Look at these pics and tell me if my distributor cap is the cause of my misfire.

[nedfunnell]

My (previously manimal's) 1985 BMW 325e is suffering from a misfire. I don't know how old the distributor cap is. I have plugs (Bosch WR9LS) in my RockAuto cart already since those look bad and need to be replaced anyway. I am wondering about replacing my cap, rotor, and wires too while I'm ordering. Unlike other cars, though, this hardware isn't trivially cheap- not like the $3 dist. cap I got for my buddy's VW bug last year. Plugs, wires, cap, and rotor are over $100.

I pulled off the cap to see what it looked like under there, and I'm not sure what this business is. It's not the carbon tracing I'm used to seeing. It doesn't wipe off of scratch easily.

So, take a look. Does this look suspect?







Sorry for the crap pictures, my Droid 3 is taking poor pictures lately. It's frustrating- I'll watch it autofocus right past a crisp imagee and too far to a fuzzy one.

[phucheneh]

Originally Posted by nedfunnell

[my phone] is taking poor pictures [all the time]

Fixed. A camera that was $100 ten years ago would take better pictures. Keyword: macro focus.

But your cap looks fine. Usually if it's causing a general poor running condition, you see corrosion on all the plug terminals. The coil terminal looks a little funky, though. What's the rotor like?

Do you know whether the misfire is isolated to a single cylinder or not? That would be the first thing to find out.

[nedfunnell]

Originally Posted by phucheneh

Fixed. A camera that was $100 ten years ago would take better pictures. Keyword: macro focus.

But your cap looks fine. Usually if it's causing a general poor running condition, you see corrosion on all the plug terminals. The coil terminal looks a little funky, though. What's the rotor like?

Do you know whether the misfire is isolated to a single cylinder or not? That would be the first thing to find out.

I read you. I have a P&S that takes very nice macros, but I left it in my parent's car on our last family vacation and it's getting mailed back to me. Gotta wait. The funny thing is, my phone takes great macros... sometimes. Just in well-lit conditions, I think.

I didn't pull the rotor tonight, my hands were freezing up (it's 25 degrees out there).

By the sound of it, I think the misfire is one single cylinder. The misfire goes away at higher RPM, though. Plug? Wire?

[SpatiallyAware]

The center electrode looks worn in an odd sort of way. Generally those are smooth, and you don't see so much black around the electrode like that. I have seen the little cutout, but it shouldn't be grooved on the flat part like that, nor that black around the center electrode.

You might try filing it just a bit, not enough to wear down the ridge, just buff it out. Use contact cleaner on all contact surfaces. If that fixes the problem then replace them both as that is generally a temporary fix.

Also do a compression test and post up what you find on all cylinders - both wet and dry. Google how to do it, it's very easy with a ~$30 compression tester that should be in any home mechanic's toolbox.

PM manimal and see if he replaced the rotor, cap, wires, plugs, fuel filter. He's a good guy online, but I wouldn't expect someone in his position to replace these things unless there were was some issue. I don't know about BMWs of that era, but most cars back then had ground or ignition power issues. It might be worth spending some time reading about common fixes to make sure everything is up to snuff.

[nedfunnell]

Update: I took some closer-up (but not so much better) pics of the terminals. New thoughts? Confirmation?



Did I mention I hate my phone's camera?

[SparkyJJO]

OK that's the cap... how's the rotor look?

[phucheneh]

Cap is worn but not terrible. I would doubt the cap and/or rotor are causing any kind of consistent misfire.

I mean, the misfire a bad cap/rotor would cause would typically be random and not isolated to a cylinder, but it would be occurring fairly constantly.

However, those parts are rarely over $30 or so. And they do appear to have a fair amount of age to them...so it wouldn't exactly be a waste to replace them.

[nedfunnell]

Originally Posted by phucheneh

Cap is worn but not terrible. I would doubt the cap and/or rotor are causing any kind of consistent misfire.

I mean, the misfire a bad cap/rotor would cause would typically be random and not isolated to a cylinder, but it would be occurring fairly constantly.

However, those parts are rarely over $30 or so. And they do appear to have a fair amount of age to them...so it wouldn't exactly be a waste to replace them.

$80.79 + S/H from Rockauto. Wireset is $38.09 for no-name and $60 for Bosch.

This car is turning out to be more of a project than I had thought it would be. I have a horrendous squealing noise from an untensioned power steering belt right now. However, when I went to tension it tonight, one of the PS pump bolts is sheared off, and the nut on the other side appears to be permanent somehow. It's square and does not move with a 250lb guy pulling on it.

In addition to the crap running and murderous belt squeal, I also have an exhaust that scrapes on speedbumps at any speed (one of the muffler clamps got torn off already) and the ride is like I'm driving through Papua New Guinea.

Great...

[nedfunnell]

Where do you think I should look next for the crap running? I still suspect plug wires because it happens when it's moist outside. Could I have a bad coil? Why in the world did BMW cram all their plug wires in that little runner when everybody else was using brackets to provide an air gap? I watched it run with the wires out of of the runner and visible but didn't see any arcing.

[phucheneh]

Heh. That square nut is welded to the bracket.

If one cylinder is constantly missing at idle, it's doubtful that it goes away at high RPM. It's just smoothing out because of the speed the crankshaft is turning at. The miss is likely there but much harder to perceive.

You really need to isolate which cylinder is causing the problem before you do anything else. Do a cutout test- remove spark or fuel (if port injected) one cylinder at a time and observe the difference. To really quantify it, just look at the RPM drop that each cylinder causes. Alternatively, pulling the plugs might give a good indicator. If it's a dead miss on one cylinder (and ignition related), the plug will be wet with fuel.

