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'96 XJ 4.0 149K miles - No Power

B

Bob Langford

NAXJA Forum User
Location
Roanoke, VA
Jeep used to delivery mail and newspapers. About 2 hrs into 52 mile 4 hr mail route Jeep starts stumbling; won't pull slight grade. Never stalls but twice I've had to limp around the remainder of the run. After 1st time this happened, I replaced upstream O2 sensor w/Bosch 13100. Next day, same thing happened. Yesterday, checked MAP. Found 4.5V at keyon, and it decreased to 1.4V running at hot idle - seems ok. Both coolant/intake manifold temp sensors resistance readings in proper range for hot idle per FSM charts. I see couple suggestions on JU about fuel and fuel pressure. I'll try to get a shop to check that for me. But, it seems odd this prob comes up after 2 hrs of running and when temp is up abv 85 outside. Anyone have comment about the fuel being the trbl ? Tried 3 local shops to get eng diag and can't get appoint for a week ! And lowest price around has been $65 to hookup to diag. So, on impluse, based only on their advert., I purchased online the Harrison R&D OBDIIscan tool ffor Windows, for $167. It should be here tomorrow. Anyone try this ? http://www.obdscan.net
 
Jeep used to delivery mail and newspapers. About 2 hrs into 52 mile 4 hr mail route Jeep starts stumbling; won't pull slight grade. Never stalls but twice I've had to limp around the remainder of the run. MIL lit, code read as P0171, bank 1 lean. After 1st time this happened, I replaced upstream O2 sensor w/Bosch 13100. Next day, same thing happened. Yesterday, checked MAP. Found 4.5V at keyon, and it decreased to 1.4V running at hot idle - seems ok. Both coolant/intake manifold temp sensors resistance readings in proper range for hot idle per FSM charts. I see couple suggestions on JU about fuel and fuel pressure. I'll try to get a shop to check that for me. But, it seems odd this prob comes up after 2 hrs of running and when temp is up abv 85 outside. Anyone have comment about the fuel being the trbl ? Tried 3 local shops to get eng diag and can't get appoint for a week ! And lowest price around has been $65 to hookup to diag. So, on impluse, based only on their advert., I purchased online the Harrison R&D OBDIIscan tool ffor Windows, for $167. It should be here tomorrow. Anyone try this ? http://www.obdscan.net
 
Turn the key On-Off-On-Off-On and wait. The Check Engine light should start blinking a series of two-digit numbers. Count them carefully, as there is only a slightly longer pause between numbers than there is between tens and ones. You should always get "five-five" which means "end of codes" but compare the rest of them at http://www.allpar.com/fix/80s-codes.html
 
I've got the code already; it's P0171 from the AutoZone OBDII scan tool. Based on that, I replaced the O2 sensor. Problem still there. But this Harrison R&D OBDscan tool works with laptop and you get a logging funtion so I can maybe start that up and it will show me what change occurs when the veh starts to act up. Their scan tool gets everything the PCM gets from the various sensors and puts in graphical format etc. See the screen shots on their web site here: Http://www.obdscan.net
 
From past exp you can only scan if its throwing a check eng lighht at you. Regardless, I would be curious to see what code comes up. Does it run ok up till a certain rpm, or sluggish along the whole band? Does it shift akwardly? Has the Cat ever been changed?
jamie
 
Is the jeep stock? Hows the tranny fluid look? Tranny maybe overheating?
 
Tranny fluid gets drained every other oil change; that happens 4-5K miles. I've had tranny cooler installed for 2 years also. When it starts stumbling, it will idle ok and you can throttle it ok in park/neutral. Most of the time it goes ok in 1st also, but when it goes for another gear is when it starts to stumble. When I got back from the mail runs, it was parked for 10 minutes, then it ran ok all the way home both days. The Harrison OBDscan tool should tell me all about vacuum, O2 sensor voltages in graph form, coolant/intake manifold temp, misfires, CPS and sync prlbs etc. It's capable of reading OBDII codes and resetting them. Unless it's a fuel problem, I'm hoping to be able to pin my problem down with this tool.
 
Bob, my money's on a bad fuel pump/regulator. You could put a pressure gauge on the fuel rail the next time it did this to confirm.

Low fuel pressure would give the lean condition P0171; and as you know, bank 1 is the only bank on an inline engine.

I don't have any experience with that scan tool, but it should be able to easily diagnose a fuel pressure problem, or anything else for that matter.
 
We had a 98 Grand that did the same thing, it was the fuel pump. JIM.
 
