Jeep cherokee tune up gone wrong.

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  #1  
Old 01-28-10, 09:24 AM
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Jeep cherokee tune up gone wrong.

I hate when this happens...I offer to give my friend a quick free tune up. Now the cherokee runs worst then when it came in. Its a 93 Cherokee 4.0.

Her old plugs didn't even have gaps left, they were bridged somehow with white buildup. The tip of her rotor was rusty. The cap was shot.etc.

I did new plugs, wires, air filter, fuel filter, rotor and cap. Now it runs like its missing a cylinder. It smooths out when you give it gas but vibrates and shakes at idle, which it never did before.

All the plug boots snapped on and are tight.

My only ideas are

A. I used an old spark plug gap tool thats been hangin on my key chain for many years. I don't think a slighty smaller gap would cause this. The gap was .035.

B. I guess the new rotor or cap could be defective.

Does anyone have any input?

It almost sounds like I knocked off a vaccum line but I checked all of them.
 
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  #2  
Old 01-28-10, 09:31 AM
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Are you positive you installed the plug wires correctly? double check your firing order.
 
  #3  
Old 01-28-10, 09:36 AM
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yea I checked the firing order. Its right on. I guess I'm gonna pull all the plugs and make sure I don't see anything unusual. This couldn't be the ignition coil, right?

The plugs that were originally in this jeep were really expensive bosch plugs that I never even saw before. They had a different style electrode. I wonder if this thing had previous problems that were resolved by putting in really expensive plugs. I used 3 dollar autolites platinums...
 
  #4  
Old 01-28-10, 09:52 AM
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I like the regular bosch platinum plugs - I've gotten good service out of them Never used any of the double or triple electrode ones. Wouldn't hurt to do a compression test while your at it.

Maybe the jeep don't know how to act with all them new parts
 
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Old 01-28-10, 11:43 AM
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IIRC, there is no timing setting on the Cherokee, right? I'll have to go with marksr on the plug wiring. Not saying you did or didn't do it, but you could have set them counterclockwise rather than clockwise. Just a thought. In handling the wires, since they are carbon based, you could have cracked the core on one of them. New wires will tell a new tale. Not likely the coil since it wasn't broke when you took it apart. They don't go bad just because you did a tune up. Try the wires and let us know how it goes.
 
  #6  
Old 01-28-10, 01:46 PM
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I would pull the plug wires at an idle, one at a time to isolate it to specific cylinders.

Usually, in that situation, it's a couple of plug wires crossed.
 
  #7  
Old 01-29-10, 06:24 AM
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I went through the plugs again. The gaps were slightly smaller so I reset them all back to .035 with a new gap tool. I tried the old rotor and distribuitor to no avail. I put on new plug wires, I checked the end of each wire to confirm spark was getting there.

I determined it must be fuel related. Must of knocked a tiny piece of debris loose when I changed the fuel filter. I put in injector cleaner and within minutes it was running much better, but not perfect. I have a feeling once a tank of gas gets ran through it, it will be fine. Hopefully I won't have to change any fuel injectors.Does this sound right?

This is kind of unrelated, but i had two quick questions maybe you could help me with.

1. I was thinking about pulling each plug wire, then putting it back on while it was running. I did this on a dirt bike once tho and got WHACKED right through the insulation. Would doing this to the cherokee shock me?

2.We ran a compression test. Most numbers were 130. Lowest was 127, highest was 140. I forgot the rule of thumb as far as the allowable gap between the lowest reading and highest. Is this motor in good shape?

Thanks for all your help!
 
  #8  
Old 01-29-10, 07:17 AM
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Engine is in average shape, but still serviceable.

As far as pulling the plug wires - that' the way you check for spark - the number your arm is the better the spark.

Actually, what you do is pull all the wires with the engine off and set the boots of the plug wires over the end of the plugs, start it, then you can hold the wire away from the business end. But even at that you can get shocked a little if a wire is leaking.

You can get insulated tools for doing it at an auto parts store.
 
  #9  
Old 01-29-10, 03:38 PM
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Strider,

You don't mean to tell me that Jeep ran good when she brought it in, with those white crud electrode-bridged plugs, do you? If so, I'd be amazed at that.

And if not, now that you can discern ONE miss, after your work - how do you not know that one miss was always there? - perhaps more silent by the fact that several cylinders were bad when she brought it to you?

Why did she bring you the Jeep?
 
  #10  
Old 01-29-10, 05:14 PM
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Might try removing the negative battery terminal, wait 10 minutes, then re-install.

Then let it idle for about 5 minutes. And drive it over 45 MPH soon.

This helps the engine computer to "re-learn".

Also another spark test is to use a spark testing tool which would typically have a gap of .25 inch. You should see a crisp blue spark. This is a larger gap than a spark plug and tests that the coil is producing a high enough voltage. (Good spark as opposed to weak spark.)
 
  #11  
Old 01-30-10, 01:20 PM
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The problem persists....

