M1211

I know there are very few 2.7 CDI diesels in the US but here goes anyway.

The engine takes a lot of cranking to fire up, sometimes it seems it won't fire.
I've replaced the fuel line 'o' rings (common issue on the early CDI). I didn't expect that to resolve this as it's usual that the 'o' rings is a cold temperature issue but aimed to eliminate as a problem anyway.
I've replaced the fuel filter, no improvement. The first filter is only a month old anyway.

I've checked the fuel pump connection and this sees only 4.5 volts (is this a red herring)? The shut down relay passes full voltage.

The issue is, I believe, air in the fuel system. When running I can see air with the diesel in the clear fuel line coming out of the fuel filter.

My thoughts are that the air is getting in at the fuel tank, possibly at the fuel pump ??

Forward of the fuel tank, underside, there is what I believe to be a cooling radiator for the return line, to cool the fuel before it re-enters the tank is my theory.

Does any one have knowledge of this issue ?
Should the pump be fed by 12 volts ?

Thanks in advance for any help.

dave1123

I'm not experienced with diesels but here goes. IMO, the fuel pump is suspect. Low supply voltage and air in the fuel are obvious clues. Can you test your fuel pressure? Do you have electronic injectors? I know the older Cummins 250 diesels had mechanical injectors and fuel pressure was low. I would think with electric injectors you should have at least 40 to 50 psi.

Well, I've blown my wad, as the saying goes. Hope it helped.

Afterthought; Air in the fuel line shows a leak on the intake side of the pump. Possible the intake screen.

M1211

Thanks for the thoughts.
The common fuel rail should have a pressure around 200psi I believe, but can't test this myself. Yes electronic injectors rather than mechanical.
I'm with you on the fuel pump intake but still question the low voltage signal to it.
On the underside of the fuel filter there is, what I perceive to be a pressure transmitter. It seems to require supply to give, as I perceive, a variable output. It may be that this causes a varying supply to the pump dependant on the pressure in the filter ??

Last night I had thought. So far as I've been seeing air at the output side of the filter supplying the high pressure fuel pump I've been assuming that air must be getting in backwards of that.
The return fuel line also passes through the filter, I'm guessing again, but this could be drawn back through the filter toward the high pressure pump again. The transmitter calling for more from the tank when pressure has dropped ??
If this is correct the air could be ingressing along the return line somewhere and then just circulating in a loop to confuse me.
Later today I intend to clamp the return into the filter to see if the air ceases.

First I must go sailing today though, cos I'm addicted.

All thoughts greatly appreciated.

ol"blue

Maybe this will be helpful. >http://www.4x4community.co.za/forum/...ad.php?t=96721


Or this. >http://www.fixya.com/cars/t13195557-...rokee_crd_2_7l

mxpxpunkrock1987

have u replace the glow plugs as these can be at fault if u did the fuel injection service and its having a hard time starting

dave1123

Hey, M1211, You're a man after my heart. I love sailing. I did most of mine off New England around Newport RI. Since I moved to upstate New York, I haven't had much opportinity. I love keel boats and the only place around here is Lake Ontario where most people have daggerboards or cats.

I still think your air leak is in the supply pump intake. The return line would show a fuel leak because it's still pressurized. I think you are right about the pressure control on the filter. It would only need to replace what the engine burned. Sounds like the high pressure system is a closed loop. You need a negative pressure to suck in air.

M1211

Wow, the thought of sailing some where like Lake Ontario, fantastic. Our little lake, by comparison, has erratic, flunky winds and when you do get going it's not long before it's time to tack. As I'm a novice and sailing my own L2 (often single handed) it'll do for now. Great fun and the swimming is good exercise too.

Now this Jeep thingy. It's not too difficult to discount the glow plugs, a warning light would indicate issue and these engines don't really need glow plug start till well into the minus temps. We're just getting down to zero as yet. Also, get it running, turn off a few minutes, and it's being the ***** again. And there is the air in the line.

So today, after my other thoughts, I have being squeezing pipes to see if the air disappears. The only one that does this is squeezing the return line from the back of the fuel rail to into the filter. Squeeze closed the air all but disappears, release and there is the air again.
I had considered already that the lower pressure side of the HP pump could suck air if the circuit is actually a loop through the HP pump.

