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  #1  
Old August 4th, 2006, 17:03
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Throttle body; bored or not too bored

Okay, I know this subject has been beaten to a pulp.... and I've done some searching of this forum (and others) for some back ground info and trouble-shooting advice.

My '00 XJ, with the ubiquitous AW4 slush box, is stock with the exception of a DynoMax Turbo cat back system which I heartily recommend for any daily drivers out there....gotta nice burble without getting ugly sounding....sorry guys but American inline sixes sound like crap with most "performance" mufflers...just MHO. But I digress.....

So I scored a "home grown" bored 62mm TB off of eBay. The machine work was okay and the hard edges of the IAC and MAP ports where "softened" with a Dremel (apparently held by someone who's drinking way too much Starbucks) to eleiminate the whistle. The swap was easy and the first thing I noticed was the off idle "punch".... I also noticed a little more spunk on the interstate....these are good things.

What I also noticed, much to my dismay, was the AW4 wasn't shifting like it used to. Rather than a nice positive shift into each gear, the tranny was oooozing it's way through the gears and into OD and lock-up. What's up???? I'd never read of anyone having this problem. So I start trouble shooting.... the TPS being the prime suspect and the PCM/TCU computers possibly having to learn new habits. Checked the TPS (with an ohm meter) and it's in fine shape with a smooth, linear change in resistance. I reset the computer again and checked for any fault codes. All seemed okay but still the slushy shifting tranny.... so I put it all back to stock. Put the stock TB back on and... voila!... the tranny is shifting like she used to. And yes, I did check and adjust the TV cable in both cases.

Has anyone else experienced this problem? Anyone have any odd problems with removing the lower ridge in a stock unit? I have to wonder why DC designed the TB the way they did... the lower edge of the stock TB definitey creates more of a venturi effect....it's gotta be there for some reason. And after seeing that a fully bored TB (62mm) results in minimal 5HP/6.5ftlb gains, I think I may just stick with the stocker.

Mike
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  #2  
Old August 4th, 2006, 21:11
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Re: Throttle body; bored or not too bored

Quote:
Originally Posted by jocko463
And after seeing that a fully bored TB (62mm) results in minimal 5HP/6.5ftlb gains
Thats not bad if you got the tb for a good price.
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  #3  
Old August 4th, 2006, 22:18
rstarch345 rstarch345 is offline
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Re: Throttle body; bored or not too bored

There was actually a dyno test on the TB's and here are the results http://www.rockymountainextreme.com/...t=30793&page=5
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  #4  
Old August 4th, 2006, 23:01
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Re: Throttle body; bored or not too bored

Quote:
Originally Posted by jocko463
So I scored a "home grown" bored 62mm TB off of eBay. The machine work was okay and the hard edges of the IAC and MAP ports where "softened" with a Dremel (apparently held by someone who's drinking way too much Starbucks) to eleiminate the whistle. The swap was easy and the first thing I noticed was the off idle "punch".... I also noticed a little more spunk on the interstate....these are good things.

What I also noticed, much to my dismay, was the AW4 wasn't shifting like it used to. Rather than a nice positive shift into each gear, the tranny was oooozing it's way through the gears and into OD and lock-up. What's up???? I'd never read of anyone having this problem. So I start trouble shooting.... the TPS being the prime suspect and the PCM/TCU computers possibly having to learn new habits. Checked the TPS (with an ohm meter) and it's in fine shape with a smooth, linear change in resistance. I reset the computer again and checked for any fault codes. All seemed okay but still the slushy shifting tranny.... so I put it all back to stock. Put the stock TB back on and... voila!... the tranny is shifting like she used to. And yes, I did check and adjust the TV cable in both cases.

Has anyone else experienced this problem? Anyone have any odd problems with removing the lower ridge in a stock unit? I have to wonder why DC designed the TB the way they did... the lower edge of the stock TB definitey creates more of a venturi effect....it's gotta be there for some reason. And after seeing that a fully bored TB (62mm) results in minimal 5HP/6.5ftlb gains, I think I may just stick with the stocker.

Mike
I've mentioned in past threads that the narrowed throat is there to increase the strength of the vacuum signal. The narrower passage speeds up the air flow. Bernouli's Principle states that the faster the flow, the lower the pressure exerted across the direction of travel. This lower pressure provides a stronger vacuum signal for the MAP sensor. The PCM uses the signal from the MAP sensor to determine the load on the engine. The pressure at the venturi is compared to barametric pressure. Engine load is inversely proportional to the difference of these two signals. In other words, if the pressure at the venturi is close to the barametric pressure, load is high. If the pressure at the venturi is significantly weaker than barametric (high vacuum) the engine is lightly loaded.

Voltage representing the absolute pressure is sent to the PCM for this comparison and is used to determine injector pulse width, timing, automatic transmission shift mapping and other tweaks on engine operational parameters.

