Engine misses and what is it? - JeepForum.com

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post #1 of 23 Old 06-02-2010, 11:01 AM Thread Starter
Lakeray
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Engine misses and what is it?

I have a 1997 TJ Sport with a 5spd that I just got. It has one problem and one puzzle. The problem is that when I hit a decent bump in the road, the engine cuts out, misses kind of. I mainly notice it in 1st or 2nd between 2,000-2,500 RPM. On a dirt track itís of course really bad. On a smooth road it purrs like a kitten in all RPM ranges. The engine warning light doesnít come on and I donít have any codes. I know itís not the main electrical since the lights donít flicker or anything else like that. I figure I have a loose connection somewhere in either the ignition or fuel system. But where do I start? Anyone know of a somewhat common place to start?

Second Iíve got two unplugged plugs. Iíve attached a pic. Their located on the right side behind the alternator. They both come out of the main harness there. One is light gray plastic rectangular shaped with a blue wire and the other is black (?) with 2 wires of unknown color. They look like they would plug together but Iím kinda hesitant about doing that. I know that wiring harness will have plugs for everything available even if you donít have it. So yeah, thereís always some extra plugs laying around. The only thing I know of that doesnít work in the Jeep is the airbag light on the dash. Doesnít come on, but the bulb could be burnt out. Any ideas?

Ray


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post #2 of 23 Old 06-03-2010, 09:54 AM Thread Starter
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Can anyone help?
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post #3 of 23 Old 07-02-2010, 12:36 PM
SouthernTJ
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I've got the same "engine miss" problem with my '97 TJ. It only seems to occur when I'm accelerating and I hit a bump in the road. If I lift my foot off the accelerator just before and during the bump, there isn't a problem. Its really strange. I had this problem last year, as well, and my mechanic found a hairline crack in the coil and he replaced it. This seemed to help for a few months, but the problem soon returned and has continued to get worse. Either the coil keeps cracking for some reason and needs to be replaced again, or the coil wasn't the problem at all.

Also, I was driving on the interstate and had been for about an hour when the engine started to miss for no reason and I was having trouble just barely maintaining 60 mph. I noticed that I was nearly out of fuel so I pulled over into a gas station, put in about 3/4 tank and got back on the road. The unprovoked engine misses went away and it just went back to missing when I hit bumps. So, I guess what I'm suggesting is that perhaps it has something to do with the fuel system. I really don't know though.

I wish I knew the answer because I'm having the same issue and need it fixed.
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post #4 of 23 Old 07-02-2010, 01:09 PM
Dogman
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Those are probably A/C connections. Do you have A/C?

John 3:17
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post #5 of 23 Old 07-02-2010, 01:09 PM Thread Starter
Lakeray
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Originally Posted by Dogman View Post
Those are probably A/C connections. Do you have A/C?
No A/C and I found those connections in the FSM.. Thanks...
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post #6 of 23 Old 07-02-2010, 01:14 PM Thread Starter
Lakeray
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Originally Posted by SouthernTJ View Post
I've got the same "engine miss" problem with my '97 TJ. It only seems to occur when I'm accelerating and I hit a bump in the road. If I lift my foot off the accelerator just before and during the bump, there isn't a problem. Its really strange. I had this problem last year, as well, and my mechanic found a hairline crack in the coil and he replaced it. This seemed to help for a few months, but the problem soon returned and has continued to get worse. Either the coil keeps cracking for some reason and needs to be replaced again, or the coil wasn't the problem at all.

Also, I was driving on the interstate and had been for about an hour when the engine started to miss for no reason and I was having trouble just barely maintaining 60 mph. I noticed that I was nearly out of fuel so I pulled over into a gas station, put in about 3/4 tank and got back on the road. The unprovoked engine misses went away and it just went back to missing when I hit bumps. So, I guess what I'm suggesting is that perhaps it has something to do with the fuel system. I really don't know though.

