Mechanic in SE Melbourne (or troubleshooting advice)

[Hamsteh]

Hey folks,

It's been a while since I last posted. The good news is I still have the XJ, the bad news is it's not starting.

So at this point I'd be happy with either troubleshooting advice, or a decent mechanic SE Melbourne (I'll have to get it towed there unfortunately).

The details:

• 1996 4.0 with 330k on the clock
• Dual Fuel (Venturi)

The issue/s:

• Was running with a rough idle that would sometimes go away, sometimes be terrible (on both LPG/Unleaded)
• A month or two back it refused to start and after some playing around, I swapped in a new crankshaft pos sensor and camshaft pos sensor. This seemed to fix, but idle still not great
• A couple days ago it decided not to start again, and hasn't since. Cranks but no combustion at all.

Troubleshooting so far:

• Cranks fine
• Spark seen with inline tester between coil -> dizzy, and dizzy -> plug (it is orange not bright blue, but this could just be the tester)
• Fuel pump can be heard priming, and fuel dripped out schrader (dont have pressure tester)
• I DEFINITELY have vacuum leaks, but dont know if this would cause a no start - and not sure how to address leaks since its all those unique-looking pipes/connectors
• Managed to get an O2 code to throw on OBD2 while revving in driveway

The patient:


Cheers,
Alex

[awg]

If you have certain failed sensors, and that failure is low resistance/short, this can affect the PCM/sensors because they share a common 5V supply, and a bad sensor can drag that voltage down.

I beleieve the front O2 sensor is one of these

You could try checking whether +5V is present at the sensor, and also the resistance of the O2 sensor ( check FSM, Google/Youtube etc)

I know an O2 sensor can be had for $34 on Oz ebay, or $44 for both (from China)

[LuluBelle]

Another Broken 96 .......
Oh NO!...... I Agree with awg .. check the voltage at the sensors It sounds like the TPS might of gone bad .. as if you have fuel and spark it should go?
As for the Running Rough did it Pop through the throttle body and Backfire? ... O2 sensor Upstream sensor in the header pipe don't worry about the cat sensor ....
was it running like it had No Guts?..... TPS or at 300k it might be the Solenoid Purge Valve ... Unique Setup on 96's
and is your only vacuum stuff on a 96
Mine is a 96 on dual fuel like yours and I have just gone through a Nightmare of Troubleshooting ending up with a Fried PCM!
On my thread "Why Wont it Start when Cold" a page or 2 back there is a lot of troubleshooting discussion and tests to perform ........ Good Luck
_____ooooo
/__l_l_,\____\,___
l_---l_l__l---[ ]llllll[ ]
_.(o)_)__(o)_)--o-)_)

[Hamsteh]

Hey really appreciate the replies folks, thanks heaps!

I am kinda under the impression that the Jeep should still start without front O2 sensor connected so I tried disconnecting it just now in case it was pulling down that 5v supply. No apparent change and no start still. I'll run some multimeter tests later when I have a bit more time.

No backfire through the throttle body as far as I'm aware Lulu, I think I replaced the TPS a year or two back but I can pull it and inspect again.

I have never heard of the solenoid purge valve! Here I was thinking I'd heard of every common XJ fault! Any advice on troubleshooting this?

Finally I'm looking through your thread now, will see what else I can come up with. In the meantime I'm going to order a fuel pressure test kit.

[awg]

Originally Posted by Hamsteh

[*]I DEFINITELY have vacuum leaks, but dont know if this would cause a no start - and not sure how to address leaks since its all those unique-looking pipes/connectors
Cheers,
Alex

vacuum leaks ??..a serious vacuum leak will cause motors to run like crap ?

would have thought it would still at least start and run rough though

I would clamp off anything obvious, bit tricky without a running engine

[LuluBelle]

while you waiting for your pressure test kit try turn key on 3 secs turn off turn on again 3 secs turn off and then repeat try and start on the 4 th go if your pump is sad perhaps a bit of priming might get you a start?.......
Dirty inline fuel filter?..... when was that last changed?
a test kit is about $30 on ebay
the only vacuum on a 96 is the map sensor front valve cover to air box ... rear valve cover to intake manifold (mine has a T piece for the Flashlube to plug in) and the solenoid purge valve and the heater tap I don't know of any others .... crank cam and tps are the only ones that would prevent a start all the rest just make it run crap ?
the purge valve wont affect starting just run terrible

_____ooooo
/__l_l_,\____\,___
l_---l_l__l---[ ]llllll[ ]
_.(o)_)__(o)_)--o-)_) ..96er

[Classic Boy]

I don’t know the specifics of your dual fuel conversion but I have worked on a lot of cars with dual fuel in the 80’s 90’s and early 2000s and my instincts tell me that based on your problem reported it is likely a control failure associated with dual fuel system. To cut to the chase when lpg is selected the power to the injectors is cut and the lpg system provides the fuel, if the gas system is faulty and the isolation of injector power is not restored then the noise stops.