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Unread 04-29-2005, 10:09 AM   #1
ERICH
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Ocassional bucking/loss of power... check engine light

Hello All
First let me tell you what I have... 1997 Grand Cherokee Laredo 173K 4.0 ltr. L6 Automatic. My wife started having some problems about 200 miles from home, she said it would buck and or loose power when encountered hills or accelerated rapidly, she would pull over and it wouldn't stall and she was then able to get back up to speed. She said that it a few times did stall out of say 3 dozen times and that the check engine light was on. She got to an autozone and I told her to buy a fuel pump relay and told her what to do, she said it was the wrong one. I bought one at Advanced and headed her way. I pulled the check codes 31 and 42. She was right the relays were not the right ones, I noticed all the relays had the same numbers on them so I used the one from the AC for the fuel pump relay. We started home and found that the problem was still there, it only seemed to happen above 65 to 70 mph. I was thinking I would replace the fuel filter and read that it is in the tank. I went advanced to have them read the codes because in the Haynes manual it gives about 5 different sub codes for each of those 31 and 42 codes. When the guy there read the codes he only got one that was 14??, he erased it and when I went inside to buy a fuel filter he found that it came as a unit with the fuel pump and that it was only available from the dealer? The check engine light has come back on and when pulled the code only the 31 came up. I have been driving it and have not been able to get it to hesitate. I am going to go get the guy at Advance to use his scanner again and this time I will write down the number.
My question is does anyone have a insight here. This thing has been one thing after another it seems, I don't want to get a whole new fuel pump assembly if I can just get the filter, and if not I think I might try to reverse flush the filter and reuse it? Any thoughts would be appreciated.
Thanks
ERICH

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97 GC Laredo 4.0 L, Auto, "Selecta Track"? 160K
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Unread 04-29-2005, 10:36 AM   #2
kemicalburns
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maybe the pump is the problem not the filter , since your in there it just makes sense to replace both period. also when was this tuned up last? did you check the cap for cracks , how about the coil possibly being bad.
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Unread 04-29-2005, 11:09 AM   #3
ERICH
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I feel as though the setup is designed to make one do that, I don't want to replace something that works... I'd rather take the tank out twice than feel like I was conned out of my money!!! I sound like I'm 98 shaking my kane at something that gets me real fired up?
Any other thoughts?
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Unread 04-29-2005, 11:15 AM   #4
greasefingers
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If you have 160k miles on her and the fuel pump is the original, then I would not hesitate to replace it. Even if itís not your current problem. Hesitation, bucking, & stalling are symptoms of incorrect fuel delivery. But it could be something electrical as well. The problem is that it is intermittent. Which means you cannot trouble-shoot unless the component is currently under the fail condition.
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94 Black Laredo 4-Liter with QuadraTrac (42RE trans & NP249 TC) 200,000 + miles purchased new

88 Cherokee 2-door with 5speed manual 139K miles(deceased) purchased new
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Unread 04-29-2005, 01:06 PM   #5
shadetree
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just a thought but, did you think about checking the fuel pressure at the rails? the fuel delivery specs might be the haynes if not i don't know where to get it however this test could show low fuel delivery pressure and hence changing the fuel pump. mine sputtered at about 130K and we changed it. works great now. my fuel filter is on the inside frame rail by the rear left tire. I don't know why some genius would put one in the fuel tank? I would look at inline filters as well.
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Unread 04-29-2005, 03:05 PM   #6
greasefingers
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Most late model vehicles have the gas filter in the gas tank, today. This is to protect the gas pump and everything outbound from it. With plastic gas tanks, it leaves only the fuel as the source for contamination. When I dropped my gas tank, after 150k miles on it to replace the pump, the bottom of the gas tank was almost perfectly clean. The fuel pump filter (a sock-like thingie) was only stained a gold color. No particles, dirt, or sludge. So there is almost no need for an inline filter (as I have) IMO.
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94 Black Laredo 4-Liter with QuadraTrac (42RE trans & NP249 TC) 200,000 + miles purchased new

