ongoing misfire ideas please

[rob walker]

With the new axle I am having to use the right foot a bit more to get the same acceleration. With the additional loading the misfire that I have been plagued with the purchase now has become more pronounced.
Roger Edwards checked the timing, stripped and cleaned the fuel tank with new filters, and ran the car for a while and felt there was no recurrance of the misfire.
However after 20 minutes of motorwary driving, as soon as I load the throttle at 3000 rpm or more I get this misfire.
I am coming to the end of my patience, the car has had electronic ignition fitted, reconditioned fuel injection pump, new plugs and leads etc.

Please all you technical gurus....any ideas, this really is ruining my experience of Pagoda ownership.

[Allenh]

Rob,  Long distance troubleshooting this type of issue is very tough.  1st, does the misfire feel as if it is a single cylinder, or is it staccato like?  IS it a "misfire" or does the cylinder consistanly NOT fire, go dead?

It would be imperative to first identify which cylinder is affected.  Then one could investigate further.  I have had a number if these 6-cyl engines apart in the past and they are very well built, I have seen this issue on other brand engines with aluminum heads when the valve seat insert comes loose in the head and floats.  Its isn't likely this is your problem, but starting with identifying the cylinder accurately is a big start.  If this was a problem before the tuneup work, those items are not the issue, it is deeper.  You will have to dig.

 

[rob walker]

Its more of a hesitation, once I get her up to running speeds and move to light throttle, the hesitation goes away. Push the throttle down more and its back.
Head came off at last service to cure a weeping head gasket and all was well inside

[Klaus]

I had the same misfire at >3,000 rpm when I had the Pertronix electronic ignition installed. Went back to the original points and everything is fine.

[rob walker]

I had the same misfire at >3,000 rpm when I had the Pertronix electronic ignition installed. Went back to the original points and everything is fine.

Klaus thanks..very interesting!

[JamesL]

have someone check the resistance on your rotor arm in the dizzy

Sounds odd but I had similar problems and the resistance was waaay up (believed to be fragmenting?)  so they popped a new rotor on and it's running really nicely now.

[bjudd]

I put the Pertronix in last summer and found that setting it to specs didn't do the trick.  It was fine without pushing it but when I did accelerate quickly it would miss.   My porsche mechanic friend drove with me to adjust it.  We would accelerate, feel the miss; he'd get out of the car & make a small adjustment of the distributor by feel then drive another couple hundred yards.  did this 4 or 5 times  making small adjustments and had it just right.  running perfectly since then.

[jameshoward]

Rob,

So are you using a petronix set-up?

James

[rob walker]

James, I am actually not sure which electronic ignition was fitted. The work was done by Silchester, when I first bought the car to try to solve the initial misfire. After fitting, it ran most of the time OK with some trouble starting and occasionally misfiring. However when the car started to go into RE, they immediately said the timing was wrong and that is the reason for the difficulty in starting. They reset the timing to correct settings, which has made starting easier and unloaded running better but as soon as I load the throttle at anything over 3,000 rpm then the misfire or more correctly hesitation sets in.
I will check with Silchester which system they use.
Looks like my summer vacation plan which was to be running around the South West in the Pagoda will have to be changed to a eurobox as I do not think I am comfortable doing such mileages until its solved....depressed in Devon

[rob walker]

Having read the 123 thread, I feel I maybe have an idea of the problem. Instead of misfire if I call the feeling a hesitation.
The previous "specialist" fitted electronic ignition due to the fact they said the distributor was worn, which they put the hesitation at about 3,000 rpm down to and electronic ignition would overcome the distributor wear.
Whe Roger Edwards checked the car they said the ignition was advanced a huge amount and this caused difficulty starting. However since resetting to correct advance the hesitation at 3,000 rpm is even more pronounced.

Has any one else expeienced this with a worn distributor, what are peoples experiences of the 123 ignition?
This presumably replaces the whole distributor is that correct?

[PnHi]

Rob
I add this as not attempting to diagnose your problem, but to pass on my experience.  I had a similar problem with my 250 and came across a used distirbutor on ebay.  I doubt I paid $25.00 for it in 1999.  Cleaned and lightly lubed it. Fitted new points and condensor,  installed it and made some adjustments over half a day.  Ten thousand miles later I haven't touched it since.  I have never redlined the 41yo motor, but I have pushed 5.5k many times.
Good Luck
Mike C
1968 250SL
Dark Olive/Cognac

[ja17]

Hello Rob,

Yes I remember when Klaus had this issue. As he said going back to the original ignition solved the problem. A defective ignition coil will also give these symptoms.

