Misfires at 2500-3000 rpm :-/

[Ulf]

My patience is wearing thin after almost 3 consecutive years without a fully functional car...
Here's the whole story, which hopefully will narrow down the options:
Summer 2017 - the car began to run erratic, with quite a few misfires - especially when warm and in traffic. I tried replacing the ballast resistor, leads and the coil (red Bosch), but to no avail.
Took it to a mechanic who came highly recommended - one of the precious "old boys", he kept the car for almost 4 months just to replace the condenser, rotor arm and the small air filter on the injection pump. He also left the car outside in the rain (it was soaking wet when I finally got it back in October), but at least it ran great except for a little hesitation between when the CSV cut out and the car was up to its full running temperature. But totally acceptable.
Spring - autumn 2018, started out great for about a month or so, then the car began to cut out completely when it got warm. I was able to restart it, but after a couple of miles, it would die on me again. Both the CSV and the WRD seemed fine, same was fuel flow. After a few tries it wouldn't start at all. Took it to a new mechanic this time for obvious reasons, who checked everything: fuel flow, return line, CSV/WRD etc. and ended up saying that the culprit could only be the injection pump. Great... So this was replaced with a reconditioned unit from Tower Bridge diesels (reputable specialist in the UK). While this was underway, he also mentioned that the condenser, points and rotor replaced by the previous mechanic and the leads were all wrong, so these were replaced again. The new pump arrived and was installed, but the car didn't run right at all - after a few trips back and forth and several adjustments, it finally ran 95% ok - a few hiccups here and there. The explanation given was that the distributor shaft was worn and wobbly, so after garaging the car for the winter, I ordered a 123 ignition based on his reccommendation as this would surely fix the last 5% and make the car run great...
Spring 2019 - took the car out of its winter storage to have the 123 fitted - big mistake... After trying and failing 3 times now, the car is still not there - it starts great and runs really well (although a bit sluggish) up to 80-90 km/h, but then the misfires starts again especially when I try to maintain a steady speed or accelerate gently. The vacuum line is fine and the plugs are brand new, so I'm completely lost here as to what could be wrong and for the first time in 12 years of ownership, I'm considering giving up ;-(

Any ideas or things to check will be greatly appreciated

Ulf


 

[Benz Dr.]

Here's my problem with all of this: several items have been changed so which one of those items are at fault or is it something entirely different?

Let's go through this one item at a time.

What spark plugs are you using?
How much resistance do you have on your coil wire and ignition wires?
What is your total ignition advance at 3,000 RPM with everything hooked up?
Are you running 1 liter in 15 seconds at your return line?

Start with those and see what you find.
Do you have at least 10 PSI fuel pressure? 15 would be better.

[Ulf]

Thanks Dan, that's why I posted the entire story to give the full picture, will ask my mechanic about the things I don't know.

What spark plugs are you using? Brand new Bosch - bought from SLS, will pull one out tonight to give the full specs :-)
How much resistance do you have on your coil wire and ignition wires? No idea, but the one I replaced myself had resistance in it (weak sparkI, which the new ones does not
What is your total ignition advance at 3,000 RPM with everything hooked up? Will ask him, how many degrees should it be?
Are you running 1 liter in 15 seconds at your return line? Haven't measured it, but when I tried last year it seemed like a LOT
Do you have at least 10 PSI fuel pressure? 15 would be better. Pass...

I'm mechanically inclined - I wish I was... :-/

Ulf

[Ulf]

Sorry - spark plugs are not Bosch, but these from NKG: Copper Core Spark Plug BP7ES

[Benz Dr.]

Those are very cold plugs. I use NGK BP5ES.

[wwheeler]

Be careful when selecting the heat range. Not all brands follow the same rule in regards to heat range. See example between NGK and Bosch. Very confusing and I found out about this the hard way.  Scroll down a bit to see the chart.
https://matchlessclueless.com/mechanical/ignition/spark-plug-temperature/h

[Shvegel]

Speaking as a lifelong mechanic I am afraid you are starting to run up against a mess.  This can be fixed but you will have to find a mechanic who is both talented and willing to start over.  Somebody missed something along the way or created a problem that needs to be found.

