build thread here once I at least had it running, but after the new DME arrived today and didn't solve the problem, I'm at a loss for where to go next.

I'd love it if any of you gurus had some time to look through were I've been and point me in the next direction.


http://www.bimmerforums.com/forum/showt ... Upstate-NY


Austin

[Brucey]

well, you need a good +12V feed to the ECU, and that has to come from the main relay (you can bypass this with a jumper for test purposes).

If you have that, and a good speed/ref signal, and a good signal on the 'start' input (derived from the starter motor/unloader relays), you should get a spark at least. Once you have spark, and a working fuel pump, the engine should fire on the cold start injector (for pre 6/87 builds).

cheers

[slofut]

well, you need a good +12V feed to the ECU, and that has to come from the main relay (you can bypass this with a jumper for test purposes).

If you have that, and a good speed/ref signal, and a good signal on the 'start' input (derived from the starter motor/unloader relays), you should get a spark at least. Once you have spark, and a working fuel pump, the engine should fire on the cold start injector (for pre 6/87 builds).

cheers

That's if you didn't pump a bunch of water and crud from the tank into the fuel pumps, filters, and on to the fp regulator and finally the injectors, because you didn't clean out the tank after sitting ten years! And don't tell me the filters will catch it ...got pics and videos. just sayin...

[AustinK]

New fuel filter and fuel pump, clean tank and new gas, but I'm not even to that point yet. I don't even care about the fuel system or air intake/vacuum at this point. Im not trying to get the car running well at this point, I can't even get a spark out of the coil directly to a spark plug.

[AustinK]

well, you need a good +12V feed to the ECU, and that has to come from the main relay (you can bypass this with a jumper for test purposes).

If you have that, and a good speed/ref signal, and a good signal on the 'start' input (derived from the starter motor/unloader relays), you should get a spark at least. Once you have spark, and a working fuel pump, the engine should fire on the cold start injector (for pre 6/87 builds).

cheers

I have all the things you list. Verified several times. But still no spark. So obviously I missed something or there is something else going on. I'm just at a loss for what to try next.

[Brucey]

some thoughts;

-the +12V feed is only 'known good' if it holds up under load. Thus you need to test it with a load (a headlight bulb or something like that) and measure if the volts hold up.

- you need a decent ground connection for the ECU

- you need a decent ground connection from the engine to the chassis

- you need the speed and reference sensors to be correctly connected (you can have them the wrong way round)

- you need to check the integrity of all the inputs to the ECU at the ECU plug

- it is best to check the speed and reference signals using a 'scope whilst the sensors are connected to the ECU

- BTW IME it is not unusual for the secondary resistance to measure 'wrong' on these coils and yet the coil can function perfectly in service; I think there is a spring loaded contact in the coil secondary that can become oxidised and measure bad without affecting the coil operation. The primary resistance is very low, because the coil sees a short pulse only to generate the spark. Briefly, the coil draws about 12A or so (and the injectors draw a lot of current too), which is more than enough to show up a bad feed or ground to the ECU; even 1/3 ohm resistance in the feed or ground will drop about four volts and this will cause the ECU to lose its marbles.

- apologies if this sounds like a cracked record but if you have no 'start' signal (pin 4 on the ECU from memory, do check this) then you will have no spark when cranking.

- is there an aftermarket alarm that has been wired into the coil circuit?

So yeah, I think you need to go back and check everything again; note that measuring a few volts on a DVM is 'necessary but not sufficient'; the tests you do should be under load wherever possible so that the integrity of the signals is properly verified.

Finding faults of this sort can be incredibly frustrating. I guess you can take some consolation from the fact that the fault is there all the time; arguably intermittent electrical faults are even more annoying.

cheers

[sansouci]

Did the PO have a no start problem as the reason to store the car? Sounds like a corrosion thing. Lots of deoxit and 'Shack contact cleaner.

[AustinK]

Did the PO have a no start problem as the reason to store the car? Sounds like a corrosion thing. Lots of deoxit and 'Shack contact cleaner.

