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Matt
Matt, Mechanical Engineer
Category: Jeep
Satisfied Customers: 20614
Experience:  BEng hons Mech engineering, in auto industry 22 years
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I have a 2003 grand cherokee WJ 2.7 crd merc unit 5 cylinder

Customer Question

hi i have a 2003 grand cherokee WJ 2.7 crd merc unit 5 cylinder etc...
my problem is this. i can only get the jeep started using cold start once started it runs fine and never cuts out it starts hot fine and will start for the rest of the day. when i leave it over night it will not start maybe draining back??? I have replaced the following:
fitted new HP PUMP
new lp fuel lines (all of them)
2 new filters
installed a non return valve just before filter inlet
installed 12 volt fuel pump
now i have no bubbles in the lines when cold but when hot they are visible in the line from the filter to hp pump. WHERE COULD AIR BE GETTING IN?????
STARTING TO LOSE THE WILL TO LIVE!!!
JODY
Submitted: 1 year ago.
Category: Jeep
Expert:  Matt replied 1 year ago.
HelloIt may have developed an air leak on the fuel supply pipe from the tank to the engine. The engine has no separate lift pump and relies on the built in one in the injection pump. If a leak has developed on the fuel suction pipe then air entering the system will air lock the pump.Try pumping up the fuel using the hand pump in the engine bay on the filter housing, then crack off / loosen each injector pipe in turn while cranking the engine and getting an assistant to operate the primer. This will expel air from the injection side and the engine should fire up. The problem will be cured by checking the supply pipe along its length for signs of leakage and repairing any you find.If you daub each pipe joint with heavy grease and the issue goes away then wipe the grease away one at a time to highlight the problem joint
Customer: replied 1 year ago.
Cheers ***** ***** appreciate that these Engines have no lift pump and instead have a crap vacuum on the engine which is not the best. Is it possible to have a leak on the return or via the leak off pipes or is it only possible to get leak on the feed? I have primed it using the electric fuel fump which make fuel poor out of the filter bleed screw but can't get it to pump through to the injectors, don't know if that is normal? Is it acceptable for any air bubbles to be visible in the fuel lines? In the morning I fire up the electric pump and unscrew the filter bleed valve and you hear a little air coming out before diesel the lock it off.
Expert:  Matt replied 1 year ago.
Hello you won't be able to push fuel past the main fuel pump with an electric pump, so not getting fuel up to the injectors when just running the electric pump is normaland a leak on the return pipe won't matter but a leak on the feed will what also worth checking is loosening the fuel filler cap as if the 1 way valve in the cap is faulty then the lift pump won't be able draw against a vacuum
Customer: replied 1 year ago.
Sorry to crush me across a bit dense but could you explain the bit about the filler cap a bit more. Like I said this air leak is not there when it's running and cold so how can it appear when hot? Cheers, Jody
Expert:  Matt replied 1 year ago.
Hello Jody
I've known the situation occur where if a vacuum is created inside the fuel tank then the lift pump lacks the grunt to pull it through the lines
and as the fuel tank empties it will create a vacuum if it cannot draw air in
hence my suggestion of loosening off the filler cap
Customer: replied 12 months ago.
Poured hot water on therastat and it started like a dream !! Faulty engine temp sensor very strange!!!
Expert:  Matt replied 12 months ago.
well done for finding thislooks like the air bubble in the fuel line were a red herringBear in mind that the site takes a deposit from you at the beginning and this is held by the site until you rate my answer at which point the cash is split between the site and the expert. so if my answers have been helpful please rate my answer.
Customer: replied 12 months ago.
Sorry to go on and yes I will rate you just wanted you opinion one last time... Changed the temp sensor and this evening didn't want to start :( poured a small amount of hot water on the thermostat/ sensor and fires up straight away! Struggling with this concept a little make know sense to heat the sensor to aid cold start! Ever heard of anything like this before because I certainly haven't.CheersJody
Expert:  Matt replied 12 months ago.
Hello Jody I'd say there's a fault inside the sensor that goes away once its heated up and so internal wires are then expanded and touching where they weren't when cold this in turn would have been sending a false signal to the ECU and so not compensating for a cold engine replacing the sensor with new should put it all right
Customer: replied 12 months ago.
That would seem to be the obvious fix so I have changed the sensor for a new oem one but same problem! Going to fetch some rope and kick the stool out i think ;)
Expert:  Matt replied 12 months ago.
Ok in that case check over the state of the wiring to the sensor and its connector as if there's a break in the wire or some corrosion then this too can create this issue
Customer: replied 12 months ago.
Will look into it tomorrow many thanks. Jody
Expert:  Matt replied 12 months ago.
understood just get back to me on this post
Customer: replied 12 months ago.
Ok Matt that's very kind of you just a quicky... How accurate does 5 volt reference need to be?
Expert:  Matt replied 12 months ago.
Hello 5V reference voltages need to be at least within 5% so they should have a steady voltage of 4.75 to 5.25V
Customer: replied 12 months ago.
So say we had 5 volts going into the sensor cold it's possible that until the sensor hits a certain temperature the voltage returned back to the ecu is not acceptable this could be due to voltage drop/bad wire on the return circuit? I'm a mech engineer but did vehicle technology as an apprentice and auto electrics is not my strongest subject :(
Expert:  Matt replied 12 months ago.
Hello that quite right, a poor earth will drop the voltage and offset the signal into the ECU, so hence my suggestion of checking over the wire for hard / damaged sections and corrosion
Customer: replied 11 months ago.
Morning Matt so I have been looking at this sensor circuit and come up with the following findings... 5 volt reference present and good earth when you plug the sensor in this voltage drops to 4.20 volts and Will not start (cold) don't know if that is normal voltage? If I heat the sensor a little on the outside of the thermistor with a lighter the voltage drops to 4.15 and the heap starts!! I bought the sensor from MB. Is it possible there are slight differences in the MB sensor and the jeep sensor? Jeep ecu Mercedes engine?? Which came out of an e270 just a thought. Cheers
Expert:  Matt replied 11 months ago.
Hello a slight difference in the sensor will have this effect as you say so it may be worth trying a Genuine Jeep sensor as the next step also carefully check the wiring for any hard sections or corroded joints as this too can offset the sensor signal
Expert:  Matt replied 11 months ago.
Hi
do you still need help?
Bear in mind that the site takes a deposit from you at the beginning and this is held by the site until you rate my answer at which point the cash is split between the site and the expert. so if my answers have been helpful please rate my answer.
Customer: replied 11 months ago.
Hi Matt do you have any figures from jeep on the temperature sensor ohms/temperature etc... There is no wire fault so need to look into dodgy sensor even though it new maybe not ok to us mb one so I have orders a jeep one to check that
Expert:  Matt replied 11 months ago.
hello its should be a Bosch NTC sensor
Expert:  Matt replied 11 months ago.
Hi
do you still need help?
Bear in mind that the site takes a deposit from you at the beginning and this is held by the site until you rate my answer at which point the cash is split between the site and the expert. so if my answers have been helpful please rate my answer.

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