Author Topic: Fuel Injection Pump Adjustment screw (Read 25302 times)

mrfatboy · « **on:** February 20, 2008, 18:17:36 »

I'm trying to adjust my fuel injection pump via the adjustment screw under the solenoids. I push in the spring loaded screw and find the "slot" and try to turn. It is frozen both "clockwise" and "counter clockwise".

The engine was off and the car has not been driven in a couple of days.

Is it stuck? How can I unstick it? Is my only option to force it? I don't want to break it. Can anybody suggest a tool that would help give me some leverage? I can't turn it with my fingers.

thanks

1969 280sl
Signal Red

rwmastel · « **Reply #1 on:** February 20, 2008, 18:56:33 »

Is this a case of "stuck rack syndrome"? From the technical manual:
http://www.sl113.org/wiki/pmwiki.php?n=Fuel.Injection#Pump

I have found this quote:
"The thing to do is put it all back together, then test its operation. It has two functions, increasing idle air (through the filter) and enriched mixture. The air function (as well as overall operation) is tested as I mentioned, by removing the filter, starting the engine, and placing your finger over the air inlet. It should suck strongly when cold, tapering to no suction when coolant reaches about 160 deg. F. To test mixture, remove cap at front of the pump (last of the pumps don't have a cap, test can't be made), screw a long 5mm bolt into end of rack, and test mixture during warmup (VERY SLIGHTLY pull out to richen, push in to make leaner). If either pushing/pulling results in significantly faster idle and smoother running, you should consider adding/ removing washers inside unit (not at base). Add to make leaner, remove to enrichen -- if you need to richen but there are no washers there, I guess you could turn in the little nut at the end of the thermostatic element, but this is normally a no-no. After shutting off the engine (or before starting it), test the rack for freedom of movement by pushing the 5mm screw all the way in and pulling it all the way out. If the rack binds or refuses to return to "neutral"when you release the screw, there is an internal pump problem that will need to be fixed."

Rodd
Pagoda Technical Manual
please contibute: http://www.sl113.org/wiki/pmwiki.php
1966 230SL
2006 C230 Sport Sedan

mrfatboy · « **Reply #2 on:** February 20, 2008, 20:08:04 »

thanks for the info but I don't think it will help me. I have one of the new pumps that doesn't have that access door.

Any other ideas?

1969 280sl
Signal Red

mrfatboy · « **Reply #3 on:** February 21, 2008, 14:29:01 »

I found a couple of things out.

1) My FI pump serial # is PES6KL 70B 120 R20Y (0408 026 017). In that wiki link that was posted below there is no part number like that for the 280sl. What does that mean? Do I have the wrong IP in my car?

2)I was incorrect before, my IP does have a rubber cap so I guess I do have access to the rack.

3)My car basically runs fine(as far as i can tell) but rich. Doesn't this mean I don't have a stuck rack? I read a post that says if the rack is stuck then the car won't run. If my rack is not stuck why would my FI pump fuel adjustment knob be stuck?

Can somebody offer some suggestions? I have been reading as many posts as I can find on the subject but I'm still lost.

1969 280sl
Signal Red

Naj ✝︎ · « **Reply #4 on:** February 21, 2008, 14:37:53 »

quote:
Originally posted by mrfatboy

I found a couple of things out.

1) My FI pump serial # is PES6KL 70B 120 R20Y (0408 026 017). In that wiki link that was posted below there is no part number like that for the 280sl. What does that mean? Do I have the wrong IP in my car?

2)I was incorrect before, my IP does have a rubber cap so I guess I do have access to the rack.

3)My car basically runs fine(as far as i can tell) but rich. Doesn't this mean I don't have a stuck rack? I read a post that says if the rack is stuck then the car won't run. If my rack is not stuck why would my FI pump fuel adjustment knob be stuck?

Can somebody offer some suggestions? I have been reading as many posts as I can find on the subject but I'm still lost.

1969 280sl
Signal Red

Hello, FB,

The wiki is still under construction, so a lot of information is still incomplete.
It just means that your pump was not known about, not necessarily that its the wrong pump in your car.
If your car is running fine, it just may be a small problem with the low revs mixture adjustment screw.