No. No starting issues when originally parked. It was a third car and needed new cats to pass inspection so he parked it in the garage. It sat for five years then wouldn't start so he towed it to a garage and it sat there for five more years. The mechanic put new fuel pumps in and cleaned the tank but that's it.

[AustinK]

some thoughts;

-the +12V feed is only 'known good' if it holds up under load. Thus you need to test it with a load (a headlight bulb or something like that) and measure if the volts hold up.

- you need a decent ground connection for the ECU

- you need a decent ground connection from the engine to the chassis

- you need the speed and reference sensors to be correctly connected (you can have them the wrong way round)

- you need to check the integrity of all the inputs to the ECU at the ECU plug

- it is best to check the speed and reference signals using a 'scope whilst the sensors are connected to the ECU

- BTW IME it is not unusual for the secondary resistance to measure 'wrong' on these coils and yet the coil can function perfectly in service; I think there is a spring loaded contact in the coil secondary that can become oxidised and measure bad without affecting the coil operation. The primary resistance is very low, because the coil sees a short pulse only to generate the spark. Briefly, the coil draws about 12A or so (and the injectors draw a lot of current too), which is more than enough to show up a bad feed or ground to the ECU; even 1/3 ohm resistance in the feed or ground will drop about four volts and this will cause the ECU to lose its marbles.

- apologies if this sounds like a cracked record but if you have no 'start' signal (pin 4 on the ECU from memory, do check this) then you will have no spark when cranking.

- is there an aftermarket alarm that has been wired into the coil circuit?

So yeah, I think you need to go back and check everything again; note that measuring a few volts on a DVM is 'necessary but not sufficient'; the tests you do should be under load wherever possible so that the integrity of the signals is properly verified.

Finding faults of this sort can be incredibly frustrating. I guess you can take some consolation from the fact that the fault is there all the time; arguably intermittent electrical faults are even more annoying.

cheers

No worries about the cracked record. Every comment is a possible solution. I was over at the shop a couple hours this morning. Tried to jumper the obc relay box under the steering wheel. No spark still. Next time I'm there I'll take your testing under load comment into account. So far I've just been testing with the multimeter.

No aftermarket alarm.

Coil is brand new. Power to the coil. Power to the injectors. Only pinouts on the DME that don't test right are from the TPS. No continuity at all there, but that should affect the spark signal, I think.

I've checked all the grounds. The only one I don't see is the one listed on the front right motor mount. Doesn't look like there's even a spot there for one so maybe this model didn't have that one? As a curiosity I did find a mechanics receipt that shows the right motor mount was replaced. Maybe the ground was removed then. Any ideas there?

[AustinK]

Jumpered the obc yesterday to rule that out. Still no spark but I'm getting some encouraging developments. I'm smelling unburnt gas at the tail pipe for the first time so I think we may be getting somewhere. That encouraged me to did deeper in to the plug wires. I ran the test on the coil that has you disconnect the DME trigger wire and hook a wire there and run it across to the negative battery terminal and try to tap out some sparks. Even with that direct set up, the spark (with the shop lights off) was so faint I could barley detect it. Battery was a 12.8vdc. Coil voltage 12.8 on a brand new coil. Brand new spark plug. Solid connection between the coil trigger terminal. So I ordere a set of plug wires. I think I was fighting several issues and I'm getting close to finding the correct combo to bring this thing to life.

Stay tuned and thanks for all your help. Wires should be here by the weekend.

[Brucey]

it is a very bad idea to try to 'tap out sparks' with this type of coil, for the reasons I described earlier. If you do this in an even slightly clumsy fashion you can easily overheat and destroy the coil primary.

In any event the 'test' is almost meaningless anyway; you can't simulate the waveform required to fire the coil well enough.

cheers

[Pod]

Probably not much help, but I had a simiar problem with one of my cars last year. After two weeks of frustrating poking around under the bonnet, testing everything, I eventually discovered that there had been a water leak at the lower left hand screen corner which had caused a relay above the footwell to rust out. As soon as I changed it, the car started.

