Hi all,
I have a 1996 Cherokee 4.0L Ltd. The engine build is Oct1995. The Jeep is converted to run on LPG as well as petrol. It’s asingle-point LPG conversion with an adapter on the top of the throttle body.When running on petrol, the engine won’t idle. It cuts out and if I try todrive it, it hits 1500 revs then backfires, the revs go all over the place andit’s a job to get it to the 1800 revs which is when the LPG kicks in. On LPG itruns OK with just a bit of a funny ‘wobble’ at around 2-2400rpm when the revsdrop down and go up again (?).

I’ve replaced the crank sensor, coil, distributor cap, rotorarm, plug leads and plugs. I’ve cleaned out the throttle body and checked allthe connections under the hood that I can see. I’ve swapped the ASD relay withanother one. The fuel pressure seems OK. I’ve done the key on-off thing and getthe following number codes: 12, 42, 27, 27,27, 27, 21, 27, 27, 55. From what Ican tell, this seems to point at the ASD, Injectors (all of them) and the O2sensor (there are two – one in the downpipe and one just in front of the CAT.
I’ve had a trawl through the forum posts and to be honest,am getting a bit lost. I’d be grateful if some kind soul could give me a fewpointers? Thanks in advance,
Colin

 

Fuel pressure "seems" okay?

Check it with a gauge. Very critical to have fuel pressure in the 40 to 50 psi range.

 

I would say you have a fuel delivery problem on the gasoline side.

 

Can you post up the pressure specs? I know Renix but not HO.

 

My 1991 Service Manual says: Fuel system pressure test - System fuel pressure should be approximately 31psi with the vacuum line connected to the regulator. With the vacuum line disconnected from the regulator, fuel pressure should be approximately 39 psi (page 14-6).

 

My 1998 FSM says 49+/-5 psi.

 

Jostled my meory. IIRC now, through 96 with return fuel line is the 31 and 39. 97 and later is 49.

 

Thanks all,
I'm going to replace the fuel filter today (old one looks like the original part!) and then on Saturday, get the fuel pressure tested. I've got an offer of a hi-performance fuel pump that's a direct swap for the original, so thinking of getting that just in case. It will pump up to 255Lph which I guess should be good for over 40+ psi. Unless there is any reason why I should stick to the original type pump, which I thing delivers around 115Lph?

Colin

 

No need to go high performance on the pump. In fact, you may create issues for yourself.

 

Thanks for the tip. Will go with a standard pump. In the meantime, I un-plugged as many of the connectors I could find under the hood, cleaned them off and sprayed them with some nano-protech. Still getting the same error codes and the 'check-engine' light was on. Then this morning, it had gone off again and the Jeep ran fine!! Checked it again about an hour ago and it's missing on petrol again! Driving me nuts this is! I'll see what my friendly expert can find tomorrow and will report back. Thanks again for all your input - it is much appreciated.

Colin