Missing over 90

[goldiloxgirl]

Hi All, my P38 (2000 model) has quite suddenly developed a random (every 15~45 sec) heavy miss fire when traveling over 90 kph. Now here's the clue: because I was pressed for time as I've a desert trip approaching, I had a major lubrication service performed by an express lube place...and they replaced the spark plugs (sourced by myself from Karcraft) and the high tension leads (which they supplied). It would be easy for me to think "ahhh, obviously one component is faulty" but I wonder if the miss may not have been there all along and merely stood out once everything was running back on specs?

Anyway, before I go changing one piece at a time (which would take a while as I then need to go somewhere to test it at speed), I thought I'd ask if anyone had experienced something similar. I know I could simply find a suitable stretch of road and keep pulling over to change everything one part at a time but every time I pop the bonnet on the side of the road I usually have well intentioned BMW driving accountants stop to rescue me..., now that's giving me ideas....mmmm.

Regards,

Lani

[adm333]

You mentioned that you have a Faultmate.

I don't, so not only am I jealous, I have no idea what functionality they have.

Can you use it to monitor the engine running to at least give a clue where the problem might be ?

One other trick that can be used to see if a high tension lead is arcing out is to observe the engine running in the dark, so you can see any flashes of light or sparks (not sure if that's applicable here)

However, as a starting point I would double check each of the high tension leads to make sure they are all seated properly at both ends. If this is done in haste (as it may be at a Kwikee Lube) the connection may be bad.

Good luck

[PhilipA]

Hi All, my P38 (2000 model) has quite suddenly developed a random (every 15~45 sec) heavy miss fire

I am not expert on 38As but if you have a heavy misfire every 15 seconds its more likely IMHO to be involved with fuel than ignition. If one cylinder were dropping then 15 seconds at 90 Kmh is every 500revolutions or so and 45 seconds is more than 1000 revolutions.

I know if I have a miss on a single cylinder in my RRC V8 you cannot feel it at those revs, the engine just feels a bit soggy.

Alternatively maybe one of your coils is faulty and you are dropping 2 cylinders at once which probably would be noticable. There should be lots of posts on how to tell, but AFAIR they drool.
Regards Philip A

[wayneg]

However, as a starting point I would double check each of the high tension leads to make sure they are all seated properly at both ends. If this is done in haste (as it may be at a Kwikee Lube) the connection may be bad.

Good luck

I would be looking at the leads also. The Thor engine has the coil packs in a pretty inaccessible spot at the rear of the engine which makes fitting new leads very fiddly and not easy to connect firmly. Also the type of fitting on the coils is different to the usual generic types readily available as universal fit. The Generic type leads will fit the plug end perfectly but although they will fit the coil connection it is not a good fit and the lead will really only be held in place by the rubber boot. If you have the old leads at least check the terminations are correct.
In my experience having just one cylinder not firing is very noticeable at whatever speed. The ignition leads on the Thor are a known weak point.
The Lead with the white ceramic insulator is the correct type.

[goldiloxgirl]

Thanks guys. I had checked the connections and they seemed okay but if the leads are inappropriate I will have to look at changing them out for original ones.

I don't know about the fuel as that was not altered during the service. I also don't know if the Faultmate can help me unless there is an actual fault logged on the car's computer but Paul would have a better idea on that.

I will cross over to the dark side tonight for an ark test and post my findings.

Kind regards,

Lani








QUOTE=wayneg;1297084]I would be looking at the leads also. The Thor engine has the coil packs in a pretty inaccessible spot at the rear of the engine which makes fitting new leads very fiddly and not easy to connect firmly. Also the type of fitting on the coils is different to the usual generic types readily available as universal fit. The Generic type leads will fit the plug end perfectly but although they will fit the coil connection it is not a good fit and the lead will really only be held in place by the rubber boot. If you have the old leads at least check the terminations are correct.
In my experience having just one cylinder not firing is very noticeable at whatever speed. The ignition leads on the Thor are a known weak point.
The Lead with the white ceramic insulator is the correct type.[/QUOTE]

[Rupert Prior]

if you can make it to the Bexley area i can do a free diagnostic with a scope, gas analyser and a code reader. it sounds like they may have fitted leads with the wrong resistance.this produces low coil output and can damage the ecu.

[goldiloxgirl]

Well Mr Admin Triple Three, you are spot on the the money. Yep, you deserve the meat tray tonight. A quick look and see after crossing over to the dark side revealed a light show rivaling the New Years Eve Fireworks Display- your choice of city. It was so pretty but under my bonnet is not the place for Auralis Range Rovis.

Thank you very much and enjoy the meat tray. :arms:

Kind regards,

Lani

Ps. I didn't have any BMW driving accountants stop to assist but I did get some pretty good help from the guys at AULRO :)



You mentioned that you have a Faultmate.
I don't, so not only am I jealous, I have no idea what functionality they have.

One other trick that can be used to see if a high tension lead is arcing out is to observe the engine running in the dark, so you can see any flashes of light or sparks (not sure if that's applicable here)


Good luck

[PeterH]

"It was so pretty but under my bonnet is not the place for Auralis Range Rovis", cracking me up here :)
Glad you found your culprit, hope you get to the bottom of it.
I had a set of custom ignition leads made up for mine, from a place called Performance Ignition Services in Nunawading, Vic.
They do Magnecore leads as well, but after a very informative chat with the expert, I ended up getting a set made up using Belden ultra low suppression cable.
It ended up costing around $13 a lead from memory, not over the top in cost.
They made a noticeable difference in performace compared to the old crappy leads that were on there, it felt much more responsive and solid to drive.
They are not THAT hard to install as some people suggest, it is a bit tricky reaching around the back of the engine and feeling your way around, maybe one of those telescopic mirrors would be a help with seeing what you are doing.
I found it hard to follow the lead diagram until I made up my own as viewed from the front of the engine. That made things much easier.
Cheers, Pete.

[adm333]

How do you know I'm not an accountant who drives a BMW during the week ???






Simple: an accountant would never have anything to do with a P38, the numbers just don't add up !!!

[goldiloxgirl]

A closet BMW Accountant... my worst fears have been realised, lol :D





[QUOTE=adm333;1298458]How do you know I'm not an accountant who drives a BMW during the week ???

[adm333]

Shoot me now.