91 XLT Seem's Gutless

[Joes4x4Ranger]

Will 31 X 10.50 X 15 tires on stock 3.73 gears make a 94K mile 4.0 manual trans seem gutless? It feels like I have no low end power unless I'm in 4 wheel drive. It bogs down and stalls when trying to climb small rocks(less than fist size) or slight grades in 2 wheel drive. I've recently replaced spark plugs, air filter, IAC, O2 sensor, and cleaned the MAF.

I do have a serious exhaust leak right at the connection of the Y pipe to the manifold, its worse on the passenger side upstream of the O2 sensor.

The engine temp never gets above the "N" on NORMAL, even in 115 degree heat and the A/C on Max. The engine idles smooth and has good throttle response without a load(reving in neutral), and I'm getting a consistant 18 mpg.

 

[Dora The 4x4'a]

no i t def shouldnt..i had 31s on 3.27 opens as did many peopel on this forum..and it went just fine..i would start lookin at my clutch or perhaps..dare i say your technique :X .. or perhaps one last thing to check on is your fuel filter and run some fuel system cleaner through the truck.

my two cents

 

[Tbars4]

...the bad exhaust leak will cause a lot of problems...get that fixed as the explorer needs that back pressure to run proper...extended use of your truck in that condition will get costly on reapirs in a hurry...

 

[Joes4x4Ranger]

...the bad exhaust leak will cause a lot of problems...get that fixed as the explorer needs that back pressure to run proper...extended use of your truck in that condition will get costly on repairs in a hurry...

I was leaning in that direction, that's the next thing on my list. I forgot to mention I did replace the fuel filter. I just got the rig about a month ago and it is a PROJECT to say the least. The freaking Y pipe clamps are rusted out at the manifold, it looks like its going to be a real ***** to get those bolts out.

 

[Dora The 4x4'a]

dang..well if the exhaust is that bad i woudl def go ther..but i cant imagine it be SO severe to cause you to bog out.. but its def a possibility..one thing is for sure you will get good power gains with gettin that fixed

 

[Dopler174]

I'm running 31's right now. It's no real difference in power from the stock to the 31's. It's going to be the exhaust leak. While your there, check out the catalytic converters. It could be due to age and mileage, one of them is clogging up.

 

[Jason94sport]

Your problems are not tire size related. Look elsewhere.

 

[Dora The 4x4'a]

i'd like to tag onto this thread if i could..i hav 4.56 gears and 35s but had this problem on the way back from the shop with just 31s..i seemed to hav no a$$..granted i didnt get on it too much kuz im still breakin it in..but did not notice much difference let alone the amoutn i would hav expected..i was having a bad! torque problem, and gettin 10mpg..so i went for the gears first since they were most expensive and would need to be done anyway.. but while lightly wheeling with these gears, i was gettin up to 2 grand befor i was even gettin the tires to spin.. what am i lookin at?

p.s. im at school so i dont hav time for this unfortunately..but i have fuel system treatment, a fuel filter, and plugs/wires that will be goin in it as soon as i get a decent break to go home.

but besides that..for quite some time i hav beenthinkn abotu a possible torque converter..

side not- A4LD has 10k on it, bought the exploder with 0 miles on that rebuild (do not kno if torque converter is original)

 

[Joes4x4Ranger]

I'm running 31's right now. It's no real difference in power from the stock to the 31's. It's going to be the exhaust leak. While your there, check out the catalytic converters. It could be due to age and mileage, one of them is clogging up.

Will rodding out the CATS have a negitive effect on back pressure? I just ordered the new Y pipe from Rockauto. I was thinking about just rodding out the CATS while I'm working on the exhaust to get better flow.

 

[Dora The 4x4'a]

yeah old cats tend to get clogged and thats NO good..plus they'll prolly leaking anyway which again loses backpressure and efficiency

 

[glfredrick]

There is no such thing as "required" back pressure in an exhaust to make an engine run. It will run fine with no exhaust at all.

I'd look at plugged cats.

Many an Explorer with miles burns oil that the owner never knows, cause it all gets burned up in the cats, but at idle on the trails, the cats load up and plug up the system.

I'd replace them with a single cat like this one:

http://cgi.ebay.com/ebaymotors/3-FL...ryZ33636QQssPageNameZWDVWQQrdZ1QQcmdZViewItem

 

[Tbars4]

...so everyone should be running 3" exhaust huh??? on stock 4.0's huh??? lol...you will start throwing codes with upgrading to a 2 1/2" pipe let alone going to 3"...i'm trying to think of a 4.0 daily driver here let alone, a bunch of stock 4.0 X's running 3" pipe...:scratch:

 

[glfredrick]

Throwing codes is a far different thing than saying that an engine needs "back pressure." The reason it is throwing codes is that the O2 sensor isn't reading the right numbers to keep the computer happy -- not some back pressure thing.

According to your logic, no racer in the world ought to be running headers and bigger pipes, and we all know they are.

