I've been searching and trying to find what the normal MAP values are in a 3.7L KJ at idle and under load, using a code scanner. Mine is running horribly and the MAP value is about 2.0ish inHg at idle and goes down to 1.5 or so under load. I'm thinking these values are on the low end, but not positive.

I have codes P0172 and P0175. Thanx.

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Civilisation exists by geological consent, subject to change without notice. -Durant

Well you have codes for it running rich on both banks. I would hook a vacuum gauge up and verify that you have the same readings as the map sensor. If so, rev the engine to about 1500rpm-2000rpm and hold it steady. Vacuum will drop momentarily close to 0, then as the rpms come up and stabilize at rpms, see if the vacuum increases or not. If it does then starts dropping and the engine starts running bad, this is a sign of an exhaust restriction, likely both cats. If your results match what I said, try loosening the exhaust pipes from the manifolds. Then retest.

Yep, rich both banks. Thanx for the info on the vacuum gauge, I have one at the shop at work and have held off buying a new one just for me to see what's going on right now, it will have to wait till tomorrow. Would this all be from hooking the vac gauge up to the hose that goes to the brake booster??

Also, this KJ has 229k on the clock. A little before 200k it had an injector go bad which caused horrible driving conditions, but it took me about 30 seconds to diagnose. It took a while for me to even get codes after the hesitation started this time, so no such luck. Also, the long and short term fuel trims are WAY negative. I don't hear anything bad when the motor runs but I'm suspecting this is not a good sign....hoping it's just a sensor but we will see. Wish me luck!! Thanx.

_________________
Civilisation exists by geological consent, subject to change without notice. -Durant

You can also check the fuel pressure,it should hold after the key is turned off for at least 30mins(no more then say 10psi drop over 30mins).Could be a leaking injector or a bad pressure regulator(the KJ uses a returnless system).The KJ uses 2 regulators,one in the pump and one in the fuel filter('02-'04 KJ's only).

I have access to my MAP values, but I have a KK with some mods that might show results that aren't typical.

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2008 Black Jeep Liberty Sport
4.7L throttle body
Old Man Emu lift
Sky Slider
Hypertech Max Energy
K&N CAI
Gibson stainless steel exhaust
Blacked out
ScanGauge2
BFG All Terrrain 225/75/16
JBA upper control arms

I initially thought I might have had a dying fuel pump but after pressing the schraeder valve and getting a spray a few feet out with the motor off, I figured it must be fine. Haven't checked with a gauge.

I'm hoping it's maybe leaky injector, based on the negative fuel trims and rich DTCs. Hoping it's not mechanical like the valves or timing chain, etc.

It's got 229k with the original pump and I believe original fuel filter. Is there a filter other than on the pump??? Where is the external filter located and how does it have a pressure regulator in it?1?!?

Come to think of it this did happen about 20 miles or so after a fill up at a station I never normally go to....??

_________________
Civilisation exists by geological consent, subject to change without notice. -Durant

What are they at idle and under acceleration?? They shouldn't be that far off, and atleast give me a ballpark idea?? I'm thinking my numbers are like WAY off but not positive, hence my post. My code reader is giving values in inches of mercury (inHg). Thanx.

_________________
Civilisation exists by geological consent, subject to change without notice. -Durant

Okay. I'll try to remember to set my ScanGauge2 when I drive to work in a few minutes.
I think I can measure in Hg. Look for a post in about 10 hours or so.

_________________
2008 Black Jeep Liberty Sport
4.7L throttle body
Old Man Emu lift
Sky Slider
Hypertech Max Energy
K&N CAI
Gibson stainless steel exhaust
Blacked out
ScanGauge2
BFG All Terrrain 225/75/16
JBA upper control arms

If you have a '02-'04 KJ the fuel filter is located right above the gas tank and just like the WJ Grands you have 3 fuel lines,the 3rd line is the actual return line(to tank) from the pressure regulator.

In the pic below the EVAP leak detection pump is outlined by a yellow box,behind that is where the fuel filter is located.




Oh and ones MAP values maybe different then anothers due to altitude differences so keep that in mind.

Here are some values. Please take these results with a grain of salt. This is from a KK with a few mods. These results are from a fully warmed up 2008 Jeep Liberty.
I set my ScanGauge2 to read pressure units in inches.

