Throttle won't open all the way

[AZJeff]

Some of the major highways here in AZ have 6 percent grades that run for MILES, punctuated by short flat sections in the middle.   There is no way you can keep enough momentum up to climb that grade without downshifting.

[Deleted]

On 6/17/2019 at 6:32 AM, schardein said:

Ensuring you are actually achieving WOT (wide open throttle) is a tuning step for old school drag racers/hot rodders who are tuning for maximum performance.

 

Most common reason for not achieving wide open throttle is carpet or floor padding/insulation not allowing the accelerator pedal full travel ("pedal to the floor").

 

If you have floor mats under your pedal, or have installed new carpet at some point, or even just have factory carpet-- do some experimenting to determine if you can get WOT by removing the floor mat/padding/carpet.

 

As already noted, look at the throttle blade, not just the linkage.

 

 

no carpets, just floor pan metal under my feet. Hot floor pan metal, but thats planned to be fixed too at some point lol

[Deleted]

On 6/17/2019 at 7:02 AM, Ωhm said:

Backprobe the TPS (KEY ON: pins B & C) at both Closed Throttle (CT) and Wide Open Throttle (WOT) (note voltage readings) using the gas pedal. Take the same readings with gas pedal disconnected and manually move the throttle between the stops. Compare the voltage readings taken. Should be the same.

your username suits you

[Deleted]

On 6/17/2019 at 8:54 AM, Eagle said:

 

That's impossible.

 

If the axles came from a 4-cylinder, they would be 4.10 gears. On 31-inch tires, with 4.10 gears at 65 MPH in 5th gear the RPMs would be 2292. The deepest gearing you can get for the XJ/MJ with a Dana 30 front axle is 4.88. Even if you had 4.88 gearing, the RPMs at 65 MPH would be only 2728 in 5th gear. And it's highly unlikely that you have 4.88 gears.

 

https://docs.google.com/spreadsheets/d/1pHFuhGgj6dQDfzyfFJH5z7NCDLW2KX3ABQgAJr3lBvM/pub?hl=en&hl=en&output=html

 

A related question, since you're running larger than stock tires AND replacement axles -- do you know if your speedometer is accurate? Have you checked it against a GPS? If not, you can download an app for your phone that will use GPS to verify your speed. (Too bad they don't have one to replace the tachometer.)

speedo is accurate give or take 1mph. and maybe I'm wrong it just feels like its screaming in 5th at 65 more so than the 4cyl wrangler I used to drive and I know for sure that thing wasnt geared up. 

[Deleted]

On 6/17/2019 at 10:54 AM, AZJeff said:

The OP talks about having trouble maintaining speed on ground that is not flat and level.  Those of us here in AZ often encounter long mountain grades on the highways, and those are a challenge for high speed driving.

 

For example, my MJ has 3.55 gears and 31 inch tires.  It's also an automatic, but it cannot hold 65mph on long  uphill grades and stay in overdrive.  It keeps wanting to kick down. My solution is to drop it out of OD when climbing grades.

 

My XJ with 3:07's did the same thing, so I wonder if the OP is expecting too much from that driveline arrangement.   Also, don't forget that, when climing moutain grades, you altitude is going up, and that means your air density is going down, so the engine is starving for oxygen to some degree.

I think you might be hitting the nail on the head tbh. Its just odd as I used to have a 4cyl '94 wrangler that did no problem on highways or even getting up to speed. 

[Deleted]

19 hours ago, DirtyComanche said:

 

Got 'em all over BC too.

 

Running on flat is absolutely different than in the mountains.  People need to accept that their gear shifting arm is going to get some exercise.

Honestly shifting often doesnt bother me, its mostly just being in 3rd gear with the engine screaming and only going 35mph lol

[Eagle]

You need to get a tachometer, even if it's a cheapie that you strap to the steering column with a big hose clamp.

[gogmorgo]

^^^ and some sort of speedometer confirmation as well. 

With stock gears, 35mph should be nowhere close to screaming in third... especially not with larger than stock tires. 

[Jeep Driver]

So, did you ever look to see if it opens all the way?

 

Just curious. 

