fes007

I have a 2000 cherokee 4.0 160k that has a persistent rough idle to it. It almost seems like a miss. The tach fluctuates a little bit at idle and I can feel the miss in the drivers seat. I have also had an issue at highway speeds at 70+ mph with the engine slightly cutting out for a split second. It runs great on the highway with plenty of power though. I am also starting to have a problem during a cold start or after it has been sitting for a few hours. It does not want to start right up like it should. From what I have been reading here it could be the Crank Position Sensor. I have changed my plugs and the old ones were in great shape. Any thoughts?

CattyXJ

When did you do wires a new cap and rotor and fuel filter?

fes007

I have the distributorless ignition. Have not changed the fuel filter since it is the tank for my model year.

CattyXJ

My fault. I didnt know the 2k's didn't have one. Or about the fuel filter. Lol. I'm worthless on this one then. Try having it hooked up to the code reader at autozone

Gee oh Dee

Codes need to be read. Could also have a bad coil pack.

fes007

The CEL is not lit so I will go and check codes with a scanner today. I did the self diagnostic test through the gauges and ignitino and received to faults.

Gee oh Dee

I don't know if the key trick works that late in the model years.

And codes will get saved in the ECU.

CattyXJ

Every time I go to vatozone to pick something up I have them scan my truck. I've had a few issues found, never had a CEL. It will at least tell you if your having a random misfire or if it's isolated to a couple cylinders.

NiteDog

No check engine light???

1)Check you diagnostic codes if you have a misfire it should tell you which one.

2) Vacume leaks

3) Cracked head

4) Cracked intake manifold

The reason I mention all this is, I had a 2001 that did the samething and I had to replace the head and intake. Also replaced purge valve on emissions and some of the related vacume lines. All this after I replaced the coil pack and plugs.

CoffeeCommando

Sounds like fuel pump to me. The next time it sits for an extended period of time, turn the key in this sequence: (from "off") Run, Off, Run, off, Run, and let it sit. When you turn it to run, let it sit for 1-2 seconds each time. On the third run, after a second, crank it. If it cranks right up (when previously it didn't) you have just deduced that it is the fuel pump that is starting to go south.

When you turn the key to run, the fuel pump primes the fuel system. If this gets rid of your hard/long starting problem, your check valve on your fuel pump (it's basically one assembly) is bleeding pressure.

The check valve's sole job in life is to maintain fuel pressure in the fuel rail/line, while the pump's only job is to push the fuel from the tank INTO the line (through the check valve). When you start having a failing check valve, you'll find it takes longer and longer to start, until eventually it just doesn't start any more.

At higher engine speeds if you start to have it sputter, or lose power, it could be (and 9 out of 10 times it IS) the fuel pump itself starting to die. It's losing its ability to pump enough fuel into the fuel lines to keep the injectors well fed. The injectors are drinking the fuel faster than the pump can pump.

If the Off-Run sequence fixes your long starts you need to get a fuel pump soon and replace it before if leaves you stranded. Not only is it inconvient, but it's another fee to pay.

..and one more excellent piece of advice, DON'T buy an Airtex!! They are the devil!

They can, and WILL, fail you. I just replaced the one I installed in May in the later part of June. I wasn't the first, and I certainly won't be the last, in the Jeep community to find out that Airtex (which I have dubbed Failtex) is a lose/lose situation fuel pump.

Go online (I recommend Amazon) and purchase a brand new Bosch. Bosch is the ONLY fuel pump you should be putting in there. Installing a fuel pump in a 97 and later cherokee is a PITA because you have to remove the fuel tank to do it. I hope it isn't full when it dies on you. Good luck siphoning it, because you can't do it through the fuel neck (where you stick the gas-gun to fill'er up). You're going to have to go underneath and disconnect the fuel neck, then slide a garden hose in there and start sucking until it comes out. I'm sure you don't like the sound of that.

So change it on your own terms when the tank is low, or get stranded and pay a tow truck 50 bucks to tow you.. then end up having to do it anyways. The choice is yours. I hope you take the blue pill.

Gee oh Dee

Or just put a fuel pressure gauge on the rail and measure fuel pressure.

Thats a bit more exact than playing with the key a bunch.

CoffeeCommando

The key method is a form of deduction which only affects the fuel system. If that fixes the problem, he has the Coffee Commando gaurantee his fuel pump is the problem.

Or you can just go spend $50 or more on a gauge and know what the pressure is. Hopefully it IS the fuel pump, because if it isn't you just bought a fuel gauge for nothing.

Gee oh Dee

What your doing in confirming the check valve in the fuel pump is working.

Your not testing anything else.

Putting a fuel pressure gauge on the rail will confirm the fuel pump is giving proper fuel pressure.

Playing with the key will do nothing of the sort.

You can go ahead and spend that $50 on a pressure gauge you'll probably use more than once, or you can borrow one from the parts store area using their tool rental program.

williams

I have a similar problem with my 2001 4.0. When ever I put a load on the engine either using the AC or towing the CIL comes on and the engine runs rough. Its been doing it since 60,000 miles (now 113,000) and some people say it's a leak in the head gasket but I never loose any water to speak of. I've had the coil packs replaced twice but does not correct the problem. When the CEL comes on it runs rough so i stop the car, remove & replace the negative battery terminal and then it runs perfectly fine...until I place another load on the engine. The code comes up misfire in cyl. #4.