fuel pressure regulator

[Arthur Dalton]

OK

Turn the AB screw back to original setting and then open it to see if you get more rpms..if yes, then how much??

[3BENZER]

about couple of hundred RPMs every half a turn.

[Arthur Dalton]

Originally Posted by 3BENZER

about couple of hundred RPMs every half a turn.

OK .. very good.
We are too Rich.

A few things have to be in order before adjusting.

First, make sure that when you push down on the link going to the FI pump, the air venturi OPENS at EXACTLY the same time [ in unison]. If it does not, then there is slop in the linkage balls ..with a car of this low miles , you should be able to just pop all balls off and stick some good grease into the ball cups. [ I use plumbers grease for this b/c it is thicker and holds up well with engine heat]. Also oil the cross link brass bushing supports.

next , put all together and then take the rubber cuff off between the intake and air filter ...Place a piece of cardboard [ or anything of such] over the
intake at idle to block any air..you should see very little rpm change [ this is just a test to make sure the air flapper is completely closing and all air to engine at idle is being supplied from the AB screw] .I expect this to be fine according to what you have reported so far. If NO, then the flapper is adjustable with the set screw...you want it to just stick closed at idle.

Now, look at the backside of the FI pump..you will see a thumbwheel. This is fuel mixture control adjutment for low rpm range. This adjust fuel when you turn it RIGHT [CW] to RICHEN .
There is a trick here , so pay special attention:
This adjuster is spring loaded and has to be pushed IN in order for its flat screw blade [ like a screwdriver] to engage into the adjuster screw inside the pump..meaning you have to turn it and press in at the same time until you feel the shaft engage the screwhead in the pump. This has to be done with the engine OFF..failure to do so will engage the screwhead and the rotation of the engine will unscrew the whole adjuster and snap the head right off. Pay attention to this WARNING.
Just imaging that you are trying to engage a screwslot inside the pump where you can not see the slot. [ try it a few times to get the Feel]
Now , once you get that adjuster in the slot, you turn it and it will CLICK These clicks are a position holding spring that allows the adjuster to be turned 1/6th of a rotation and then the spring locks it into place ..so, 3 clicks would be 1/2 a turn. The spring is just there to keep it in place after you adjust it.

Now , in your case , we know that we are too rich b/c the RPM at idle can be adjusted too high by adding air with the BS. So, you want to turn the thumbwell 2 CLICKS CCW, thereby leaning the fuel a little. Then resatart the engine and smooth it out with the BS to attain the highest and smoothest idle. If it is still too high , do the pump some more ...[ a vac gauge helps here , but I do it by ear after all these years]
The concept is that the fuel MIXTURE is correct if the proper idle RPM is attainable with the BS at its highest possible setting..if the rpms are too high, you have too much fuel, if the idle is too low , you do not have enough..it is a balancing of the thumbwheel for fuel and BS for air [ at idle,. engine warm].
Read this a couple of times and feel free to ask if I have not explained it well.
A final thought .
These engines like to run rich at idle [ they actually call for 3/5-4.5CO ..high by todays standards], so over many years I have found that they run best when you get the highest rpm setting between the pump and the AB [without going past normal idle spec rpm] and then turn the AB in enough to drop the rpms about 50-100 rpm..that is a sweet-spot that works well.
Also, be aware that MFI tweaking should be done after ignition specs and valve adjustment are in order to assure perfection...but if you car is runnng well, this can do the these and you will then be able to make any further adjustment whenever...
After you have done this tweaking , you want to clean the plugs [ or take the car for an uphill load/hard drive to clean them, ] and recheck their condition after a few days. If you still have a sooting/rich condition, we can then take a shim out from the bottom of the WRD [ oval shim] to lean out the entire range...wait up on that....
Clear as mud?????????????

[3BENZER]

Arthur,

Great instructions and very clear. I will do the tweeking and psot back.
Thanks again for your valued help.

Cheers

[bbiggbob]

Hi Arthur,

Nice detailed walk-through you have going.

I thought this might be in order, or at least the right place to ask about it.
I have an '82 380 sel and I am considering adding a hydrogen booster with the hydroxy gas being injected through the top of the air cleaner cover.

With this in mind, the understanding you will need less gasoline injected to perform. Supposedly, the hydroxy gas adds its own special power in reducing fuel consumption which in return increases your mpg.

So long story short, I found this thread and its been very insightful and you mentioned in your last post that you could further lean throughout the entire band by removing a shim.