I'm not aware of any sensor on this engine reporting anything about fuel to the PCM. I replaced the fuel pump about 18 months ago when the stock pump failed. Replaced the filter at the same time. I'm betting it's not a fuel issue. I really hate the idea of taking the veh to a shop who will find the engine running just fine (of course it will, it takes a couple hrs in 85+ outside air temp for it to start acting up), diag ok and I pick it up with nothing done but reduce my bank account by a couple hundred dollars. Unfortunately, I don't have anything in my tool kit that can test fuel pressure especially out delivering mail when this problem starts happening. So I'm going to run this Harrison tool with my notebook PC with veh loaded up with US Mail this coming Monday, set the logging function going and hope to get some data that points to causes.
 
I check my fuel pressure with a 99 cent tire pressure gauge and a valve core puller. Just push the gauge on firmly and straight and it won't leak. Shake the gas out of the gauge when you're done. Works fantastic. You can rev the motor (push the throttle body) with one hand and hold the gauge with the other.

Jared:patriot:
 
You can use a r-12 low side guage set to check your fuel pressure. I have a VAG-COM setup made for VW's that now has generic OBDII because VW is going to that on their engine controls. It's neat watching your o2 sensor's reading go up and down about once a second as it's supposed to. You sound like me and will find watching your engine's sensors change as you drive. Just make sure you watch the road and not the computer or you'll hit a mail box!

JoBo

Edit: I forgot to mention, the codes will untill a certain amount of start/start cycles have occured so you should be able to see them.
 
Thanks for the two good suggestions for checking fuel. Carried mail today and had no prlblms at all ! Temp only got up to low 70's here in this part of Virginia, though. My Harrison R&D OBDscan tool didn't arrive today. Have to wait until Monday then.
 
I'm not aware of any sensor on this engine reporting anything about fuel to the PCM. I replaced the fuel pump about 18 months ago when the stock pump failed.
Click to expand...
Bob, you're right in that a scanner dosen't read fuel pressure, but when the pump loses pressure you'll see a lean A/F ratio develop.

I can't figure out why a change of only 10-15*F in ambient temp would cause a failure in anything. After all, the underhood temps are much higher than ambient, and the fuel pump is submerged in gasoline, and shouldn't be affected by air temps......? Maybe it's running time that affects it?

Anyway, it'll be interesting to see what the scanner picks up.
 
When things are working correctly you'll see the o2's reading pulsate up and down. With it running lean as in not getting enough fuel I don't think you'll see it pulsate back and forth.

JoBo
 
Finally received the OBDscan tool by Harrison R&D. It works as advertised. No problems loading the software on my notebook and when connected to the OBDII port on my XJ, displays come up every time. Today during the mail route about 2/3 way through, the Jeep started loosing power again. Another hot day outside here; probably middle 80's. I didn't have the notebook PC with me because I couldn't decide where to put it with mail up to the roof and on all horizontal surfaces ! But, when I got back home, I hooked up and found P0171 code set. MIL came on during the run, but by the time I got home, Jeep was running ok again. Nothing obviously amiss from the displays except for MAP reading. It's on average only 3.5 inches of hg. On my 1999 Wrangler, MAP reads about 3 times that at hot idle - 9 or 10 inches of hg. So, I thought I'd swap the MAP sensors between the two Jeeps and make another mail run. The administrator of this bulletin board won't allow me to post any .jpg files, so I'll try to get a couple up on some web space in an hour or so. You can see what the screen displays show with this OBDscan tool.

Bob L.
 
Here are two screen shots from the OBDscan tool. http://members.cox.net/13regatniv/obdiiscan.htm I didn't shut the Jeep down when I got home; just let it idle in the driveway. I don't know anything about the fuel trim numbers shown. I can tell you that when I first hooked it up, the short term trim was different than what is shown here. Maybe 4 or 5 percent negative. The second screen shows the upstream O2 sensor apparently working ok. The only thing I see is a much lower MAP reading that my '99 TJ. I'm not sure what the MAP value should be on the XJ. I know the vacuum is about 17 inhg using a vacuum gauge. That's vacuum, the MAP is reporting pressure. Any comment ?
 
Come to think of it, there is something else that doesn't look right. Ignition advance shows to be 14 degrees. I thought it was 1.4 degrees, but there really isn't a decimal there. Is that normal for this engine at idle ?

Bob L.
 
you know I had a VW jetta do that to me once. But it was an all of the sudden wouldn't fix itself thing. Turned out that the Cat converter went bad. It would idle fine but once it hit anything more that 2000 rpms it would sputter and stall really crappy stuff. Maybe your converter is going out and closes off once it gets too hot? Unlikely but its a thought.


On the other hand I had a ranger that wouldn't pull any hills and was really weak but was a constant problem that started slowly. Turned out my distributer was off and the engine was detonating. Cracked the driver's side head in Six places. I drove it like that for a long time. All of the cylinders on that side had almost no compression.

Sorry to throw more worried at you!
 
With that many miles, my bet is on a clogged Cat.
 
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