[CodyItaliano]

The car runs fine overall now with the new distributor cap and rotor, wires, and new plugs. Although, I still suspect a weak ignition coil. It is original.

Anyway, the car is running rich. That throws off the O2 sensor making it bog. I can spray brake cleaner into the throttle body, and will clear up for a minute. But then starts running rich again. Has a new O2 sensor also.

Maybe not burning the fuel completely could be the problem? Maybe I need to adjust the Lambda setting? Don't even know if that's possible on my '91 420. I just know its running rich. As much as I drive, I really don't see a fuel mileage problem, but it could be better.

I was smoking sometimes, where I thought I was burning oil, but its definitely just running to rich. The smell gives the smoke source away. And of course, there's the sooty plugs. Not oil fouled. Before the wires were changed, it was fuel fouling the plugs bad. The wires were again, original.

Last part of the ignition that isn't new is the coil. I have two EZLs and they are both in good working condition, and swapping them makes no difference.

There was one other thing, there is a coolant temp sensor, the one on it intake on the left hand side of the car. It is a 4 contact one that will affect ignition timing and fuel adjustments. It was just a little out of OHM spec when I tested it last. But only slightly. I may go ahead and change it anyway.

 

[drswiger]

Have the same problem. Hate the smell

 

[CodyItaliano]

Went ahead and just ordered the coil. Might as well, mine has been on the car for 177XXX miles. If that doesn't do much, next step is looking into doing more testing, and/or just replacing old original sensors. I even had looked into the EHA adjustment or replacement.

I did however spray some cleaner into the intake, it did help. I just hope the computer that I have in the car now isn't going bad. I was used. Came out of a car with under 80000 miles, don't remember the mileage. It had improved the performance quite a bit compared to my original computer.

 

[drswiger]

Went ahead and just ordered the coil. Might as well, mine has been on the car for 177XXX miles. If that doesn't do much, next step is looking into doing more testing, and/or just replacing old original sensors. I even had looked into the EHA adjustment or replacement.

I did however spray some cleaner into the intake, it did help. I just hope the computer that I have in the car now isn't going bad. I was used. Came out of a car with under 80000 miles, don't remember the mileage. It had improved the performance quite a bit compared to my original computer.

Am I correct that you had changed the O2 sensor? Did that help at all?

 

[CodyItaliano]

I did replace the O2 sensor, twice. The first one had a slow reaction time.

I can't find any other sensors between the intake and the O2 sensor that would be affected by cleaning particularly. There are position sensors, but nothing that I can find that spray cleaner should make work better except the O2 sensor.

I just going to install the new coil tomorrow and see if I see an improvement. Being this is a CIS-E system, it is screwy as hell.

I have even thought about what else can make it run rich. Maybe the fuel accumulator? Mine did smell of fuel on what I'd say is a vacuum port, that runs to the right side valve cover breather. Although, I don't see how much vacuum is applied. The part I'm talking about is at the side if the fuel distributor. It's about $100 or so. I also noticed a while back that the pressure regulator back by the pumps does not have a vacuum line connected, but all I could find was a pinched off hard metal line. I plan to investigate that by looking at another car like mine. There's actually one next door to my shop that is just sitting, that they couldn't figure how to bleed the rear brakes. I'm sure they won't mind if I have a look under there.

Just never have taken the time do get around to these things until now. Things have been going well, so I'm more motivated for some reason.

Hopefully tomorrow, I can install that coil and get something good out of it. Until then, I won't know. But I'll post up my results.

 

[Teutone]

Tried leaning out the air/fuel mixture?
Are spark plugs burning uniform in color?

 

[CodyItaliano]

Yes, the plugs are pretty uniform each time i've looked at them, until this last time before I changed the wires. All were the same except for the wire that wasn't producing much spark.

Now for the fun stuff. There were two models of the ignition coils listed for the W126, 86-91 models. Mine uses the first one, but the second one was listed, and is what I got. I've ordered the correct one that will come in tomorrow.

Notice they are mirror images of themselves

0221502433 or 00086

0221502435 or 00087

 

[CodyItaliano]

Well, I did replace that coil. It did improve power and I now have a perfect idle, and great exhaust note. No more lumpy sounding exhaust! So I can only assume that the original coil was a little bit weak. Not dead or horribly bad, so I'm keeping it as a spare. Just in case.

Now, for the rich running, it isn't as bad. Maybe I will clean and gap the plugs a bit wider. I have them set at .035 in., and I've seen other people say to gap them at .042. I was just going by my owners manual. On most every car I've had, I like to set the gap at .040, so since it's not too hard to do, I may try it.