So I now sumise that air is getting in at the rear of the fuel rail. Aside from the union where the pressure sensor screws into the rail there is a small flexi from the injectors leak off, then there is the return that goes forward to the HP pump.
I feel (hope) I have eliminated all other possibilities so now I aim to remove the fuel rail, strip the back end, and rebuild resealing as I do.

This on a motor with only 51k miles, I guess I'm just unlucky.

The link to the copper washer issue sounds more like the fairly common 'black death' problem with Merc diesels (maybe others too ??). I can't see how the seal of injector to head could cause any 'air' to pass. It's an excessive term but relates to the passing of gasses by the copper ring seal leaving tar deposits on the head. The engines can still run well enough but with a smell in the cab and a put putting under the bonnet.
Remove injector (can be a problem if the issue has been left), clean the head very well, new washer, clamp bolt, and all should be good. Great care taken to clean the bolt hole or the head can be punctured by swarf.
On these though if it's either of the rear 2 injectors blowing the head needs to come off as they're under the bodywork. I would be tempted to use a hole saw from above, but hopefully I won't have the problem.

dave1123

I'm trying to picture your system in my head. I'm pretty good with hydraulics. You must have a pressure control of some sort on the back of the fuel rail that bleeds pressure to the return. The return is probably under negative pressure because of the suction of the high pressure pump. You are right! you could be getting air into the return line. I should have awaken to the fact that that line is clear plastic and would not withstand a lot of pressure. Duh!

If you are getting air into the injectors, that could account for all kinds of erratic combustion.

My sailing experience was with a 16 foot Cape Cod Knockabout. Heavy lapstrake hull and very forgiving. We used to enjoy "frostbiting", that is sailing when it was cold enough to freeze the spray on the canvas that would shatter when we came about! We pushed the limits by sailing in water that was cold enough to kill us if we capsized. Ah, to be young again!

M1211

I'll attempt to describe, although a drawing would be better I'm sure.

From the fuel tank, I assume pumped. Although the 4.5 volts could feasibly be reading across the resistance of the float level winding. I would expect one wire feed to this though going to earth via the resistance winding.

Fed to filter, from filter to low pressure pump.
From low pressure pump to high pressure pump, this line has a 'T' to the pressure check point.

From high pressure pump to fuel rail, this being the common rail to the 5 injectors. This point being the end of any feed line and any 'high' pressure feeds.
The fuel rail has a pressure transmitter to the front.

The leak off of the 5 injectors are series connected and goes to the back of the fuel rail connected to the rail by a banjo as a 'T' as this point also feeds back to the filter.
Above this a push in connector goes into the fuel rail, this feeds forward and into the high pressure fuel pump, to recirculate unused fuel I imagine.
The fuel rail has a pressure transmitter to the rear of all this.

At the filter the return from the rear of the fuel rail 'T's into the filter and also returns to the fuel tank, but via what I assume to be a cooling radiator underside, and forward of the tank. My thoughts are that the returned fuel is cooled for safety.

Air can be seen in the clear line from filter to low pressure pump, and then in any clear lines there after.
Crushing closed the return from the rear of fuel rail to filter stops the passage of air.
Crushing the line from leak off to rear of fuel rail makes no difference to the air , but causes the engine to seriously falter, my thoughts are that the pressure transmitter doesn't like it ??
Crushing the return line from rear of fuel rail to high pressure pump also stops the passage of air. I was fooled by this earlier so I stripped the back of the fuel rail assembly.
On seeing this later I now deduce that the high pressure pump is the culprit.

This gets a bit complicated now. Some time ago the high pressure pump was dripping. I removed to fit a service kit. On removal I found the back plate to be loose, so I replaced the obvious 'o' rings, tightened and refitted. All was good, I thought.
Stripping now I can see a chewed component of the pump in the main chamber. A spring has then been allowed to enter the chamber a little and is chewed also. These I believe to be part of the intake valve that opens with positive pressure. The service kit doesn't provide these 2 components so I've sourced a replacement pump, and hope.

I'll update on my progress. If nothing else I've learnt more, I think.
But now me brain 'urts.

dave1123

My brain is toasted too, but I think you nailed it. The high pressure pump is the culprit. Not having known about previous problems with it was critical.

Good luck with it and keep on jeepin'

Afterthought; My experience with jets reminds me that kerosene (diesel, jet fuel) has air dissolved in it and at high altitude expands. This is solved by a surge tank that allows the air to bleed off. Your air bubbles may be caused by the reduction of pressure and may be normal. Don't know.