Noob Has A Problem!!!!!!

[mjestes17]

Hey guys, I just recently joined this forum because I bought an 89 comanche pioneer w/ the straight 6 4.0. It only has about 130k and it ran great when i bought it. Within the last few weeks, I've been noticing my jeep start to sputter and the idle got a little rough. It gradually got worse and worse until I got scared to drive it because I didn't want to make matters worse. At first I thought it would be a fuel problem, so I changed the oil, oil filter, and fuel filter. That didn't help the cause. So I changed the spark plugs. Still nothing. So I dug deeper. I dropped the gas tank, bought a new tank and pump, and installed them both to no prevail.

 

At this point I went from fuel to engine components. I have an HEI aftermarket distributor that was installed by the previous owner. Cracked it open, bone dry, no damage. I checked my fuel lines for leaks and I don't seem to have any (I'm not a genious but I didn't see/smell anything out of the ordinary). Sooooo since I'm assuming it had nothing to do with the spark, I started buying new parts associated with the ignition. I replaced the TPS, I replaced the IAC, and I threw in a new Crankshaft Sensor. STILL HASN'T SOLVED MY PROBLEM!!!!!!

 

As my jeep sits right now, it fires up perfectly with the turn of the key every time. After I fire it up, it runs good for a few seconds, then it starts to slowly choke itself out and eventually dies. Sometimes within only a few seconds of starting......It sputters when I drive down the road with a very evident loss of power. I used to be able to hop on the freeway, pass people doing 80 plus mph, and everything would be dandy. Now I can't even take it past 50mph because it starts shaking and it has no power. It chokes, sputters, shakes, and doesn't want to stay alive. I have to hold the brake down at every stop light and maintain a constant 900rpm with my driver foot.

 

somebody please help me out! this truck is my daily driver and i need it back in running order ASAP!!!!!!!!

[Backdraft]

Is your MAP sensor hooked up and working?

[Geonovast]

Why are you assuming it has nothing to do with spark?

 

What's your fuel pressure?

[Comanche County]

Yes, check fuel pressure. Check the spark plug wires, you didn't mention those. Check the vacuum lines to the MAP. You can refer to this guide to confirm if your sensors are working: http://www.lunghd.co...Diagnostics.htm

[mjestes17]

You're right, I shouldn't assume it has nothing to do with spark because I'm definitely no expert. I guess I just figure since everything is so new and it was running perfect that it couldn't be the newest parts. I haven't checked any pressures or any voltage anywhere because I'm not too keen on how to do that yet but I really appreciate the web link and ill follow it to the T. Is there anything else that could be making this happen? Anything a new-ish guy like me wouldn't know about? Also, how do I test or figure out if I have a vacuum leak? Is there a link for that as well?

[Comanche County]

I think I'd ditch the aftermarket HEI distributor and put a stock one back on. Not sure what kind you've got but I've had one where the coil under the distro cap was bad causing all sorts of bad running issues. Go back to stock, the stock ignition system isn't too bad at all and cheap as dirt. There's no reason to run some crazy distributor on an otherwise stock engine.

[Eagle]

You haven't mentioned checking either the coil or the ignition module. You also haven't mentioned if the aftermarket distributor works with those or replaced those. The factory ignition is (was) a high-output ignition, so why anyone would have installed an aftermarket distributor is beyond my understanding. My best guess is that there was a problem, he tried to "fix" it, the fix didn't work so he sold the truck.

[mjestes17]

The aftermarket distributor has the coil pack inside of it so I'm not sure how to tell if that's the problem or not. Ill go ahead and swap back to stock to see if that fixes the problem. I don't think he sold the truck because it had a problem. It ran perfectly fine for about a month before it started acting up.

 

When I go back to the stock distributor, will I need a new coil pack?

[mjestes17]

Is there a certain way to install a distributor so the timing doesn't get screwed up or do I just simply throw it on there and hook it up in correct firing order?

[Comanche County]

You can pull the old distributor where it is as long as the new distributor goes in with the rotor pointing at the exact same same spot.

 

But I always rotate the engine until the #1 cylinder is a at top dead center, mark where the rotor is pointing, then pull the dizzy, and replace.

 

If the old coil pack is still on the inner fender well then use it, if not, 15 bucks and a trip to the JY and you're set.

[mjestes17]

Okay thanks for the tip. Ill find some time this week to hit the JY. They had a manche at the local jy but it's gone now. Thank God xj's are a direct fit

[mjestes17]

do you guys think it might just be the injectors? i hate pouring money into this thing with no prevail.

