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Unread 10-29-2012, 10:29 PM   #1
svshaw82
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Rough idle then smooth?

Hey guys...

got something weird going on. I just installed the ford orange 19lb injectors, and have developed something weird.

My XJ will idle normal for a moment and then run rough (almost to stalling) then like catch itself and be back to normal. It does this at stop lights, park, only at idle speed. Driving has no effect. No stumble, no loss of power, shifts great, lots of power.

My questions is whats up with the idle? I didnt have this issue before the injector swap, and these are good injectors...

Idle normal, then bad, then normal. Cycle back and forth, in drive at a stop, or in park. Weird!

Any thoughts I can chase? Thanks a bunch!

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Unread 10-31-2012, 06:52 AM   #2
svshaw82
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bump... no thoughts?
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Unread 10-31-2012, 07:10 AM   #3
cruiser54
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See if you didn't somehow bump the hose/tube from the throttle body to MAP sensor.

I would also do this sensor ground test since you had to disrupt that harness to install the injectors.

Cruiser’s Renix Sensor Ground Test


This sensor ground circuit affects the CTS, TPS, IAT, MAP, ECU and diagnostic connector grounds. It’s very important and not something to overlook in diagnosing your Renix Jeep as it is common for the harnesses to have poor crimps causing poor grounds. If any or all of the sensors do not have a good ground, the signal the ECU receives from these sensors is inaccurate.

Set your meter to measure Ohms. Be sure the key is in the OFF position. Using the positive (red) lead of your ohmmeter, probe the B terminal of the flat 3 wire connector of the TPS . The letters are embossed on the connector itself.
Touch the black lead of your meter to the negative battery post. Wiggle the wiring harness where it runs parallel to the valve cover and also near the MAP sensor mounted on the firewall. If you have an 87 or 88 with the C101 connector mounted on the firewall above the brake booster, wiggle it, too.

You want to see as close to 0 ohms of resistance as possible. And when wiggling the harnesses/connectors the resistance value should stay low. If there is a variance in the values when wiggling the wires, you have a poor crimp/connection in the wiring harness or a poor ground at the engine dipstick tube stud. On 87 and 88 models, you could have a poor connection at the C101 connector as well.

Revised 06/12/2012
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Unread 11-02-2012, 08:10 AM   #4
svshaw82
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I did break the map sensor hose while removing the fuel rail. It was hard plastic and snapped right off. I replaced it with a rubber hose as a quick fit. I did check it while running, I can pinch the hose and the engine dies.

As far as the grounding check I have not seen that procedure before, very interesting! I will have to give that a try this weekend. Thank you very much cruiser54!
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Unread 11-02-2012, 08:12 AM   #5
svshaw82
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One thing as far a ground is concerned... I have replaced the negative ground engine block location from the dipstick to another bolt hole area when i went through my harness and refreshed my connectors.
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Unread 11-02-2012, 08:14 AM   #6
cruiser54
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Quote:
Originally Posted by svshaw82 View Post
One thing as far a ground is concerned... I have replaced the negative ground engine block location from the dipstick to another bolt hole area when i went through my harness and refreshed my connectors.
That's fine as long as the connection is CLEAN and TIGHT.

Never hurts to add the extra cables. Especially with cold weather coming.

Do the sensor ground test. Easy fix if that turns out to have too much resistance. Do everything else in the ground refreshing procedure if you haven't already.
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Unread 11-02-2012, 10:53 AM   #7
ExgrayXJ
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In searching for something else a while ago, I believe it was about replacing injectors, the poster made the remark that the battery should be disconnected (neg post) for a period of time (20 mins?) ground the cable end to something for a few sec,.
This supposedly makes the computer relearn some parameters.
I tried it. I think it helped.
Also helped with my erratic idle speed problem.

Maybe wishful thinking...
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Unread 11-02-2012, 01:49 PM   #8
cruiser54
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Quote:
Originally Posted by ExgrayXJ View Post
In searching for something else a while ago, I believe it was about replacing injectors, the poster made the remark that the battery should be disconnected (neg post) for a period of time (20 mins?) ground the cable end to something for a few sec,.
This supposedly makes the computer relearn some parameters.
I tried it. I think it helped.
Also helped with my erratic idle speed problem.

Maybe wishful thinking...
Does not affect Renix in the least. It goes pretty much brain dead every time you shut it off.
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Unread 11-03-2012, 07:27 PM   #9
svshaw82
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Ok well I did the ohm check. I didn't have anything change while wiggling. Stayed pretty much between 1.9 and .08 ohms on my meter. Also dis this check over various other metal spots around and on my engine. Has the same reading all over the place. Guess my grounds are good. Unless 1.9 ohms are too high?
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Unread 11-03-2012, 07:28 PM   #10
svshaw82
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Sorry I meant .8 ohms not .08 in the last post
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Unread 11-04-2012, 08:30 AM   #11
cruiser54
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Quote:
Originally Posted by svshaw82 View Post
Sorry I meant .8 ohms not .08 in the last post
You had to wiggle the harness that carried these particular grounds when you did the injectors.

Should stay less than 1.0 ohms. Have you ever refreshed your grounds to be sure? Takes about 20 minutes and then you'd know for sure. All explained here:



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
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Unread 11-04-2012, 10:23 AM   #12
svshaw82
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Yeah I have relocated my negative ground to another bolt. Those ground wire spoken of in that article you copied... I have cut and extended them to the negative battery terminal. I had some issues with then in the past when they pulled out of the crimps while I was going a tune up
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Unread 11-08-2012, 07:11 AM   #13
svshaw82
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What if I went through my harness and made new ground at ever point I could? Like run a splice on the ground and a leg to metal ground, thought the harness. I have noticed cylinder six has been misfiring. Its the only spark plug wire I can unplug and have the engine "not change" when idling. Unplugging 1 - 5 makes the engine wanna die.

The plugs are new, so is the spark plug wires. Cap and rotor a a few years old. New distributor about 4 years ago.
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Unread 11-08-2012, 07:28 AM   #14
cruiser54
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Quote:
Originally Posted by svshaw82 View Post
What if I went through my harness and made new ground at ever point I could? Like run a splice on the ground and a leg to metal ground, thought the harness. I have noticed cylinder six has been misfiring. Its the only spark plug wire I can unplug and have the engine "not change" when idling. Unplugging 1 - 5 makes the engine wanna die.

The plugs are new, so is the spark plug wires. Cap and rotor a a few years old. New distributor about 4 years ago.
That could be the injector harness/plug causing the misfire. Wiggle teh connector and also look and see if the harness has chafes near the rear of the engine.

If you have a mechanic's stethoscope you can listen to hear if the injector is indeed firing.
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Unread 11-09-2012, 10:58 AM   #15
svshaw82
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I just swapped the injectors, I can feel it clicking. Wiggling does nothing. Harness is good. Still have all the looming over it, supported well too. Is it possible to have a bad spark plug even if the end of it looks good? Cap and rotor cause misfire? I unplug number 6 and the arc is insane! I unplugged it once with my hand and the arc jumped through me... damn that hurt too! So at least I know the coil is good, lol! I did another time and used my hose puller pliers, arc was jumping over 1" away from spark plug wire. Ive taken the plug out before and the end looked ok, checked the gap to .035" and put it back in.

Im assuming that because of the power of the arc my coil, cap, and rotor are ok. Is it possible for a spark plug to ground out before it reaches the electrode?
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