Issue with poor running

[mdl]

I'll ask because I'm completely out of ideas, I'll try and be as extensive as possible here. I know it's long but any suggestions are much appreciated.
-------------------------------
1996 sport 4.0, np321, aw4.
-------------------------------

This happens mostly through highway use but also if I drive spirited it will happen as well. At first it isn't as noticable but you can feel it happening. What's going on is for example on the highway, I'll be driving along at 65mph and I will feel the power cut off and come back and cut off and come back. When I lose the power it lasts for about one second then comes back. If I slow down almost to a stop, it runs crappy. I can smell somthing nasty which I'm assuming is the exaust. It's strong. Somtimes after I start going again from a stop, lots of black smoke comes out of the exhost. Initially I thought oil leak so I went down and cleaned the whole area well then replicated the problem, not a spec of oil to be found anywhere in the area.

When it happens, the check engine light comes on. I pull the codes and it allways points to running rich or lean, can never make up its mind. It also finds a fault with my upstream O2 sensor, which I have replaced twice.

Also when this happens, I am usually running very hot. I have flushed my cooling system a few times since and I'm sure its not an issue with the level of coolant.

Any suggestions? I believe that's all the details, if you don't understand somthing or you need to know somthing else I can be more specific.

Thanks so much in advance!

[jeepdude10000]

ok u go through ur problem, but u dont say what u have checked, i leaning towards the temp sensor, or bad wiring.

more info would be nice.

[Timber]

I'm having this problem currently as well (after dunking the entire front end this past weekend--thank god for my MadXJ snorkel!). I get a P0171--too rich on Bank 1. I understand that, in my case at least, the downstream O2 sensor is probably related to the problem; I have also read, however, that it could be a faulty IAT sensor. I don't have the overheating problem too, though, and I hate to bring this up, but--is a cracked head/head gasket a possibility?

[Hellbent]

just thought i'd throw this out there....
a friend of mine with a 95 yj had almost the EXACT SAME symptoms, the problem would come and go, seemingly at random. turned out to be a bum map sensor. just a thought....

[lilredwagn]

just thought i'd throw this out there....
a friend of mine with a 95 yj had almost the EXACT SAME symptoms, the problem would come and go, seemingly at random. turned out to be a bum map sensor. just a thought....
Second the MAP as a strong possibility. Unfortunately on the '96 it's $80 to find out by trial and error. Not that it's a bad thing to have a spare around - it's bound to go out sooner or later.

[mdl]

So far:

Replaced - Upstream and downstream o2 sensor, TPS.
Checked - Just the obvious

[mdl]

Second the MAP as a strong possibility. Unfortunately on the '96 it's $80 to find out by trial and error. Not that it's a bad thing to have a spare around - it's bound to go out sooner or later.

Yes but there should be a way to test it with a multi meter

[Hellbent]

should be able to test it's response with a vacuum pump and a multimeter. is that one of the years w/the map mounted on the tb? if it is, i have seen a few of those with that little bitty intermediate hose slipped off or cracked. could cause the same type of issues.

[lilredwagn]

Yes but there should be a way to test it with a multi meter
http://www.naxja.org/forum/showthread.php?t=99181
I hadn't bothered to bump it for update, but the answer seems to be "NO"

You can still test it the old fashion way with a voltmeter probe while the engine is running (and possibly with a vacuum pump and voltimeter if you also add a 5v power supply to the equation), but I don't think that would give any help with an intermittent problem. Exactly what codes are you getting?

[Hellbent]

Test the MAP sensor output voltage at the MAP sensor connector between terminals A and B With the ignition switch ON and the engine OFF, output voltage should be 4-to-5 volts. The voltage should drop to 1.5-to-2.1 volts with a hot, neutral idle speed condition.
Test powertrain control module (PCM) cavity A-27 for the same voltage described above to verify the wire harness condition. Repair as necessary.
Test MAP sensor supply voltage at sensor connector between terminals A and C with the ignition ON. The voltage should be approximately 5 volts (±0.5V) Five volts (±0.5V) should also be at cavity A-17 of the PCM wire harness connector. Repair or replace the wire harness as necessary.
Test the MAP sensor ground circuit at sensor connector terminal - A and PCM connector A-4. Repair the wire harness if necessary

try this...

[CartsXJ]

Or you could build yourself an adjustable MAP sensor for about $15 tops and try that.

[Timber]

Or you could build yourself an adjustable MAP sensor for about $15 tops and try that.
That doesn't replace the sensor. It is a DIY add on that makes it adjustable; your original still needs to work properly.

[CartsXJ]

ok, so how does that work? ft the adjustable completely bypasses the factory MAP sensor? The factory has three wire; power, ground and output. and you are bypassing the output with the adjustable unit, correct? I mean you are taking a 12 volt source and droping it down to whatever voltage works for you jeep and sending that to the computer. Why wouldn't it work?