I couldn't believe this thing was even running with the old plugs in it either. Mind boggling, but yea, it definitly ran better when she brought it in then when she left. She brought it in just for a tune up, which usually takes me a half hour and comes out flawless.

I used one of those spark plug testers at the end of each wire, probably with a gap of an eigth inch or so. The sparks would alternate blue, orange and yellow on each cylinder. Is this sure fire sign the coil is weak. I'm sure the junky spark plugs were putin a pretty good demand on the coil. It probably dosn't know what to think with the new plugs haha. And a weak coil I think would cause random misfires like its doing now. Regardless, should I have seen all blue sparks, or is half yellow half blue acceptable?

Its gotta either be the coil or a fuel injector.
 
  #12  
Old 01-30-10, 01:51 PM
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Well, you never know. But the coil probably can't percieve any difference of if when the coil shuts of it's primary current to send current instead to the high voltage secondary, if the current jumps a gap or simply goes out the plug wires directly to ground. But do check to make sure no gunk or carbon on the coil. If this is a simple coil, maybe you could swap out quick with another vehicle, unless hookups are different. My 90 Dodge has the same simple type as was used in cars that date back well into the last century. I'd let you try mine. If it is not a simple bleed off to ground problem, as perhaps visibly seen at the coil (maybe by gook or by spark at night), often bad coils let vehicle run good say at idle, then break down at high speed.

Have you tried ohms testing every plug wire to check for consistency? (Remember if you use a voltmeter, that the range setting will have to be set to a higher range, to capture the reading, as resistance is high, in resistor plug wires! Look for conssitency of readings among them all.) Or identifying the down cylinder by pulling one plug wire one at a time, then switching around plug wires on 2, to see if now you shift the miss to another cylinder? And/or look for electrical seepage under the hood out in the dark. You may have damaged a frail plug wire, unknowingly, by removing it, if it was on it's last legs.
 
  #13  
Old 01-30-10, 03:17 PM
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Following is an additional test you can do on the coil using an ohm meter. (This test would require the factory specs for the coil which would be in a factory service manual set)...
Coil Test - Testing Your Ignition Coil - Coil Resistance Test - How To Test Your Ignition Coil With an Ohmeter
 
  #14  
Old 01-31-10, 08:05 AM
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Wink

One thing to keep in mind is that I myself have seen it, as well as other Chrysler mechanics over the years, even though other mechanics will argue that it doesn't matter, is occasional problems with Chrysler engines (ignition systems) not running well on other brands of spark plugs. I just recently helped a female mechanic remedy same situation on another help site. Her van was running rough, she replaced plug wires,cap etc, and plugs, only to have it run worse as well as go in to a no-start situation occasionally. After double checking everything, and triple checking others, I advised her to take her bosch plugs back, and get champions as listed on label, as well as owners manual. The parts guys insisted that the plugs could not be the problem, (maybe they didn't sell Champions) but in the end, she bought a set of Champions as recommended, gapped them as recommended, installed them, and with a big THANK YOU, replied to tell me all was well again, and van was running like a charm. She was another mechanic who had never heard of that. I ran into it as far back as late 80's, and it has popped up numerous times since. Another thing to take into consideration would be the possibility of carbon build up, especially those that had the corroded/carboned plugs. Personally, I'd get a can of combustion chamber cleaner spray from Chrysler and give it a treatment as well to clean up those cylinders. Get the spray that you use to spray into throttle body and follow directions. I'm not pushing products here, only stating what I've seen work well over the years.

Note: RC12LYC @ .035 were originals. Or 3412 for single platinum, or 7034 for double platinum. Personally at this point I'd go with originals @ about $3 each.
 
  #15  
Old 01-31-10, 09:00 AM
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I haven't cracked open a spark plug in a long, long time. I can no longer remember what they look like in the hidden part of the white porcelain. If there is a resistor there, perhaps some brands of plugs have too great of a resistance than what some coils and resistor plug wires can overcome?
 
  #16  
Old 01-31-10, 09:54 AM
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I have been wondering this whole time if it was the plugs. I guess its worth a try. Weird how a 30 min job always takes several hours over several days.

When I checked the plugs after she drove for 30 min. they all looked good, just like they should. You could tell they had all been firing, and were a perfect color of a well running engine.
So the misfire is random and sparatic. I guess I'll change the plugs again and ignition coil.

If this dosn't solve the problem, is it safe to say its a fuel injector/injectors? Has anyone ever knocked a piece of crud loose changing the fuel filter?
 
  #17  
Old 01-31-10, 10:06 AM
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I always find it best to replace with factory specification parts. So good idea to use factory specification plugs, spark plug wires, coil, etc.

All this stuff is designed to work together.

Also spark plug wires "might" be designed by the vehicle manufacturer to not put off electrical "noise" which could cause problems with the engine computer or sensors associated with the engine computer.

