W123 Performance/Maintenence: Fuel pressure testing, Overflow valve teardown (WK716 and BF7591D)

Gotta have fuel to make power. We test the fuel pressure on our W123 to see if it could be causing any issues.
This tests the Overflow valve and Lift pump (and kinda fuel filters as well)
If there is something restricting the flow like a clogged filter, the overflow valve spring has collapsed, or the lift pump has failed it could drop your power dramatically, or possibly even cause stalling, hard starts or worse!
Not a hard test, and pulling the overflow valve apart isn't rocket science either, Come along as we dig into more of our fueling system.
Key things in video:
0:00 Introduction
1:12 Component locations
2:13 Needed stuff
2:57 Use 17MM wrench to remove outlet fitting from secondary filter
3:07 Stock fitting removed
3:20 Modified banjo fitting
4:05 Prime system to get air out
4:32 Fuel pressure with stock filter
5:30 Healthy pressure.
6:02 Disassembling overflow valve and “repairing”
9:28 reassembling overflow valve
10:30 pressure with BF7591D 2 micron filter
10:58 The one caveat to running a finer filter
11:36 My thoughts on why you want the 2 micron filter
Here are some links to products we used in this video on amazon in case you want to try this, purchasing from these links may earn us a small commission that helps us keep doing videos like this one:
M12x1.5 Tapped Banjo bolt: hamzn.to/2yRTRkN
1/8 NPT to ¼ Flare fitting for fuel pressure gauge below: amzn.to/3a1aSpk
Fuel pressure gauge: amzn.to/3e9nwpr
Alternative gauge for possible permanent installation:
Gauge itself: amzn.to/2UZmlBI
90 degree Elbow: amzn.to/39XZWbS
Use the same M12x1.5 Tapped Banjo bolt: hamzn.to/2yRTRkN
Things you need to use the gigantic primary "prefilter" that I have:
Filter housing: amzn.to/31lon0T
Mesh filter: amzn.to/39VP14r
Fittings: amzn.to/2XqYBHq
3/8 fuel line: amzn.to/3gtDdZy
Clamps for fuel line: amzn.to/31mavUd

[@trythistv]

Here are some links to products we used in this video on amazon in case you want to try this, purchasing from these links may earn us a small commission that helps us keep doing videos like this one: M12x1.5 Tapped Banjo bolt: hamzn.to/2yRTRkN 1/8 NPT to ¼ Flare fitting for fuel pressure gauge below: amzn.to/3a1aSpk Fuel pressure gauge: amzn.to/3e9nwpr Alternative gauge for possible permanent installation: Gauge itself: amzn.to/2UZmlBI 90 degree Elbow: amzn.to/39XZWbS Use the same M12x1.5 Tapped Banjo bolt: hamzn.to/2yRTRkN Things you need to use the gigantic primary "prefilter" that I have: Filter housing: amzn.to/31lon0T Mesh filter: amzn.to/39VP14r Fittings: amzn.to/2XqYBHq 3/8 fuel line: amzn.to/3gtDdZy Clamps for fuel line: amzn.to/31mavUd

[@Hopeforpeace]

Thank you for showing me all the different shortcuts love your videos.❤

[@makingcookingfixing]

Super helpful video! Thank you! Great to se how that overflow valve works and where it is located. I have a hard starting problem, and I'll be ordering this valve and a lift pump and valves for it.

[@trythistv]

Glad it helped you out! I'm working on a video testing my lift pump and overflow valve for proper flow right now.

[@ebutuoyebutouy]

Precise, concise, and articulate. Nice. Thanks for sharing.

[@trythistv]

Thanks for the compliments! I've got some more really neat stuff in the works for this car!

[@thisis777]

Thanks, great! The spec for OM617 fuel bypass valve is 0.6-0.8 bar at idle speed and min. 1.3 bar at 3000/min.

[@rebor9022]

Yes, Mercedes recommend lengthening spring to 26-27 mm.

[@trythistv]

Excellent information! So vaguely 8-10 psi at idle rising to near 19 psi at 3000rpm, I'm happy knowing mine is a squeak above that, if nothing else it will help fill the elements nice and quick, worst case I get a little less flow through the OFV because its a bigger restriction

[@rebor9022]

Yes, and fuil pump is old. Valves in pump have a wear. That is the reason to stay in the mb spec and don't rise pressure higher.

[@RomanDirge]

This is a super helpful series, just saved a w123 from the crusher this week and these have been great for understanding what I’m looking at! Keep it up! I’ll be modifying mine with you lol

[@trythistv]

I've got more videos coming eventually if I can ever get work caught up, it's been wild the past couple months!

[@RomanDirge]

@@trythistv you can do it! The internet needs you!

[@IncahootswithChrist]

Great video. Good breakdown of the fuel pressure regulator. Not many people even know it exists. Also, kudos on the 2 micron filter/water separator mod. Agreed that it may foul sooner but the advantage of filtering out more debris is [in my opinion] well worth it. This could even prevent injector fouling and/or cylinder wall scoring. Love the videos (and OM6XX engines) hitting that subscribe button.

[@trythistv]

I wish I had the brains to have made this video back when I first found one that was so collapsed the car would barely run. This one was quite healthy, I'm looking into a readily available spring to replace the collapsed ones so that we don't have to stretch and hope for the best, I'll be sure to post an update once I figure something out on that front!

[@pinzgauernorcal]

these videos are very useful thanks!

[@jdere31760]

Trythistv, BRILLANT! Excellent how to video on fuel pressure checking a W123.

