Engine Tone

Damn problems never end... This time when i turned on the jeep instead on idleing at 700-1000 like it normally does it idled at 1500 for a brief 10 sec and went down . Even tho it went down--once i pressed the gas pedal the engine vibrated around 1600-2200RPM , this would only be felt inside the car and really not outside weather under or in the engine bay. Other wise the jeep drives ok, but around that RPM it feels weird. After cleaning he tps, o2, iac connectors it seems to idle a bit better but it still doesnt feel right at that rpm band (1600-2200) .

When you push the accelerator slowly in nuetral it feels fine as it increases but as soon as it gets to that rpm it feels as if there is a sudden tone change and shudder ?

I need a few suggestion before i give up and let someone look at it...its been too long this thing has been acting retarded.

Thru my other posts i have done the following, to help the sitaution..
1. Replace Motor Mounts/Tranny Mounts (helped for a while or rather hid the prob)
2. Replace Spark plugs / Wires (champion/bosch)
3. Repalce cap and rotor with one from napa
4. Changed motor oil / filter and tranny oil
5. Reset ECU

thx
pete

What year XJ ? if it´s a Renix, try a nice smooth accelration on the interstate through the 2000 RPM area in high gear, if it bucks and misses around 2000 RPM it is often the O2 sensor.
The Renix TPS is known for messing up at around 1/3 pedal, there was a TSB for this. Mine had a dead spot at around 1/3 pedal, that I could see with an old analoge ohm meter. Sure messed with my shifts as it was the tranny half of the TPS. Yours may be the motor side fo the TPS.
Is it a vibration or the motor running crappy? One way to tell if it´s the motor is to hook up a vacuum gauge, if the motor is running crappy the needle will wag. A quick test for ignition misses is to hook up a timing light to each plug wire in series and look at the light shined onto something dark, you can see an ignition miss.
Vacuum leaks usually make for a crappy idle, often don´t affect the motor much at higher RPM´s.
Both my Renix and my OBD 1 XJ´s idle up a little, at start up, then settle in after a few seconds.

8MUD what is TSB? Sorry in advance for any stupidity on my part.

I think its the throttle position sensor

I own a 88 XJ and seems like I have replaced everything. I recommend you find a mechanic who understands the Renix ignition system used on your XJ. they used in 87-90. I moved to this town, called the dealer and talk to the service dept. I askef if they had a guy who understood 88 XJs, they brought out their senior guy and we talked. I felt like he knows his stuff and use him every time I go in.

IF you had a guy like that you trusted you could take it in, tell what the problem is and let him figure it out. He will hook up the test set to the computer and he will check out all the sensors, injectors and he will see how all the pieces are working. Once he has the information he can tell you what needs cleaning/fixing.

I recommend as general maintenance to replace the Throttle Position Sensor, it just wears out. I changed mine at 130K miles. You may also want to change the MAP sensor, and the manifold temp sensor. They all wear out.

You also may want to get the throttle body cleaned as part of the exam. It might be time to get professional help, may be the best 1.0 hours of mechanic labor you pay for while owning the XJ.

TSB = Technical Service Bulletin. I think. You can go on Jeep.com and they have info on recalls, I think alldata.com is where you can find the service bulletins.

Well first of all my jeep is a 94 xj in which the gay computer reports no damn problems- no codes show up.

So i am not sure if the o2 sensor thing still applies but let me know if it does ?

pete

Pete, you are not listening. I suggested you take the XJ into the shop and have a mechanic check it over. The computer test set does A LOT MORE than just read error codes. The trained mechanic can observe things like pulse width of the injectors, output of the oxygen sensor, operation of the TPS.

I am advocating you go to the step you can not accomplish without a computer test set. I purchased a Snap-on MT2500 computer test set to see what my 88 XJ is doing. You can also look at ebay for the snap on tool or you can buy the Autoxray tool for $300 - http://www.autoxray.com/products.aspx?sub=scanners&id=32

You are at the cross road of throwing more parts at it as a guess OR pay somoene to figure it out. I had a problem a couple years ago where my MPG went down to 15 mpg vs the normal 20 mpg on the highway. I tried everything and could not figure it out. I took it to the mechanic and he figure out the EGR valve was stuck open. Once he figured that out the first 1.0 hour of labor was included in the diagnostic fee, so it only cost my the part of the part since I had already decided to pay them to figure out the problem.