Running a throttle body without the narrowed venturi provides a weaker signal to the PCM which, in turn, adversely affects engine and transmission operation. Over time, the PCM will try to compensate for what appears to be a lighter load on the engine with changes to fuel trim maps. This is based on feedback from the O2 sensor. The transmission doesn't have this feedback loop so the TCM continues to operate on the assumption that there is less load on the powertrain that there actually is.

Some of the perceived benefits of a bored throttle body will diminish over time as the PCM adjusts to the new vacuum signal. I would be wary of any claims of HP increases and fuel mileage improvements without the proof of independently run dyno tests run specifically on a Jeep 4.0 engine.

The typical butt dyno seem to have a high margin of error.
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  #5  
Old August 5th, 2006, 00:00
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Re: Throttle body; bored or not too bored

These are my opinions:

I think the lip on the stock throttle body is to smooth out the initial pressing of the throttle. Even though the NVH advancements didn't officially start till around 96, I think Chrysler got a head start on the "harshness" back in 91 when the H.O. came out. I think the original plan for the H.O. was for a 62mm throttle body.(The intake manifold inlet was 62mm for all engines 91 +) But I think after some preliminary testing the engineers found it was too fast off idle. In other words, "too harsh" for "normal" drivers, so they put that lip on it.

Fortunately, the lip is easily removed with common tools.

I could understand that the average sap wouldn't like getting sucked into their seat with every tap of the throttle but I sure as heck do.

My engine just surges off the line from idle to 2000 rpms. It feels great.

As for the the MAP sensor issue, I think the computer can learn from the changes. It did indeed run rough when I hooked up my bored tb. But it smoothed out after about 20 minutes. The biggest thing is to make sure the throttle body is bolted tight to the intake manifold but not enough to strip the threads. (I know this first hand, what a PITA to have to get my tap and die set out when I didn't have to).
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  #6  
Old August 5th, 2006, 08:28
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Re: Throttle body; bored or not too bored

Did you reset the AT kickdown cable? Try these instructions.

I have a 60MM TB and AW4 auto and it pulls harder from off the line, revs higher before it shifts, and will downshift sooner than before at 50+ mph


The automatic transmission kickdown cable will need minor adjustment for proper operation after installing your bored throttle body.

Early model JEEPS have a clip on the transmission cable sleeve were it snaps onto the bracket.
Pull the clip up with a small Flathead screwdriver, feed the slack in the cable into the sleeve and
push the clip back down to lock the adjustment in place.

Late model JEEPS have a half round push button cable lock. Push the half round button located
at the back of the bracket and push the cable into the sleeve. From the drivers seat, push the
gas pedal all the way to the floor, you will hear a clicking sound as the cable resets.

You may have to adjust the automatic transmission cable a couple of times for correct transmission operation
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  #7  
Old August 5th, 2006, 14:12
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Re: Throttle body; bored or not too bored

Thanks for all the inputs....

MaX...

Thanks for the background info on the TB throat; I understood the TPS has a direct link to the tranny computer (TCU) but I never thought the MAP would have an effect. After reading some more about the interaction of the PCM and TCU, I can see where the bogus info was coming from (newer XJ's have a communications link between the PCM and TCU...the older ones don't). I had the 62mm TB on for over a week and the shift quality didn't improve at all; I was afraid of burning up the clutch packs with the lazy shifting I was getting.

J99....

The unit I was using was bored out to the maximum diameter (62mm) and I guess the loss in vacuum signal to the MAP/PCM was causing the problem. I've got a spare stock TB that I may try removing the lip on..... that may work better overall. It'll at least make a good experiment. The off idle punch (or lack of it) seems a logical reason for the narrowed throat because with the stock TB she's a little anemic off the line. I'll make sure on the air-tight seal.

Tim....

Appreciate your suggestion. Yes, I did readjust the TV (throttle valve) cable. It's not a kickdown cable like your basic TH350; what it's used for is a mechanical linkage to control internal operating pressures of the tranny. This linkage lets the tranny know, essentially, how far your foot is into the gas. The more you're mashing the gas, the higher the load and the higher the internal operating pressures will be for shifts and such. It's a pretty important adjustment. The GM TH700R and 200R trannies had this setup.

rstarch....

I found the same link you did but forgot to tag it. Thanks for posting it. I was surprised by the results. The thread is kinda long.... you have to wade back 4 or 5 pages to find the meat of the test.


Mike
00XJ
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  #8  
Old August 5th, 2006, 14:53
xj_nutt xj_nutt is offline
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Re: Throttle body; bored or not too bored

jocko463,
I did notice the same thing (Tranny not as eager to shift as it used to) after installing a new 62mm Throttle body.

Even though I do notice the off idle quicker launch, I am now wondering weather I actually gained any real hp/torque by installing this 62mm TB, especially at higher RPMs.

Another question is: Is it maybe better to just add a spacer to the Stock TB, rather than bore the Stock TB to 62mm?????

My XJ is a 2000 Sport with Auto Trans.

