I 'tightened' up my diesel return fuel lines.....wow! - PeachParts Mercedes-Benz Forum

caracine · #1 04-01-2019, 04:17 PM

Hi everybody,

I thought I 'd share the outcome of my latest adventure with dealing with engine shake at idle in my 1983 300D Turbo Diesel.

Of course, we all know the benefits of having a breach-free, non-leaking fuel system in our diesels. Any air aloud into the fuel system will make performance suffer to say the least.

This means no leaks or soft connections of any type on the input side before the lift pump AND on the pressure side after the lift pump.

Keeping hose-clamps on the rubber hoses
tight and the clear fuel lines around the secondary fuel filter leak-free has been discussed and is widely known for the most part.

Here's my discovery and I apologize if this has been discussed before:

I recently changed my return lines that run from each injector in a series and was not too happy about how tight they were.

I know that leaking return lines have a lot to do with how smoothly these engines run at idle so I decided to install small fuel injection hose clamps on each connection to make sure they didn't leak.

All I can say is- wow! What a improvement on not only idle but on throttle response and power. This car that I've owned happily for 11 years (with 363K) has never felt this way. The amount of torque this engine can have, without any other modifications, is making my neck sore.

The improvement in the power-band in each gear is simply awesome. I can now take the Santa Cruz mountains freeway with no kick-down issues due to lack of power. I don't even notice when the turbo kicks in like I did before.

I highly recommend this cheap fix for all return lines on the OM617.95x diesel engines.

I bought a bag of (20) small fuel injection hose clamps on Amazon for about $12 so it's not a risky prospect.

I'd like to know if others have done this to their return lines and what the outcome was if possible.

Just thought I'd share this tid-bit of info. This forum has help me keep this car on the road all these years! Thanks!

Have a great day!

Chris Racine

Shern · #2 04-01-2019, 05:08 PM

Interesting... Can you share a picture?

Quote:

Originally Posted by caracine

Hi everybody,

I thought I 'd share the outcome of my latest adventure with dealing with engine shake at idle in my 1983 300D Turbo Diesel.

Of course, we all know the benefits of having a breach-free, non-leaking fuel system in our diesels. Any air aloud into the fuel system will make performance suffer to say the least.

This means no leaks or soft connections of any type on the input side before the lift pump AND on the pressure side after the lift pump.

Keeping hose-clamps on the rubber hoses
tight and the clear fuel lines around the secondary fuel filter leak-free has been discussed and is widely known for the most part.

Here's my discovery and I apologize if this has been discussed before:

I recently changed my return lines that run from each injector in a series and was not too happy about how tight they were.

I know that leaking return lines have a lot to do with how smoothly these engines run at idle so I decided to install small fuel injection hose clamps on each connection to make sure they didn't leak.

All I can say is- wow! What a improvement on not only idle but on throttle response and power. This car that I've owned happily for 11 years (with 363K) has never felt this way. The amount of torque this engine can have, without any other modifications, is making my neck sore.

The improvement in the power-band in each gear is simply awesome. I can now take the Santa Cruz mountains freeway with no kick-down issues due to lack of power. I don't even notice when the turbo kicks in like I did before.

I highly recommend this cheap fix for all return lines on the OM617.95x diesel engines.

I bought a bag of (20) small fuel injection hose clamps on Amazon for about $12 so it's not a risky prospect.

I'd like to know if others have done this to their return lines and what the outcome was if possible.

Just thought I'd share this tid-bit of info. This forum has help me keep this car on the road all these years! Thanks!

Have a great day!

Chris Racine

Diseasel300 · #3 04-01-2019, 06:03 PM

If you used the correct size hose in the first place, no clamps would be required. The return side of the fuel system is only under a couple PSI during operation, clamps are dramatic overkill.

BWhitmore · #4 04-01-2019, 06:28 PM

It seems like in this case the clamps made a big improvement for a small cost and a small amount of labor.

hercules · #5 04-01-2019, 10:16 PM

Thanks for sharing. Question:were the fuel hoses not a tight fit.
Normal fuel injector return hose is 3.2 mm inside,3.5 mm works but is
not as tight,poss leak after a while. So,is this a good fix for us all or worked
because fuel hoses were oversize??

OM617YOTA · #6 04-01-2019, 11:37 PM

I've had great service with 1/8" fuel injection line. 1/8" = 3.175mm

Not "original" but when it's in a swap anyway, I don't worry about it.

renaissanceman · #7 04-02-2019, 12:50 AM

If any of you need true 3.2mm nylon braided viton rubber hose, PM me. It's nice stuff. Should solve any air issues without clamps, but I had some flat spring clamps made too. I havent tested them on my Mercedes yet, though.

Diesel911 · #8 04-02-2019, 07:15 PM

Quote:

Originally Posted by BWhitmore

It seems like in this case the clamps made a big improvement for a small cost and a small amount of labor.

I skeptical about that. I have 2 times on the Mercedes and 3 times on my Volvo Diesel that uses the same Injector Bodies and return system had return hose leaks and never had it effect the idle on either Engine.

I only knew I had leaks by the smell.

Never seen that to be the case when I worked in a Fuel Injection Shop either.

So for now for me it remains a theory that needs to be supported by info from others.

Shern · #9 04-02-2019, 07:21 PM

That restored power drove him right out of his thread...

renaissanceman · #10 04-02-2019, 07:31 PM

I'm pretty sure return lines have nothing to do with power, air in the system, etc.

On the other hand, air in your return lines can indicate air ingress elsewhere in the system.

barry12345 · #11 04-02-2019, 08:17 PM

Unless someone can explain what occurred. I have to wonder if elimination of the leaking allowed more pressure to develop on the backside of the relief valve. Present by gravity normally plus a slight buildup with system flow. I would have to look if a bad secondary fuel filter may be involved.

Over the years I remember some complaints when the hoses where leaky. Yet never a signifigant power loss. Unless I missed it. I slightly remember some concerns as a source of air causing issues was suspect. This I can see at idle.

In general I felt most hoses where replaced rather than waste fuel.

Graham · #12 04-02-2019, 08:40 PM

Quote:

Originally Posted by barry12345

Over the years I remember some complaints when the hoses where leaky. Yet never a signifigant power loss. Unless I missed it. I slightly remember some concerns as a source of air causing issues was suspect. This I can see at idle.

In general I felt most hoses where replaced rather than waste fuel.

I recall there being starting problems on some diesels when return lines were leaking. Never understood why but the truck owners did have a theory (likely air related)

On w123, I bought the proper OE hose and they don't leak. Had to make a new plug for the end that fitted properly.

I have bought those small clamps off Amazon and used them on the return line on a marine diesel. But it had different size hose.

By the way, OP also posted on Benzworld-Diesel. Someone from AutopartsArizona posted something that just made the OP look stupid. Seems to me, not smart for company to do that to potential customers!