88 Cherokee 2-door with 5speed manual 139K miles(deceased) purchased new
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Unread 05-03-2005, 01:03 PM   #7
ERICH
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Code 31 more specifically 1494

Hello
I got it scanned and it came up as 1494, which the haynes manual says is "leak detection pump switch does not respond to input". Now before I got it scanned this time it did buck once ( I quickly eased off of the gas) as I tried to gun it at an uphill stop light, and this was still the only code? Can anyone tell me what this really means, is this what is causing my problem as the code 41 has not reappearedsince swapping the relays?
This might be related, I thought a CV joint might be going but then realized that it made the same amount of noise turning either way. So I take a look up underneath there to find that it u-joints instead of CV's. Well both are shot to s__t, real bad, could this be sending a not so clear message through the speed sensors and thus be a part of my problem? I got new u-joints and going out to pull the axles now.
Thanks
ERICH
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Last edited by ERICH; 05-03-2005 at 01:18 PM..
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Unread 05-03-2005, 02:20 PM   #8
greasefingers
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Good luck with the U-joint replacement(s). At any time during the hesitation/stalling situation, did the engine backfire?
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Cheers Steve

94 Black Laredo 4-Liter with QuadraTrac (42RE trans & NP249 TC) 200,000 + miles purchased new

88 Cherokee 2-door with 5speed manual 139K miles(deceased) purchased new
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Unread 05-03-2005, 02:27 PM   #9
ERICH
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No, no back firing?
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Unread 05-03-2005, 07:28 PM   #10
ERICH
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Come on, who knows what this code means?
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Unread 05-04-2005, 05:31 AM   #11
greasefingers
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I asked if it back fired, becasue that is a sign of a gas starved engine.

Sorry, 1993 to 1996 models do not have a code 31. Someone with a later model should be able to help you.
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Cheers Steve

94 Black Laredo 4-Liter with QuadraTrac (42RE trans & NP249 TC) 200,000 + miles purchased new

88 Cherokee 2-door with 5speed manual 139K miles(deceased) purchased new
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Unread 05-04-2005, 08:54 AM   #12
ERICH
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Greasefingers
Now I see why you said good luck on those u-joints, I could not get those 3 star shaped nuts to the back of the hub to budge, its originally from NH so they are a little corroded. I hate to say it...I am bringing it to the garage today to get them to deal with it. Just the u joints, thats all I trust them to do.
Thanks
ERICH
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Last edited by ERICH; 05-04-2005 at 09:04 AM..
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Unread 06-20-2011, 01:35 PM   #13
fotonm
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After having this same problem on my 94 with a 5.2 I changed EVERYTHING that people have been talking about on here the TPS, New Tranny, New fuel filter, New fuel pressure regulator. Sometimes it would run great then other times just very sluggish and especially between about 1000 to the 2000 rpm mark. It didnt matter if it was hot or cold just very frustrating and intermittent.

Well I started to suspect a vacuum leak. While monkeying with the vacuum lines and wiggling them I got a surge and thought I was on to it. It wasn't the vacuum after all.

It was the wires that go into the TPS and when I would wiggle them it would surge and even cut off the engine. I unplugged it and Ohmed out the wires while my ohm meter was plugged into and wiggled the wires and I didnt get any Resistance drop. I figure out that the pin that comes out from the ground part of the TPS was not making a good contact with the connector. When it was not making a good solid contact I would get the problem.

You can fix this one of two ways.... you can replace the entire plug assembly to one where the female end of the connectors make a better contact or you can take up the slack in the now too loose female end with a small piece of wire inserted into the tooled out female end (lol) and now it wont be like a hotdog in a hallway and will make a good ground. Plugged it all back in and now runs like it should with full power all the way through the spectrum.

This worked for me so you may try this!! Its a connection and grounding problem in the TPS connector not an actual prob with any of the devices.

if your grounding and connections in the TPS are not solid it spikes all up and down sending the wrong voltage to the rest of the injection system.
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