I threw a bottle of FI cleaner into the gas tank, full bottle to half a tank (directions say full tank, so kind of a stronger dose). I thought I noticed immediate improvement but it wasn't so, the stutter remained.

Last night I replaced my plug wires (bosch, installed a year to a year and a half ago) with the old Bremi wires that were on the car when I got them. I tested the resistance across all of the wires, the Bosch wires were roughly all about 1.3k and the Bremi was roughly .95 to 1k! I'm using the proper H9DCO non-resistor copper core plugs and I put the Bremi wires back on. Taking this a step at a time so I know what the problem was once I get this fixed.

All of the plugs looked good, a few had some buildup likely from burning some oil but nothing drastic. Number six however, was wet and smelled of fuel. What could be causing that? Bad spark? Bad injector?

If the stutter at idle doesn't go away I'll be inspecting the distributor and rotor next, again, installed when the plugs/wires were installed roughly a year to year and a half ago.

Any ideas about the wet plug? I'll also note that it showed carbonization right up past the threads onto the body of the plug! It was in there tight however so I'm not sure how that happened. Again, any ideas or suggestions much welcome. I might just replace all the plugs but finding the correct H9DC0s was hard enough the last time.

Most certainly a bad plug or wire termination ... Replace that plug alone - if necessary, get any fit replacement one, just to see if it solves the problem. Clean the inside of the wire connector to remove carbon. If this solves the problem, shop for the correct spec replacement plugs.

Steve

The problem with most other fi cleaners is that they are solvent based cleaners ie, petroleum based.

Redline is synthetic, thus does a much better job than any other product off the shelf.

You have to ask yourself: if I had an ignition problem, wouldn't the "miss" happen past 2k rpm too?

If you can't order the redline from Canada, let me know and I'll send it to you. You I have clogged injectors, period. If the redline does not work, then they need replacement.

Following that logic wouldn't clogged injectors affect my performance past 2k as well?

If you look at the tip of an injector, it resembles an old school brass water hose. If you can imagine it spraying at low volume(idle), it would just kind of pee out. Without it spraying out proper, you wont get proper combustion. When not clogged, it will spray with a conical spray pattern,(think windex spray bottle) when clogged, it squirts like a squirt gun.

As you increase pressure, (wot) the hose will start to spray like a mist or something along that line. The result is proper atomization of fuel= no random misfire.

Im willing to put my money where my mouth is. Ill send you 2 bottles of redline, ($10e) or ill send you a set of clean injectors. (new are $30e)

If it does not work, I won't ask for any money. If it does, I will ask for the cost of the redline, + shipping. The injectors I value at $20 as well.

Nobody else on here is as sure about your problem as I am. I have spent thousands chasing the same stupid problem, just to solve it with new injectors. I will warn, you may have to make a small adjustment to your duty cycle, however, my car cleaned itself up after a tank or two.

A wet plug means fuel is getting there and never burning. No matter the injector spray pattern, with a proper spark and compression, the mixture will fire - and thus no wet plug. So, you have either no compression - which you appear to have - or no spark. With the plug insulator surface carbonized, there is a lower resistance to ground for the high voltage than the spark plug tip, and it is OUTSIDE the combustion chamber. Possibilities are a cracked insulator, broken plug center conductor, a broken plugwire termination, or insulator contamination. Once carbon tracks have formed, you will not be able to clean the plug satisfactorily. Replace that plug, clean the plugwire end, and see what happens.

I have had injector, plug, AND plugwire failures over the years in our M102, and no matter what injector issues you may have, a wet plug is an ignition issue.

Steve

I've had a slightly rough idle since I got the car at 62k miles. Now 129k and never have figured it out. All ignition components, all fuel components minus pumps including rebuilt and flow tested fuel distributor. Perfect compression perfect leakdown. All vacuum hoses replaced. All engine + trans mounts....

I just gave up and feel like its just part of the CIS-E system's imperfections. Drives fine soon as on the gas and I get 18-20mpg average.

Checked the distributor cap and rotor yesterday, it appeared as though there might have been a bit more wear/corrosion on the number six wire .. I lightly sanded all the contacts in the cap and the brush on the rotor and put all back together. Driving to work today, engine got up to temp .. stop and go traffic .. smoooooooth idle! But, this could just be a fluke so I'll put the celebrations off for now and put some more miles down before calling it good. There is still an ever so slight stutter, but it's basically how the car has always run, certainly nothing like how it was. That slight stutter is hardly noticable and when it's absent you can't even tell the engine is running, this in drive too!

might seem like an obvious question.are you running 91 octane?

Yes. Only the best for the benz.

