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M2 hard start

Skyline

Expert Expediter
Owner/Operator
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Here is a challenge for all. I have a Freightliner M2 106 with the 260hp Mercedes. About a year ago I started having starting problems. This happened in both warm and cold weather. I replaced filters, checked wires and did everything possible. Some tech on the internet suggested I replace the check valve located between cylinder 5 and 6. I did this and at the same time bled the diesel at the injectors. I can not remember if there was much foam at that time I did bleed the diesel. I also unplugged both the computers and checked the connections. I basically fiddled everywhere. I started the truck and never had the problem again until two weeks ago. I did everything again as last time, except replacing the back flow valve. I do not think that it can be the valve again, as anyone rarely replaces this valve in the first place. I did bleed the diesel at the injectors thoroughly, bit there is lots of foam and I am not sure if this is air or just the pressure? I checked for leaks, and tightened everything a possible could. Once the truck sits for a couple of minutes it would struggle to start, 9 out of 10 times. Batteries are very strong. No fault codes. It definitely sounds as if it first has to build fuel pressure again. Could also be the ignition that controls the compression relief? What really baffles me and what I do not understand, is that, if I let the truck roll slowly and clutch start (manual) it, the engine fires immediately without any hesitation! Where did the fuel come from suddenly? Why does it start easy now? This mystery is beyond my understanding. Thank you in advance for any feedback. Kind regards.
 

davekc

Senior Moderator
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Could be a crack in the back flow valve. Fuel pressure at ignition start is different than a clutch start. My advice would be to pressure test the fuel system with a set of gauges. It could be a leak in the lines all the way to one or several of the injectors. That type of leak won't likely throw a code. A drop in voltage outside of the parameters at the pump would so it wouldn't be the first place to look.
As strange as it sounds, we have a truck do something close and it wound up being a gasket from a fuel filter that separated at removal. They installed new filter and we now had two gaskets. Air pulling in between was making it difficult to start. Certainly a strange one. emoved the old gasket reinstalled filter and no problems.
 
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BobWolf

Veteran Expediter
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Most engines use a set of O rings these can wear and allow air to be forced into the fuel system on the compression.
 

Skyline

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Thank you Bob and Dave. These are very valid points and I will have it checked.
 

usafk9

Veteran Expediter
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I'd second Dave's comments, particularly with attention to the fuel pump. I've gone through one, and I know of another who has gone through two. Also, I'm a bit curious if the intake grid is heating.

Lastly, 'cracking' those high-pressure lines is a bad idea. The inside of those nuts is coated with a teflon film, and is good for torquing down one time......when it is installed. I'd keep a close eye on those, specifically if yours don't have a small rubber and metal damper on them. Then you'll see exactly how strong your fuel pressure is...when it sprays all over the inside of your engine compartment. Ask me how I know.

Nevermind. Don't.

At any rate, can you please report back your findings? I'm well invested in these engines, and always love to learn more.
 

Skyline

Expert Expediter
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I will check on intake area. I know you are well invested, in the form of a new engine recently? ha. I will certainly make my findings known to you all. Thanks again.
 

Skyline

Expert Expediter
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Needless to say, the problem went away right after I did this post and will probably stick its ugly neck out at a very inconvenient time in the future.
 
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