But I have a feeling that there's something else needing fixing. I haven't had any luck getting the ball out that caps off the adjustment screw for the fuel mixture. Maybe I should even consider replacing the EHA? I did however notice, while pushing down on the metering plate that there is a bit of fuel running down inside. I assume there is a pintle of some sort that is leaking under the fuel distributor. I only noticed this because it was night time and I had a nice bright flash light shining in there. I may consider replacing the entire fuel distributor though.

I just have a feeling that this lovely ethanol in the fuel is messing things up. I'm just glad this isn't an oil burning problem that I was afraid of. I was reading on here or maybe a VW forum, that using a bit of two cycle oil in the fuel will help with the ethanol's unwanted effects of degrading seals and what not in the CIS fuel systems.

 

[CodyItaliano]

Ok, I had noticed upon pushing down on the metering plate, there was a little vague stream of fuel. I believe this to be coming down from the fuel distributor plunger.

Maybe, just maybe, this is why my car is running rich at idle? And perhaps has been a cause of many other drivability problems, in combination with worn out bits I've replaced.

So, since I scored an EHA valve from a low mileage '91 420SEL, I have thought about installing that if I still have problems after replacing what I believe is a leaking O ring.

I plan on buying a few fuel distributors, just to tinker with. I'd like to specialize in repairing these, as there's only a handful of people that I know here in town that really know what they are doing with the Bosch CIS systems.

Now, I ordered a total of four O rings from my local MB dealership. Luckily, I do get a shop discount. Although, they were still stupidly priced. But oh well, I know they will fit correctly, and I don't have to worry about poor quality products. Below are pictures of what I purchased. Only waited one day for delivery, luckily they have a warehouse in Houston!

012-997-97-48
EHA valve O rings, you need two.

004-997-07-48
Fuel distributor base to plenum O ring

014-997-34-48
Plunger tapered/stepped O ring, which I think is the root cause of the fuel seepage

Now, just to get into that mode of wanting to pop the fuel lines off and tackle this little project. I maybe just go ahead and buy a fuel distributor from the junk yard and take it apart first. That way, if there's anything at all I'm going to run into, I'll know. There's a spring that I know will pop out, and I need to probably measure with a feeler gauge the nut on the bottom and some other things, just incase adjustment is an issue.

I had seen one sort of taken apart at the junk yard last weekend, and whoever messed with it took that nut off that secures the plunger in and it fell right out. So, this is why I'd like to take precautionary measures. And then I'll have one to rebuild and get comfortable with disassembling.

I will be including pictures, now that it's easier with my new iPhone 5S. Absolutely love it and is making my life easier in my automotive field. BTW, how'd these pics come out? They are untouched.

 

[luckymike]

Pics are great, Cody.

I just did the control piston seal replacement. I made one mistake. I thought one had to loosen the large locking nut so I carefully marked it, and the body of the fuel distributor, and the slotted nut that actually holds the control piston in place.

After removing the locking nut, it became clear that there was no need to remove it to replace the seal. This fact was confirmed by the factory manual which I hadn't noticed beforehand.

You just carefully measure the depth from top of the slotted nut to the top of the locking nut. Probably around 6mm. Also mark it's rotation position. You want to get that nut right back where it was.

Otherwise, it just rotates out, bringing the seal with it. You've already noticed the seal is directional so just install the new one the same way, rotate the nut back to its original position, and Bob's your uncle.

Be careful to not drop the control piston, it will fall right out and is super precision machined.

Mike

 

[CodyItaliano]

Awesome. That's some good advice.

I think people make these fuel distributors out to be so very hard to work on. But just like rebuilding a carburetor, it's not that terribly hard to do.

Just knowing that springs may pop out and other bits, I will likely do this over a five gallon bucket to be on the safe side. This was mentioned in someone else's thread, but for a complete rebuild and taking the whole thing apart.

 

[luckymike]

I agree with you and wouldn't hesitate to dive into one of these if I had to. I like the instructions that ship with the eBay repair kits.

 

[CodyItaliano]

I spent $18 on four O rings. Granted they are very much genuine MB, I could have purchased a kit online.

 

[CodyItaliano]

Well, I installed the EHA that i'd got from the junk yard. Car ran great, except the damn EHA is leaking from its orifices. I was hoping it was just the O rings, but no, its a leaky EHA that I got. Didn't pay anything for it, so its no loss to me. But I had to put back the original. I think that is what is acting up. After messing with it, sometimes it'll bog a bit when its first started. So off I go to go grab a few more and the junk yard and hope to find one that works with my car. It'll be damn near $300 for a new one, which I may just have to end up getting. But I think the duty cycle is throwing everything else off when it starts to act up. I'll let you guys know how it works for me.

 

[fizzizist]

once you get the eha you would need to adjust the duty cycle. there are ones on ebay that i got that came with a warranty. i paid like 70$ for it.

