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Old 12-03-2006, 06:36 PM
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2.5l Spark knock

My poor little 4 banger is getting bad mileage and has a terrible spark knock. Replaced plugs and wires, made sure they were gapped right, no help.... any one else had this problem, or have any ideas? I aslo have used fuel injector cleaner, seems to help for a little bit, not much though.....

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Old 12-03-2006, 06:44 PM   #2
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What's a spark knock?

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Old 12-03-2006, 06:58 PM
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SPARK KNOCK

Definition: This is the pinging or rattling noise sometimes heard during acceleration that indicates detonation is occurring inside the engine
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Old 12-03-2006, 07:03 PM
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this is a better definition:
Spark knock is when the spark of the spark plug ignites the fuel/air charge in the combustion chamber sooner then it should.

mine only occurs during acceleration.....
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Old 12-03-2006, 08:42 PM   #5
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somehow the distributor cap is off causing it to happen? Maybe bad tank of gas? (lower octane rating the more likely to get knock)
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Old 12-04-2006, 01:38 PM   #6
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^^^ yah - replace the cap and rotor as well. If the rotor is a little sloppy that might be causing it. Bout how many miles are on the motor? I doubt it would be the distributor giving the slack.... but check and see if your timing has jumped.
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Old 12-04-2006, 02:25 PM   #7

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coil may be going bad too. had a bad coil in mine and gave me all sorts of problems.
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Old 12-04-2006, 02:49 PM   #8
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On my 95 I switched a couple wires when I did a tune up. Ran similar to what you are saying. Make sure you have the firing order right.
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Old 12-04-2006, 05:40 PM   #9
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coil may be going bad too. had a bad coil in mine and gave me all sorts of problems.
usually when a coil goes, its gone. The tollerances that they need are pretty tight and if they fall below on either side it won't even start the car... but I would suggest a nice MSD blaster coil. For the money, is a great upgrade!
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Old 12-04-2006, 10:10 PM   #10
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I was curious about this, so I did some research. From what
I've found, it is a serious issue that has to do with a problem with the ECU. MSD may be a good solution though...
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Old 12-05-2006, 07:48 AM
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its got 66 thousand on it..... thanks for all the info guys, rely appreciated, I'll keep everyone updated, little crazy round here with the holidays and all.....
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Old 12-05-2006, 08:49 PM
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I was curious about this, so I did some research. From what
I've found, it is a serious issue that has to do with a problem with the ECU. MSD may be a good solution though...
What kind of a problem and how serious? Cap and rotor are new, nothing is loose or anything, wires are all in the right place, so should I try replacing the coil and go from there? Any advice would be helpful..... money's tight till after Xmas, so I don't want to go buying parts hoping they work..... Thanks a bunch guys!
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Old 12-05-2006, 11:08 PM   #13
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From what I have read, it seems to be very serious. I don't want to scare you. Keep in mind, it's just internet banter I have seen on it. The info I saw pointed toward a computer issue and the solution was not cheap.

If it were mine, I'd probably have to break down and get a pro to check it out.
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Old 12-05-2006, 11:29 PM   #14
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^^^ when it comes to ECU problems, yes. A Pro is the only way to fix that.
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Old 12-06-2006, 01:24 PM   #15
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From my experience, what it sounds like is either spark or fuel. It seems you've worked on the spark, so I would assume it's the fuel. Either your fuel injection is not operating properly, or your computer is not giving the proper information to the operating systems. Can't get more specific than that.

I also recommend a professional, even though I hate to do that unless you have someone that you can trust. It could be something simple like an injection cleaning, but most garages are in the business of making money and like to add on extra work that can't hurt, but one may not need.
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Old 12-06-2006, 04:20 PM   #16
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I don't believe fuel is the issue. The spark timing being off is what causes spark knock. I've done a lot of reading, since a few days ago, I had never heard of it.

The spark timing being off usually affects only one plug, so adjusting the time is useless.
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Old 12-06-2006, 04:42 PM   #17
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how long has it been doing this? on my old truck, 1 bad tank of gas would make it ping like the devil for that entire tank, plus 2 more tanks of premium.

does the engine seem to be running any hotter?

do the newer jeeps have an EGR system? a stuck EGR valve would make it run lean and ping.

if its only been a short period....fill up with premium gasd and run a bottle of chevron techron.

pull your plugs....see what they look like. if one is whiter than the others, its leaning out on that cylinder and that one is your problem. if they ALL look white, theyre ALL leaning out.

dont take it to the stealer just yet....
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Old 12-06-2006, 04:47 PM   #18
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Oh, I didn't notice, was the distributer replaced ?

This is only my opinion based on my own past problem with another vehicle, but I had a computer problem that caused the same kind of knock (that a spark timing problem would cause). The mechanic told me the computer was telling the injector to send the fuel a "half beat" off. He may have been making up a story, I'm not knowledgeable enough about auto-computers to know better. It ran normal (without the knocking) after the computer was replaced ($300). This was not on a Jeep though.
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Old 12-06-2006, 04:54 PM   #19
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That sounds right. I hadn't thought of the fuel being sen through the injector in poor timing, but rather the spark being sent in poor timing. I guess it could go either way.
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Old 12-06-2006, 04:56 PM   #20
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if he can identify which cylinder is pinging, he can swap injectors to identify if its the injector itself or the computer deal y'all are talking about....
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Old 12-06-2006, 05:23 PM   #21
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How have you driven your four-banger? Think about if you are ultra-conservative and seldom really rev hard to high RPMs. If you do drive like that, there's very good chance your engine is loaded with carbon which causes knock and pinging. The built-up carbon continues glowing after the ignition stroke so it prematurely ignites the fuel during the next compression stroke which causes knocking and/or pinging.

