96 GC 4.0l running rough
 

HI
I have a problem with my Grand Cherokee. It idles Rough and loses power quite badly but this only happens occasionally. I have tried all the usual culprits I.E. throttle body sensors (IAC,TPS,MAP) I have checked the wiring on them as well, I have also cleaned the throttle body. The battery is all fine, I have checked the Earths but am unsure how to check them thoroughly. the strange thing is I also hae a single point LPG conversion on it aswell and that never has any problems. I am totally at a loss with it. I have asked many people online and in person about it and they cant really think of anything. also I have done Voltage and Resistance checks on the IAT and the engine coolant temperature sensor and they all seem to be operating fine. Hopefully one of you Guys can help me out. I just have no idea what to try next. I did think it could be something to do with the fuel pump but I dont know, It seems fine????? I have been told that it could be something linked to thye fuel delivery electrics. Can anyone help! Thanks JayDee

single point LPG conversion ? What is this first off.

I use to have a '94 with he 4.0L that had about every problem you could think of.

When you say power lose, what do you mean? Engine die? can't move? Need a bit more info on this one..

Single Point LPG is a conversion for the engine to run on Liquefied Petrol Gas. I am from the UK and Autogas is half the price of petrol. Single point means it is mixed with the air at the throttle body with a gas mixer as opposed to a multi point system which has seperate injectors for the autogas. when it plays up it has an inconsistent Idle and then it calms dowen then as soon as you put it in drive it starts going up and down all over the place. but I can never get anyone to see it doing it. Thanks

Thanks for the info on Single Point LPG

Being in the states that's rather rare.


ok, have you tried a good old tune up? New plugs, wires, cap and rotor? I'd start there.

Hi
yeah fuel prices are bad here they really riup us off. its 1.03p Pounds a litre for petrol now.
Anyway I have changed the Sparkers and the Leads. I was going to change the distributor and rotor arm etc but they all run with the gas aswell but the gas runs fine. but I think regardless of that I will take your advice cos I have been meaning to for awhile.
another interesting point I forgot to mention is that I have found when I remove the neutral cable from the battery for a short amount of time the problem goes away for awhile and then it comes back. I dont get how that is working unless the ECU is relearning the fault after awhile. And it doesnt really like reverse to much when it is playing up.
What do you think?
cheers mate

removing the negative cable for a few min. will reset your computer..

So it has something happening it just don't like..

Do you have any ideas on where to look or any tests I could do to check it. thanks

I'll have to look for the write up but if I recall.

You turn the ignition to the on position DON'T start it
The check engine and other idiot lights should go off
When it goes off start counting if you reach 25 or higher before the check engine light comes back on the computer is on it's way out.

I be leave that was the test I was told to do. I'll do some searching and see if I can find it for sure but you can try that and see what you get.

thanks for that I will try it and get back to you? I have been scouting around and one guy on the forum said it might have something to do with the clock spring in the steering column? apparently it can give bads voltage signals to the TPS etc. What do you think ?
I am unsure but am going to disconnect the plug from it and give it a little while but if i unplug it I lose my driver airbag, horn and cruise control so its a little bit dodgy, but should be ok for a test but I am going to wait until my GC has a bad day again and then I should hopefully see results quite quickly.
Thanks Again

hello jaydee your grand runs on lpg what sort of mileage are u getting out of it on petrol or gas ive just got mine last week it seems to run fine

Hi Man.
She runs fine but I only have a single point system so she does a little bit less than she would on multi point. I bought her with single point already installed but am looking to upgrade to multi point if a system comes along on ebay at a good price. I assume if you have just had yours converted you will be on multi point sequential injection, My friend has a 98 GC 4.0l on multi and it is fantastic, good mileage, no decrease in power.
I am in the UK and petrol is between 98.9p to 103.9p a litre at the moment and autogas is between 45.9p to 55.9p so I can run my GC for the same price as a 2.0l, so if you are getting about 23MPG on average with petrol you are looking at an equivalent of roughly 38MPG according to the difference in price.
I have a seventy litre tank under my GC (to save boot space they put the tank underneath and fit a smaller tank for petrol) when full it holds fifty seven litres ( it holds only 80 percent of its capacity to allow space for pressure changes). With fifty seven litres in the tank I get 200 miles out of her on the highway and that costs me on average 28 pounds if it was on multi it would probably get about 220-230 out of it. I dont know much about fuel costs in the states but I know its cheaper than here so you are looking at really good value for money. I will always have Gas now its great!
Hope it goes great for you! Tell me how you get on and what you think!
Cheers man