 

[wooky_chew_bacca]

Well, I installed the EHA that i'd got from the junk yard. Car ran great, except the damn EHA is leaking from its orifices. I was hoping it was just the O rings, but no, its a leaky EHA that I got. Didn't pay anything for it, so its no loss to me. But I had to put back the original. I think that is what is acting up. After messing with it, sometimes it'll bog a bit when its first started. So off I go to go grab a few more and the junk yard and hope to find one that works with my car. It'll be damn near $300 for a new one, which I may just have to end up getting. But I think the duty cycle is throwing everything else off when it starts to act up. I'll let you guys know how it works for me.

Don't give up, took me getting a 3rd EHA from the yard before I got one that didn't leak, 30 bucks (for the 3) beats 300 any day

 

[joshlarsen]

Cody, are you experiencing a doggyish feeling around 4K RPM on your 420? Im still struggling with mine being doggy in the higher RPMs and poor fuel mileage. I spent to much money and time on this car now to not get it fixed. Mine was using lots of coolant and determined it to be either a bad intake gasket or head gasket so tore the engine down and sure enough I had water in the drivers side exhaust manifold. So replaced all of the upper end gaskets including head gaskets, new cams, and new rockers in and the car now runs pretty good and smooth but dogs out in the high RPM range. I have replaced plugs, plug wires, rotor, cap, coil, fuel filter, and the list goes on. The only thing i havent touched is anything in the CIS and injectors.

Is their any way to test the EHA?

What OHM readings is the temp sensor suppose to have?

How can i test the injectors? I know they are pressure brake so need to some how pressure test them. But is their any way to do it without any special tools? What pressure are they suppose to brake at?

How does the fuel distributor designate which cylindar gets fuel when?

 

[CodyItaliano]

That sluggish, or lack of power at higher RPMs kind of comes and goes. I had replaced a number of things. I want to replace the EHA and the TPS and see if that helps. All the parts on my car are original with over 170000 miles on it.

I will have to check the duty cycle when it starts to act up, I haven't had a chance to do it lately. Most of the time, the engine has plenty of power. But there's the occasional situation where it just lags. I really believe it to be sensor related, or otherwise electrical.

Search my user name for the threads started by me, and you'll see what I've experienced and done so far. I'm hoping to find a good used EHA, I just need to find the time to go and look in the junkyard for one. I work Monday through Friday, so my only free day to do this would be on Saturdays. And just my luck, we are going to have shitty rainy weather Saturday, or else I'd be out there looking. I may go anyway, a little rain never hurts anyone. And I have boots I can wear, so I might go for it.

BTW, this rich running usually occurs when the car has been running for over 20 minutes and usually is happening when I have been driving on the freeway. It also happens if I'm idling, like at a fast food restaurant drive through. Its not always happening, but when it does, you can smell the fuel not being burned and smokes from the exhaust. Not coolant, not oil, but fuel.

I have considered the fuel distributor or injectors, but I am trying that EHA first.

 

[luckymike]

Cody,

You might try running a couple wires into your car from the EHA so you can read the duty cycle while you're driving. Then, when the car acts up, you could compare your readings.

I've done a lot of fiddling with the EHA. If you want to discuss, send me a private message.

Edit: You're actually checking mA with this method, not duty cycle.

 

[luckymike]

Cody, are you experiencing a doggyish feeling around 4K RPM on your 420? Im still struggling with mine being doggy in the higher RPMs and poor fuel mileage. I spent to much money and time on this car now to not get it fixed. Mine was using lots of coolant and determined it to be either a bad intake gasket or head gasket so tore the engine down and sure enough I had water in the drivers side exhaust manifold. So replaced all of the upper end gaskets including head gaskets, new cams, and new rockers in and the car now runs pretty good and smooth but dogs out in the high RPM range. I have replaced plugs, plug wires, rotor, cap, coil, fuel filter, and the list goes on. The only thing i havent touched is anything in the CIS and injectors.

Is their any way to test the EHA?

What OHM readings is the temp sensor suppose to have?

How can i test the injectors? I know they are pressure brake so need to some how pressure test them. But is their any way to do it without any special tools? What pressure are they suppose to brake at?

How does the fuel distributor designate which cylindar gets fuel when?

Josh,

Section 07.3 of the factory manual is your friend for these answers.

A couple people on the forum have made injector testers. You can test spray pattern without special tools by rerouting the injectors into glass jars but to pressure test, you'll need to make or borrow something, or send them out. If you want to send them to me I can test them. I did this: http://www.benzworld.org/forums/w126-s-se-sec-sel-sd/1706202-homemade-cis-injector-tester.html

All cylinders get fuel all the time. CIS means constant injection.