XJ from OZ

Hi all , been a member for years but forgot password so rejoined ! . Anyhow hope someone can help , I have a 1997 XJ 4.0 Auto , runs well normally but of late on cold mornings it starts up first time everytime , runs for about 30 seconds then starts chugging and surging , its not a miss , but more like fuel starvation . After its chugged along for a half mile or so it gets better as it warms up , then runs fine for the rest of the day ! . The truck uses no water or oil , no engine lights come on , and if I restart it and its still warmish there's no problem . Im inclined to think fuel filter , fuel pump relay or o2 sensor ,anybody got any ideas ? thanks in advance for replies.

fuel pressure test first and yes sounds like a fuel filter

Thanks for reply , I will post my progress , hopefully helps the next bloke.

Is there a intake air temp sensor ? I read this can cause these kinds of problems.


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The most common and most logical thing to suspect is a failed check valve on the fuel pump and/or faulty injectors bleeding down. Simply fuel pressure testing will prove or disprove this theory.

The 1997-2001 fuel filter assembly is not serviced unless fuel pressure testing shows fuel pressure or fuel volume delivery issues.

The second most common cause for the described symptoms would be a faulty O2 sensors.



The fuel pump check valve is supposed to hold pressure in the fuel line while the engine is off. The check valve is located on the fuel pump and located in the gas tank. A failed check valve allows the fuel to drain back to the tank. This results in one or more of the following symptoms:

SYMPTOMS

• Longer than normal cranking times
• Never starts on first try, almost always starts on the second try
• Rough idle for a few moments of idling
• Rough running for first ½ block of driving
• Little or no fuel pressure at the fuel rail test valve similar to this -

1- Key in on position; fuel pump primes for 2 seconds then stops. 0 PSI
2- Cranking over the engine. 2-3 PSI
3- Engine starts and idles for 20 seconds. < 5 PSI
4- Engine idles and fuel pressure creeps up to 45-50 PSI.


POSSIBLE CAUSES

• Failed check valve on the fuel pump in the gas tank.
• Leaky fuel injector(s) may be the true cause of your problem, but more likely they are simply contributing to the check valve issue.

Testing of the fuel injectors should show if any are faulty and are allowing fuel to drain into the cylinder. Either problem can allow heat soak to vaporize the remaining fuel in the fuel rail, and you may be dealing with a bit of vapor lock as well, especially in warmer weather.

1. Connect the gauge at the fuel rail and start the engine. The gage should read 49 psi plus or minus 5 psi.

2. Turn the engine off and immediately clamp the fuel line just ahead of the fuel tank. Watch the pressure gage and see how long it takes to loose pressure.

If the pressure remains at 49 psi for an extended period of time then the problem is in the tank - probably the check valve. If the pressure falls below 49 psi fairly rapidly then the problem is probably one or more leaky injectors.

There are a few solutions to the problem –

1. Turn the key to ON for 5 seconds and let the fuel pump prime. Turn the key to OFF, turn the key back to ON for 5 seconds, start the engine.

2. Crank the engine for 3-5 seconds, pause, and crank the engine again. It will almost always start on the second try.

3. Replace the fuel pump assembly in the gas tank. The check valve is not a separate part and cannot be serviced. This is both expensive and time consuming because you have to remove any hitches and skid plates and then remove the gas tank from the vehicle.

You can use solutions 1 or 2 for as long as you want to, they do not harm anything and the fuel pump will continue to function for many more years.

O2 sensor will do that

Digger87xj said:

O2 sensor will do that

Click to expand...

Exactly.

Any check engine light?

Thanks for all replies , ill give it a go on the weekend.

No check light , just started it and same again , stuttering till run for a while then gradualy gets better , ill try fuel filter first ,thanks.

P.S. The fuel pump primes and the truck starts straight away every time , just 20 to 30 seconds latter it seems to suffer from fuel starvation , when cold that is !

There can be enough fuel in the fuel rail to start, but with a faulty check valve there also can be a large air pocket in the fuel lines that will cause stumbling until it is eliminated.

Tim_MN said:

There can be enough fuel in the fuel rail to start, but with a faulty check valve there also can be a large air pocket in the fuel lines that will cause stumbling until it is eliminated.

Click to expand...

O'k' , so would you suggest a new fuel pump ?

Do what works for you. I would perform the fuel pressure tests above and determine the actual cause of the symptoms before undertaking any repairs. The check valve on my 2000 failed 5 or 6 years ago. I am cheap, and have a tow hitch and skid plate on the rear, the thought of wrestling with both of those verses living with a few quirks leads to the easy answer for me, await total failure of the fuel pump.

Yep ill do it step by step , i'll borrow a fuel pressure tester tomorrow , in the mean time ive bought a fuel filter , 40 bucks at parts store 10$ on Ebay ! , oh well ! . By the way this fuel filter has something rattling around in it , is that normal ? , cheers.

Just a small update , sprayed cleaner in throttle and opehings , fitted new filter , checked for error codes -none, pushed in shraeder valve when running , plenty of juice , bloody thing runs as shit as before , any ideas ?

Forgot to add , checked a couple of plugs , clean as a whistle. Next up test TPS and disconnect OS2 .

Well disconnected o2 sensor this morning , drove around the bloke a few times and .............. truck runs fine ! , strange thing is hasn't thrown a check light yet ?

OD NO ! , Went for a longer test , drove 5km all fine , stopped to buy a drink , started back up and crap again ! , drove home at 40kmh , bucking revs up and down , next idea ?

Re-connected o2 15 minutes after last run , started up and drove around block o'k'! , go figure , im leaning towards a dodgey fuel pump perhaps ?