If so, you can either try to blow the carbon out by revving your engine hard repeatedly to high RPMs either in your driveway or just day-to-day driving. That's often successful but it can take a while. The other method which I prefer is free and can be accomplished in ten minutes. It's an age-old technique that leaves the engine clean as the proverbial whistle inside and is nothing more than carefully (!) feeding it 12 to 16 ounces of tap water through the throttle body as you keep the RPMs up a tad to prevent stalling. This creates little shock waves inside the combustion chambers which break up the carbon which is then blown out through the exhaust system. Yes this method is effective and no, it is not some new thing I or someone just dreamed up. Done with care, as in not accidentally dumping the entire container of water into the engine too quickly, this is safe and effective. Feed the water slowly enough that it takes a minute or so to drain the 12-16 oz. into the throttle body.
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Old 12-06-2006, 05:30 PM   #22
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^^ I've heard of this, and it's $70 cheaper than the "decarbonizer" chemical my mechanic used to get the same outcome. Never tried it myself, kinda considered it one of those stories that you dare your buddies to try, and if it works you tell them "see, you gotta believe me".
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Old 12-06-2006, 05:54 PM   #23
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i've done the watre trick before but i used a spray bottle so itd be misted and go to the cylinders evenly. just make darn sure not to put too much.

a safer alternative is a can of sea foam sucked in thru a vacuum hose. works great for decasrboning an engine.
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Old 12-06-2006, 06:41 PM   #24
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i've done the watre trick before but i used a spray bottle so itd be misted and go to the cylinders evenly. just make darn sure not to put too much.

a safer alternative is a can of sea foam sucked in thru a vacuum hose. works great for decasrboning an engine.
A mister puts in too little water at a time to be effective.
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Old 01-03-2007, 05:40 PM
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took me a little while to work up the nerve to pour water into my engine, but alas! worked amazingly well, getting better mileage and it sounds alot better!! This site is the bomb!! Thanks!
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Old 01-03-2007, 10:19 PM   #26
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took me a little while to work up the nerve to pour water into my engine, but alas! worked amazingly well, getting better mileage and it sounds alot better!! This site is the bomb!! Thanks!
There ya go, see this stuff isn't always just made up!
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Old 08-10-2009, 07:00 PM   #27
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I am having the same problem and want to try Jerry's tip. I'm an exteme noob so can some one tell me exactly how I go about finding where to pour the water into the throttle body? I dont know what to open up for access to the throttle body. Also, does the car need to be running when pouring the water into the throttle body? If anyone has pictures, that'd be a BIG HELP!

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feeding it 12 to 16 ounces of tap water through the throttle body as you keep the RPMs up a tad to prevent stalling.
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Old 08-10-2009, 07:50 PM   #28
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A mister puts in too little water at a time to be effective.


I will sometimes put a brick on the footfeed and then go get the garden hose and just let it suck it up for hours on end. I take my converter off if i am going long term like that. man just noticed this is an ollllllldddddd post.
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Old 08-10-2009, 08:21 PM   #29
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I am having the same problem and want to try Jerry's tip. I'm an exteme noob so can some one tell me exactly how I go about finding where to pour the water into the throttle body? I dont know what to open up for access to the throttle body. Also, does the car need to be running when pouring the water into the throttle body? If anyone has pictures, that'd be a BIG HELP!
Yes the engine MUST be running and you really should have the rpms up a tad to prevent stalling as you trickle the water into the throttle body intake. You CANNOT DUMP OR POUR the water in, it must be slowly... s..l..o..w..l..y trickled in. For a container the size of a coke can which works very well for this, it should take around 2 minutes to trickle the entire can in, no less. I don't want to scare you but if you were to accidentally dump the can in all at once, you'd likely have a ruined engine from hydrolocking it.

You only need a screwdriver to remove the big black air tube from the top of the throttle body, pictured below. Once the air tube has been removed, start the engine and while holding the engine rpms up a tad, like to 1500 rpms or so, start trickling the ater into the center of the throttle body's air intake you uncovered when you removed the black plastic air intake tube. The vacuum present there at the throttle body's opening when the engine is running will suck the water right in.

This will generate micro-shockwaves within the combustion chambers and dislodge any carbon buildup which will be blown out through the exaust.

Benefits: Free, fast, effective.
Drawbacks: People who cannot avoid dumping too much water in at once should not attempt this.
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Old 08-10-2009, 08:40 PM   #30
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Thanks Jerry. I just picked up the Sea Foam Motor Cleaner from Pepboys. Would it be ok to use that in the throttle body also? It's the spray kind so not sure.

i'll wait for your response and will give either a try tomorrow afternoon when it's brighter outside and report back my results. Hopefully it's a not cry for help about a ruined engine.

Thanks.

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