I await your continued detail description as how to do that exactly. I know my car is different than the gentleman’s you are helping, but I imagine the process would be very similar.

Once again, it is incredible to have people such as yourself taking the time and effort in sharing and helping. Thank you.

Have a great day,
Bobby

[Arthur Dalton]

B,
My Expertise is on the Bosch PES/Port Injection-Mechanical FI of the early chassis...but you may want to try the Performance section of the Forum

Thanks for the compliment.

http://www.peachparts.com/shopforum/mercedes-benz-performance-paddock/?daysprune=-1

[Tassie Tiger]

I was motivated by Arthur's in depth response on how to check for correct mixture at idle speed and therefore last weekend I performed a couple of checks on my 250SE. Mine was also running rich at idle, however, I turned the FI pump adjuster at least 6 clicks CCW to lean out the mixture but did not see a recognisable difference in idle speed. I performed this in increments of two clicks before checking idle speed.
What is the median set point of the adjuster and how many clicks can be turned CW and CCW before the limits are reached?
I look forward to any advice on this matter.
Regards,
Tassie Tiger

[Arthur Dalton]

Did you check both the CSV valve and the Throttle plate before leaning the pump adjuster ? Did you check the air slide for shut-off in the WRD??

All of these have to be done First so that you are assured ALL fuel is coming from pump ONLY, and ALL air is coming from Air Bleed /Idle screw ONLY.

If any fuel or air is coming into the engine from any other source, then the fuel mixture can not be metered with the adjuster.

[Tassie Tiger]

Arthur,
CSV works properly - no leaks. The WRD works fine - I cleaned this out a couple of years ago and the suction ceases when engine has warmed up.
I did not perform the throttle test (with cardboard over throttle opening) but I visually inspected it and it looked completely shut. I will cover the opening and advise results in the morning.
Regards,
Tassie Tiger

[Tassie Tiger]

Arthur,
I have just checked the throttle setting with the cardboard test and can confirm that the idle speed dropped. I deduced that the throttle flap was not completely closed. Indeed, the flap was slightly set open and I adjusted the set screw to ensure the flap was completely shut. I opened to idle screw and the idle was still high. I then turned the mixture screw two more clicks CCW and adjusted the idle speed to approx 800 rpm. I could not get much more speed than this. The throttle linkage balls needed minor adjustment after this work was performed.
I put the car into gear and it stalled. I am now in the process of adjusting the constant speed solenoid setting to allow for approx. 700 rpm when in gear.
Regards,
Tassie Tiger

[Arthur Dalton]

OK...you are close ..but.......

If the max rpm you can get with the BS is 800, then I would like you to richen the pump a click or two [ cw] and then see if the BS will get you another 100/200 rpm max.

The reason for this is these early pumps run better on the rich side of spec [ 3.5-4.5 CO] . So, what we are doing is setting the mixture slightly richer in order to obtain a higher than spec. RPM, and then we DECREASE that rpm back down to spec. by CLOSING the BS just a tiny bit. This gives one the proper RPM while having the CO on the upper end /limit of factory spec. . You will then find that the pumps transition from low range to mid range will be much smoother and that little jerking driving [lean]they are famous for @ low rpm will be gone.
I can tell this sweet spot by ear from the exhaust note. It has a slightly deeper tone . [ If one just sets the idle mixture for the spec rpm @ idle with no load, then with a load the engine will actually be a little lean..this trick adresses that possible condition]
One can also use a vac gauge on the intake to get the mix too..what you want is highest/steady vac reading from BS at about 900/1000 rpm and then drop the rpm with BS closing without touching the pump adjustment. While doing this , watch the vac gauge..it should still hold a decent vac ..if it drops just a little ,that is OK, but if it starts to colapse, the pump will need another click..it is a balancing act, but we want to balance on the Rich side ,but only ever so slightly.
Correct way is GAS Analyzer, but this works and you will get the feel of it after a while. It is not as complex as guys would have you believe..it's common sense.
If I have not been detailed on this or it is confusing , ask away...............................tech writing is not my Forte.

