Air in fuel

[Neil]

Asking for a friend. He has a 2007 ML 3.2L diesel manual.

Quite often, more so under load eg towing caravan, he will lose power and has to stop and bleed the system with the lift pump.

This has been going on for a couple years, he has tried many remedies, new pump housing, replaced lines etc. Replaced the diaphram, new seals.

He is at a loss where to look next, even considering changing to an electric pump system.

The strange thing is, a neighbour with virtually the same car is having the same problem so theirs cannot be isolated incidents, someone else must have had the problem.

HELP!

[Speedy70]

I had a similar issue with my ML when towing under hard acceleration or up long hills where the car would go into limp mode. Mine was due to an over-boost issue. I can't recall if a check engine light showed on the dash, but it definitely logged an error code. Best bet would be to get a scan gauge or similar to see if there are any error codes logged on the ecu, which might point you to the problem. Only other thoughts are the fuel rail pressure limiter is popping. I have had this issue as well but neither of the issues required me to re-prime the fuel system. I assume that your mate would be running a clean fuel filter if he has done the other stuff mentioned.

[harland]

There is only 1 supply hose that comes from diesel tank. If air is being drawn into system it is happening somewhere between pump inlet and diesel tank.
- Thoroughly check fuel line for cracks or splits around all connections between fuel pump and fuel filter, fuel filter and diesel tank.
- Thoroughly check fuel pipes and hoses for places it could rub through.
- Try lightly twisting fuel hose where it connects to pipes to make sure its not too loose.
- Make sure hose clamps are clamping correctly and not too loose.
- Check fuel inlet pipe into tank to check it for any cracks, where fuel level goes down air is drawn in.
- it is possible the primer is leaking air,
- Just some thoughts for now.

[Cowboy Dave]

Is he using the original spring type hose clamps? They tend to lose some of their clamping power I reckon. I've seen cable ties used to improve the seal although obviously upgrading to a better quality screw clamp would be less redneck as an approach.

How does he diagnose it as air in the fuel? Just because he can fix it with the primer or is there some other factor?

[gspy4u]

not a clogged or restricted fuel filter is it ?

[ag9111]

not a clogged or restricted fuel filter is it ?

Yep
Change the fuel filter.

[coughy]

ok i put it out there what about a blocked or parshily blocked tank breather
when it happens next before priming the pump open the tank to see if it hisses like it is sucking air in when cap removed???

[Neil]

Thank you for all your suggestions, I shall show them to him today & will let you know of any (un)successful outcomes.
Regards
Neil

[Neil]

Fuel filter has been changed. The upper housing/lift pump changed also.

Clear fuel hose has been run from tank to filter & no air can be seen.

He is about to buy a new (sender??) for under the fuel pump, the water alert sender in case there is leakage through it.

On a recent caravan trip to & from Jurien Bay WA / Pinjarra, the return trip had head wind so used more fuel. He had to stop several times to bleed the pump. If he doesn't stop quickly enough it throws a code which related to MAP Sensor??????

Cheers Neil

[harland]

The blocked fuel tank breather is a very worthy check, for fuel starvation issue. Just curious when the low power is noticed, what leads your mate to believe there is air in fuel, is it running rough at idle or hunting while trying to maintain speed, or are air bubbles visually seen from discharge outlet of fuel filter housing if hose removed?
MAP sensor fault codes, How many km on the engine, could he have the classic carbon in inlet manifold issue and his MAP sensor hose that goes from intake manifold to MAP sensor on firewall be plugged with soot? You could remove the hose and blow air or contact cleaner or something through it and clean MAP sensor with contact cleaner and allow to dry then refit hose.
To see if there is a carbon build up in manifold, unbolt EGR valve from top of intake manifold and if there is severe moist black carbon build up seen, get it cleaned properly, especially if your towing a caravan. Hope you sort it.

[Neil]

Sorry Harland, I haven't been on for awhile.

Through experience he has found what his problem is, air in fuel. He has fitted a clear hose when bleeding and gets a lot of air. He now goes straight to the lift pump when symptoms arise & is able to pump the air out. Once done the car is happily mobile again, for a while.

We all agree the error code - MAP sensor is a red herring. The inlet manifold has been replaced when I owned the car and he periodically cleans the sensor hole. This does not seem to be related to his issue.

Cheers Neil

[harland]

-If you have access to another fuel filter housing try swapping that out and see if problem follows into the other car.
Have you inspected the fuel inlet hose from tank to fuel filter inlet.
-There is 6 clamps and 3 pieces of 12mm inside diameter high density fuel hose that would not be longer than 30 cm ea. just try twisting hose where it clamps onto steel fuel pipe in 6 places, it should not twist easily and should be tight.
- Try replacing clamps with screw type clamps to ensure clamp security.
- Could try removing hose from fuel filter inlet and fuel tank suction, block 1 end off with a 12mm plug and clamp and plumb the other end with a 12mm barb into a steel fitting and using an air regulator and 1/4" tap apply 5 psi and turn tap off spray joins with soapy water to check for leaks. or apply negative pressure and another gauge before tap and see if it holds a vacuum. This will ensure there is no damage to steel pipe that runs through chassis.
- Just buy 3 new pieces of fuel line from Mitsubishi and use screw type clamps.

[Neil]

Well, at long last the problem here seems to have been solved. Under normal driving the problem hasn't surfaced yet but his caravan hasn't been towed since the (hopefully) cure, that will be the confirmation.

Having tried everything else it was decided to remove his tank to see if there were any issues there.

YES!.

It was found that on the bottom of the fuel pick-up tube there is a small filter. The base of this was so close to the tube end that under high fuel demand the base was getting sucked onto the tube, effectively cutting off fuel supply!

The fix was to cut a X on the bottom of the tube with a 1mm cut off wheel & re-install.

Fingers crossed.

As i said in the original post, a neighbour is having similar problems, his is next to have the tank removed.

This info may be of use to somebody in the future.

Regards
Neil

[hvac guy]

Pics ??

[Neil]

Sorry, all re-assembled now.