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H i Greg,
Its NOT a header problem. Actually, I thought it was a wrongly-designed 2-1 joint problem and thats why I had a proper one made; so the exhaust system is out of the question now. When you're looking for a 'ghost' problem everything looks suspicious and everything has to be eliminated one by one!
Jim K.

I know what you mean. I had a running problem I couldn't figure out. I changed every component on the car's SDS system, sensors, computer, coil packs, etc. It turned out to be a bad intake valve causing low compression in cyl #3. Grrr...

Greg

JK,

I had a similar problem, but it was ignition related. The engine winds up fine to 6K rpm in 1st and 2nd, but in 3rd or higher it would sputter at around 6K rpm. It was a coil problem. Well in any case I have a CDI unit going in with coil over plugs, no more dissy. Doing this so that when I go to the 24V it's going to be a plug and play deal when it comes to electronics.

Can you explain why it is also gear related? Is it load related?

Yes its load related. Higher pressures inside the cylinder require higher voltage to break down the spark gap. Thats when an engine is prone to misfire. If the existing current can find an easier path than the spark gap, it goes for it!
Jim K.

Jim, hang in there. I have this 12v motor waiting patiently to be modfied for our local racing series when your book comes out.
Of all the misfires I have had only one has been non electrical related and that includes five 12v motors and six 24v motors and I must add the exhaust manifolds were far from any work of art. That particular misfire was pretty hectic and was a inner valve spring that broke.
Keep up the goodwork and its always great to read your posts.
Ps I think Baz has dissapeared. Will go past these holidays to see what he is up to in that dark room he is always in .

I had a misfire once..and she never let me forget it either.

Hey Bozzo.Got an idea for ya. Why don't you bribe your mate (the one with the chassis dyno) so you can use it for a couple of hours to do some experimentation. If your problem is load related, I think the best way to test this sort of thing out is being in a static situation whilst varying the loads. Perfect.

For my business I use a dedicated liquid petroleum gas vehicle (LPG). This thing developed a misfire (not the same chick) and it was load related. Stuck it on the dyno and very quickly identifed two faulty high tension coils on cylinders 3 & 5. While idling, there was no problem at all.

I know this is simplistic and I am hoping you haven't tried it already.

Failing that just pray to you Greek God of lightning bolts, Zues.

I'll try one more thing with the spark dept. and if I fail, in the spirit of what has been happening downtown lately, I'll torch the sucker!
Zeus' distant descendant.

I'm impressed with your persistence with the Bosch Moronic, Jim . Most would have turned coats and headed for a programmable compoota.
Cross firing type miss-fires always look like a real possibility with a distributor. As does weak spark energy from too many HT leads and other voltage dropping devvis's (read: dev-is's. plural of a devvis (dev-is), similar too, but different from a device. Dependent on the level of stupidity) like rotor buttons, distributor caps and other 'Alfa Romeo-type-isms'.
Beat said (standard Borsh) arrangement with a stick, and replace with a proper programmable computer and a direct fire ignition system to achieve max. results.
Bare in mind, said results are no relation to Max, or any of Max's immediate family.

Could also try rotating distributor anti-clockwise as much as possible before you get miss-firing at idle, so that when the engine requires maximum ignition advance, it has more of the rotor button to use without running off the end and potentially causing a miss-fire or cross-fire .

Take the average DIY who will (someday) read the book. Average means someone who wants some more power (10-20%) out of their daily driver by using most (if not all) existing parts to keep costs down. You can see this person will probably see even a cam change as radical and costly. I do have another stand-alone ecu but as you can see I'm still playing the Bosch game with the std cams, not having gone to anything like 3.3 or 3.7liters, which for most parts of the world are impractical (tax and fuel costs). I even think that using Motronic is unfair, as the vast majority of V6 cars have the old L-jet. Going for a 3.7liter 24v with Motec or similar would interest very-very few owners. I have checked this with the Italian site (almost non-existent 3liter cars) and the French site, where a cam upgrade is like halfway to the moon! Besides, there is only so much I can do within a reasonable (hahah, yeah right!) budget...Believe me, I have spent about 10 times more than any book royalties can make up in the next 5-7 years!
In retrospect, if I was going to start now, I'd do a good rebuild and port job and then I'd stuff a GG SC kit in there and forget about it! A LOT cheaper and MORE power! And I'm NOT advertising Greg here, its a simple matter of economic sense vs results!
Jim K.

A simple way to check for weak spark would be to put an MSD ignition amplifier in there.

If you're interested in trying it I have one to lend out to you (long term).
Would cost you a schnitzel though...

I wish that was the problem Mats! My JK200 CD ignition puts out more than 210mJ/spark, while the MSD HVC (I have one here and performance tested it sometime ago) will go 160mJ single spark -after ~6krpm. Its not a weak spark; spark diversion (or scatter) is what I suspect. I'll find out soon enough, probably this weekend (if it stops raining that is)
Jim K.

JimGreek wrote:Fast running out of ideas, I want to try one more thing: lock the distributor advance mechanism, as I'm running Motronic and the JK200 CD. Don't ask why...consider the rotation of the dist.rotor because of the springs/weights vs the Motronic ecu-generated advance curve. Now think of the width of the rotor outside terminal...is there a chance for crossfiring at high rpm/load? Electrically it makes sense: the spark is enough for 1st gear, but gets diverted a bit on 2nd (high load) and completely diverted in 3rd (higher load). Don't elaborate on this, you'll only confuse me but believe me this is a distinct possibility of spark wandering under high load conditions.

Jim K.

If you're still using the advance mechanism that would be a serious suspect... I had a 3.0 converted to Motronic from a 164 ( with the l-jet dizzy) once and it didn't run very nice higher in the revs. when i locked the entire mechanism it was a lot better.

Good luck with it... As for the costs of building and testing the engine, just add a few euros to the book, most here won't complain...

Heela Jim,

On the dutch forum there was something similar on two different cars.
You probably have a nice rebuild engine So I'm not saying it is related but type it down anyway.

It happened with 75 TS's which are also motronic 4.1 (but 4 cil) .... they did cut out at higher rpm when used on a track.
With warm oil and >5500-5700 rpm they started to mis beats.
These where abused/worn/>200k km engines. The problem was speculated to be a wandering of the 60-2 wheel wrt the crank sensor.
Worn main bearings .... the changing distance between wheel and sensor when you run through a natural frequency? which would make a a weak/inconsistent trigger signal at that rpm?

A scope reading of the crank sensor signal is maybe something which could help to address this. A bit difficult to do when when it only occurs under load, though....

Saluti,
M

Jim has a modified distributor I think, one with weights. The one I have is with the vacuum advance. How do you lock that? I just disconnected my vacuum advance, does that mean the ignition advance will follow my ECU or do I still need to "lock" it somehow?

I had the one with weights and springs in it. i just replaced the springs with solid wire so the weights couldn't affect the timing anymore.

I expect leaving the vacuumline of would stop it working too if it is only vacuumoperated that is.