Full throttle - 29.4
Mild acceleration - mid 20's
55mph - 21-22ish
Idle at a stop sign in gear - at or very close to 10
Idle in park - at or very close to 8

_________________
2008 Black Jeep Liberty Sport
4.7L throttle body
Old Man Emu lift
Sky Slider
Hypertech Max Energy
K&N CAI
Gibson stainless steel exhaust
Blacked out
ScanGauge2
BFG All Terrrain 225/75/16
JBA upper control arms

Keep in mind, those are manifold absolute pressure readings, not vacuum readings. Your vacuum gauge won't match that.

wow, so those are way off from what mine is reading on my scanner. I wonder if that means the MAP sensor is junk, or the sensor is correct and I've lost vacuum due to mechanical issues?? Motor doesn't make any noises or anything.....just runs like it's only firing on 5 cylinders or so. Hmmmm.

Thanx for the readings!!

_________________
Civilisation exists by geological consent, subject to change without notice. -Durant

X2.

_________________
2008 Black Jeep Liberty Sport
4.7L throttle body
Old Man Emu lift
Sky Slider
Hypertech Max Energy
K&N CAI
Gibson stainless steel exhaust
Blacked out
ScanGauge2
BFG All Terrrain 225/75/16
JBA upper control arms

No problem. I hope this helps a little. I should thank you, too because I think I found a new setting I would like to monitor while driving.
Keep us posted, and hopefully we can figure this out.

_________________
2008 Black Jeep Liberty Sport
4.7L throttle body
Old Man Emu lift
Sky Slider
Hypertech Max Energy
K&N CAI
Gibson stainless steel exhaust
Blacked out
ScanGauge2
BFG All Terrrain 225/75/16
JBA upper control arms

Hmmm, so MAP values won't match vacuum, grrr. Well, I vacuum gauged it and it was a little on the low side and fluttery indicating questionable valves and late valve timing. Still, I believe that my MAP is way off so I bought one just now. Started to change it and realized I had removed the TPS, grrr. TPS, easy to change. MAP sensor, not so much. Wish I had changed it a few years ago when I changed the AC compressor!! Lots of heat in this area, the connector is not cooperating and the plastic wireway breaks up when touched. Anyone know what size the bolts are?? smaller than 8mm it seems.

Thanx everyone for their help.

_________________
Civilisation exists by geological consent, subject to change without notice. -Durant

Hold the boat skipper. If you have a flutter on the vac gauge, that's a mechanical issue right there that needs addressed. Knowing the history of these engines and broken valve springs, before you go past go, and collect $200, or throw any parts at it, you NEED to find out why there is a flutter. That will skew map sensor readings big time, and confuse the heck out of the PCM!

But...but...but, I just want to change a 26 dollar part (which is no easy task let me tell you) and be all set!! No such luck this time? Oh, the bolts are 7mm for future reference and I wish I had a 7mm ratcheting wrench!! I don't have it all changed out just yet, had to work on the backup vehicle tonight!

I did grab a compression tester from the shop but didn't get to using it tonight. My plan was to change the 26 dollar part, which I thought would be a usual 10 minute affair, and then do the compression test. Things don't always work out as planned.

So I guess the question now is what kinda repairs can I do without pulling the heads?? Broken valve springs are common? Can I change valve springs by keeping each cylinder filled with compressed air?? Oh boy!

_________________
Civilisation exists by geological consent, subject to change without notice. -Durant

It's always nice to hope for a cheap fix with a simple electrical part, but when you have a test that showed you a mechanical problem, you gotta get dirty, sorry bud, lol. In theory, if you locate a bad valve spring, you could use compressed air to hold the valve shut and change the parts needed. Here's the catch. A lot of times, the valve face can become coated with crude from not sealing, and you can't get the cylinder to hold air. Did you have any misfire codes? If you do, it may or may not point to the cylinder that has issues. If there was a misfire code, I would check the compression on it first. You'll find a weak one, most likely, and if so, pull the valve cover for that head and look very carefully at the springs. Intake is the most likely culprit.

No misfire codes, which really had me stumped with the two banks both indicating rich. 20-30k ago I had a cylinder misfire code and it was a bad injector. No problems since.

I hope I can fix the problem with springs or something. The thing is the problem just all of the sudden happened. Power good and smooth, and then it just ran crappy. The motor doesn't knock or tick or anything either which is very surprising!!

I guess I'll report back when I get the cylinders compression tested. Wish me luck, and thanx again for the help!!

_________________
Civilisation exists by geological consent, subject to change without notice. -Durant

Sounds typical of a broken valve spring. It's a mechanical failure, so it would be a night and day difference when it happened. Because it screws with the MAP sensor readings, the PCM sees less vacuum and thinks the engine has a bigger load on it than it really has, and gives it more fuel.