Ok, drive home stutter returned. boooooooooooooourns

Still, I didn't replace the distributor, I only cleaned it up. The stutter is definitely not nearly as bad as it was so i think I'm on the right track.

And thank you Lorainfurniture for the very generous offer but I wouldn't feel right it. I do believe that injectors would improve the car's performance and likely the fuel economy, which is really poor right now but I do think there's an ignition issue causing the stutter.

What I don't understand is why it runs good cold, but not hot. Does the resistance change in the cap or rotor? Tolerance? It's not an open/closed loop thing because the stutter is there when coolant temp is below 80 on a restart but not on a cold started engine. Warm start kind of situation where the coolant temp is not 80 but not cold, stutter is there.

Hey smp

Ok, I finally remembered my password, been since 2008. :-)

Watched your vid, that is not a stumble, damn she falls on her face. Just some ideas since we are systematically troubleshooting. :-) I read through what you have done so far, actually you're ahead the game, good going.

1. EGR - yup if it won't hold a Vacuum it's done. Don't know if cleaning would do any good. You can also pull the vac line, depress and then hold you finger over the vac line fitting and the diaphragm should hold open. But, the EGR only is working when fully warm. Disclaimer, I own a 2.3 and thing are the same for a 2.6 but the way they get there can be very different. I see yours attaches to a box on the firewall where as mine is fed over the valve cover and up front to a Vac/Temp valve. When cold, the Vac/temp valve is closed anyway. Test is to rev UP and quickly pull the vac line and you should hear the EGR slam shut, takes a few times to be sure. But for now, you have blocked it off.

2. 50% Duty Cycle - is that fluctuating around 50% or locked. She must fluctuate once full warm. Locked at 50 is an O2 fault. I know you replaced it, might have a bad connection??

3. Vac - 13-15 is low with a real vac gauge on a running engine. I can't relate to a static vac using a pump. Can you get a reading with the mity vac with the engine running, or it's only a pump. I don't see how a pump could even work, you have a great big leak at the Air Flow sensor so I must be misunderstanding how you are using it.
14-17 and a steady Needle implies a Timing Issue. Good is 17-22 Hg on a healthy engine and your compression numbers look real good.
Cool link on how to use a Vac gauge, old school stuff before OB2 code readers.
Intake Manifold Vacuum Tests


4. I don't think just one injector could cause this, meaning your #6. This is a major air/fuel issue.
Here is an interesting link almost exactly how you are going about it. He found the air flow boot under the Air Flow sensor bad. You can see how he was chasing just as you are. Good possibility. I dont' know what MB he has. The manual pics are really bad. You can see the part at ********az 2.6 fuel/air Air boot.
Hesitation, KE-Jetronic problem? - Page 2 - MBClub UK - Bringing together Mercedes Enthusiasts

I think I would start with a smoke test. $1 cigar and 2-3 feet of vac hose that will fit on the fitting you found on the intake manifold. Block off the intake, mmmm tape or saran wrap/rubber band or a surgical rubber glove. block off the hose/ valve cover to air cleaner.

You can build a smoke tester from a garden hose sprayer but a cigar works very well. Take 4,5 or 6 blows, don't have to blow hard just give it some time.

Next plan we already discussed the importance of a smooth air flow sensor, must be clean. I am thinking IF not an air leak then the air flow sensor and it's relationship with the potentiometer and even the EHA.

Seems by the vid your ICV is not functioning 100% either but it might just be this Air Boot and the ICV can't keep up.

A lot of ignition issues can change as the engine heats. I would still replace that bad plug - you have a spark leakage issue there. The contamination may be getting more conductive as the plug heats. Also, the ignition coil tends to weaken with age, and heat makes it worse. Worthwhile replacing if the plug alone doesn't solve it.

Steve

Sorry, no way one bad plug/wire/injector would cause the main issue of no acceleration. It's a air/fuel issue and not getting instant fuel enrichment. It starts OK, the idle doesn't seem all that bad at this point nor does is sound that bad on slow increase in RPM. If it's bad then of course change it but it won't help much.

IF you had a well running 6, you could pull a plug wire off , now a dead cylinder and it would rev up better than the video.

1. For a "to the floor" response. You also need to check the Throttle Switch function of full closed and WOT. And the Decel Switch wouldn't hurt either.
2. I would still Smoke test for VAC leaks.

3. Sticking Air Flow Sensor and then
a. The potentiometer or Air flow Position sensor-
b. The fuel distributor "Plunger" could be leaking or sticking. Not so easy save for last.
4 th item that controls acceleration is the fuel pressure regulator.