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Go Back   PeachParts Mercedes-Benz Forum > Mercedes-Benz Tech Information and Support > Diesel Discussion > Diesel Performance Tuning

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  #31  
Old 12-04-2014, 03:01 PM
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Quote:
Originally Posted by OM616 View Post
At that pressure with the stock pump spring, how much by pass fuel are you seeing?
You are right, the overflow volume decreases a little bit, but not that much.
Tested with my old untouched presupply pump with 130k miles on it I had like 10%less overflow volume.

Or to give an example. This August I had some fuel with ~50% gasoline in my car.
After I went shopping (I drove the car for 1hour before) the car would not start when I wanted to leave after 20min shopping because of vapor bubbles in the fuel system.

1. cranking 2 seconds long - nothing happened
2. cranking - after 5 seconds I already heard a few cylinders reporting for duty and stopped
I did wait 5 seconds
3. cranking - after 5 more seconds the engine ran, not nice, but it ran.
And after hitting the gas once the idle was normal.

What I want to illustrate with the example, the overflow volume is still quite sufficient. Even with the wrong fuel.

Quote:
Originally Posted by OM616 View Post
....I installed a stronger pump spring in my pumps and am running 30/36 psi with a good amount of bypass fuel.
Be careful with stronger springs. Too strong springs in the presupply pump can cause bad engine behaviour.

Diesel fuel canīt be compressed and so it does not store any pressure. The spring in the presupply pump can store the pressure so to say.
If the spring in the presupply pump is too strong the pump stroke is finished earlier through the bigger spring force, but the time until the pump-cam loads the spring again is too long then. In that case the oscillating pressure can cause uneven fuel loading of the elements.
I donīt say it will, but it can.

Gruß
Volker
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  #32  
Old 12-06-2014, 01:35 PM
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I guess I will try streching my springs and see,what happens
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  #33  
Old 12-16-2014, 02:39 PM
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I went to adjust mine,found no spring,now it won't start.
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  #34  
Old 12-16-2014, 03:47 PM
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Performance Overflow Valve

Quote:
Originally Posted by oldsinner111 View Post
I went to adjust mine,found no spring,now it won't start.

What car? Engine?


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  #35  
Old 12-16-2014, 03:51 PM
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w126 1983 300sd>cracked injector lines,and fuel weeped out of them.
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  #36  
Old 12-16-2014, 05:11 PM
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If My primer pump worked I could bleed all air out.But Its been no good for 4 years.Guess I'll put my electric pump on it to prime it.
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Last edited by oldsinner111; 12-17-2014 at 04:34 AM.
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  #37  
Old 12-18-2014, 05:04 PM
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Quote:
Originally Posted by volker407 View Post
Be careful with stronger springs. Too strong springs in the presupply pump can cause bad engine behaviour.

Diesel fuel canīt be compressed and so it does not store any pressure. The spring in the presupply pump can store the pressure so to say.
If the spring in the presupply pump is too strong the pump stroke is finished earlier through the bigger spring force, but the time until the pump-cam loads the spring again is too long then. In that case the oscillating pressure can cause uneven fuel loading of the elements.
I donīt say it will, but it can.

Gruß
Volker
One issue I found after installing a stronger pump spring was that the fuel pressure was erratic because the pump could not fill fast enough. i opened up the check valve passage ways which helped a little, but I found that installing a large prefilter vertically so it had an air pocket in it solved the problem. The air in the filter would act as an elastic of sorts, allowing the fuel pump to draw in a charge quickly and then the lower pressure in the filter would draw fuel in slower, like a capacitor does for an electrical circuit.

When I put the engine in the 201 chassis, I used the electric fuel pump to supply the lift pump. I made a pressure regulator to control the pre lift pump pressure, that really made a difference on the top end fuel supply. The stronger pump spring makes the lift pump really want to pump a lot of fuel so I am able to maintain a high pressure with more return flow that OEM. I can see the pressure pulses being at a higher frequency if the return flow was restricted, (not allowing the piston to follow the cam and bouncing off the top of the lobe). I am running a higher volume bypass as well and my thinking is in order to have increased volume, the piston must be following the cam profile closer on the return side, so it could then be argued that the pump frequency should be lower that OEM.. All theory of course..

My goal was to increase fuel supply and pressure, pressure frequencies were not a consideration really, but worth keeping in mind should any strange performance be experienced..
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  #38  
Old 12-19-2014, 09:33 AM
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what happens if spring and ball is missing?
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  #39  
Old 12-19-2014, 12:27 PM
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Quote:
Originally Posted by oldsinner111 View Post
what happens if spring and ball is missing?
Nothing, or almost nothing. The engine wonīt start or if it starts it will have no power.
I think it would make sense for you to buy a new overflow valve and a new hand-primerpump

Gruß
Volker
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  #40  
Old 12-19-2014, 03:19 PM
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I will have to wait for tax refund time
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  #41  
Old 12-19-2014, 04:25 PM
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If you have any left and it will fit the M pump, I'll take one. Circumstances require me to remove the IP again so I'll install your valve while I'm at it. Do they come with new crush washers?
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  #42  
Old 12-19-2014, 05:30 PM
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Quote:
Originally Posted by KarTek View Post
If you have any left and it will fit the M pump, I'll take one. Circumstances require me to remove the IP again so I'll install your valve while I'm at it. Do they come with new crush washers?
I have 2 springs left. I should have another 10 after the New Year sometime. I "have" a box of OFVs but cannot locate them. My overall marketing strategy needs to be tweaked because OFV (the first 10 to 15) was supposed to be no biggie. I figured I could replace those sold through trips to the yards, but I have not been able to hit the yards like I used to (stupid back), plus I did not think I would be dumb enough to misplace the ones I had.

So, I am now offering the following"

$40 shipped BUT $5 refund if you send back your old OFV (assuming it's rebuildable.). I sort of feel bad delaying folks ... especially since my garage is a little disorganized. No aluminum washers. I think they are around .35 cents a pop. The refund has to be within 45 days of original purchase for PayPal to permit refunds OR I have to catergorize the transaction as a dispute. I prefer to avoid that.

PM if interested.
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  #43  
Old 12-19-2014, 05:31 PM
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And yes, M pump is fine. I have a "M" pump on my OM617.912 and it has one of these little gems.
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  #44  
Old 12-20-2014, 04:55 AM
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I thought both springs were on the fuel filter holder.I checked both,but no springs.I was careful in case a spring shot out.
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  #45  
Old 12-20-2014, 07:53 AM
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Quote:
Originally Posted by oldsinner111 View Post
I thought both springs were on the fuel filter holder.I checked both,but no springs.I was careful in case a spring shot out.
Take a peek at posts #1 and #7 ... it shows what the OFV looks like and it's general location. Springs on a fuel filter ????
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