Strange warm-up problem with LPG and Petrol

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Joined:Mon May 02, 2011 10:37 pm
LPG System:Single point
Car:Jeep Grand Cherokee
Strange warm-up problem with LPG and Petrol

Post by JeepLover1 » Mon May 02, 2011 11:01 pm

Hi Guys
I am hoping someone my be able to shed some light on a problem I have been trying to solve for over 12 months now. My vehicle is a 1998 Chrysler Jeep Grand Cherokee Limited with a straight 6 engine of 4.0 litres, whci was converted sometime prior to my ownership to LPG. My problem is mainly with start-up and/or Cold start. The vehicle is started as I was instructed with Petrol and then switched over to LPG once it reaches normal operating temperatures. Right, as soon as the engine fires up it runs erratically, seeming to rev a bit like a 'boy racer revving at the traffic lights. once the cold start/choke goes off it then runs quite normally. Any attempt to pull away during this 20/30 second warm-up period results in quite violent lurching. Once initially warmed up she runs relatively fine until switch-over to LPG when it appears to run with more power and smoother than on Petrol. However, if on a journey I run out of LPG and have to switch back to Petrol it takes several miles before the car will run smoothly and there is a definate slight power loss. The strange part is though, if I leave the car in the Petrol mode and drive solely on Petrol, even initial start-up the following morning and the subsequent running is as smooth and normal as it should be.
My local garage mechanic has checked out the car on several ocassions including the injectors, the throttle body and other potential vacuum leak points, the plugs have been changed several times, distributer cap and rotor arm, all to no avail. I also had a tune-up mechanic look at the vehicle and he said it was a mystery as his code reader/scanner showed up no faults. My local LPG dealer has upgraded the cars system to the latest standards, as these were sadly lacking when I bought the car, and he could find no answer to the problem. So I am now at my wits end to know where to look next. I just wondered if anyone had experienced similar or could suggest a possible answer. Thanks for reading anyway. Barry

Joined:Tue May 17, 2011 10:42 am
LPG System:singlepoint
Car:v6 3.5 shogun

Re: Strange warm-up problem with LPG and Petrol

Post by tubbs » Tue May 17, 2011 11:14 am

Hiya, the ecu is moving out of its parameters when running on lpg. What you need to do is find the memory wire at the ecu. It will most probarbly be a red wire and the only one that is live when the ignition is switched off. That needs to be relayed out so the ecu is open circuit when the ignition is switched off.
When the key is turned and the relay is triggered shut the ecu will be reset to its base parameters, any old school lpg fitter will know this trick so if you feel unable to tackle this yourself then find someone who has been in the gas trade over 10 years and explain the problem. If they know their stuff they will know exactly what to do.

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