No martin i am listening i thought you meant all that because you were talking about an older renix system which is a lot harder to work with and i dont have.

The thing is all the mechanics i know i dont trust and the others want 125$ just to look at the damn thing, which is a bit much especially if it turns into a big thing. In the last few months i have spent hundreds on this thing not to enjoy it but just barely to maintain it.Anyway I am not here to complain, i love this thing and want it fixed if it doesnt cost to much.

I had a local friend lift the jeep on his car auto lift and we ran the jeep while it was on th lift and it felt the vibe was coming from the bellhousing area. I think my last ditch effort before i can afford to have someone look at it will be to pull the tranny and look at the flexlate. If its the flexplate great if not i will have wasted my time and then will have someone look at it in a while when i can.

Pete

funny thing last night while changing my temp sending unit

i brushed up against my map sensor and actually moved the bracket it was on ,

well didnt move it back
and it idled like a drag car cam over real hard

then i found out it was map sensor so i moved it and it adjusted my throtle and made theidle smooth again

may or may not have anything to do with your symptoms

i just felt it wierd and funny how it worked

ya i just made sure the map and 02 sensors were connected and the connection was clean.

Anyone know where i can get a flexplate other than the dealer...he wants 130$ for the flexplate ?

pete

Martin may be right, XJ´s have certain weak points or sicknesses, it sometimes better to get it to an mech. that works on these things everyday.
Having said that, the places around here get you in the door and rarely let you back out, without $400-500 bill and all to often, don´t fix what you took it in for, in the first place..
If you haven´t had the flex plate out, chances of it being bad are slim. Usually what happens is it gets bent when splitting or reconnecting the motor and tranny. Or the bolts come loose. I learned the hard way to Loc Tite the bolts in.
The last time I toruble shot and found loose bolts. I made a pointer from a piece of welding rod, removed the dust plate and ran the engine. You could see the wobble, with a good flashlight. Have heard of a few guys having front bearing problems with the AW4 (rare), they are usually noticed when the seals fail.
The last time mine vibrated a lot, it was a loose plug cable boot at the plug. I found it the hard way, in the fingure out the crotch.
Is it vibrating at a stand still or just when the wheels are turning? Flex plate turns, when the tranny is in neutral, don´t have to have it in gear.

No the jeep will vibe at any gear weather its in park drive or nutral as long as it gets to a certain rpms its felt inside. This jeep had the tranny out twice so i guess its a possibility its cracked , what do you think ?

pete

Could be the flex plate bolts are backing out. I`d check through the dust shield and see if the flex plate is wobbling (with the motor running). Then maybe seperate the torque converter from the flex plate, push the torque converter back towards the tranny some (it will slide towards the tranny a bit) and try and wiggle the flex plate some with your hands. You can see guit a bit of the flex plate through the dust shield, with a flashlight, while turning the motor over by hand.
Flex plate/torque converted bolts, seem to be more common than broken/bent flex plates.

All the bolts are really tightened to the max. Tho i noticed when i ran the motor with the inspection plate off i could see it kinda move up and down a small bit while it was turnin. Not sure tho as it seemed like a very small amount.

pete

PS. I am still trying to get ahold of the flexpate locally. I am tryin to aviod places like autozone/kragen...I called carquest and they say they dont list it and napa has no idea as hey say it isnt in their books...Anyone have a part number for the HO flexplate.

Really not much to a flex plate, unless it´s bent enough (or the bolt holes are stretched) to make the torque converter wobble quit a bit, I really don´t think it´s the problem.
The flex plate is really only a piece of sheet metal that connects the crankshaft to torque converter. The torque converter is heavy enough to cause the motor to wobble pretty good, if it´s not turning on a true axis (probably more noticeable at a lower RPM).
I´ve checked them before for round and end play (wobble). Picked a ridge on the fley plate and/or the torque converter, used a piece of welding rod with a loop around a dust cover (inspection plate) bolt, bent it to just contact the ridge on the flex plate´(kind of like a pointer) and turned the motor over by hand. 0.060 or 1/16" of play is probably OK, most I´ve checked had around 0.030 or so of play. They don´t seem to be a zero tolerance type item.

