Jeep Cherokee 2.7 Starting Problems

[UKcherokee]

Jeep Grand Cherokee Limited - Mercedes 2.7, 2003.

5 Cylinder diesel engine.


I have been experiencing engine starting problems and the Jeep agents are unable to diagnose the problem using the electronic method and more diagnostics will – no doubt – break the bank.

The engine starts normally at ambient temperatures above 12 C.

At air temperature of below 11C and above 7 C, three glow light cycles and two 15 seconds cranking starts the engine.

With the air temperature below 7 C the engine will not start at all resulting in a discharged battery.

The above were after the Jeep had been left out overnight.

The first step was to check if the glow plugs are operational. By removing three of the and shorting on a battery we found them okay, although the mechanic thought they were not because they had black tips.

The second thing I did was to replace all the O rings on all the fuel pipes and I replaced the rail to high pressure pump hose and the fuel filter to low pressure pump hose. A bit of a sod of a job really. Cleanliness here is priority. Wash the hose plugs with a paint brush and PLENTY of methylated spirits. You don’t want grit blocking the ejectors, that can be VERY expensive.

The hose from the rail to the high pressure pump MUST follow the same routing as the old hose followed. You will have to remove the metal pipe off the common rail which is easy enough. It has two unions and a bracket support to undo before you can remove the pipe.

Underneath the high pressure pump there are two plastic clips retained with a plastic clip cover that swings down. The trick is how to get the cover off. The awkwardness of this took two hours of struggling and fiddling about with a screwdriver. The trick is to lever the top down to release the clip and the cover just flops down. You have to mainly do this by feel as you cannot see the top of the clips and be warned, they are easily broken. I took the serpentine belt off partially off the top right hand wheel – I levered it off and on by putting a hammer head under it. The belt will not come off and it is easy to lever on again. By levering it off, it just gives enough clearance to get at the two hoses at the bottom left of the high pressure pump.

Now a word about the fuel bleed valve. After doing any work on the fuel system, you HAVE to pump the air out. The bleed valve is easily spotted and accessible. It is near the common rail and is about 7 Cm long with a collar facing forward and has one fuel pipe attached to it. It has a plug shaped a bit like a golf tee. To remove this, push the collar backwards – it feels as though it does not move, but it does – about half a millimetre – but this is enough to release the golf tee and you can pull it off.

To purge the air from the system you have to insert a tube to push the ball bearing off its seating and suck out the air.

I bought a hand pump from E-Bay – one of those sorts with an in and out tube on it. The ONLY hose to use to suck the air out is an old plastic fuel hose like the fuel filter to high pressure pump hose. Cut three V shaped cuts in the end of it. This is to let the fuel through when you use the hand pump.

I noticed that fuel was absent in the high pressure pump outlet so I pumped out through the bleed valve and filled the system with fuel. The engine started as it should.

I then pushed my fuel hose in the bleed valve and cranked the engine and the fuel was expelled with a good force that tells me the high pressure pump is okay.

On removing the fuel pipe from the bleed valve I could hear hissing although there was no fuel being expelled so there is a vacuum behind the sprung loaded ball bearing. This was proved correct when I squirted a bit of fuel into the bleed valve and I could see it being sucked back. See * for the explanation of this.

I then connected my manual hand pump to the fuel feed pipe and attempted to suck fuel from the tank. It took a bit of strength to do this, although, blowing back fuel and then sucking it up again proved to be slightly easier but it still requires some force to suck the fuel up.

Now I KNOW there is no fuel pump in the tank from people more experienced in Jeeps than I – and if anyone can provide a link to the exploded pictured manual 2.7 fuel system I would be grateful.

The fuel filler cap was tested by mouth. I can suck air into the tank side and blow out but with resistance. Please could someone with the same model go out to their car and see if they can suck and NOT blow – even the smallest amount.

I then disconnected the fuel feed line at the filter and connected a long transparent tube and filled it with fuel. The engine started as it should with an air temperature of 12 C.

I left the vehicle overnight and with fuel in the long transparent pipe I tried to start the engine temperature below the 7 C.. It started as it should.

Therefore, the problem was air leaking into the system – but where?

On removing the rubber hose from the fuel filter and examined this closely, the internal bore of the hose was cracked, so I renewed this together with the other hose from the black gismo on top of the fuel filter to the fuel return pipe.

(*)That cursed little black gismo was a major source of the fault of engine not starting. In it is a sprung loaded ball valve to stop the fuel draining back into the tank and creating a vacuum at the fuel bleed valve and sucking in air.

When I replaced the fuel filter I removed the old gismo and looked through the straight piece of pipe and I could see daylight. Not knowing what it was supposed to do I did not question this. On the new gismo I could not see daylight – and that’s the way it is meant to be.

A mechanic told me of the troubles with the gismo, and he said that with every fuel filter change he also renewed the black gismo.

So, all in all, I think the fuel system is poorly designed. All I have to say is KISS. Keep It Simple Stupid – something which Jeep have not accomplished on this model.

They could learn a lesson or two from Mitsubishi – but that’s another story.

To cap it all, if you have the same difficult starting :-

1. Change the fuel filter AND the black gismo on top. It is necessary to remove the bleed screw and fill the filter with diesel. It is no good running the engine and cracking the bleed screw – you will only suck in air to the fuel system as it is under vacuum – NOT pressure.

2. Change the rubber hoses leading to the fuel filter.

3. Check for air in the fuel system. Look at the plastic fuel tube under the high pressure pump or any clear section of fuel tube you can see and check for air bubbles either with the engine running or not, and try bleeding the system.

If there is air – change the six ‘O’ rings on the plugs of the fuel tubes. Good luck on finding only the ‘O’ rings. Normally it is a complete hose purchase – oh – and don’t use ANY ‘O’ ring other than the ones designed for the purpose. They will rot in no time at all.

I shall also investigate why the glow plug tips are black. Any thoughts on this one? I am curious to know if the glows only operate while the indicator shows on the dash or do they stay on after it goes off.

Of course, there could be other faults that could cause difficult starting but at least this is a starting point. It’s the way I went – right or wrong ……….

I have taken the trouble to write this article because – in my experience - there is a reluctance from Mercedes and Jeep dealers to try to help the DIY mechanic in the UK. The text book answer was for me to take the vehicle into their workshop so they “Could have a look at it”. £300, US $450 or AUS $700 or more saved perhaps?

Despite the above, my Jeep is the most luxurious and comfortable car I have owned, and its worth paying out to keep it on the road.

Thanks to alphalitalia for his help.

Regards

Pete – UK – October 2012.