Do you hear a constant rhythm to the misfire or are the intervals between misses more sporadic?

[manimal]

Hey Ned! Been a little crazy and havent checked at in a while. While you were at shop last week did you talk to my tech about your other issues?

I am sorry your having some trouble man. Call the shop today and talk to Evan my import tech.

Sadly most of the problems you have had I warned you about. Like I mentioned an E30 is a labor of love after all these years. Call my tech Evan and he will trouble shoot it no problem.

Is the shock we replaced last week for you fine?

Did you keep your ugly toyota as a DD? I remember telling you it was a good idea.

When I bought the 325 I spent no time on the engine since we were going to swap in something else and boost it.

Just read your other thread. Crazy about the plugs. I remember telling you to do them and wires as well as the intake boot first thing.

[Jimzz]

Cap looks ok. Check the resistance of each terminal with an ohm/volt meter but I doubt it will show bad.

The rotor look ok as well?
And the $38 plug wires at rockauto are not bad. The Beck Arnely ones for $50 are prewarped like oem but either one of those 2 will work fine.

[JCH13]

I'd check plugs and wires and make sure there's no moisture in the plug wells.

FWIW I doubt the misfire is going away at high RPMs, it's just harder to notice. I thought the same thing when a coil failed on my Crown Vic.

[nedfunnell]

Plug wires ordered, we'll see what happens when those are on.

I've got to take a look at that snapped bolt. Phuchenene, you seem to know about that: My first inclination is to try and torque that square nut enough to break the weld and take the whole thing off, broken-half-bolt and all, then just replace it with a nylock. Think that'll work? If not, I'm going to have to try and drill it out, which, just.. I hate that.

[phucheneh]

Stop throwing parts at it...for all you know, you have a piston with a hole in it. Diagnose the problem first.

I doubt you'll break the threaded bit off the bracket. At least not without risking collateral damage...would probably have to cut it. Why did the bolt break? Cross-threaded?

Maybe take a pic. Can the P/S pump be removed? And/or the bracket?

[HowlerMonkey]

Cap is servicable but worn from excessive spark plug gap.....or bad wires.

[nedfunnell]

Well, I should have listened- new plug wires didn't solve the problem. So now I've got new plugs and new wires. Since it's a moisture related issue, should I be looking now at the distributor cap O-ring?

[oldsmoboat]

Did you check the cap for cracks? Let's see the rotor.

[SpatiallyAware]

What does the coil look like? Have you looked to see if there are any specific coil issues with that car?

[phucheneh]

Originally Posted by nedfunnell

Well, I should have listened- new plug wires didn't solve the problem. So now I've got new plugs and new wires. Since it's a moisture related issue, should I be looking now at the distributor cap O-ring?

Did I miss the 'moisture-related' thing or did you fail to mention that?

So it only misfires when it rains? If so, yes, that strongly implies an ignition problem, but you could have some other less-likely electrical issue.

Coil, especially a plastic-cased, epoxy filled one, would have been the first place I looked for a random misfire. Again, though, you never pegged it down to random or cylinder-specific.

I swear, I'm trying to help here. But you gotta give us all the information and try our suggestions (re: diagnosis, not random part replacement).

Get an empty spray bottle with a 'mist' setting. Fill it with water. Spray the coil while the car is running and see if you duplicate the problem. You may also see visible cracks in the casing, but these can be hard to detect with the naked eye.

Is the coil by chance mounted on the firewall? 'Cause that makes it even more likely to be the culrpit.

[nedfunnell]

Phu: See my earlier thread: http://forums.anandtech.com/showthread.php?t=2279958
I should have linked to that one in the first post.

I'll see if I can find a mister bottle. The coil is mounted on the fender.

Since it's intermittent, it's hard to say if it's random or cylinder specific. At some times I would have sworn to you it was cylinder specific because I thought I heard "1-2-3-4-5-miss" at idle. However, sometimes, it also seems to have general sporadic misfire all over, because the engine just won't make power at all under load, not just a single cylinder misfiring. (It will happily rev high with the clutch in, though)

I went with the plugwires first because I guy I met locally who had an E30 with similar symptoms said it was plug wires "for sure". Well.

[phucheneh]

Originally Posted by nedfunnell

Phu: See my earlier thread: http://forums.anandtech.com/showthread.php?t=2279958
I should have linked to that one in the first post.

I'll see if I can find a mister bottle. The coil is mounted on the fender.

Since it's intermittent, it's hard to say if it's random or cylinder specific. At some times I would have sworn to you it was cylinder specific because I thought I heard "1-2-3-4-5-miss" at idle. However, sometimes, it also seems to have general sporadic misfire all over, because the engine just won't make power at all under load, not just a single cylinder misfiring. (It will happily rev high with the clutch in, though)

I went with the plugwires first because I guy I met locally who had an E30 with similar symptoms said it was plug wires "for sure". Well.

There is never, ever a 'for sure.' Correlation/causation and all that.

My 'for sure' advice: ignore the advice of anyone who thinks they can tell you 'for sure' what is wrong with your car without even looking at it. There are a lot of mechanics who diagnose soley based on past experiences. And they fuckin' suck at their jobs. Comeback kings.

[nedfunnell]

OK, hold on just sec- does the O-ring mount in the rim around the outside between the bolt circle and the cup inside? If so, I think mine might be entirely missing. I have a black dust shield inside and assumed the o-ring was in there.