[Timber]

To quote Dr. Dyno, "This device adjusts the injector pulse width by modifying the output voltage from the manifold absolute pressure (MAP) sensor to the ECU. Increasing the pulse width adds more fuel and eliminates the surging and bucking of lean-running modified EFI Jeep 4.0 engines. Matches fuel curve to airflow changes such as high-flow TB, ported head, header, longer duration camshaft. Easy Installation; Includes Module and connectors with pre-wired splicing setup. If you consider the Turbo City unit to be too expensive, you can copy Dino's homebrew MAP adjuster very inexpensively."

In other words, they are adjusters--not replacers. They take the output of a working MAP sensor and allow it to be tailored.

[CartsXJ]

ok never mind, it adjusts the input voltage to the MAP, I for some unknown reason thought it adjusted the output voltage. I just read thru the destructions again. I built the unit, just haven't hooked it up yet, good thing, huh

[radardog]

try the fuel filter.. i havnt had this happen to my XJ yet, but my old suburban did that too, and it was the fuel filter. as soon as i changed it it stopped.

just some food for thought, sometimes it is the dumbest simplest thing you would never think of

[mdl]

OK, It's still happening.

-Both 02 sensors Replaced
-TPS Replaced
-Fuel Filter Replaced
-Plugs Replaced

Pulling code : P0171 - P0171 System too Lean (Bank 1) every time it happens.

Checked all general wiring and the obvious. I would like to avoid replacing the MAP sensor if possible, its an expensive bump. Any cheaper ideas?

Buddy of mine says its a possible fuel injector issue...

[Ecomike]

Check for vacuum leaks first! Also check, and test the fuel pressure and the fuel pressure regulator. The pressure regulator is vacuum operated on the front end of the fuel rail. I hear the MAP sensors are very robust and rarely fail, but a vacuum leak anywhere can cause problems and the MAP sensor depends or getting the correct vacuum reading. To be too lean you are getting too little fuel or too much air, or the electronic (ECU) timing is off allowing too little fuel in though the injectors.

Also check the EGR circuit to see if it is hung open.

Mike McGinness
South Houston, TX

[aardvark4x4]

Partially blocked Cat or muffler?

[jbassxj]

I seem to be having this issue now, I've replaced my upstream 02 sensor and now the code p0171 still shows up...

did you every figure this out?

[Timber]

I had convinced myself it was the MAP sensor or a vacuum problem at/near the MAP (even though I couldn't get conclusive VOM readings), then I just took the $65 plunge one day at AutoZone for the upstream O2. Immediate fix for me. I'd look into the MAP sensor and vacuum lines.

[98XJSport]

Check out the coolant temp. sensor perhaps? That could cause lean/rich conditions I would think...

[jbassxj]

I had convinced myself it was the MAP sensor or a vacuum problem at/near the MAP (even though I couldn't get conclusive VOM readings), then I just took the $65 plunge one day at AutoZone for the upstream O2. Immediate fix for me. I'd look into the MAP sensor and vacuum lines.


Here's the gist of backstory:

replaced exhaust manifold.

Car ran lean afterwards, CEL came on, found the code, immediately replaced upstream 02 sensor. That helped, but still the car idles high when in park and idles slightly rough when in drive. Started to go back and check some connections and realized (I'm a complete idiot for this) that I didn't tighten the connection to the air filter box properly - so I thought that this was where the vacuum leak was coming from and possibly the car will run properly now. Connected that properly, reset the pcm, took it out for a drive.

When I first start it, it's good to go and seems to run 85% properly (like it's supposed to run, can feel some shaking/vibs when I'm in the driver seat). When I put it in park after reaching a destination, it does an un-natural high idle of about 1100-1300 rpm <-- that tells me something is still wrong.

If the MAP sensor was not working properly, would it spit out a code? I've check the other vacuum line connections and they all seem to be alright. Would an over-tightened throttle body (bolts connecting it on) lead to this issue? Also, their is another connetion line that goes from the engine to the intake manifold (more towards cylinder #'s 5 n 6) that I think I might've over-tightened - (sorry I don't have the correct name, bu tthis connection is one that is scrwed in at the intake manifold and tightened there)... could that lead to this issue as well? Those are the only other things in my head that I need to check, weather so far has permitted me from doing so. Any other stuff I could check?

Check out the coolant temp. sensor perhaps? That could cause lean/rich conditions I would think...

It can and I'll check it again cuz I've fixed that before.

[jbassxj]

nvm, did a butt load of searching.

cleaned the TB, tightened up all exhaust manifold bolts since it had been past 100 miles since installation (I think). That fixed the high idle issue, but it was still idling ever so crappy, so I sea-foamed it and it seems to be 95% great.

so I guess I answered my own question :)