4.0 takes a long time to start up, sometimes won't start

TheBoxerator · 02-19-2009, 12:43 PM

My 95 YJ (4.0 automatic, fuel injected) takes a really long time to start. I turn the key and it will crank for several turns before catching. Occasionally if I let off the key when I think it's caught and started, but hasn't, the jeep won't start at all. The last time it happened, it wouldn't start for a good 20 minutes. I finally did get it to start by letting it sit for 10 minutes, then turning the key with the gas pedal floored. This took 2 or 3 minutes, but eventually she started up and I was on my way.

It's started fine since then, but this isn't the first time it's happened. I recently had a problem with it idling low and not starting, but I replaced the crank shaft sensor and that seemed to fix it.

Any ideas?

**Mean Max** · 02-19-2009, 01:16 PM

Quote:

Originally Posted by TheBoxerator

My 95 YJ (4.0 automatic, fuel injected) takes a really long time to start. I turn the key and it will crank for several turns before catching. Occasionally if I let off the key when I think it's caught and started, but hasn't, the jeep won't start at all. The last time it happened, it wouldn't start for a good 20 minutes.
This usually happens to our 4.0L Jeeps when the throttle plate & idle control motor are dirty. Try cleaning the throttle assembly & idle motor.

I finally did get it to start by letting it sit for 10 minutes, then turning the key with the gas pedal floored. This took 2 or 3 minutes, but eventually she started up and I was on my way.
Part of your trouble may actually be your technique. With a fuel injected engine, the TPS sensor lets the computer know what position the throttle is in, including fully closed. The system parameters are designed to have the engine started with the throttle closed. Opening the throttle, even slightly, can adversely affect the ability of the engine to start quickly & smoothly. Try keeping your foot completely away from the pedal when starting, sometimes your instincts are to push the pedal even if you're unaware that you're doing it.

It's started fine since then, but this isn't the first time it's happened. I recently had a problem with it idling low and not starting, but I replaced the crank shaft sensor and that seemed to fix it.

Any ideas?

Again, cleaning the throttle plate & idle motor can do wonders for this symptom in many cases. Also consider a TPS replacement as a possibility if the problem persists.

The idle motor is on the left in this picture, the TPS is centered with the throttle plate.

azgurney · 02-19-2009, 01:37 PM

Where did you get the cps. I bought a cps at NAPA as a trail spare several years ago and decided to try it to make sure it worked. One time with it on the Jeep just died on a trail and would not start. I started checking spark etc and then it started fine without finding anything wrong. Several days later at a gas station the Jeep would not start. After letting it set 10 minutes it started right up without doing anything. You do not get a check engine light when this happens. I then put the stock oem cps back on and have not had a problem since. I will only buy oem cps from now on.

planedog · 02-19-2009, 02:28 PM

Worn-out camshaft, guaranteed.

durangoyj · 02-19-2009, 02:35 PM

My 93 started having this problem recently. I'll have to try cleaning it up first since that's the cheapest, then start replacing stuff. Update this thread if you get it worked out.

$300xjwith250k · 02-19-2009, 03:14 PM

my jeep had the same prob. my friend and jeep dealers head guy for 27 years told me to put a new coolant temp sensor in and now all is well

TheBoxerator · 02-19-2009, 04:01 PM

Quote:

Originally Posted by planedog

Worn-out camshaft, guaranteed.

Guaranteed, huh?