Calgary Jeep Association

4x4 Related Groups => Tech Talk => Topic started by: prelude48 on March 17, 2010, 08:36:11 PM

Title: Random hard start (long)
Post by: prelude48 on March 17, 2010, 08:36:11 PM

Hey guys, first post here. (Great forum btw)

(I did a search)
98 Cherokee Limited 4.0 255,000km

I Bought it 4 days ago and i have just done the basic tune-up stuff like
fluids and plugs.

Problem- The jeep runs ok (bit of a rough idle) good power etc, but for some random reason it takes like 5-10 seconds to start or will take the second attempt to actually start and then it fires right up. Now its totally random.

Explanation- I am trying to diagnose a drive train noise so i have the jeep in the air and wheels spinning (don't judge my safety ;)) and I am listening around, shut the truck off, check parts, start and spin wheels again etc..This goes on for a while, all of a sudden no start, so i try a second attempt and nothing, hold peddle down like its flooded and it starts but really badly and wont idle. So i restart with throttle open again and feather a bit so it will idle and its rough but idles. Then smooths out and runs fine...starts like a champ like another 5-9 times while I am doing my diagnostic thing.
So after searching only guess i can come up with cps..it doesn't seem to be fuel related but i also haven't tested it either. Any help from you jeep guys would be great. Thanks for reading my novel. :)

(I did find the drivetrain noise, t-case)

I have a fair amount of mechanical experience under my belt, just to clarify.

Title: Re: Random hard start (long)
Post by: Justink on March 17, 2010, 10:00:57 PM

Had the same problem but mine only did it when it was cold.  Turned out to be one of the sensors on the throttle body.  It almost felt like trying to start a carb on a cold day,  It would take around the 5-10 second mark but then I had to keep it running for about 45 seconds before it would run on its own.

Title: Re: Random hard start (long)
Post by: prelude48 on March 17, 2010, 10:09:32 PM

Thanks for the reply,

Any idea what sensor?

Title: Re: Random hard start (long)
Post by: Justink on March 18, 2010, 07:16:15 AM

I honestly have no idea, someone else may chime in.

Title: Re: Random hard start (long)
Post by: XJHERO on March 18, 2010, 02:53:41 PM

he is talking about the TPS (throttle position sensor)
its easy to change

Title: Re: Random hard start (long)
Post by: Bnine on March 18, 2010, 03:13:38 PM

Put a fuel pressure gauge on the rail and watch for leakoff. May be a weepy injector. Common reason for hard starts and slightly choppy idle.

Title: Re: Random hard start (long)
Post by: prelude48 on March 18, 2010, 03:25:21 PM

I had a 99 Tj with 4.0 in it and it had a bad tps sensor and its not making any of the signs the Tj did so i personally doubt its that.. I will try to find a fuel pressure tester tomorrow. Thanks for the replies so far.

Title: Re: Random hard start (long)
Post by: apeman on March 19, 2010, 03:30:04 AM

Sounds more like the CPS, than the TPs...i have a spare if you want to try it...otherwise you can also try one of my spare computers and see what difference it makes...although its doubtful.
My 99 did the same thing.