Hopefully, one of the pump experts will chime in and offer advice.

naj

68 280SL

mrfatboy · « **Reply #5 on:** February 21, 2008, 14:53:19 »

thanks naj.

So I just inserted a 5mm bolt in the rack "hole" at the front of the FI pump. It slides backwards and forward and returns to neutral on it's own. So it would seem I do not have a stuck rack.

However, my FI Fuel adjustment knob is still stuck

It's now up to the experts to chime in

1969 280sl
Signal Red

rwmastel · « **Reply #6 on:** February 21, 2008, 22:07:03 »

quote:
Originally posted by mrfatboy

1) My FI pump serial # is PES6KL 70B 120 R20Y (0408 026 017). In that wiki link that was posted below there is no part number like that for the 280sl. What does that mean? Do I have the wrong IP in my car?

I think your pump is correct. Member "TheEngineer" has one in his car, see his post on 02 Oct 2005 in this thread:
http://index.php?topic=4192

Rodd
Pagoda Technical Manual
please contibute: http://www.sl113.org/wiki/pmwiki.php
1966 230SL
2006 C230 Sport Sedan

Benz Dr. · « **Reply #7 on:** February 22, 2008, 08:24:14 »

The adjustment knob has a screw driver blade on the other end which is the sloted type. When you push it in it simply engages into the slot on the screw.
What you might be able to do is to get a large socket and remove the nut that holds the thumb screw in place. This will remove and contain the thumb screw. The end of the blade may be slightly damaged which is preventing it from mating up with the screw on the end of the governor assembly. I've seen this happen before and sometimes the pump has to be removed to repair this problem. Pump removal takes about 1 - 2 hours.

Dan Caron's
SL Barn
benzbarn@ebtech.net
slbarn.mbz.org
1 877 661 6061

glennard · « **Reply #8 on:** February 22, 2008, 09:28:26 »

Sounds like someone tried to turn the adjustment screw WHILE the engine was running. This could mean bye bye to the blade. If so, you need a new blade inside. Another post talked about this.

ja17 · « **Reply #9 on:** February 23, 2008, 06:52:55 »

Hello,

The slotted scew in the injection pump also has a hex head. Two small leaf springs on each side of the screw create the "click" adjustment. The screw can be stuck of or jambed. Engaging the screw when the engine is running is definately a problem. However doing this normally will wind the screw all the way out or jamb it against the rear cover of the pump, damaging the screw or it's engagement with the adjuster.

Download Attachment:

ijection pump with back off.JPG
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Download Attachment:

iinjec 23.JPG
63.94 KB

Joe Alexander
Blacklick, Ohio

pagoden · « **Reply #10 on:** February 23, 2008, 17:19:24 »

Hello messrs. fatboy & ja17 -

I have recently developed what may be the same problem on my own 1969 280 SL, and "developed" is the word as it went from turnable to stuck in one brief tuning session. I had (as I'll bet many others have) recently rationalized the linkage --MANY thanks, Joe-- and went from 1700-1800 revs down to ~1600 with the 2-3 clicks I gave it at the end of that session (without a re-start at that time). After warm-up the next day,adjusting the idle air bleed brought it back up where we started. 'No problem', thought I, and laid hold of the knob. It turns freely until pressed into the IP case, in which position it is immobile in both directions. I have been wondering if I have somehow pushed it off-line from its proper path into some place where the blade could be lodging, and the photos just posted show at least one place --the leaf springs--where this might be happening, perhaps to us both.

And to muddy the waters a bit, just now I learn that all of this is taking place just at or very near a boundary between two separate adjustment systems in the IP. 'Yikes', sez the newbie.

Thoughts, Joe? (As ever, the support of any and all in this group is solicited, nearly crucial and very much appreciated.)

Denny
1969 280 sl 670/904 4spd

mrfatboy · « **Reply #11 on:** February 25, 2008, 19:12:36 »

When I push in the spring loaded adjuster knob I do "feel" the slot. It feels like a nice fit. When I try to turn it CW & CCW it just wont budge. It doesn't slip out of the slot so I am assuming there is nothing broken. It just seems seized.

Dan,

Your suggestion seems like a good one. I didn't know I could remove just the knob. I'm assuming once I get it off I should spray some WD-40 on the screw and then insert a screwdrive to try to turn it?