[Deleted]

7 hours ago, Eagle said:

You need to get a tachometer, even if it's a cheapie that you strap to the steering column with a big hose clamp.

its all in the plans, reading what ive seen suggested to me here definitely helps me understand what I need to do now. She still gets me to work every day though so it could be worse lol

[Deleted]

6 hours ago, gogmorgo said:

^^^ and some sort of speedometer confirmation as well. 

With stock gears, 35mph should be nowhere close to screaming in third... especially not with larger than stock tires. 

speedo is accurate as long as my gps app is accurate. Even google maps says my speedo is accurate. Thats why I'm starting to think its not stock gearing, I just need to get the back in the air so i can spin the tires and count the driveshaft rotations to really make sure. 1st gets me to about 10-15mph before it start getting really loud, 2nd to 25, 3rd to 35, 4th to 45 nd 5th i use for anything higher than like 50, with the fastest ive gone being 70mph (downhill). That gives you a little insight as to what it looks like when I'm accelerating in a straight line at least

[Deleted]

I'm starting to feel like a raving mad man over here haha, maybe my truck is fine and I'm the problem. Maybe I'm shifting really early thinking its high rpms when its not. Long story short I need to fix my Tach or buy a temporary one, and figure out what kind of gearing I got going on. The throttle opens up all the way inside the throttle body so what I thought was the issue originally wasnt even it. Ill figure this out though, itll take some time since I'm busy during the week and the 110F temps of arizona are discouraging, but ill get it all situated. Currently i think its a mix of A: old truck B: 4.10 or 4.88 gears and C: user error 

[Pete M]

a quick way to determine gear ratio:

 

-put truck in neutral

-jack up one rear tire

-rotate that tire around exactly twice while counting the times that the driveshaft rotates

-if the driveshaft rotates around 3 and a half times, you've got 3.55s.  If it spins around just over 4 times, 4.10s

-if the truck has a posi or locker, then you need to jack up both rear tires and spin them around just once

[Eagle]

It's small -- not what you'd want for racing -- but it'll tell you how fast the engine is spinning, and it's cheap:

 

https://www.amazon.com/dp/B01I1A1UL8/ref=psdc_15729791_t3_B01I1A2HLA

 

For a couple of bucks more, this one includes a pedestal so it would be easy to mount to the steering column with a hose clamp:

 

https://www.amazon.com/NCElec-Universal-Backlit-Tachometer-Gasoline/dp/B01M6D0IRJ/ref=pd_sbs_263_2/134-2065384-1246316?_encoding=UTF8&pd_rd_i=B01M6D0IRJ&pd_rd_r=b31f37bd-92a4-11e9-8704-597ede040640&pd_rd_w=GGf7t&pd_rd_wg=Pm8ZR&pf_rd_p=588939de-d3f8-42f1-a3d8-d556eae5797d&pf_rd_r=RWV5R4M7ZH39AZ5KV947&psc=1&refRID=RWV5R4M7ZH39AZ5KV947

[Deleted]

14 hours ago, Eagle said:

It's small -- not what you'd want for racing -- but it'll tell you how fast the engine is spinning, and it's cheap:

 

https://www.amazon.com/dp/B01I1A1UL8/ref=psdc_15729791_t3_B01I1A2HLA

 

For a couple of bucks more, this one includes a pedestal so it would be easy to mount to the steering column with a hose clamp:

 

https://www.amazon.com/NCElec-Universal-Backlit-Tachometer-Gasoline/dp/B01M6D0IRJ/ref=pd_sbs_263_2/134-2065384-1246316?_encoding=UTF8&pd_rd_i=B01M6D0IRJ&pd_rd_r=b31f37bd-92a4-11e9-8704-597ede040640&pd_rd_w=GGf7t&pd_rd_wg=Pm8ZR&pf_rd_p=588939de-d3f8-42f1-a3d8-d556eae5797d&pf_rd_r=RWV5R4M7ZH39AZ5KV947&psc=1&refRID=RWV5R4M7ZH39AZ5KV947

Thank you! the day this truck sees a racetrack is the day i win the lottery though lol