[Ulf]

Speaking as a lifelong mechanic I am afraid you are starting to run up against a mess.  This can be fixed but you will have to find a mechanic who is both talented and willing to start over.  Somebody missed something along the way or created a problem that needs to be found.

I completely agree, but there aren't that many to choose from anymore as most of the older ones are retired and the young ones are inexperienced, but I have tracked down a former Mercedes mechanic and w111 owner who's willing to take a look at it once the brake issue (see other thread) is fixed, hopefully end of this week or early next week. Whenever I meet other Pagoda owners here, they complain about the same lack of competent mechanics, so perhaps I'll widen the search to find one in northern Germany or southern Sweden instead...

[ja17]

I would check the fuel pressure while the engine miss is occurring. If the fuel pressure drops, its fuel delivery problem. If the fuel pressure does not drop, go through the ignition again.

[Ulf]

I would check the fuel pressure while the engine miss is occurring. If the fuel pressure drops, its fuel delivery problem. If the fuel pressure does not drop, go through the ignition again.

How's that done on a practical level?

Br

Ulf

PS: I bought the hotter spark plugs as Dan suggested and they seem to have taken the edge of the misfires :-)

[boterinse9]

Hi Ulf   Im new to this site just got verified been reading all the good stuff I have a 70 280sl 180 silver had it since 95   never ran 100% after warming up always ran rich found out that  the previous owner ha played with the fuel injectors adj  got that straightened out passed the pollution test with flying colors  ,  took out the factory plugs a few yrs later and installed a set of E3 spark plugs the result was great it felt as if i got a push from a Corvette car runs great at 50--75 mph no missing smooth as silk  Also made a linkage adjust  learned that from  a Dutchman Kent Bergsma Check out his web site    [  Mercedes source.com ] he  is working on a red 280 sl   named HAPPIER  he shows the rehab  he is a great help  ,,, hope this will help you some  but those plugs  really made me a believer  no more stalling and stuttering at the light or shifting to neutral...     hope the message makes it   im a novice at this hi tech crap  lol    regards...

[teahead]

maybe take out the injectors and have them tested?  For spray pattern, etc.?

[russelljones48]

Not sure I can contribute much here as to the specifics of the car and your problems but here's some things that are common to most/all engines.  You haven't mentioned the results of a "leakdown test".  That will tell you if there are any problems with the rings and valves.  Any good mechanic should be able to perform this test.  A compression test is not as good.  Based on your description I think this test will show that everything is OK but it's almost always worth doing and will verify the basic "health" of the engine.

Since you seem to have run into a couple of "guess and replace" mechanics I would recommend that you find a mechanic who can actually diagnose the problem BEFORE making any more changes.  This is a repeat suggestion but here's some suggestions as to how.  There are most likely only 2 possibilities for your problem if the leakdown test shows all cylinders as "good" - a faulty or irregular spark or a change in the A/F ratio that is sufficient enough to cause a misfire.

The distributor can be pulled and fully tested on distributor machine.  Make sure the next mechanic has one (or access to one) and knows how to use it and understands the results.  The only other components of the ignition system can be similarly tested (coil, wires, plugs, ballast) but it seems all of them have been replaced already.  Have the mechanic check that there isn't a loose or frayed wire in the primary circuit to the ignition as well.  You want the mechanic to tell you how he would test the component and what the results are and should be..

Second possibility is fuel - or more specifically A/F ratio at your specific problem rpm range.  Some good suggestions have already been made here and I'm a novice with the Bosch mechanical injection.  And it seems that many of the components have been replaced.  However, what's been replaced would most logically impact all cylinders.  I would want to know if it's a particular cylinder that's failing.  Find a mechanic who can determine which cylinder(s) are failing and ask him how he/she would do that.  Post it here for commentary.

