92 Jeep Cherokee Laredo, intermittent start

[mrhugg883]

Hello to all, I'm new to the forum and decided to try to solve this problem through experience of others if Possible. I purchased my 92 Jeep Cherokee Laredo, 4.0, 2 1/2 yrs ago. I drove it often for 2 yrs with little trouble other than needing a new radiator. This last winter, around January, the Jeep had a failing battery and bad fuel regulator. I replaced both. The main problem is the irregular starting. Sometimes it will start right up and sometimes it just cranks and cranks. During the no crank period it will seem like it wants to start but just not quite getting there.
Since replacing the Battery and Fuel regulator, I have also replaced the coolant temp sensor, Coil, pickup coil, distributor, rotor, Starter(due to increased cranking), spark plugs, wires, ECM, Trans control module, MAP sensor, Air Charge sensor, CPS, Oxygen sensor and all relays. After all the parts replaced I also had the local Jeep service center do a diagnostic. The found all In order and couldn't fix the no start issue. The mechanic there suggested checking grounds which I had already done. I have also cleaned all connectors to sensors and all connectors within the harness including the firewall fuse panel connections. I had found some that needed cleaning but nothing out of the ordinary for it's age. The symptoms are the intermittent starting, hard shift into overdrive, hard stumble at about 3200 rpm no load, 2800 under load, over heating due to a lean burn condition that causes the exhaust manifold to glow red which has produced cracking at the welds. If anyone has any fresh ideas that may help me, it would be very much appreciated as this is my daily driver and I have not been able to get out of town due to it's unreliability. Thanks in advance.

[fredjacksonsan]

Wow. Definitely a tough one to figure. I would have said CPS (crankshaft position sensor) but you've replaced that - although I have heard of bad ones being installed.

The tough issue is the lean burn...sometimes the O2 sensor. How is your air filter? Have you cleaned the intake bore? How many miles on the Jeep?

There's a "how to" fix a no start Jeep and I'll point you to that. Also, there should be someone along shortly that knows more electronic stuff than me.

No start thread.

Good luck, keep us posted.

[MagicRat]

Originally Posted by mrhugg883

, over heating due to a lean burn condition that causes the exhaust manifold to glow red

Wow..... under normal driving conditions (ie, not towing a trailer up Pikes Peak) two causes of both symptoms is late valve timing or badly leaking ("burned") exhaust valves.

Excessively-lean mixtures will definitely not do this.

I would suspect this is caused probably by a worn timing chain that has now skipped a tooth and/or the cylinder head needs to be rebuilt.

Both problems would also contribute to your hard-starting problems.

Late timing can sometimes be confirmed by attaching a vacuum gauge to the intake manifold. If the vacuum is much below 18 inches (mmHg) at idle, the timing may be late.

Burned exhaust valves can be confirmed by a cylinder leak-down test.