[waqas]

A defective ignition coil will also give these symptoms.

Joe, how does one go about testing whether or not the ignition coil is working correctly? (besides the swap-out 'technique')

[rob walker]

Thanks guys, some good information to go over with Roger Edwards in an attempt to find a solution.

[Nosilw]

As I installed a Petronix kit into my car I dropped one of the nuts down into the distributor.  When I retrieved it I loosened one of the springs that control the advance.  I reconnected the spring it but stretched it a little in the process so it was no longer "tuned."  As a result the car would run fine at low speed or when I was static testing it but would misfire when under load or during rapid acceleration.  If the car was brought up to speed slowly it behaved fine.  I had the distributor rebuilt and in conjunction with the petronix it has run great since then (over 7 years).  A second thought would be the vaccum advance has some issues and it is causing your misfire - the distributor timing is not advancing properly and misfires are resulting.  Two long distance, little information, possibilities.

[ejboyd5]

Coil.

[paulr]

Hi Rob

a few things to add to the mix.

I have a 123 and it's fine although I have had some problems with misfiring too. I have to assume that the 123 is working correctly and that it is just an intermittant niggle. RE  are reluctant to really admit that further more intimate relations with the engine will bear better results than they have been able to ordinarily achieve and perhaps next time you have a tune up the mis fire has mysteriously disappeared. I love the guys at RE but think I might try someone else just to see what they do when asked to deal with this kind of problem. Just because RE are good they might not be the best all the time, especially when they are busy. I often find bits missed, tools in the engine bay etc.

Silchester are NOT one I would go to...oh no ! I can't remember the name of the guy that used to be in Swiss cottage that has moved to the NCR. He was in Mercedes avenue. I'd try him..nothing to lose.


I wouldn't worry too much about a 3000 rpm splutter on the way to Devon. I do it often and have rarely had any worries.


I hope this helps a little.

[Cees Klumper]

Hello Rob - having read through the thread, some thoughts.

I have had a few intermittent miss / hesitation problems over the years. The causes were:

- spark plug wires
- the spark plugs themselves
- somewhat loose bracket holding one side of the linkage rod going over the valve cover
- an incorrect distributor type

So most of the time, but not always, it was ignition related.

In your situation, I would seriously consider putting in a 123 ignition module; for starters it will eliminate the distributor and ignition settings as possible culprits as the 123 replaces the entire distributor and points. Even if this is not the cause of your problem, the engine will most likely run smoother no matter what else you do. I have found it a very worthwhile upgrade that I did last summer, even though my engine was running fine before the swap. Do make sure the vacuum line that governs the ignition advance is functioning properly because that is one element that the 123 cannot rectify and also depends on. If you have not tested / replaced the coil, that would be another important step, along with testing the wires. The 123 comes with a new cap and rotor. Replace the spark plugs.

I would check, or have RE check, the fuel injection linkages.

Hope this helps!

[rob walker]

Paul, Cees. Great thanks for the advice. Rob

[rob walker]

Paul, Cees. I think I will go for the 123 just from a piece of mind and will change the coil and leads, so I erradicate the electrical side of things. Not sure if the fuel pump could be erratic?
The main problem I have had with RE is that I am always short on time as I have to get the car back to storage and flights back to Turkey for work, so I can never spend time with them going out after the work.
I think in reality I will shelve the work till next spring when I will be back in the UK (and Spain) full time and can work through this more easily and under less time pressure.
I have another toy I can use in August so not so critical.
Rob

Hi Rob

a few of things to add to the mix.

I have a 123 and it's fine although I have had some problems with misfiring too. I have to assume that the 123 is working correctly and that it is just an intermittant niggle. RE  are reluctant to really admit that further more intimate relations with the engine will bear better results than they have been able to ordinarily achieve and perhaps next time you have a tune up the mis fire has mysteriously disappeared. I love the guys at RE but think I might try someone else just to see what they do when asked to deal with this kind of problem. Just because RE are good they might not be the best all the time, especially when they are busy. I often find bits missed, tools in the engine bay etc.

Silchester are NOT one I would go to...oh no ! I can't remember the name of the guy that used to be in Swiss cottage that has moved to the NCR. He was in Mercedes avenue. I'd try him..nothing to lose.


I wouldn't worry too much about a 3000 rpm splutter on the way to Devon. I do it often and have rarely had any worries.


I hope this helps a little.

[knirk]

Rob,

It may have nothing to do with your problem, but it's a very easy thing to rule out.

I had misfires a couple of years ago. One member suggested to disconnect the el cable to the the fuel shut off relay on the IP. So I did and the problem went away. You can give it a try.