1998 Jeep Cherokee 4.0 Gremlins

[streetxj]

Good evening everyone,

My dad just bought a nice 1998 jeep cherokee 4.0, but it has a couple of issues. There is a even misfire at idle which smooths out completely as soon as you raise the rpm and the cranking sounds slow. It has a new fuel pump, new IAC valve, new Crank Position Sensor, new radiator and new battery. There is no detonation and the truck does not overheat. Oil was old, but it smelled like pure oil and there was no gas smell and it was a normal old oil color. It didn't have any milky color to it. The jeep does have a stereo system with amp and sub-woofer. The slow cranking itself might be a voltage issue due to the stereo. Can that also cause the idle missfire? I'm thinking TPS, or ignition problems. I would like to hear other opinions.

Thank you.

 

[98NWCherokee]

How fresh are your tune-up parts? I had a Ford F450 missing at idle last week and it just needed fresh spark plugs, wires, cap and rotor. The slow crank could be a weak battery. You should get it load tested as our XJ's do NOT like low voltage in the battery. It can present all kind of problems and should be addressed. I had a slow crank in my 98 last year and after load testing the battery I did a volt drop test on the starter circuit and ended up replacing the starter motor. It cost $42 and has been cranking like a dream ever since.

 

[streetxj]

How fresh are your tune-up parts? I had a Ford F450 missing at idle last week and it just needed fresh spark plugs, wires, cap and rotor. The slow crank could be a weak battery. You should get it load tested as our XJ's do NOT like low voltage in the battery. It can present all kind of problems and should be addressed. I had a slow crank in my 98 last year and after load testing the battery I did a volt drop test on the starter circuit and ended up replacing the starter motor. It cost $42 and has been cranking like a dream ever since.

Cool. Thanks!

 

[birchlakeXJ]

Absolutely agree with the recommendations from 98NW.......

Never underestimate the importance of fresh tuneup hardware. Simple stuff first; always.

For a 98, I'd go with Champion copper plugs (verify gap is at .035) quality plug wires, cap and rotor. For a "new-to-you" vehicle, replacing all of the above is a really good idea, unless you have (believable) evidence that it has been done recently. Doing it now establishes a baseline for future tuneups. Check air filter while you're at it. It wouldn't give you these symptoms, but gotta check and replace it if necessary when performing a tuneup.

The stereo should NOT cause slow cranking unless you're leaving it on while the vehicle is parked which is discharging the battery. Any parts store will load test your battery for no charge. You can get a bad battery from the parts store, so wouldn't hurt to verify to be sure. But before that, remove battery cables from the battery and thoroughly clean them and the battery posts until shiny. Inspect battery and starter cables closely.

I would absolutely recommend freshening engine grounds. Connections and grounds. are extremely important and you often can have a problem with them that you can't see at first glance. Here's more on grounds.

Good luck and keep us updated!
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Grounds can be the root cause of many electrical gremlins. Refreshing grounds is NEVER a bad idea, and the investment of your time in this procedure is always well worth it!

You can't tell much of anything by looking at ground connections!! You must remove, scrape, clean until shiny the cable/wire ends and whatever they bolt to. Be sure to remove all paint from any ground connections.

Start with the one on the back corner of the head, and where it attaches to the firewall, as it deteriorates over time and is an area that makes it susceptible to damage. Best to replace that woven cable with a #4 or #2 gauge cable. You can attach the one end to the intake manifold if you would like.

Next go over to the engine dipstick tube stud. Remove the nut and clean the wire ends and scrape the block until shiny at the stud. Reattach tightly.

If you are so inclined, add at least a #6 cable from the negative terminal of your battery to one of the bolts on your radiator support.

 

[streetxj]

Thanks! ^ We took a closer inspection and the engine needs a rebuild. It was never maintained. The intake is soaked in oil, there is the miss and there is smoke blowing out of the valve cover breather and the oil dip stick tube and a constant clacking noise. The oil is as black as can be. New radiator, but it has brown water.... It's a beautiful 98' cherokee that my dad just bought for 1600 bucks. He was quoted 1400 bucks for complete rebuild and 600 bucks for labor (taking out the old engine and re-installing it after rebuild). We are going to get a couple of more quotes. When the new motor goes, we will definitely get a new thundervolt catalytic converter and new 02 sensors.