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  #1  
Old 04-14-2019, 12:35 PM
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616 Rack limiter removal/tuning

Been poring over the archives for anything and everything
MW pump related, concerning om616 performance.

Seems like that was a forum phase that happened 6-8 years ago.
I have the google doc "Bosch M/MW pump theory" and have read about everything I could load onto my screen...

I'd love to know if any of the pioneers are still around?

Any of you 240D 616 drivers still rolling around with either your rack limiter removed, or otherwise dialed in?

This is an intimidating affair. I'd be grateful for guidance.

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  #2  
Old 04-15-2019, 12:53 AM
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the removal can cause the injection duration to exceed the ability to burn the fuel dramatically increasing egt without any appreciable power gain. i would recommend around 2-3.5 turns in on the limiter max after that it wont help your power any just make for hotter egt's. all this is assuming you have a turbo or some other way of getting more air into the engine since 616's are basically maxed out stock as far as ability to burn more fuel. the 5.5mm elements are not good for any real power when i went to the 8mm M pump on my 617 it gained quite a lot even off boost from the shortened injection duration and timing.
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1985 300D om617: 8mm M pump 175cc 5200rpm, holset he221w @ 30psi, large A2W ic, compounds on the way.
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Old 04-15-2019, 12:34 PM
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Thanks for the advice.

No turbo (yet). I've read quite a few accounts from other 240 drivers who've only turned up the pump and still realized some gains. I have considered installing a wider intake manifold, however.

Did you also make an adjustment or recommend making an adjustment to Max Throttle Tension?
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  #4  
Old 04-16-2019, 10:47 AM
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yes you should slightly increase the max throttle stop. be careful doing so as too much can cause the governor to bind up. also be sure to check the linkage is moving to the new limit.
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1985 300D om617: 8mm M pump 175cc 5200rpm, holset he221w @ 30psi, large A2W ic, compounds on the way.
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  #5  
Old 04-16-2019, 07:48 PM
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Quote:
Originally Posted by R-3350 View Post
yes you should slightly increase the max throttle stop. be careful doing so as too much can cause the governor to bind up. also be sure to check the linkage is moving to the new limit.
Is there anything I'm aiming for in particular? Or is it an arbitrary number of turns?
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  #6  
Old 04-16-2019, 09:26 PM
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try .5 to 1 at first and maybe 2-3 max be prepared to block the intake in case it sticks the governor. it shouldn't need much to make it use the extra rack travel.
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  #7  
Old 04-17-2019, 08:18 PM
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I really appreciate it.

Two further questions… When removing the back plate from the IP, should I expect a bunch of oil to drain? If so, must I replenish this oil or does it come from the engine after I bolt everything up.

And last, Is the throttle stop adjustment made from the outside of the pump? In other words, I don’t need to have the body open for this?
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  #8  
Old 04-18-2019, 01:20 AM
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theres not too much oil in the pump and the mw is fed from an oil line off of the block by the timing gear hump (the M pumps feed from a hole in the shaft the drives the pump). that being said there may be around a pint or less in there so put something under the car before pulling the cover. also helps to lightly coat the cover in a sealant before reinstalling i like the permatex aerobic sealant since it doesn't grab as hard as rtv but stops oil well. this will make your life easier when you pull it again in the future (you will since once you start getting a bit more power out of it it gets addictive). as for the stops move the linkage and look to see what it hits at either extreme of travel. it should be relatively easy to adjust the stops but again be careful doing so as it can lead to real issues if it binds the governor. i like to have a square of plywood or something similar that will fit over the intake on hand when firing up engines i have tinkered with the pump on just in case.
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1985 300D om617: 8mm M pump 175cc 5200rpm, holset he221w @ 30psi, large A2W ic, compounds on the way.
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  #9  
Old 04-19-2019, 11:40 AM
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Quote:
Originally Posted by R-3350 View Post
theres not too much oil in the pump and the mw is fed from an oil line off of the block by the timing gear hump (the M pumps feed from a hole in the shaft the drives the pump). that being said there may be around a pint or less in there so put something under the car before pulling the cover. also helps to lightly coat the cover in a sealant before reinstalling i like the permatex aerobic sealant since it doesn't grab as hard as rtv but stops oil well. this will make your life easier when you pull it again in the future (you will since once you start getting a bit more power out of it it gets addictive). as for the stops move the linkage and look to see what it hits at either extreme of travel. it should be relatively easy to adjust the stops but again be careful doing so as it can lead to real issues if it binds the governor. i like to have a square of plywood or something similar that will fit over the intake on hand when firing up engines i have tinkered with the pump on just in case.
Excellent points, thank you!
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  #10  
Old 07-31-2019, 01:36 PM
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My 616 has left the 240D it was in and is now in a Jeep Comanche. It recently had 617 turbo manifolds and a stock K26 turbo added. I spent a lot of time getting the pump dialed in pretty well while the motor was in the car and found this thread while I was refreshing my memory on pump adjustments since the turbo needs more fuel.

In my many, many adjustments to the stock OM616 MW pump from an 80 240D, here is a quick mental dump from what I have learned. I also followed the Pump Theory google doc and have talked with the guy who wrote it quite a bit.