[@trythistv]

Thank you very much! It's a critical part of getting proper performance, and some have suggested that excessively low fuel pressure could cause accelerated wear on cylinder 1, I'm not certain on the reasons, or if that is true but it's not hard to avoid!

[@ImpalamansGarage]

Really good tips! Thanks!

[@trythistv]

Thank you! I've got plenty more stuff in the works, work is killing me right now though, trying to squeeze in some video stuff when I can though!

[@CrToloss]

I appreciate your videos ❣️❣️❣️

[@trythistv]

Glad they're helping you out!

[@coachgeo]

you happen to have any info on the "nippled fitting" into this lift pump? Am converting to AN6 fittings and really need this to replace all my horrible fuel lines and leaks. (on a horribly done customized conversion yet.... HAS to be my daily driver ASAP)

[@trythistv]

I'm fairly sure the inlet and outlet fittings also serve as the check valves for the lift pump, I'm not sure what option there would be to convert to AN without removing the fitting, getting the check valve and any portion that could be damaged by heat removed, and then welding or brazing a fitting to the barbed portion.

[@livium2002]

Awesome results !

[@Robin96]

I replaced the overflow valve on my mercedes 124 with om602 NA engine. I buyed it on ebay, there was this model and a model that is for 124. I choosed the 123's model because the newer model was quite expensive. The car starts up better now and the jerking stopped when i floor it on 1200 rpm

[@trythistv]

Good deal! Having good fuel pressure makes an alarming improvement in performance and even starting and such as you noticed. Probably keeps the injector pump healthy longer too

[@pinzgauernorcal]

can you do a video about auto trans including Bowden cable, VCModule, Vmodulator instructions on adjusting each, testing internal pressure of trans.

[@trythistv]

That is an excellent idea! I may have to break that into more than one video due to the complexity of the transmission adjustments, but I'm sure plenty of these cars are running around with poorly adjusted transmissions that would benefit! I will put it into my list of things I want to make videos of! Thanks so much for the reccomendation!

[@leandrocarvalho2573]

Perfect video! Congratulations. Could you help me? In my engine, the pump works very well in neutral shift. Rpm reach a red range in the indicator, and my pump shutdown to idle condition. But When I work shift in "D" ( the engine need more fuel flow), my pump don't reach the red range! The pump shutdown in 3000 rpm ( white range). What's happening? I saw everything, less this overflow valve and the control valve on booster pump discharge. Help me my friend. 🇧🇷

[@trythistv]

The first things that come to mind are fuel filters (Remember, there are 3: the tank strainer, little plastic "primary" right before the lift pump and the spin on "secondary") If your filters are good and you've got good fuel pressure, the next thing is boost, the banjo fittings on the intake and ALDA tend to clog up with soot if your car is equipped with EGR, they can be unscrewed and cleaned out, the "overboost solenoid" is another common failure point, I made a video showing some of those things to check here: kzbin.info/www/bejne/onKqdqSijpypj7c I'd run a gauge to where I could see it while driving, and if the fuel pressure isn't dropping out under load then it has to be the ALDA limiting fuel, which could be the banjo fittings, overboost solenoid or turbo isn't making boost pressure

[@ronstahr]

pls provide a link to where to buy the filter mod - love the vids !!

[@trythistv]

If you mean the 2 micron secondary, I've got a video on that mod: kzbin.info/www/bejne/gISwgGiJg8trnbc Which you'd need these products to replicate: Time-sert 14155 (10 pack): amzn.to/2U7HUOS Baldwin BF7591-D: amzn.to/38I9lE9 Or if you're talking about my giant primary filter/strainer mod that I haven't made a video on yet, but solved my issues with terrible quality diesel around my area: Filter housing: amzn.to/31lon0T Mesh filter: amzn.to/39VP14r Fittings: amzn.to/2XqYBHq 3/8 fuel line: amzn.to/3gtDdZy Clamps for fuel line: amzn.to/31mavUd

[@ranger854433]

hi ,i have a 1985 OM616 , when i pulled the overflow valve the bolt was there but the ball and spring are missing , the end of the bolt is open that goes into the pump , any help or advise , should i maybe add in a fuel pressure regulator into the return line , if yes what pressure should i set it at , please reply

[@trythistv]

I'm fairly certain there should be a ball and spring, you did get the right one? The inlet from the filter should be a straight through banjo fitting, but the return that's between the IP and the block should have the spring. I've seen people mix them up when assembling a pump and it makes the car run terrible. Pressure should run around 20ish psi and not drop below 10 under full throttle full load conditions (like pulling up a steep hill with the throttle floored)

[@ranger854433]

@@trythistv so should i install a adjustable fuel pressure regulator on the return line and set it to say 18 psi , or what do you think,,

[@trythistv]

Certainly worth a shot, keeping that pressure in the IP has got to help, some of the newer engines used an oriface instead of the overflow valve but the 616 and 617 should have been the same for the entire run, I think the 60X series was when they switched away but I may be waaaay off on that, adding a pressure regulator can't hurt, especially if you can check your pressure like I did in this video and verify that it is staying up around 20ish psi, low fuel pressure isn't good for performance, and can slowly hurt the IP and engine, usually it'll cause accelerated wear on cylinder 1, but would take quite some time to do so.

[@pmkleinp]

My friend's spring was 20mm.

[@trythistv]

That isn't awful by any means, but is still squished down enough the fuel pressure could be a bit lower than ideal for sure.

[@almazplusmaria]

hello! can you please make a video about adjusting injection pump drip method please

[@trythistv]

I'm planning on it! I'm gathering all the stuff for injection timing, and a bunch of transmission stuff too, along with a whole list of other things I wanna tackle incrementally