Now, another VERY Important additional/different info on your chassis as compared to the original posters car is you have an early pump [R18 series for 129 eng.] and these pumps have there own oil RESERVOIR. [ the posters later (R20 and on) have engine recirculation oil feed, requireing no maint. and does not apply. ]
So, BEFORE ANY ADJUSTMENTS can be made to this style pump, it is of the utmost concern that the oil level in the pump be correct and verified as not to contain any petro/gas contamination. You prolly already know this , but in case you don't, , I mention it for you and mainly for the Archieves ..
On the rear of the pump there is a "T" handle oil dip-stick..unscrew it with engine off and check the oil level of the pump. It should be EXACTLY at the level indicator line on DS.
If it is over -filled [ very common b/c many owner don't even know it is there, as it is hard to see ], the governors will NOT operate correctly for fuel mixture metering control.
What happens is the reservoir gets gas mixed with this oil and the level rises, screwing up the mixture controls of the pump...BAD !!!!
This is a normal use occurance and Benz has an interval for changing this oil [ I don't remember what that time frame is, I just check the DS every few thoudsand Km......but I am a maint freek..so just DO check it routinely.]
And , do check that FIRST before any adjustments or all will be in vain.
There is a trick to changing the oil in these pumps and it should be done as soon as one sees a rise in DS reading OR the oil is dirty and has a smell of petro. If guys knew what damage can be done to their pump by not checking/mantaining this pumps oil supply, they would s..t themselves.
The only way to get the oil out is to suck it out with a fine tube from the DS hole. There is an "OEL" filler cap, but that will not get the oil out of res.
A trick I use is a large mouth glass bottle [ pickle jar] with a 1/2" hole cut out of the cap. Then I drill a smaller hole to insert a tight fitting rubber tube. ON the other end of the tube you use a thin pipe to fit thru the DS hole to the bottom of the res. cavity..
Any plastic squirt bottles inside lift tube works well here. Just make sure it is long enough so it can't accidentally drop into the pump. Now you just take a vacuun cleaner and put it over the 1/2" hole @ the jar cap and you will see the fluid drawn into the glass jar until the pumps res is empty. The jar is just a drop tank and the fluid will go to the bottom and stay seperated from the vac air.... KISS ....You can use any vac contraption, that is just an easy one that most guys have the stuff for lying around the house/shop. I have a finished off one with refrigeration fittings that hooks up to an actual vac pump, but the jerry rig one is fine.
I have even seen guys use the squirt bottle neck and pump it by hand, but that is too crude for me and does not do a good job..
The oil refill is with standard engine oil and the capacity is approx 7 oz. Refill is thru the cap, and another trick is to clean the air filter in the cap [ I use kero and blow dry]
That filter is the pumps vent and another ignored item that will cause hell with the pumps oil cavitating and internal pressure build-up.

I am waiting on the original poster to reply back and I will then write a little linkage adjustment piece.

One last thought about these early self contained oil resevoir pumps..they are actually preferred over the engine fed later ones by most guys who really know pumps b/c if kept maintained , they do not suffer the contaniments and water problems that the engine crankcase oil fed versions do. I believe Benz went to the later design b/c as the owner base grew, less maintainence was sought as owners were just not maintaining the oil in their pumps , which I can understand ...My preference, of couse, is the early Reservoir pumps..for sure.

[Tassie Tiger]

Arthur,
I will turn the mixture screw another two clicks CW to get a richer mix and increase the max idle speed as you suggest. I checked the FI pump oil reservoir and the level is higher than the mark. I sucked the oil out with a syringe and thin tube about a year ago and the task took ages. I will try your method with a vacuum cleaner and jar this weekend.
Thanks - I will post a reply on the outcomes of this exercise.

[Tassie Tiger]

Arthur,
the idle speed increased by richening the mixture and I backed the BS off to approx 800 rpm. I also sucked out the excess oil in the FI pump reservoir and topped it up with fresh oil to the dip stick mark. The idle in "Park" is perfect and after some adjustment of the constant speed solenoid, I could get approx 600 rpm when in gear. This is still a little low despite the adjustments being in their maximum positions.
I noticed that if I increased the throttle lever manually, the idle (in gear)would not improve, however, by disconnecting the rod to the intake flap, I slightly depressed the FI pump rod and the idle speed increased and was smooth.
I am assuming that the linkages between the FI pump and the air intake flap need some tweaking as it seems the fuel/air ratio is on the lean side or is the mixture at idle still lean?
I would be very interested in reading about your linkage adjustment piece.
Regards,
Tassie Tiger

[wbain5280]

There is no fuel pressure regulator on this engine. Thre are two fuel pressure dampers, one before and one after the injection pump.