Distributor cap shocking discovery

Post Fri Jun 06, 2014 10:10 am

Ha some cooling problems as per my other thread. Busy checking all hoses last night with the engine running, touched the head were the distributor cap bolts on, had a small electric shock.

Is this normal? Something's telling me this shouldn't happen.

Post Fri Jun 06, 2014 10:22 am

Did you have wet hands at the time? Check it with the engine running in the dark, and look for stray arcing.

This could explain your kangarooing issue - could be time for a new cap and/or rotor arm. Also check that the covers (parts 14 and 15 in the diagram below) are in place:

http://www.realoem.com/bmw/showparts.do ... g=12&fg=05

Post Thu Jun 19, 2014 11:03 am

No, the cap has no covers, I have them on my old engine so I'll take them off and get them on the new one. o arcing or anything coming from the leads.

I took the spark plugs out the other day to see their condition (only been in the engine for less than 1000 miles) and they looked fine, except two had a burn mark on one side, on the hex nut area, and there was some oil on there as well. No oil on the electrode side, just where the ht lead connects to the plug. Could this be oil leaking from the rocker cover gasket? If so:

1 - Would a leak in the rocker cover gasket cause my rough running engine?
2 - Would oil leaking into the spark plug well cause a misfire?

The misfire starts to happen when under load and after the engine has warmed up a bit. Then it occurs intermittently either when just driving normally, accelerating or just when at idle.

any suggestions for me to try are very welcome!

Post Thu Jun 19, 2014 11:12 am

Yes, the oil could be leaking from the r/c gasket. The oil shouldn't cause any misfiring problems. However, the two burn marks are a cause for concern, and suggest the HT may be arcing across to the hex nut for some reason.

Again, check with the engine running in the dark for signs of stray arcing on the affected plugs.

I would suggest checking that the engine-to-body earth strap is securely connected and perhaps trying another ignition coil.

Post Thu Jun 19, 2014 11:20 am

Ok. I couldn't see any arcing the other night but I was quite close to a street lamp so wasn't that dark.

How would I sort it if the HT leads were arcing across the hex nut? I've already changed the leads and that didn't change anything. new plugs maybe?

I have a new coil, distributor cap and rotor arm ready to put on, as mine were old anyway so they needed changing, so I'll put them on over the weekend and see if that helps.

Post Thu Jun 19, 2014 11:23 am

Did you fit genuine BMW HT leads, or aftermarket tat? And are the spark plugs gapped correctly?

Post Thu Jun 19, 2014 11:35 am

I fitted genuine BMW leads. I used the recommended NGK BPR6ES but didn't check the gap. I jstu assumed they would be fine. Should I have checked them? I'll do so tonight anyway just to see. I'll take a look on the wiki to see what the gap should be.

Post Thu Jun 19, 2014 12:49 pm

Yes, they should be 0.028" (28 thousands of an inch).

Post Mon Jun 23, 2014 9:40 am

Finally got round to checking a few things on the weekend. I found that when carefully taking the ht leads off the plugs with the engine running, I can hear the spark arc the gap from the lead to the plug. This doesn't happen on lead number 2. I changed the leads and the same thing happened, changed the coil and it was the same there also. I got my distributor cap off and there was a small crack only visible on the inside, close to point 2. Would this be causing my issues with weak/no spark at plug number 2?

I took the cap off my old engine to see if that made a difference but unfortunately that was in a worse state than mine so I haven't been able to test another yet. Going to get a new cap anyway but just wondered if this was likely to be the cause?

Thanks!

Post Mon Jun 23, 2014 6:25 pm

A crack in the cap is quite likely to cause running problems, especially under load, and is probably the source of your electric shock.
Not a good idea to pull spark plug leads off of a running engine with a modern ignition system. If the coil arcs over, either externally or internally, from the king post to the '-' terminal, it will send a several thousand volt pulse back into the ECU!

Post Tue Jun 24, 2014 10:00 am

Right ok. Thanks for the word of warning. It wasn't me that pulled the leads off. My girlfriends dad's a mechanic and I asked him to have a look at it. That's what he did. I'm not comfortable messing with engine electrical things on a car, especially when it's running! He won't be doing that again soon then!

I'll try a new cap and rotor arm and see if that helps!

Post Mon Jul 07, 2014 12:25 pm

Finally received my new distributor cap. Now there's no misfire which is great!

But now I have another niggling problem...

When trying to start from cold, on occasions it fires up for 1-2 seconds then dies. If I hold the throttle open slightly the revs jump from around 500rpm to how ever much I have the throttle open, it does this about 3 times then settles and works as normal. The only other thing I sometimes encounter which I don't know if this would be related to the problem above... If I quickly open the throttle the engine seems to choke a bit and goes down to about 400-500rpm as it's going to stall, then go back to normal and work as it should again.

Wondered if any of you guys had any idea? I have cleaned the ICV, tried cleaning the TPS but unsure about 'drilling a hole for the oil to drain out' thing I've read about. Where do I drill? And how far in? I don't have any obvious leaks, injectors are of an unknown condition as I haven't sent them off to be cleaned yet (next thing on my list). No idea when the fuel filter was changed last, I haven't changed it since I bought it a year and a half ago so I have a fresh one to go in this evening.

Any of these or other things that would cause this?

Cheers!

Post Mon Jul 07, 2014 12:58 pm

dirty injectors could be part of the problem, get them cleaned first before you drill into anything.

Post Mon Jul 07, 2014 1:32 pm

Injector refurbing is always a good idea, but check that the car is maintaining fuel pressure at the fuel rail while the engine is off. There are four possible reasons why it might not, one of which is one or more faulty injectors.
Cheap £10 fuel pressure gauge off ebay is good enough to check.

Post Mon Jul 07, 2014 3:17 pm

Ok, I was going to send the injectors to injectortune asap anyway as I might as well do this. I'll also get on ebay and get pressure gauge and search the wiki for a how to and what figures I should be looking for!

Post Mon Jul 07, 2014 4:15 pm

2.4-2.6 bar is what this guy got:

http://www.e30zone.net/modules.php?name ... 8&start=50

Bear in mind, that the M20B25 has a 3.5 bar fuel pressure regulator, so anything up to that is good; obviously, the fuel pressure will vary dependent on engine speed and load.

Post Mon Jul 07, 2014 7:27 pm

The gauge should read exactly what's written on the side of the FPR if you blip the throttle wide open, and a bit less with the engine idling. If you pull the small vacuum pipe off of the FPR, it should read what's written on the side all of the time.
In your case, the main thing you're looking for is that most of the pressure is still there the following day, before the engine is cranked.