Word of caution: the google doc says to get an EGT gauge. I strongly suggest you do this. I bought one for $22 on ebay. I drove it for a month after adjusting the pump and before I put the EGT gauge on. There are a couple long climbs on my commute that I found my EGTs were getting way too hot. I put a new head gasket on before the turbo as a preventative item and did not see any damage to the gasket, head, or pistons but it was definitely a gamble.

I reused the gasket on the back cover probably a dozen times before it finally broke and started to leak. Several ounces of oil will come out depending on how recently the engine was running but it is not like you lose half a gallon. I immediately got rid of the straight slot screws and swapped them for normal bolts so I can use a 1/4" ratchet to get it on and off easier.

Timing helps noticeably. If nothing else, marking the pump and bumping it 1/8" advanced will make up for the chain stretch the motor probably has. Lot's of info out there on how to properly drip time pumps.

Torque capsule: tricky to adjust because of slotted jam nut. Much more than 3 turns in and it becomes impossible to adjust the idle to a point where it is happy. It does make a pretty good off the line difference. Adjusting the idle can be annoying. I eventually started leaving the back cover off while I set the idle because there isn't that much oil flowing through there in the 20 seconds you need to find the sweet spot.

High idle screw: I found this is where I got the most power increase from. Possible to adjust this by only removing the vacuum shutoff and leaving the cover in place which is a bonus.

Rack limiter: also makes a noticeable difference at full load, but has a significant impact on EGTs. I basically have my torque capsule in 3 turns and a longer than stock high idle screw for as much throttle response as possible and use the rack limiter to keep EGTs in check.

With the turbo, I am now in the process of dialing the rack limiter back in to where my EGTs are OK.

Overall, I would approach tuning these pumps with caution but if you take a spin through that google doc a few times and get your head wrapped around what you're doing, it's not too bad for a competent shadetree mechanic to tinker with IMO. It definitely makes the car noticeably better to drive.
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Old 07-31-2019, 05:51 PM
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This is incredible, thank you.

Few questions...

1.) In your torque capsule section, you also mention adjusting the idle. I have two images, each with different names for the two internal screws that have anything to do with idle.
On image a (from top down), there is something labeled "High idle, Maximum RPM," and below that and to the left of the full load/rack, something labeled, "Coarse Idle Rpm screw"
On image b (from top down), these positions are labeled, "Max Rpm limit" and "Idle governor spring"

I hope that's clear... So which idle adjustment are you referring to? Does adjusting idle become necessary after fiddling with the torque capsule, or just necessary in general after adjusting anything on the pump (like rack for instance?)?

2.) Did you make these adjustments pre-turbo? and if so, did you modify your air intake in any way? what was the difference like?

3.) When you saw the EGTs rising, how did you respond?
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  #12  
Old 07-31-2019, 07:47 PM
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You will most likely have to adjust the idle after adjusting the torque capsule. The screw labeled idle governor is what you need to worry about adjusting. Three turns in on the torque capsule will likely need roughly one turn in on the idle governor screw, but you’ll need to play with it yourself.

All of the tuning I did on the pump until last night was before I turbo’d the engine. I did not modify intake at all and deleted the second muffler. The pump adjustments absolutely help it drive better even without a turbo, particularly the torque capsule and high idle (max rpm limit in the pic above). Those mods help off the line and low to mid range.

I use the rack limiter to set max EGT. All of these adjustments inside the pump affect how much the governor and your right foot affect rack travel. Your foot on the floor wants to pull the rack forward, the governor is constantly limiting how much it can move forward based on RPM. If you could have full rack movement all the time, you’d be able to turn the car behind you black with soot. What the rack limiter does is provide a dead stop for the rack. Even if you have your foot on the floor and your high idle screw set aggressively, the rack will not move further than the limiter (which does not move once you set it).

I have the high idle and torque capsule set very aggressively for getup and go but the rack limiter set to keep my long hill foot on floor EGTs around 1250-1300.

Hope this helps. Happy tinkering!
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Old 08-03-2019, 11:27 AM
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Again, thank you... that's really encouraging to read. Half the responses I've gotten have alluded to pump adjustments making no difference unless one can also increase airflow -which I intend to do down the road, perhaps by adding a turbo. For now, however, I'd be quite happy with a little more pep in my 616.

Aside from the EGTs, any other disadvantages you experienced by "turning up the pump?"
(smoke? fuel economy? ect)

Also, do you recall the number of turn-ins you gave your rack limiter?
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  #14  
Old 08-03-2019, 07:04 PM
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Contact Dave a/k/a OM616 on the forums. He’s probably done the most tinkering with the 4 banger I had a thread on STD started a long time ago You can do some things to make it peppy but it’s a 4 cylinder indirect combustion MB engine which is probably tired. If you want to invest up to $8k you can have a kickazz 4 banger
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  #15  
Old 08-05-2019, 05:37 PM
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I did not find any negative effects from the pump tuning. Easy enough to keep it from smoking and little timing advance helps economy.

Agree with everything Greazzer said. It will be a little peppier, maybe a 10% increase but will not be transformative. The turbo on the 616 in my Comanche has been absolutely transformative.

Dave is the man... he is the one who wrote the google doc. Most of what I have provided I found while tinkering under his guidance.

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