[AustinK]

Probably not much help, but I had a simiar problem with one of my cars last year. After two weeks of frustrating poking around under the bonnet, testing everything, I eventually discovered that there had been a water leak at the lower left hand screen corner which had caused a relay above the footwell to rust out. As soon as I changed it, the car started.

Any idea which relay it was?

[Pod]

Probably not much help, but I had a simiar problem with one of my cars last year. After two weeks of frustrating poking around under the bonnet, testing everything, I eventually discovered that there had been a water leak at the lower left hand screen corner which had caused a relay above the footwell to rust out. As soon as I changed it, the car started.

Any idea which relay it was?

No, but there aren't many there. If you look up under the dash, you will see them all. Just remove one at a time and examine/swap it.

[AustinK]

it is a very bad idea to try to 'tap out sparks' with this type of coil, for the reasons I described earlier. If you do this in an even slightly clumsy fashion you can easily overheat and destroy the coil primary.

In any event the 'test' is almost meaningless anyway; you can't simulate the waveform required to fire the coil well enough.

cheers

Thanks for the clarification. There is a pelican parts article that described the process. I didn't realize it was a flawed process. The new wires showed up today so I'll head to the shop in the morning and see where I get.

[slofut]

Austin, any progress here? Did the plug wires make any difference? I doubt this is the no start problem though as I can't see all the wires being bad at once. I keep thinking the crank sensor, but if it's bad it would also cause the fuel pump not to fire also, am I right? For what it's worth, my last new crank sensor lasted about 2k miles. AND it went bad during troubleshooting a hard start/no-start condition! Talk about frustration trying to follow a logical troubleshooting path, like shooting a moving target.

[AustinK]

Austin, any progress here? Did the plug wires make any difference? I doubt this is the no start problem though as I can't see all the wires being bad at once. I keep thinking the crank sensor, but if it's bad it would also cause the fuel pump not to fire also, am I right? For what it's worth, my last new crank sensor lasted about 2k miles. AND it went bad during troubleshooting a hard start/no-start condition! Talk about frustration trying to follow a logical troubleshooting path, like shooting a moving target.

Plug wires came in Thursday but I haven't been able to get to the shop to try them out. Two of my rental properties are vacant and then a friends rental property had a toilet fall through the floor so that killed yesterday and this morning. Now I've been out clearing driveways. I'll have time to get over there tomorrow.

I think the main coil to distro wire was bad so that's why I just ordered the whole set.

And while we're talking about the wires....the main wire came with instructions to cut it to length and then a little tube of silicone lube to allow the boot to slide on. I've never seen one like this. Anything special I need to do to make sure it makes a solid connection?

[AustinK]

Still no spark with the new wires. I thought I was on to something though. I tested the speed and reference sensors again and they both checked out so I decided to test the harness side of the connector and they tested good too (connectivity to the correct pin on the DME end of the harness. But then I tested the wires individually to make sure there wasn't a short to ground and it turns out the yellow wire on the reference sensor was shorted to ground. So I fixed that hoping for the best but still no spark. I'm just really at a loss now.

[Brucey]

in all fairness there is no way new HT leads can make a coil work that didn't work before, is there...?

For all parts of the Motronic system there are tests that are recommended. You need to carry out those tests exactly as prescribed; right now one or more of the tests you have done is giving you a false indication.

So feeds and grounds need to be tested under load, the speed and reference sensors need to be tested for the signal integrity using a 'scope, you need to test leads for continuity under realistic load.

If you do all the tests in the right way and they show good, it can't not work....

cheers

[AustinK]

in all fairness there is no way new HT leads can make a coil work that didn't work before, is there...?

For all parts of the Motronic system there are tests that are recommended. You need to carry out those tests exactly as prescribed; right now one or more of the tests you have done is giving you a false indication.

