BMW 635 Misfiring. Please, help!

[Dolud]

Hello.

So It's been 4 weeks I'm trying to figure out whats the problem with my BMW 635 1985. It is USA version with m30b34 engine. For some reason engine keeps shaking (probably misfire). This shaking/misfiring is constant - so it is shaking on idle and when I press on the gas. Shaking is random. I've did bunch of tests and replaced critical components - no success Don't know what else I can do...


What I've replaced:
- New distributor cap/rotor
- New spark plugs (bosch with correct 8mm gap)
- New Fuel pump. I did WALBRO 255 in-tank conversion
- New fuel pressure regulator
- New set of injectors
- New vacuum lines
- New rubber intake boot
- New exhaust (complete from the headers up to the end)
- New exhaust gaskets
- New valve cover gasket
- New Oxygen sensor
- New battery

Tested:
- No vacuum leaks
- Took MAF from my friends working e24
- Checked resistance on various sensors
- Compression ±130 psi across all 6 cyl
- Adjusted valves to 0.3mm specs

This is how it looks:



This is how it works:

[jmile46]

Mann that is a gorgeous shark! Love the Rfs! How does the car run? I see it shakes bad but does it stumble, die? Possibly motor mounts shot? Check spark plug wires for corrosion and possibly a valve adjustment is all I can think of

[Dolud]

Thank you! Sadly those RF's got stolen but I'm switching to BBS RS now It does not stumble or die. Idle is steady. Motor mounts are completely new. Spark plug wires are new. Valve adjustment is done to factory spec (did it last week).

[jmile46]

Thank you! Sadly those RF's got stolen but I'm switching to BBS RS now It does not stumble or die. Idle is steady. Motor mounts are completely new. Spark plug wires are new. Valve adjustment is done to factory spec (did it last week).

Then I am at a loss. Sorry to hear about the rfs! Thats awful.


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[1986series6]

Have you isolated which cylinder is not firing?

Pulling off spark plug wire to see which cylinder is not firing.

If there's spark to that cylinder then it must be fuel.

Is the injector from the misfiring cylinder getting electrical input from harness, if not why.

The only connection to random misfiring I can think of is injector timing.

Each bank of 3 cylinders get a gas squirt every revolution so it's hard to figure

why you would get random misfire fuel related. Have to check the pulses

going to each injector if the connection to each is ok.

[slownrusty]

Why did you upgrade to the Walbro, have you confirmed the fuel pressure at the engine?

[Dolud]

Every single cylinder is firing. Unplugged wires one by one on distributor - every wire has spark. When I disable cylinder by unplugging wire - its starts to shake violently. This means that misfire does not completely disable a particular cylinder... If I unplug injector - same thing will happen - I will just disable the cylinder.

Have you isolated which cylinder is not firing?

Pulling off spark plug wire to see which cylinder is not firing.

If there's spark to that cylinder then it must be fuel.

Is the injector from the misfiring cylinder getting electrical input from harness, if not why.

The only connection to random misfiring I can think of is injector timing.

Each bank of 3 cylinders get a gas squirt every revolution so it's hard to figure

why you would get random misfire fuel related. Have to check the pulses

going to each injector if the connection to each is ok.

- - - Updated - - -

My low pressure in-tank fuel pump was failing. The car would not start when I was low on gas. I had 3 options: 1) buy original fuel pump for crazy 300-400 usd. 2) buy crappy airtex fuel pump for 150 usd 3) buy powerful walbro 255 for 100 usd and do the conversion. I can verify that fuel pressure is ok (actually I've attached pressure gauge to fuel line to monitor the pressure).

Why did you upgrade to the Walbro, have you confirmed the fuel pressure at the engine?

[dmac156]

Looks like you've been very thorough. What about the crank position sensors? If those are bad, I think they can result in the issues you are seeing. It's worth researching.

[Dolud]

Tested sensors resistance - all within factory specified range. I'm not sure if they can cause misfiring... I thought those either work or not. If they are dead - then car just wont start. But I really don't know, maybe they can work and give bad signal to ECU.

Looks like you've been very thorough. What about the crank position sensors? If those are bad, I think they can result in the issues you are seeing. It's worth researching.

[dmac156]

Tested sensors resistance - all within factory specified range. I'm not sure if they can cause misfiring... I thought those either work or not. If they are dead - then car just wont start. But I really don't know, maybe they can work and give bad signal to ECU.

I think you are right, they would either work or be dead. The problem happens at idle, and when reved up? If it was only at idle, the idle control valve could have something to do with it.