[Geonovast]

Have you actually checked the spark with a plug out of the head and grounding it to the block?

 

How old are the wires?

 

What's the condition of the ground strap on the back of the head?

[mjestes17]

I haven't checked the spark, but I'll do it like you said. Are you talking about the plug wires? Because they're as new as the HEI distributor that the previous owner had installed so still pretty brand new. I'll have to check out that grounding strap that you're talking about, I honestly didn't even know it existed. I'm slowly gaining knowledge of my manche and I really appreciate all the insight. Please standby for my response. Again, thank you for helping me and being patient!!!

[Eagle]

None of us likes to waste money throwing parts at problems with no result, and we don't generally start off by suggesting that you throw parts at anything. We generally suggest taking some time to figure out what the probel might be, THEN take a deep breath and throw a part or two at it.

 

The problem is, some people read ONE response and then rush out to buy that part, while three other people are explaining why that part can't be the problem.

 

I know you want your truck running and on the road, but it's more than twenty years old, and somebody has been changing things. You cannot reasonably expect to figure out what's wrong just by guessing. You will have to investigate, test, diagnose ... and then mutter incantations on the night of the full moon to the Jeep deity of your choice.

 

Basics: To run, an internal combustion engine requires three things: fuel, air, and spark. You have an aftermarket distributor, so spark is (IMHO) immediately suspect. Easy check -- pull a plug wire off, hold it in INSULATED pliers near a head bolt, have someone crank the engine, and hope you see a big, fat, blue spark jump from the wire to the bolt.

 

Try that, and report back what you found.

[cruiser54]

Could be as simple as this.

And did you adjust that new TPS?

 

Renix Ground Refreshing

The Renix era XJs and MJs were built with an under-engineered grounding system for the engine/transmission electronics. One problem in particular involves the multiple ground connection at the engine dipstick tube stud. A poor ground here can cause a multitude of driveabililty issues, wasted time, and wasted money replacing unnecessary components.

The components grounding at the dipstick tube stud are:

Distributor Sync Sensor, TCU main ground, TCU “Shift Point Logic”, Ignition control Module, Injectors, ECU main ground which other engine sensors ground through, Oxygen sensor, Knock Sensor, Cruise Control, and Transmission Sync signal. All extremely important stuff.

The factory was aware of the issues with this ground point and addressed it by suggesting the following:

Remove the nut holding the wire terminals to the stud. Verify that the stud is indeed tightened securely into the block. Scrape any and all paint from the stud’s mounting surface where the wires will attach. Must be clean, shiny and free of any oil, grease, or paint.

Inspect the wire terminals. Check to see that none of the terminals are crimped over wire insulation instead of bare wire. Be sure the crimps are tight. It wouldn’t hurt to re-crimp them just as a matter of course. Sand and polish the wire terminals until clean and shiny on both sides. Reinstall all the wires to the stud and tighten the nut down securely.

While you’re in that general area, locate the battery negative cable which is fastened to the engine block just forward of the dipstick stud. Remove the bolt, scrape the block to bare metal, clean and polish the cable terminal, and reattach securely.

Another area where the grounding system on Renix era Jeeps was lacking is the engine to chassis ground. There is a braided cable from the back of the cylinder head that also attaches to the driver’s side of the firewall. This cable is undersized for it’s intended use and subject to corrosion and poor connections at each end.

First off, remove the cable end from the firewall using a 15mm wrench or socket. Scrape the paint off down to bare metal and clean the wire terminal. Reattach securely.

Remove the other end of the cable from the rear of the head using a 3’4” socket. Clean all the oil, paint and crud from the stud. Clean the wire terminal of the cable and reattach securely.

A suggestion regarding the braided cable:

I prefer to add a #4 Gauge cable from the firewall to a bolt on the rear of the intake manifold, either to a heat shield bolt or fuel rail bolt. A cable about 18” long with a 3/8” lug on each end works great and you can get one at any parts store already made up. Napa has them as part number 781116.

A further improvement to the grounding system can be made using a #4 cable, about 10” long with 3/8” terminals at each end. Attach one end of this cable to the negative battery bolt and the other end under the closest 10mm headed bolt on the radiator support just forward of the battery. Napa part number 781115.

If you want to upgrade your grounds and battery cables in general, contact Jon at www.kelleyswip.com. He makes an incredible cable upgrade for a very reasonable price.

 

Revised 11-28-2011