What exactly on an engine measures the back pressure anyway? Just curious... I'm a master tech with an arsenal of Snap On scanner tools and I've never seen that one...

 

[Tbars4]

...anything can be built and modified to perform...and for your information, i am running borla's, legal headers with full california emission's... again, i am also running 2 1/4" pipes on my '91 X...on my 2.3 ranger i run 2 1/2" catback exhaust... as for saying to run with one cat instead of two, if you are in a state that has emission testing, good luck...and again, i do know guys who drop their complete exhaust and have dummy co2's, but that is not what you want to do to your stock 4.0 daily driver...
...here is an excerpt with some enlightening info for the rest of the readers as to their stock 4.0...

It's Not How Big Your Pipe Is..............
Some people believe that the bigger the exhaust pipe diameter, the better the system. Bigger isn't always better. Systems that are too large in diameter can actually hurt performance.

Generally, switching to a performance system that is 1/4" to 1/2" inch larger than stock will provide you with the best horsepower increases. To determine which pipe diameters will be best for your system, decide what RPM range your engine will operate at, most of the time. Smaller diameter pipes will produce low to mid RPM torque. Larger diameters produce mid to high RPM torque. For the 4.0L Ranger, 2.25" - 2.5" is about as big as you want to go. Bigger isn't always better. Systems that are too large in diameter can actually hurt performance. improved flow is what you need. Besides the lost back pressure by running too large, or at an extreme -- straight pipes (with no muffler) you lose a lot of low end torque.

 

[Joes4x4Ranger]

Throwing codes is a far different thing than saying that an engine needs "back pressure." The reason it is throwing codes is that the O2 sensor isn't reading the right numbers to keep the computer happy -- not some back pressure thing.

According to your logic, no racer in the world ought to be running headers and bigger pipes, and we all know they are.

What exactly on an engine measures the back pressure anyway? Just curious... I'm a master tech with an arsenal of Snap On scanner tools and I've never seen that one...

I agree somewhat with your logic, BUT those race cars are high reving and have LOTS of pieces and parts that DEMAND larger pipes. Slapping headers and big pipes on a bone stock engine will hurt performance. You gain top end but sacrifice the low end torque back pressure helps provide.

 

[glfredrick]

First, I'm recommending a replacement CAT -- not an entire exhaust system. If you check the cats under your Explorer, you'll see that they are about 3" inlet, if not larger...

Second, you're right about the race car stuff, but I'm not talking about that.

 

[glfredrick]

Bigger isn't always better. Systems that are too large in diameter can actually hurt performance. improved flow is what you need. Besides the lost back pressure by running too large, or at an extreme -- straight pipes (with no muffler) you lose a lot of low end torque.

This is true, but not for the stated reason. It is NOT back pressure, but instead the ability of the exhaust to flow rapidly enough to utilize the pulses of the firing of the engine to scavange the next cylinder. Back pressure is never desired in an exhaust system, and having it is death to any performance.

Here is an article the describes the process:
http://www.tomorrowstechnician.com/tt/tt020526.htm

On both turbo and naturally aspirated engines, the actual exhaust system pressure can be measured by removing an oxygen sensor and inserting a pressure tapping tool directly into the exhaust manifold or pipe. In most cases, the exhaust pressure shouldn't exceed 2 psi at 2,500 rpm.

Another good article:

http://www.superchevy.com/technical/engines_drivetrain/exhaust/0505phr_exh/

 

[Jason94sport]

3" is a little much I think. You could just get a direct replacement from Magnaflow. This is what I did. Bolted right up. No fuss.
Got it off Ebay for $55 brand new.

 

[Willard]

There is no such thing as "required" back pressure in an exhaust to make an engine run. It will run fine with no exhaust at all.

I'd look at plugged cats.

Many an Explorer with miles burns oil that the owner never knows, cause it all gets burned up in the cats, but at idle on the trails, the cats load up and plug up the system.

I'd replace them with a single cat like this one:

http://cgi.ebay.com/ebaymotors/3-FL...ryZ33636QQssPageNameZWDVWQQrdZ1QQcmdZViewItem

So are you saying that the cats can get plugged on the trail and then clear up once you get moving? I was always under the impression they never really changed like that, they just slowly clogged up.

 

[TedJ]

I do have a serious exhaust leak right at the connection of the Y pipe to the manifold, its worse on the passenger side upstream of the O2 sensor.

If you've got an exhaust leak upstream of the O2 sensor, it won't run right. The O2 will not be getting an accurate reading, so the mixture will be off. Ususally not enough to be out of range and set a code, but enough that it will run like garbage.

I saw a Hyundai Accel ($400 stereo, $250 car) and it was blowing smoke and chugging like crazy. One of the hangers rusted off and there was a ~1/4 in hole in the pipe upstream of the O2. Car ran like new once the hole was welded up.... And new plugs were put in (covered in carbon and crud) Since the rest of the exhaust system offers restriction, and there is no restriction on the hole, more exhaust will flow out of the hole than you would think.

-Ted