'75 240 D M-style IP Theory - Help! - Page 2 - PeachParts Mercedes-Benz Forum

psfred · #16 12-26-2003, 11:39 AM

The shims around the diaphram control the amountof fuel delivered for a given amount of vacuum, and there is a procedure for setting this correctly (plus fiddling about with it after the factory settings).

The maximum fuel delivery setting is the screw tith a lock nut below the governor at the rear of the pump. A small adjustment in will reduce the smoke. A small adjustment at the max speed screw will result in more vac at "full throttle" and should also reduce the smoke some.

Adjustment of shims to give less fuel at low vac may tix the problem, but I've not done this and defer to those with greater experience.

Sadly, the governor only sees the difference between ambient air pressure and manifold pressure, not absolute MAP, so it will overfuel at high altitudes if set for best performance at sea level, and will lack power at low altitudes if set for minimal smoke at high altitudes -- same reason carbureted engines run over-rich at high altitudes.

Needless to say, be very carefull to get the vac governor actually attached to the fuel rack when installing, and be prepared for a run-away engine when you first start up -- if the rack isn't properly connected, it usually falls full open and since the shutoff works by pulling the rack back to the no delivery position using the governor linkage, it won't work. You must loosen the cap nuts on the injectors before the engine blows.

Peter

Fisherman · #17 12-26-2003, 01:35 PM

As I keep going through the logic and reading everyone's input things are falling into place (as much as my simple mind will absorb anyway

). There are also a couple of jobs on the CD that are hidden. In other words they do not have a direct link via the main menu but if you read through the jobs then they are noted and you have to search the CD to find them. I like having more information than less...

A couple of these have shed a little more light on the topic.

Steve, I understand what you are saying and agree. Sorry that my thick skull could not get it the first time you helped me with this problem.

There is an issue still unresolved with the IP diaphragm. The manual continually states to ensure that it is holding vacuum which is one of my problems. It bleeds down, albeit pretty slow but this may not be related to the metal to metal connection there. Seems like the culprit but it might also be o-rings around the "tickler" shaft. Probably not truly related to my max fuel problem though... Still needs to be fixed. The methodology for testing this vacuum is very simple and applies next to no vacuum to the area so I am not certain that a minor (as in slow) leak really effects this very much.

I do have one point that I am unsure about. Assuming that the vacuum connection is sensing vacuum via the intake manifold and with my understadning of gasser vacuum will the manifold actually increase vacuum as you get closer to WOT or would it begin to dissipate vacuum as you approach WOT?
In my van if I have the pedal to the metal climbing a hill I will occasionally get defrost (no vacuum default) due to lack of vacuum being created by the intake.

I have checked and rechecked the "compensating" path on the diaphragm and have it set as close to 1.1 mm as I can. The connection to the rack is solid so I don't anticipate a runaway as it slips over and locks onto the back of the rack but as always I keep 2 17mm wrenches handy whenever I first fire her off after displacing the pump.

Peter, I believe you hit on the adjustment and I was just going to post a pic asking for identification of the adjustment at the back of the pump with the logical recognition that this bolt (with locknut) controls how far the rack can move forward hence full throttle position. I now believe that this is the control for max fuel delivery.
here is the pic. The adjustment is via 23 connected to lever 9 which adjusts how far 6 can move. Turning in reduces the amount of travel and out increases. with the hammer down I think the rack just travels to the stop (6 hits 9) and away you go pumping in as much fuel as it can.

DaBenz, it was your photo that got me thinking about this adjusment, thanks.

If it is this simple and this fixes my problem I have put everyone through a lot of digging for a simple answer... Sure wish they would mention this adjustment in the manual...

Again, thank you all for your valuable input. It is always nice to have others to bounce ideas/questions off as I continue to discover new things related to these great old cars.

psfred · #18 12-26-2003, 04:08 PM

Yup, that's the screw. I've been told not to turn it more than 1/4 turn ether direction.

Peter

Fisherman · #19 12-26-2003, 06:27 PM

I try not to get carried away with adjustments on things that few (let alone me) can speak to...

This whole thing is soemthing of a debacle as it seems that the only other thing to do would be to send the pump top the pros but the nearest one for me is in the Willamete valley and guess what, they're just a little over sea level. I'd probably get it back fully tuned to their altitude...
Go figure.

dabenz · #20 12-26-2003, 11:00 PM

I guess I'm the thick headed one here. So here's my first question: What does "My 240 blows clouds of smoke at 3200 feet and up. At sea level there is none." mean? Are you staying up there or going back and forth? That max fuel delivery screw acts like a doorstop. I value psFred's opinion, but I think he's wrong here, especially if you stay up there in the dry country. And I don't think the IP shop is going to do much for your governor that you haven't or aren't going to do anyway.

Second: could you list the filenames you're referring to? I would like to look at what you're looking at. I'm also slowly building a separate directory, as I've noticed the same thing on my disk. Thanks.

To answer your question: yes the venturi will create more vacuum at the fitting when running wide open. But there are other practical limits, such as the "limiter" built into the fitting at the throttle body and the travel limits of the diaphragm.

stevebfl · #21 12-26-2003, 11:21 PM

I might have misunderstood, but let me just state: manifold vacuum is greatest at closed throttle and is zero at full throttle.

When at zero vacuum (full throttle) the rack position is set by the full load adjustment.

Fisherman · #22 12-27-2003, 10:13 AM

That's what I thought on the vacuum. Full throttle no vacuum.

As far as elevation yes, I live in a city that is at 3200 feet above sea level. I have gone to the Bay Area and Oregon coast with this car and experience the no smoke situation during those trips.

