fuel dist control piston seal replacement - PeachParts Mercedes-Benz Forum

p7fan · #1 08-10-2011, 03:14 PM

After many, many hours of chasing a rich idle/cruise concern. I finally found the culprit. Has anyone changed one of these (89 560sec)? I understand I first need to measure the height setting prior to removal. I also read somewhere that there should be .06-.08 play in sensor plate before the control piston actuates. Since I reset the sensor plate (was too high) I would then need to lower the height setting on the control piston to achieve the free play.
Am I on the right path here or is it "stinky thinking"?

thanks

John

ps2cho · #2 08-10-2011, 03:29 PM

Unless the Fuel distrib has been meddled with before, there should be no need to mess with the control piston at all.

Are you sure you reset the sensor plate height correctly using a depth gauge?

p7fan · #3 08-10-2011, 04:15 PM

The fuel dist is a reman, was installed by previous owenrs indy. I reset the plate height as per the MB instuctions (via all-data). Did not see a mention of depth gauge, just to set it at the upper edge lip of venturi. Mine was about 3mm high. I figure that since I lowered the plate that I would need to adjust the control piston height to achieve the proper free play in the piston.

Long story short: The car ran/idled fine. I was slow at work, decided to go ahead and replace intake gaskets, donuts, injector seals, holders, all rubber lines, and ignition wires. Figured at the age it couln't hurt and I may get an even better idle quality and maybe a few more mpg after some adjustments. Got done, lit her up and she is running super rich, cant adjust it out. After checking everything...I find fuel running down control piston. I realize the should be some seepage to lubricate the piston. But when holding it at cruise I can see fuel passing by under the sensor plate.

p7fan · #4 08-10-2011, 04:26 PM

ps2cho
How did you ever make out on your fuel dist rebuild attempt?

ps2cho · #5 08-10-2011, 04:56 PM

worked out great, but I found the remanufactured one had a little more power. I don't know though since the EHA was common factor to both that I had. Who knows how the condition of the EHA and whether it needs to be adjusted in combination with the associated fuel distributor.

That, or I did not align each chamber quite precisely. Its difficult to do without a real flow bench.

p7fan · #6 08-10-2011, 05:43 PM

Good deal it worked! From my studies very few have had and sucess with that.

From what i've read it seems that the EHA is set to the individual fuel dist. I intend to check the ma reading on mine once I get everything else dialed in. In reading the Landiss/Brotherton and other articles; it seems that the EHA is the key to "drivability nirvana".

ps2cho · #7 08-10-2011, 08:42 PM

That's what my findings have been also. Fuel distributors and even EHA pressures are basically worthless when it comes to driveability. They prove nothing other than the fuel distrib is not clogged. The EHA adjustment seems to make a dramatic, almost shocking change to power.

I believe the reason why it worked was that I used the correct sealant between the two halves, and used an abundant while keeping each chamber taped off so that any extra would not seep in. I assembled as carefully as I physically could. Like I said, lining up the chambers was the toughest task. I bet one could make a tool the width of each chamber shaped like an allen key for alignment.... That would be the BOMB.

p7fan · #8 08-10-2011, 09:55 PM

I'm truly hoping I don't have to go that far into the fuel dist. The diagnostics that I have done so far show that injector spray and volume are ok. I just need to repair the fuel leak past the control piston. Anything that I need to watch out for before undertaking this; other than measuring the height setting first?

thanks

John

ps--saw a porsche 928 site that showed a step by step rebuild. They used Indian Head to seal. Saw another site that recommended spray on Halomar (sp?).

ps2cho · #9 08-11-2011, 09:50 PM

Well either your control piston has worn as it is machined to a precise size, or the o-rings inside the distributor are worn possibly.

I've noticed that some fuel injector cleaners weaken the o-rings inside the distributor and that is why I do not advocate using injector cleaner at all, at the very least nothing harsh through any CIS-E system. Use of good quality fuel is the best approach.

I used indian head seal. Found it at a local pepboys so was not difficult to find.

p7fan · #10 08-12-2011, 08:59 PM

Well, replaced control piston seal last night. Had to fab up a tool to get it done...... Car runs the same, no better, no worse. I'm truly running out of ideas.

As a professional tech; the amount of grief i'm having to take is tough. The upside is: hell they have no idea what's wrong either!

ps2cho · #11 08-12-2011, 09:01 PM

How do you know its overfueling at idle?
I would flow test the system with injectors disconnected and see what happens

Here is how I did mine. You should be able to do the same deal with your V8. Its all CIS at the end of the day.
Preferrably use a spare set of injector lines as not to ruin the nice bends from factory:
http://www.youtube.com/watch?v=uVQWB_LjYL8

p7fan · #12 08-12-2011, 09:16 PM

What stinks is I dont have a 4 gas. I believe it to be running rich through-out the range. Duty cycle hangs around 0 or is fixed there. It is fouling the pass side bank (not wet, but heavy black carbon). Thing smells awwwwful......

ps2cho · #13 08-12-2011, 09:41 PM

You need to concentrate getting duty cycle back within system adjustment specs. Have you kept leaning the mixture out until it begins reading? You should be able to do. If not, its an auxiliary problem, not a fuel distrib problem. The duty cycle is very simplistic.

p7fan · #14 08-12-2011, 09:57 PM

i don't know what you mean by auxiliary problem. I can lean it out to shutdown without getting a duty cycle that makes any sense.

I'm checking between pins 2-3 with a snap-on dvom set to duty cycle.
Checked fuel pressure on upper and lower. Variance 7psi on cold start.
EHA ohms at 20
Checked power and ground supply at ECU pins 1-2
Checked resistance of ground pack at throttle link.
Checked spray and volume of injectors on problem bank
Smoke tested for vac leak
Replaced o2 sensor
R/R cam covers and verified cam timing (running out of ideas)
Checked ovp
Checked air flow sensor sweep
Checked throttle switch
Checked coolant temp sensor resistance at ambient and op. temp

Checked my sanity....long gone.
Mind you it was running/idling fine before I started!

ps2cho · #15 08-16-2011, 12:37 AM

What sort of amperage are you getting from the EHA?

I believe 0ma means the mixture is within stochiometric ratio based on the readings from the o2 sensor.

The duty cycle feature is completely unrelated to input from the O2 sensor. That is why I believe your problem lies elsewhere. If the o2 sensor is reading heavily lean/rich, it will influence the EHA to adjust accordingly. Now, if the fuel mixture is realistically very rich and the EHA is struggling to keep it running by leaning the mixture out, the duty cycle might NEED to be at 0% to keep it running. That does not mean that duty cycle is giving you the reading, it simply means at the mechanical standpoint -- that specific piston height is helping you.

Start by probing EHA mA and it will tell you what the O2 sensor is providing to the EHA.

The CIS-E system is frustrating...it just takes time and patience, and usually a lot of tweaking that defies common sense.