TOPIC: '98 Jeep TJ 2.5L - Canada

Hi from Saskatchewan. Just moving a former post to a better location:

Just finished mileage check after first finished groove on a 98 Jeep TJ 2.5L. This was the 3rd time trying to get the angle right because of the venturi style throat below the plate. I ended up opening up the throttle plate about 1/16" to increase the angle and slid the cutter straight down the plate. 0 to 60 mph was over 1 sec. faster, 60 feet shorter, LTFT down to -8 from 4, and mileage up 25% (17.5 to nearly 22mpg). Plugged pcv and re-routed IAC to just over the throttle axle on both sides.

Also a note about cutting the idle re-route on this particular 2.5L: the original gasket was not very wide, and I did not check closely enough, so my first cut for the re-route bypassed the gasket on the narrow side, after the first inch, causing an early bypass on one side, and a vacuum leak on the other (too wide and past the gasket): my first cut. So I filled it. I looked more closely, traced the gasket on the bottom of the throttle body, and cut again. Because of the narrow gasket, plus the throttle body throat being about 1/4 " narrower that the intake plenum it sits on, the overall area of the mating surfaces is small. With a 1/4 " bit, you may have maybe 1/16" of gasket on both sides to seal, and with hand cutting, (mine anyway), I had less, so I ended up with another vacuum leak: my second cut. So, for my third cut, I first made a 1/4" aluminum plate to go between the TB and plenum, with the bore cut the same diam. as the TB bore: more leeway to work with on both sides. (To clarify: there was enough metal on the bottom of the TB to re-route with, but because of the plenum design being so slim, a lot of the metal of the TB was overhanging in the air.) I did have to re-bend the throttle bracket so my shift points were back to original because of the change of position and geometry because of the 1/4" aluminum spacer at the bottom of the TB.

I will start cutting deeper on the re-routes I think, because here now when it is above zero, I have no issues, but will I have issues at -20 to -30 C? I might. We will see.

Luke Wickenhauser
Gadgetman Saskatchewan

Hi again. One more clarification: When I added the 1/4" aluminum plate, I made the dimensions large enough to go beyond the outer perimeter of the TB. I also made a larger gasket from edge to edge.

Luke
Gadgetman Saskatchewan

Hey Luke, this is Tracy G Gadgetman Reno. Congrats, sounds like you have a winner there! My first real groove was on a 91 Jeep cherokee owned by a neighbor. He handed me 2 TB's from identical junkyard Cherokees, so I hadnt seen the manifold/TB bore difference or the mounting gasket. Off I went merrily Grooving and rerouting the IAC path, using trenches like you did. So here is the TB pre-Groove:

next Grooved and IAC reworking in progress:

Now with the IAC slot in TB bore filled in and holes angle drilled thru to connect bypass trenches w/IAC cavity:



So I'm all proud and even label it thinking I'm done. Oops, gasket mismatch! So I fill in trenches and re-cut going more outboard. Marked gasket edges; wound up partly filling small round pockets between TB bore and outer gasket edge to improve gasket seal. All done:



So I wonder how similar your Jeep was to this Cherokee? I have no data; OBD1 and owner doesnt drive it much. But it ran Very well after install and PCV cap-reroute, and it still badly needs a tuneup!! Was really Practice for me!! Happy grooving! TracyG Gadgetman Reno

Sorry Luke and everyone, I'm not very good at doing photo inserts yet, but the whole story is here just a bit jumbled!! LOL, Gadgetman Reno TracyG

Good day to you ALL!!!

Great work on documenting the process here, Tracy, as well as for the candor about the mis-cut. "Oh, well. Fill in and re-cut!" That's EXACTLY the attitude that enables a great experimenter to be... well... Great!

Judging by the amount of scraping on the plate, I would guess this Groove is probably too shallow of an angle. You might want to check that..

Great job!

Ron

Hi Tracy,

Thanks, yes it looks fairly close. I do have photos that I will post when I have a bit more time. Yours was a 2.5 L? Looks like it. The 4L cherokee seems to have more of a mating surface so the re-routes were easier, although I had to go deep, deep so it would have enough air flow. I will be posting once I get some issues cleared up with it.

Have a great day.