I wish I knew the answer because I'm having the same issue and need it fixed.
I've been tracking wire connections and grounds the last week. Lots of bad connections and corroded grounds, so I've been rewiring. I hope to have that wrapped up this week. INCLUDING checking the fuel pump electrical connections. Then I am going to check the coil. If thatís it I may try to isolate it from getting any vibrations as best as possible...
Ray

p.s. Used to live in Idaho Falls and miss it...
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post #7 of 23 Old 07-02-2010, 02:45 PM
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Quote:
Originally Posted by Lakeray View Post
I've been tracking wire connections and grounds the last week. Lots of bad connections and corroded grounds, so I've been rewiring. I hope to have that wrapped up this week. INCLUDING checking the fuel pump electrical connections. Then I am going to check the coil. If thatís it I may try to isolate it from getting any vibrations as best as possible...
Ray

p.s. Used to live in Idaho Falls and miss it...
Navy Nuke?
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post #8 of 23 Old 07-04-2010, 04:47 PM Thread Starter
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No ATC...
Lots of navy people came thru there...
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post #9 of 23 Old 07-14-2010, 08:21 AM Thread Starter
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Ok, an update. I looked at the crankshaft position sensor. On the wires from the sensor they have a spot that the insulation looks melted but not the wires themselves. There is continuity between the B and C terminals, but I canít hold the prongs on there good enough when I shake the plug. I may go ahead and replace it but Iím trying to keep my spending below the radar from my wife. If I do replace it, is it one of those cases where I should use OEM? When I looked at the upstream O2 sensor, 2 of the 4 wires had been spliced together so who knows about this. Additionally I just noticed that it stumbles and falls on itís face when I try and maintain a steady speed in the range between 2,000 and 2,500 RPM when I hit a bump. If Iím increasing speed it doesnít do it.

I also (when I was under the hood) noticed that there are two ground straps hooked to the fire wall. One goes to the engine block but the other is hanging loose. I know there are always unused connectors and stuff, but an unused ground strap?

Ray
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post #10 of 23 Old 07-29-2010, 06:13 PM
SouthernTJ
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I finally just decided to take mine to a mechanic and he replaced the crankshaft censor. He said the computer was picking up errors, but for whatever reason it wasn't showing up on the dash. He also said he tapped the sensor as it was running which about caused the engine to kill and that this would explain why the tach was jumping. I haven't gotten to drive it yet to ensure this fixed the problem, but I'm hoping this is the solution.
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post #11 of 23 Old 09-01-2010, 09:35 AM
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Did this fix it? I have a 97 and I have the same thing. Stumble and miss around 2000 RPM, but mine seems to happen more often when the engine is cold.
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post #12 of 23 Old 09-01-2010, 10:32 AM Thread Starter
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I went ahead and replaced my crankshaft sensor. No change...
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post #13 of 23 Old 09-01-2010, 11:05 AM
freshlikefruit
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most commonly the crank sensor will show signs of wear at about 2200rpm with a manual trans. it will miss sporadically. mine has done this twice, the first time i just pulled it and ran new wire from connection to sensor. that worked great for about 35000 miles, but now the sensor itself is failing. in my case at least, the wiring got too close to my borla header and began to melt.

97 tj, dirt on it
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post #14 of 23 Old 09-01-2010, 11:08 AM
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u might also try your cam sensor, its under the dist cap and looks like a black plastic disc matching the radius of the cap. when these fail it can cause intermittent missing, but as for hitting bumps to provoke it, i have no idea

97 tj, dirt on it
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post #15 of 23 Old 10-06-2010, 10:11 AM Thread Starter
Lakeray
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Originally Posted by freshlikefruit View Post
u might also try your cam sensor, its under the dist cap and looks like a black plastic disc matching the radius of the cap. when these fail it can cause intermittent missing, but as for hitting bumps to provoke it, i have no idea
Replaced cam sensor. No joy...
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