One Job that I can think of off hand is number 03-300. It is actually listed as 30-300 on the CD adn there is no menu listing for it on the CD. Adjusting regualting linkage for left hand steering cars.

psfred · #23 12-27-2003, 10:28 AM

Steve:

Yes, there is zero manifold vac at full throttle, but the absolute pressure varies with altitude, so the amount of air (mass) going down the intake is greater at lower altitudes. The only real problem with the vacuum governors that I can see is that they cannot compensate for barometric pressure, so they overfuel when the barometric pressure drops -- fuel delivery is determined, indeed, by diaphram position, but that position is determined not by the mass of air passing the intake, but the difference in pressure between the atmosphere and the intake. One must "choose" the barometric pressure for pump calibration, and higher or lower pressures will cause power loss or overfueling.

The ALDA has an anaeroid element. This permits a measurement of absolute pressure, so that the IP will meter fuel much more accurately for all barometric pressures. Hence less (although porbably not NO) smoke at higher altitudes. Like my old Audi Fox with K-Jet -- didn't smoke at high altitudes, but talk about lack of power!

Peter

stevebfl · #24 12-27-2003, 12:29 PM

As I think about it you are right about the altitude compensation.

My discussion had to do with the mechanism of control. I had to think hard about it as its been a few years since I actually tried to modify mixture on one of those pumps. I thought that the control theory might have been interpreted that the vacuum tube had venturi vacuum in it rather than manifold vacuum. The two are exactly opposite. Venturi vacuum would be higher at greatest airflow rate while manifold would be minimal.

I actually spent some time dealing with the vacuum control of a gullwing which had a similar pump. I had to separate memories to be sure that venturi vacuum wasn't used.

Fisherman · #25 12-27-2003, 08:55 PM

Why, because I can...
So what you have at the back to the pump is a spring and diaphragm working with/against each other for control fo the throttle. At low throttle positions the diaphragm acts as a regualtor of sorts (vaccum supplied by intake manifold) allowing for fine control on the rack via the governor "tickler". Actually this tickler arm relieves pressure on the spring. At heavy or WOT the diaphragm has nothing to do with the pump and the amount of fuel delivery.

Since this is a 240 automatic we know what the main throttle position is for most of the driving time...

The shims that are behind the governor spring shim out the spring balance aganst the diaphragm to provide you with a WOT maximum engine speed. Since this car is rated at 5400 rpms no load and I have no way to check this I thought I would play around a little... Dangerous but true

So I took out all the shims behind the spring to try to make up for the slight vacuum leak that I have in the diaphragm body. The throttle still feels fine and I cannot recognize any differnece in my max no load. I'd never run it there anyway but by removing springs I figured I would be safe since this only reduces the no load max speed.
This resulted in a decent change int eh pedal movements and just like before you either have the car basically at WOT or just a light touch on the pedal to keep the current speed. Never slow down once you get it to speed...

Okay, so that helped a little with the smoking problem but still could put out a cloud if I hammered down.

So now to the max fuel adjustment on the back of the pump. There is a stop inside the pump that adjusts by screwing in or out the stud on the back of pump. As Peter noted it should not be played with randomly but then hey I got 268,000 on the clock and figured what can I do except cut the power. Well after 2 1/4 turns (tried small increments) I have a 240 that now has a little less power than before but who's going to notice except that the car does not smoke AT ALL!!!!!!

I cannot tell you how thrilled I am to know that this worked! In hindsight I may have gone a 1/4 turn too far but it's really cold right now so minor adjustem4nts wil come later. For now it drives great in town, climbs the big hills in 3rd gear like before and does not smoke out the guy behind me when I put the medal to the metal.

Thanks for your help on this everyone!

Steve, I still have one final question... To the pros out there is there a trick to sealing the diaphragm section fo the pump? Perhaps mine is warped but I finally gave up and went witht he removing some shims to help the diaphragm overcome the lack of vacuum seal...

psfred · #26 12-27-2003, 09:06 PM

Fisherman:

For best power you want to see smoke just visible over the trunklid at full throttle, about 45-50 mph in 3rd gear, full load.

About a quarter turn back would do it. No smoke is nice, but you are giving up too much performance in a 240.

Peter

Fisherman · #27 12-28-2003, 12:45 PM

However since it snowed 4 inches last night it will have to wait. I figured Mommy would be happy since people will stop flipping her off if she drives the little car now...

The most embarrassing thing was actually this summer sitting at a stop light with the AC on and you could see this cloud rising from the back of our car and wafting through the intersection.

psfred · #28 12-28-2003, 03:15 PM

Fisherman:

What's your oil consumption like? Smoke at idle sounds more like a timing problem or a bad vac pump diaphram letting oil into the intake than an IP control problem!

Peter

Fisherman · #29 12-29-2003, 09:20 AM

Even after 1100miles roundtrip to the Bay Area last year I did not have to add any oil.
Generally speaking it is down a quart at oil change time every 3000 miles. Not bad for a 75 with 268,000 on the clock.

If the oil consumption had been up I probably would not had done the head work that I just finished but I thought I'd try to get another 100K out of her before really tearing into things. In fact I will probably sell her before that.

I really want a 115 300D!

As to visible smoke under acceleration I think I'm a little lean because I can see smoke when under full load in second heading away from a stop but maybe only a wisp every now and then at full throttle in 3rd. I'll try to dial it back out a quarter turn but not today. We just got another 6 inches of the white stuff last night with 10 inches possible by tomorrow...

Ronkat81 · #30 10-06-2011, 07:06 PM

I'm glad for these photos!