Well 8mud i will open the inspection plate tom to check again, but i dont see what else can be the prob. I have checked the ignition system for misfires, all the mounts and all things that normally cause this sort of thing. Dont get me wrong i am not sure myself this is the prob. SO you really dont think its he prob, with all that i have already done ?

Anyway i will see tom and report back. I will grab a really big bar and try to pry on it maybe i will find a crack of some sort or maybe its unbalanced of some sort for the 150000th time.

Tho when it vibrates it happens mainly exactly at 1600RPM and a bit above. What i dont get is if it was cracked wouldnt it shake at all RPMS .

pete

Ok i a havnt had time to take off the inspection plate yet but i realized something very interesting today while i had the hood open. With the engine on at idle it sounds normal (loud diesel engine..lol) but as i rev it (using throttle cable on engine) it reaches a point where on the passanger side where the oil filer is it make a very scary vibe noise. The vibe is mostly felt at the end of the engine (end = further back neerest to firewall).

I am not sure if this helps at all....Ohh and i took the jeep to AAMCO as they offer free inspection. THe tech guy looked and heard it and said he would lift it and see . After that he had it on the lift and said it sounds like a messed up flexplate, but he cant be sure and would need 100.00$ for further diagnoses.

Pete

I´m just thinking probabilities and possibilities. I´ve bent flex plates, but it was on a lot heavier vehicles with a lot more horsepower (mud pit). They vibrated much more at idle than at higher RPM´s. Just as a side note, I´ve bent them to where they looked like pretzels when the bolts were removed.
There was a thread about a 1600 RPM vibration (in I believe was a guys 95) last summer. Eagle came up with some likely possiblilities. Mostly to do with octane sensitivities and iginition timing.
What you are discribing sounds like a harmonic, harmonic balancer, the wieght of the torque converter and other balancing techinques are in the motor to compensate for this.
Could be a flex plate, but like I said that, would be pretty low on my list.
Might want to remove the plug cables from the plugs one at a time, with the motor running. Best to remove them all first with the motor stopped and make sure they all go on and come off easily. Then with a good pair of gloves on remove them one at a time, with the motor running at 1600 RPM. If you pull one and the vibration/harmonic doesn´t noticeably change much, you are probably in the right area.
Take a close look at the harmonic balalncer.
If a motor runs too lean in a certain RPM range it can cause a harmonic. Haven´t seen it on Jeeps, but Dodge is notorious for having loose timing chains that can cause harmonics. A reference mark on the balancer, will jump all over the place at certain RPMs, you can see it with a timing light. Just a troubleshooting technique, not to be confused with actual timing.
Vacuum leaks can lean out, a cylinder or two. This can also cause a harmonic. You can usually see it with a vacuum gauge, the needle goes a little crazy.
The last time mine shook at a specific RPM, it was ignition related. I didn´t notice it too much at idle or above 2000 RPM, but in the low mid range it would do the shimmy shake.

8mud i am not trying to convince anyone what or what not this problem is, i am just trying to find out what it can be and cant. As for the flexplate i am guessing that its not twisted or bent like you mentioned but rather cracked like others have suggested. You say you have a hard time believeing its the cause and i am wondering why you are saying so.

As far as ignition stuff is related i have replaced components such as the cap , rotor , plugs and wires like i have said earlier. I just disconnected the first two wires (sereately) while the engine was running and the engine tone at idle changed a small bit and it felt diff when revving it, and the spark seems good.

Like i have said before the only reason i am thinking flexplate si because of the circumstances that i have taken care of and how the car drives normally at higher and much lower RPMS. But then again it seems flexplate related isues i have read caue ticking noises, which i really dont have. Whata are symtoms of a cracked flexplate but not twisted one ?

As far as the harmonic balancer how does one check that ?

Pete