Here is a page all about spark and wires...
Spark Plug Wire Test

All about "EMI" or ElectroMagnetic Interference...
Electromagnetic interference - Wikipedia, the free encyclopedia
 
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Old 01-31-10, 10:07 AM
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Ohhh. You say the misfire is sporadic now. Hmmm. That makes things tougher. Harder then to tell what cylinder might be the faulty one. Maybe the problem is not even isolated to one particular cylinder at every misfire.

But I'd surely check and look for spark leakage at night.
 
  #19  
Old 01-31-10, 10:10 AM
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If all else fails, following is a page on random misfires and things to check / test...
Random-Misfire Page
 
  #20  
Old 01-31-10, 11:07 AM
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She says the problem seems to smooth itself out when she gets around third gear. I've been thinking vaccum leak since the beginning but can't find any loose hoses in the vacinity of where I was working. I did notice a hiss when she turns off the motor coming from the brake master cylinder. I don't believe that this would cause these problems though, right?
 
  #21  
Old 01-31-10, 11:33 AM
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It could. Try plugging the vacuum hose going to the power brakes. (Cork or whatever.)

The brakes should still work and there is the emergency brake. And only you should test drive it, not her. No tailgating! Be careful test driving - deserted road best!
 
  #22  
Old 01-31-10, 01:00 PM
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These were the plugs that were in it.
Bosch Plugs

I'm thinking about buying some new ones and trying them again. The Bosch website says...


"0.3mm Diameter Pure Platinum Centre Electrode

Better performance
Better ignitability
Reduction in required voltage
Centre Electrode Diameter Comparison

Increased Fuel Efficiency, Smoother Idling and Acceleration

Heavy duty tapered electrode for reduced electrode temperature, and improved access to air & fuel mixture."


But it also says for use on a 1995 and later. This vehicle is only a 93. Any opinions on swapping a new set of these plugs back in?
 
  #23  
Old 01-31-10, 03:38 PM
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Originally Posted by strider380 View Post
She says the problem seems to smooth itself out when she gets around third gear.
MORE information. Keep it coming. After awhile, at this rate, I think the problem may go full circle, and fix itself.
 
  #24  
Old 01-31-10, 06:00 PM
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Is the owner's manual in the glove box?

Does the owner's manual say what type of spark plugs should be used? (Usually in back of owner's manual along with oil types to use, etc.)
 
  #25  
Old 01-31-10, 06:42 PM
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I wouldn't bother repeating something. If you want the original plugs for it, just ID the vehicle and engine for an auto parts store and ask for OEM plugs and the gap.
 
  #26  
Old 02-01-10, 02:11 PM
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We put in Autolite platinums for 3 bucks each which is what autozone listed on their computer. The problems getting worse. I guess I'll try the ignition coil first. That sounds reasonable, right?


Thans for sticking with me through this everyone.
 
  #27  
Old 02-02-10, 07:43 PM
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See notes at my other post, for champion numbers.
 
  #28  
Old 02-02-10, 08:40 PM
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Did you try isolating the miss by pulling plug wires?
 
  #29  
Old 02-04-10, 05:16 PM
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So I went to the parts store and ordered OEM champion plugs. Turns out they are a copper plug, and autozone sold me platinum plugs. Problem solved!!! I had no idea, i thought a spark plug was a spark plug. And to make it worst, these platinum plugs that were causing me issues wern't even the plugs I asked for originally. They were a dollar more each, the autozone guy slipped em in instead.

Any ways it's a huge weight lifted off my shoulders. This thing runs great now. I want to thank everyone for bearing with me through this. I feel like I should have known better but I honestly had no idea. I really hope someday this thread will help another helpless individual such as myself. Thanks everyone!
 
  #30  
Old 02-04-10, 05:23 PM
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Good Job!

Now quick return it before something else goes out!
 
  #31  
Old 02-07-10, 08:43 AM
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As I stated in my original post, there are many mechanics, parts guys etc all over the country that will argue that with you, and if I hadn't seen it, been there, I'd probably never would have believed it either. That's why it only had to happen once to me, for me to remember it. The part manufacturers will also argue with you, but then again, they are trying to sell parts. The other hard part is that some mechanic will tell you he's been running another brand for years with no problem. I just won't chance it, anything Chrysler/Dodge/Jeep, or even related, gets Champion, as listed on sticker.
Scary part is, I first ran into this 20 years or more ago. (EEEEEEK ! getting old)
 
  #32  
Old 02-07-10, 06:40 PM
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Originally Posted by Mike.B View Post
As I stated in my original post, there are many mechanics, parts guys etc all over the country that will argue that with you...
I try not to get advice from parts guys...

One time I installed a new 6000 lb. trailer axle along with new electric brakes, bearings, and drums. (Not cheap!) The manufacturer's instructions said to use a specific type of bearing grease. One auto parts store did not have it and the guy said "any bearing grease" would do fine! I went to another store and found the right type of grease...

Then another time I was installing factory air conditioning in a vehicle. A parts guy told me I did not need to evacuate the A/C lines with a pump! That I could just fill the system with refrigerant! (I don't know where these people come from?)
 
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