juz1970

Hello jeepers.
I am posting this here because although I have minimal modifications I do have a single point injection LPG system installed on my 1996 Cherokee 4.0L LTD.
While it seems to be running fine on LPG I cannot get the car to run on petrol. It starts easily but then dies immediately. I can get it to run for a bit if I really pump the throttle but real rough.
This is what I have tried to eliminate the problem... I have eliminated all vacuum leaks in the intake, I have replaced the TPS. I have replaced the entire sender unit including fuel pressure regulator.
Fuel lines are clear and pressure is not a problem. I have just reco'd all the injectors and confirmed they are all working. Since the car runs fine on LPG I think the ignition system is fine.
this is definitely a fuel problem and it is not the injectors or pump. I am not sure where to go next. I am suspecting a sensor is malfunctioning but not sure where to look next. Since the LPG flow is
controlled by vacuum and not the computer then I can only conclude that either the computer is faulty or is getting some faulty input. Can I please have some suggestions on where to look next?
Thanks in advance.
Justin from Australia

cruiser54

Do you have a fuel pump ballast resistor on that 96? If so, it could be bad. It's okay to bypass it.

Morat

Can you read the fuel trims? With a single point system they could be way out of whack after running on LPG and the ECU isn't able to compensate in time to keep it running. I don't know how long it runs for but If it's way lean it might build up enough fuel while cranking and then die after the fuel has been burnt off.

If you can't read the codes just disconnect the battery for a few minutes to reset the trims and see if it makes any difference.

(I'm not an expert)

juz1970

Thanks for your replies.
not sure what a balast resistor is or if my model has one..where would I find it if I did?
I had the battery out for an hour yesterday whilst flushing the injectors so I assume that would reset the trim, or do I need to bridge the terminals and turn headlights on etc?

juz1970

ok today I have reset the computer to factory...cleaned up all the earth connections and seem to have made an improvement. now it idles beautifully for sometimes 15 seconds before it dies.
I have looked and I do not think my model has a ballast resistor unless they have hidden it somewhere.

cruiser54

I was sure I attached a pic of the resistor. I guess not. Here ya go.

juz1970

I wish my model had one because it does sound like a bad resistor but alas. ..it can't be that as I don't have one. I visited your website and read all your tips....wow. the answer must be in there somewhere.
attempted to adjust my tps but I do not think it will rotate far enough to increase the output to 17% of the reference voltage. The readings on my (sh1tty) multimeter were 5.11V and 0.68V and this is after rotating as far as I could.
in any case I have finally got it to throw a code but cannot extract it because running it at 2500rpm is not possible so I am going to have to take it in to be scanned.