Make sure you take the next mechanic out for a ride and that the problem occurs.  SInce the problem seems intermittent this is critical.  Have the mechanic tell you what he/she thinks is the problem and what/how they would test to verify the failure of the component before anything else is done to the car.  Be willing to pay for his/her time and post the discussion here for commentary.

This is a very smart bunch of folks with lot's of experience - let them get you back on the road with a reliable car you can enjoy

[Ulf]

UPDATE - This issue is now cured by my new favourite mechanic, who found out the 123-distributor was defect and rebuild my old distributor with new bearings etc. fitted it with Lumenition, adjusted pump settings, timing etc. Car now runs great and the 123 will go back to the seller - hopefully for a full refund :-)

Thanks for all your valuable input

Ulf

[Cees Klumper]

Congratulations on getting it sorted, finally. Sounds like you did have multiple issues going on since the 123 ignition was not introduced until sometime during this journey. Hope you get to enjoy the car some more before winter sets in.

[cfm65@me.com]

Hi Guys,
Has anyone else had problems with a 123 Dizzy?
The one on my E Type seems to have the same problem, jerking at around 2500 rpm.
The one on my Pagoda is 100%
Regards
Chris

Wonder if I can swop them around?

[Tyler S]

Chris, Make sure you are using a 1.8 ohm coil or above. No ballast resistor/primary resistance wire in the circuit. Also I have seen 123 distributors take out coils and secondary ignition components that were probably on their way out before the switch.

[teahead]

Ya, 1st I've heard of anyone having a 123 defect.

Usually it's due to installation/configuration/wiring problemos.  And/or you're using the "E" curve and your emissions equipment (speed relay, etc) not working for those who came from 062 distributors.

[Shvegel]

I used to be a trainer for BMW.  They allowed me to give a talk on electrical diagnosis called 7 Ways To Step On Your Own "Manhood".  One of my bullet points was "New Means Never Ever Worked."  Pretty much why most manufacturers us the phrase "Replace with a known good unit."  You mechanic obviously is aware of my first bullet point "Trust Someone Else."  When someone brings you a problem and they say "I checked this and I checked this." Smile, nod your head, wait until they walk away then start over because they probably missed something.

[Mike Hughes]

I used to be a trainer for BMW.  They allowed me to give a talk on electrical diagnosis called 7 Ways To Step On Your Own "Manhood".  One of my bullet points was "New Means Never Ever Worked."  Pretty much why most manufacturers us the phrase "Replace with a known good unit."  You mechanic obviously is aware of my first bullet point "Trust Someone Else."  When someone brings you a problem and they say "I checked this and I checked this." Smile, nod your head, wait until they walk away then start over because they probably missed something.

... and what were the other five bullet points?  Those two certainly reflect automobile business realities pretty well  ;^)

[Shvegel]

Trust someone else.
Trust yourself.
Trust your equipment.
Ignore the grounds.
Use the wrong diagram.
New means Never Ever Worked.
Ignore that it came from a body shop.

I had all my students write down my phone number then told them if they hadn't committed all 7 in 6 months to call me.  No one ever called.

[Benz Dr.]

I had a 350SL in a while back and the thing would not accelerate. It ran OK but had no power under load but as soon as you let off on the gas pedal it would smooth out nicely. When ever I see electrical tape or crimped on ends I start getting suspicious.

 In this case it had a new throttle switch which I promptly ignored because, well........it was new, right? Well, it was a piece of junk. Replaced it with an old dirty on the outside looking one and the car took off like a jack rabbit! One of the fastest D jet cars I've ever driven. Man what a sweet drive.......

It went from awful to awesome in one fix.   

Reminds me of the three great truths after age 60:

never pass up a chance to go to the bathroom
never waste an erection
and never trust a fart

[cfm65@me.com]

Thanks Gents,
You inputs are much appreciated. I have swapped coils some time ago.
I am on my way to a six month visit to the UK, today.
I will only be able to look at the problem in February next year.
Regards
Chris

[zak]

Dan, you are a wise man....