So feeds and grounds need to be tested under load, the speed and reference sensors need to be tested for the signal integrity using a 'scope, you need to test leads for continuity under realistic load.

If you do all the tests in the right way and they show good, it can't not work....

cheers

ok. I'll start at the beginning again. I can just use a test light to test under load, correct. I've actually never needed to test a circuit under load so I'm not familiar with the process, but I've done some reading online this afternoon and that looks like what most people do.

Also, can the main relay be bad if I'm getting power to the injectors? I assumed if I felt it click and the appropriate sockets test at 12v and I get power through the DME to the injectors it has to be good, but a couple other sites are saying that it could do all those things but still be bad.

[AustinK]

Figured out how to load test with a lightbulb. I'll get set up for that and test wires this weekend.

Did some more tests today. I switched the sensor positions and got nothing. I also stopped by my friends auto shop and chatted with him for a while. He sent my on my way with a noid light to test for pulse to the injectors. I got nothing. No light period. I'm not sure how to interpret that yet in terms of exactly when the injectors get a pulse. My guess would be that the pulse comes in time with the coil firing and it's not so I'm not surprised I'm not getting a pulse. But that may be flawed logic or a sign of an additional problem.

So since I don't want to drag the car to a real shop with a scope and have them test the speed and reference sensor for waveform, I guess I'll just order two new ones. It's actually worth it to me to shell out the cash, because then I'll know for a fact they are good, and the time and logistics to get the car anywhere this time of year is definitely not worth my time.

So when those come I really hope to get somewhere.

Stay tuned.


Oh and on a side note...I almost killed the whole build before it got off the ground. I was frustrated the noid light didn't work and wanted to feel some sort of progress for my shop time tonight so I sat in the drivers seat and dusted the dash and tried out the electronics to see what works and what doesn't I was surprised to find most everything works. The screen for the OBC is back lit but nothing shows on the screen. But the OBC is jumpered so I'm not worried about that now anyway. It got crazy when I turned the A/C fan on for a second. The blowers took a second to start but then started moving air pretty good. I only had them on for three or four seconds. Anyway, I got back out of the car and I smell fire and see smoke coming from the engine bay. Oh crap! And its coming from what I now know is the blower motor under the shield in front of the windshield above the firewall. But at the time all I saw was pretty thick electrical smoke coming out from both sides of the shield. I'd never even paid much attention to that part of the car so you should have seen me run trying to figure it out. I grabbed the fire extinguisher first and had it near, then did the screwdriver dance looking for a phillips short enough to let me get at the screws that held the shield in place. Then I had to find all the screws in the mushy pieces of firewall foam/rubber that was still in place. All I kept thinking was...that's a lot of wires going under that shield. If that loom melts I might cry. So it turned out to just be the motor itself seized and burning. An easy replacement for another day. Fun fun.

[hornhospital]

Whoa! Wait, the OBC is jumpered? That may be your no start culprit right there.

[AustinK]

Whoa! Wait, the OBC is jumpered? That may be your no start culprit right there.

It wasn't jumpered for the first couple weeks of testing. I jumpered it on advice from the e24 guys on bimmerforums. As I understand it, if the code was activated, jumpering it will bypass that....is that not the case?

[jps635]

I'm far from a 'no start" genius like some of the guys here but I do know that speed and ref senors can test all good per the text book tests, but still be bad. To this day i still don't know which one killed my engine dead while driving through a busy (for NZ) town, but replacing both fixed my problem after weeks of testing and trying a 2nd ecu from the other side of the planet.

[AustinK]

I'm far from a 'no start" genius like some of the guys here but I do know that speed and ref senors can test all good per the text book tests, but still be bad. To this day i still don't know which one killed my engine dead while driving through a busy (for NZ) town, but replacing both fixed my problem after weeks of testing and trying a 2nd ecu from the other side of the planet.

I'm to that point now myself. Two new ones should be here by the weekend. Fingers crossed.