I know it used to turn because when I had the engine rebuilt I watched the mechanic turn the knob (engine off) when we were dialing it in. I have not touched it in 7 years.

1969 280sl
Signal Red

Benz Dr. · « **Reply #12 on:** February 26, 2008, 00:53:02 »

Well, it must be siezed or stuck somehow. It's not an easy place to work even if you do get the back cover off. If it was me I'd pull the pump and not waste time. There's something decidely wrong with your pump and a rebuild or just a nice calibration could be in order. During calibration the pump guy will have the back cover off to make adsjustments. If he can't move the screw I'm sure some of it would come apart. Calibration should run about 300 - 400 dollars. It's all about the amount of set up time and tests that have to be made. Worth it really.....

Dan Caron's
SL Barn
benzbarn@ebtech.net
slbarn.mbz.org
1 877 661 6061

glennard · « **Reply #13 on:** February 26, 2008, 09:53:25 »

Kinda basic but, does the knob turn both directions before you push it in? (Answer is probably yes.)

Benz Dr. · « **Reply #14 on:** February 26, 2008, 10:07:54 »

The knob turns in either direction before and while you push it in. If it doesn't, then there's something badly wrong inside.

Dan Caron's
SL Barn
benzbarn@ebtech.net
slbarn.mbz.org
1 877 661 6061

mrfatboy · « **Reply #15 on:** February 26, 2008, 11:05:07 »

glennard,

yes, the knob freely spins in either direction before I push it in.

@dan,
I have been resisting taking my pump out and having it calibrated or overhauled for years :oops: . The car drives well (but rich) so it doesn't seem justified yet. Plus this is giving me an opportunity to learn & check all the other things that could bei causing the car to be rich. I would actually prefer the IP just really give out and force me to pull it

The only other tibbit of info I can give you at this moment is that the pump seems to have a mind of its own. The mixture seems to change everytime I start the car. I just can't seem to nail it down. Somebody also mentioned it could be a worn distributor. It could have even been you

. I seem to try tackle this problem every year or so

I'm goving over all the linkage, wrd, csv, etc. again today and will report back.

1969 280sl
Signal Red

hands_aus · « **Reply #16 on:** February 27, 2008, 05:47:04 »

mfb
have you checked the points rubbing block for wear?

One local club member went on a long run only to have the distributor shaft completely rounded off. That introduced some chaos to his trip.

Apparently it was because the distributor shaft hadn't been lubricated for years.

Bob Smith (Brisbane,Australia)
RHD,1967 early 250 SL, auto

Benz Dr. · « **Reply #17 on:** February 27, 2008, 11:44:28 »

Hummmmmmm....... there's a clue here.

You say the pump has a mind of it's own, constantly changes its running charateristics and goes rich? Doesn't that sort of point to wear or something going on inside of the pump?

Don't wait for the pump to pack it in. That's a bad idea.
I had a pump go out on me while I was driving right after I changed the engine oil. I turned around and headed back home ( 10 miles ) and by the time I got there oil was pouring out of every seal and crack on the engine. There was more than two litres of gas in the oil and it damaged the engine. This was a long time ago and today I'd have it towed home.

Still feel lucky?
Bite the bullet and get your pump looked at.

Dan Caron's
SL Barn
benzbarn@ebtech.net
slbarn.mbz.org
1 877 661 6061

rwmastel · « **Reply #18 on:** February 27, 2008, 18:51:48 »

Could poorly or variably timed ignition give the same symptoms (reading spark plugs, measuring exhaust emissions) as running rich/lean? I was thinking that if the system is set up lean, maybe spontaneous poor ignition is masking itself as random richness? Just a thought, probably wrong.

Rodd
Pagoda Technical Manual
please contibute: http://www.sl113.org/wiki/pmwiki.php
1966 230SL
2006 C230 Sport Sedan

jwalk · « **Reply #19 on:** April 26, 2008, 21:52:22 »

Hello,

This thread seems a good place to ask questions, Can the idle fuel adjustment screw be backed clear out when adjusting? If six clicks = one turn, how many turns are possible? If the middle of travel is the optimum or original set position, how does someone reestablish this?

With thanks
jwalk

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Author Topic: Fuel Injection Pump Adjustment screw (Read 25302 times)

glennard

glennard

jwalk