[Dolud]

No, the problem is constant though all RPM range. It constantly shakes/misfires. When I press gass I can still feel the vibration 'slight misfire'.

I think you are right, they would either work or be dead. The problem happens at idle, and when reved up? If it was only at idle, the idle control valve could have something to do with it.

[jmile46]

Perhaps investigate the ecu doesn’t have broken solders. Do you have a spare you can swap in?

[Dolud]

Yes thats a good idea! I've removed ECU - it looks virgin outside... never opened. Already asked a friend to give me spare ecu for a "test swap".

Perhaps investigate the ecu doesn’t have broken solders. Do you have a spare you can swap in?

[slownrusty]

I recently spoke to Mark D'Sylva at Enhanced Automotive Tech and we had a good and lengthy discussion as to the eraatic beahviour the ECU can cause as they age, you've changed everything that could be a cause so quite possibly it may be ECU related. Mark can re-solder the problem areas or he can send you a tutorial if you're handy with a solder gun.
This is a great read:
http://e28-535i.com/technical/e28-ECU_Repair.php

[jmpower]

Hi
I think you may be on the wrong road. You have said that every cylinder has a spark, if so not a spark issue.

If you disconnect a plug wire and the engine runs worse, then that is a good cylinder which is helping the engine to run.

If you do this with all six cylinders and the result is the same then all six cylinders are firing.
If the same thing happens when you disconnect the injectors and the engine is worse then all the injectors are working.
The issue is then an air/fuel mix issue.

Can you increase the RPM to above 4000rpm and hold for a while and see what happens?

[Dolud]

Same thing on 4000 or 5000 rpm! I can still feel the misfire. BTW it wont rev past 5000 rpm.

Hi
I think you may be on the wrong road. You have said that every cylinder has a spark, if so not a spark issue.

If you disconnect a plug wire and the engine runs worse, then that is a good cylinder which is helping the engine to run.

If you do this with all six cylinders and the result is the same then all six cylinders are firing.
If the same thing happens when you disconnect the injectors and the engine is worse then all the injectors are working.
The issue is then an air/fuel mix issue.

Can you increase the RPM to above 4000rpm and hold for a while and see what happens?

[Dolud]

I am good enough with soldering iron! This is very good idea - I might try to re-solder critical areas on ECU and see if it helps.

I recently spoke to Mark D'Sylva at Enhanced Automotive Tech and we had a good and lengthy discussion as to the eraatic beahviour the ECU can cause as they age, you've changed everything that could be a cause so quite possibly it may be ECU related. Mark can re-solder the problem areas or he can send you a tutorial if you're handy with a solder gun.
This is a great read:
http://e28-535i.com/technical/e28-ECU_Repair.php

[EuroGeorge]

Have you checked resistance for the throttle position sensor? Check ALL the connectors from the harness. From a simple approach, make sure the connector to the AFM is solid and the intake boot is tight from the airbox through to the throttle body.

I had a problem years ago where the car would idle fine with the hood opened but die when closed after driven a couple of miles. Long story short, I had a small crack in the coil wire at the coil and the spark was jumping off and grounding to the underside of the hood... I found this AFTER going through all the inspections and test you have done.

[jclausen]

How is the valve adjustment and the all important oiling tube system

[Dolud]

Even if I unplug the throttle position sensor and other sensors - I still have that misfire Its not the TPS or AFM...

Have you checked resistance for the throttle position sensor? Check ALL the connectors from the harness. From a simple approach, make sure the connector to the AFM is solid and the intake boot is tight from the airbox through to the throttle body.

I had a problem years ago where the car would idle fine with the hood opened but die when closed after driven a couple of miles. Long story short, I had a small crack in the coil wire at the coil and the spark was jumping off and grounding to the underside of the hood... I found this AFTER going through all the inspections and test you have done.

- - - Updated - - -

As I said before - I did re-adjust all the valves to factory 0.3 mm spec Oil tube is ok. Cam lobes are not worn out.

How is the valve adjustment and the all important oiling tube system

[dmac156]

Any chance that it could be the coil? I know you have spark which means it's not completely dead, but it could be intermittent. We're all rooting for you! Hope you get this resolved soon.

[88m53453]

Swap the coil , cap and rotor from your friends car. I know they were replaced, but it's easy to swap and rule them out. Are the plugs black or nice and tan ? Reading the plugs could tell the entire story.
Since all cylinders are equally working. I would say check the grounds , there is one under the intake manifold. Reflow the solder joints as has been suggested.