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  #9  
Old August 5th, 2006, 21:27
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Re: Throttle body; bored or not too bored

Quote:
Originally Posted by xj_nutt
jocko463,
I did notice the same thing (Tranny not as eager to shift as it used to) after installing a new 62mm Throttle body.

Even though I do notice the off idle quicker launch, I am now wondering weather I actually gained any real hp/torque by installing this 62mm TB, especially at higher RPMs.

Another question is: Is it maybe better to just add a spacer to the Stock TB, rather than bore the Stock TB to 62mm?????

My XJ is a 2000 Sport with Auto Trans.
Check out MaXJ's reply....I think he hit the nail on the head with the MAP, PCM and TCU interface. I've read (although I can't put my finger on where) that in the later model years, there is a communication link between the engine computer (PCM) and the tranny computer (TCU); earlier model XJ's didn't have this and each computer operated on its own with its own specific sensor inputs. So, on many older engines the TPS (Throttle position sensor) was the primary input to the TCU.... on the newer vehicles like yours and mine that is not the case. I reinstalled the stock TB and everything is running fine... tranny has nice crisp shifts once again. Maybe the stock TB with the ridge removed will work better than the 62mm......

As for the spacer, my take on it is that it is more effective on the older style intake manifolds; the newer ones have a large air plenum/chamber that the spacer helps create on the older manifolds. The spacer shifts the torque curve a bit (lower or higher I'm not sure which). Since it's easy to install and remove you can be the judge....If you don't like it, put it all on eBay and you can probably get most of your money back (from the TB and spacer).

Mike
00XJ Sport
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  #10  
Old August 5th, 2006, 22:05
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Re: Throttle body; bored or not too bored

http://cgi.ebay.com/ebaymotors/JEEP-...QQcmdZViewItem

I put this on my 2000 XJ with the OEM throttle body and it worked well. Definatly a low cost one but is 1" thick made from aluminum and comes with all hardware. Fit great... I was worried about build quality on it since it was cheap but it is very professional looking. all smooth edges. no blemishes
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Old August 6th, 2006, 00:10
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Re: Throttle body; bored or not too bored

My 99 xj was a transition year, and that is good for me. Stock, my engine came with the older style heads (0630 that flow as well as the original H.Os) and the new intake manifold. So my engine was ahead of the game compared to other stock engines.

With reasonably efficient heads and intake, I can honestly say that the bored throttle body and spacer were worth my time and money. I bought the throttle body for 8 bucks at a junkyard, and bored it at a machine shop for 40. Like I said in other post, I got my smooth bored tb spacer for less than 30 bucks shipped off ebay.

As for tranny issues I haven't had any. It does take more throttle to get it to "kick down" but the tranny hold gears much better than before because of better airflow at lower throttle openings.
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Old August 6th, 2006, 00:34
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Re: Throttle body; bored or not too bored

One thing I forgot to mention is that the intake mods work the best with a good exhaust system. One concept from thermodynamics is that the mass flow rate and the energy associated with it, is conserved. In other words there can only be as much air mass entering the system (engine) as leaving it.

A good intake with a stock exhaust won't gain as much as a good intake and exhaust.
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  #13  
Old August 6th, 2006, 06:44
badron badron is offline
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Re: Throttle body; bored or not too bored

Never any 1/4 mile or 1/8 mile or 30-60 back to back test. If it really pulls any better it WILL show up somehow with a stopwatch. Seat of the pants are for testing recliners not engines. If you just want to think you are going faster stick your head all the way out of the window next time you punch your Cherokee. Dyno test are kool but even them don't allways tell the story when it comes to true gettyup and go power. Plus lets see 5 over 190 = zilge . s**t

Last edited by badron; August 6th, 2006 at 06:52.
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Old August 6th, 2006, 09:33
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Re: Throttle body; bored or not too bored

Quote:
Originally Posted by j99xj
... As for tranny issues I haven't had any. It does take more throttle to get it to "kick down" but the tranny hold gears much better than before because of better airflow at lower throttle openings.
"hold gears much better" Is that the same as not shifting when it's suppose to? It would be interesting to hear your explanation of the mechanism the tells your tranny about the better airflow. You must have the special MAF sensor.

Lower flow velocities are when the venturi effect is most needed. Low velocity equates to a lower vacuum signal to the MAP. As mentioned, the venturi speeds up the flow velocity to boost the vacuum signal.
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Old August 6th, 2006, 10:02
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Re: Throttle body; bored or not too bored

I have a 62mm bored TB that I purchased from http://www.thefastman.com/Throttlebodies40.asp

I installed a K&N FIPK at the same time and noticed a nice difference. With the shift points I did notice that they seemed to grab harder in my AW4, and I liked it. Soon after I installed the TB and FIPK I installed a Banks header and Magnaflow highflow cat and catback. I feel that all the upgrades really correspond well together and am very happy. Highly reccomened

99 XJ AW4
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