Luke

Hi Ron, Hi Luke! Thanx Ron! You're right this was before the new bit angle recommendation, did this Jeep in early March. It's true the new increased angle leaves far less scraping on the throttle blade, as I discovered today. I did another Mopar this time an '01 PT Cruiser 2.5L USA. More on that one later. Luke, this was an inline 6 Jeep 4.0 L a '91. Just curious, did your Jeep have an O-ring or a flat gasket to seal the TB? I can see how re-routing an IAC airflow path could be a challenge if it uses an O-ring. Anyhow Keep Smilin' and Groovin' everbody... (So if you smile for a Stranger and he asks why, just grin an' say: "Groovy, just Groovy, Baby!") 'specially if you can say it like Austin Powers...TracyG Gadgetman Reno

Hi Tracy, On the 2.5L Jeep, it had a flat gasket, and the potential mating surface of the plenum and TB was only what the gasket covered. I used a 1/4" burr (I wanted to use a 3/8 bit but that would have been gasket edge to edge) to re-route the idle passage, as I needed it as wide (and I went deep) as possible because of the idle air demand at -20 to -35 in winter. In doing so, I ended up with a 16th inch leeway each side, which wasn't enough for my liking and bit-chatter. So after 2 vacuum leaks, that's when I went to the plate to make full use of the potential mating surfaces between the plenum and TB base.

Have a great day!

Luke

Hi Tracy & Luke,
I'm new to the idea of rerouting the idle air and wanted to thank you guys for these posts and especially the photos. I just recently read Ron's article about it, but since the TB he showed in the pic's had the idle air coming in pretty much at the end/mating surface of the TB I wasn't sure how to reroute when the idle air comes in deeper inside the TB (as it did on the Isuzu I recently grooved) Thanks to Tracy's pic's and you guys' comments, I think I now realize how it's done - by making a hole or two from the former idle air entrance up to the mating surface of the TB, then finishing the remaining reroute on the surface.

Hi Luke and Johnathan! Well in this Groovy gig, it seems you always have to be ready to learn and adapt/improvise. The US Marines have a saying--"Improvise, Adapt, Overcome!" When you have landed on an enemy-held island 1000's of miles from freindly help, the fleet that landed you has just been mauled and summarily departed and you as a task force are on your own failure is not an option (this happened in Aug. 1942 at Guadalcanal.) Anyhow Im glad the pic's helped thats why I put 'em up. That is just what I came up with, you try to understand priciples then apply 'em. I too considered cold weather plus A/C operation on the '91 Cherokee. So Luke did you have a custom spacer made how was that created? Love to see some pics if ya got em! and Johnathan if you get into doing chainsaws and other small stuff let us know about it, I'm intrigued!
Have a great one guys!! TracyG Gadgetman Reno

Hey Jonathon, hey Tracey!! I was going to set aside some time tomorrow to figure out the photo attachment bit and I just found out I have deleted all my gadgetman photos! AHHHH!!!!
So, I will do some dismantling and take a few more photos. Darn. Anyway, regarding the spacer/plate that I used on the 2.5L jeep, it was just a piece of 1/4" aluminum stock by 4" wide and a piece 4" cut from that. I used a bi-metal hole saw to cut the proper sized TB hole. Once I have the photos, I will explain more thoroughly.

Take care,
Luke

Well, I got more info on this 2.5 l jeep, plus a head-scratching question that I hope someone will be able to verify or figure out.

My first info at the start of this thread stated that I did the groove 3 times, the 3rd time just sliding down the throttle plate but with the plate wedged open about 1/16" with good results. I wanted to try the new bit angle, so I filled in this groove, and tried with the new angle. This being my first, it looked as if I could have chewed it out with my teeth with better results. The long term fuel trims went back up close to original (about 4) and mileage dropped drastically. The cut was very rugged. So, I filled it again, and wanting to duplicate the former long term fuel trims of -8, and chicken to do the new groove on this again, I cracked open the throttle again, (maybe a bit wider than 1/16") and cut the groove again as carefully as I could by sliding down the throttle plate again. I expected to see the -8 long term fuel trims again, but instead, they went to 0, and never lower (at 60 mph as before with the -8 LTFT). The funny thing was that my mileage seemed to have gone up. I got 25 mpg (Can) on highway driving, verified twice, and 23.4 mpg on short runs/gravel/and highway.

So my head-scratching question, is this: are long term fuel trims a relative number based on certain moveable data such as throttle position, air density (mass) etc, and therefore an increase in mileage can still be achieved in a situation as mine, when I seemed to get better mileage with a lower LTFT reading, as compared to what I originally got, or is it that I really haven't tested the mileage thoroughly enough and I just have a lot of human error here? Any opinions are most, most welcome!

Now an update as of the last tankful: the jeep started to start hard, with a rough idle, and the mileage is now down to 18MPG and it looks like it is a bit worse now. I am suspecting a separation in the epoxy fill. Tomorrow, I will take of the throttle body and fill it, and try the groove again, but more carefully with the new angle.


Anyway, here are some pictures of the process, the idle re-routes and the plate/spacer that I used (see my previous explanations in this threads).





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Hope these make sense: from i-photo and have an info (i) icon on them where I gave more info: don't know if it will transfer to this page on line. Just in case.....

Luke