Jeep Cranks but Wont start. Is it CPS?
 

My '99 xj was driving fine all week and today i hopped in and it wouldn't start. The engine cranks but it wont turn over. I am able to push the gas while turning the ignition and the engine will rev but as soon as i let off the gas the engine dies off. Any clue as to what it could be? I have read that a common problem is the CPS but if the CPS was bad wouldnt the engine not rev since i wouldn't be getting a spark?

i get that when the battery has been completely drained for the first 10 mins after a jump start.

i am no mechanic but i don't think this is a crank shaft position sensor issue. yes it will stall your vehicle if its going out but not consistently every time you let off the gas. my jeep currently is down to this issue and the heat outside keeping me from doing any real work.

but your problem reminds me of a dirty, failing or failed oh heck what did they call it something like an iac control.

mine was not bad just dirty, took off the air box housing and hose, i ended up taking off the carb and cleaning the whole thing instead of just that part this jeep i bought somehow had sand all over in the airbox, carb, and on that part, probably only got an air filter put on just before i bought it.

i couldn't get that part off itself which is why i took the whole carb unit off.

anyways thats my thought could be right could be wrong but cleaning it would never hurt especially if its not been done in a long time.

ryan

Okay thanks! I'll try cleaning out the IAC and see if it works out. Certainly won't hurt.

when you step on the gas while cranking it will spin over faster as it can not SUCK air in as apposed to throttle butterfly being shut.. do you have spark ? do you have fuel pressure ?

i have fuel pressure. Replaced fuel pump 500 miles ago

did you check? or are you guessing because its only 500 miles old it is not dead ? these things eat fuel pumps.. if its an airtex or what ever they are called

Ive been able to get it to idle. I just have to rev it at low rpm for a minute on startup. :D

weird.

When my CPS went down(and out of the blue-no warning symptoms at all), the engine would just crank with no firing at all... Took me three weeks(here and there fiddling on it) to narrow it down to CPS(process of elimination). Once i spent the time kissing the tranny/flywheel putting it in and rigging a magnetic fishing hook(since one bolt fell into flywheel), fired right up!

probably a bad IAC/clogged iac. Pull the throttle body and clean iac and passage and hopefully that fixes it or worst case you need a new one. oem is best but i used a SMP iac from rockauto and it's still going

Also post your tps readings especially the throttle closed reading

Key the ignition and let the computer tell you what's wrong. Trust me-it'll save you a ton of time.

Clean the throttle.body, IAC, and check the cables. Rule them out. Have you thought about a tank of bad gas?

He has a 1999. The key trick won't work. He needs a code reader or scanner to show the codes.

Yeah get a good scanner and read for codes.

Make sure you can test for " pending codes " if there is no CEL ( Check Engine Light )

If I have a suspicious condition, I drive around for few miles with the scanner hooked up monitoring and recording data .... sometimes a fault will pop up without setting off the CEL and then clear themselves.

"Cranks" = "turns over". The engine parts go roundy round.

"Turns over" does NOT mean, "starts". It means (get ready for it), turns over.

Duly noted