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upshift light on reverse of normal vacuum leak? where?


 
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saharatj98
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Joined: 22 Nov 2004
Location: Federal Way, Washington USA

PostPosted: Tue Nov 15, 2005 10:15 pm    Post subject: upshift light on reverse of normal vacuum leak? where? Reply with quote

Another sad Jeep story. Bought it new 11/96 1997 4cyl 5spd. Got divorced I kept my 98 Sahara she kept her 97 SE. Long story short she gave it to me last year. Now it has 143,000. It ran a little rough but passed emissions with flying colors. I immediately replaced all fluids as I used to maintain it religeously when it was in the house. A simple tune up helped the idle and I also replaced the timing chain/gears and guide because it was ticking at idle. Noise gone:). Burns no oil or uses any:). Last month the upshift light would start to light up under moderate acceleration? I replaced the exhaust manifold(cracked). While I had everything apart I checked the vacuum lines and everything seemed ok. It has always had a starting problem since I got it back. Starts fine cold, warm it will not start the first time you turn the key. You can crank it for 15 seconds and nothing. Turn the key off and try again it fires right up. I don't know if it is a computer problem or what. I drained the gas tank and cleaned out the in tank filter since Jeep wants $800.00 for a new filter since it is part of the pump. Made no change in the hard starting problem. Injectors spray even. Anyone know where the upshift light gets it's signal from if it is a vacuum line or a sensor? Anyone have any thoughts as the the hot start issue? I know the basics of what could be wrong, but I figure maybe there is a "most common" thing that causes problems on these. Thanks:)
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ThePhantum
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PostPosted: Tue Nov 15, 2005 11:33 pm    Post subject: Reply with quote

When you tuned it up did you replace the O2 sensors?

The upshift indicator is triggered by the PCM...so it sounds like another symptom. The first thing I can think of (if you haven't done it already) would be to disconnect the battery for about an hour. That will reset the PCM and just might clear up the problem.

If that doesn't work, eliminate the fuel system as the culprit. You can check it by connecting a pressure gauge to the service port of the rail. Then check the pressures both when hot and when cold. It should be somewhere around 49psi...give or take a few pounds.

If the fuel system checks out, then you're into sensors...hopefully one of the above helps clear it up...or at least narrow it down. Let us know.
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saharatj98
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Joined: 22 Nov 2004
Location: Federal Way, Washington USA

PostPosted: Tue Nov 15, 2005 11:43 pm    Post subject: Reply with quote

The o2 and cat were replaced shortly before I got it back because it was ran until it did not start anymore. Nice huh? Love getting back a vehicle that was maintained like that. I am sure the check engine light must have came on long before the bad o2 destroyed the cat. I'll disconnect the bat tomorrow and let you know. I dropped the tank last month and cleaned up the filter since you can't replace it alone. I think fuel pressure is ok but I was going to check it. Reason being is you can crank it first for only a few seconds then hit it again and it will fire right up or sit there and crank on it probably longer than I'd want to and then hit it a second time and it fires right up. If the fuel pressure was low I would think it would not start up right away the second time after only blipping the key the first time when it will sit there trying for 20 seconds or so too which is redundant and hard on the starter anyways. I had crank sensor issues on my 2001 XJ 4.0 which did similar things but it would run rough at times and set a code and that started when it was only a few months old and happened two more times while I owned it.......When it ran rough I mean it was running on 4 cylinders! The TJ is only deviating by about 50 to 100 rpm.
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ThePhantum
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PostPosted: Tue Nov 15, 2005 11:52 pm    Post subject: Reply with quote

So it was basically run into the ground....that was nice of her.Rolling Eyes

Since you've tuned it up, changed the timing chain, etc. I would disconnect the battery before I did anything else. The PCM just might be working off some of that old data/history.
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T.O.W. Vehicle
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Joined: 15 Jun 2004
Location: Summerville, SC

PostPosted: Wed Nov 16, 2005 6:14 am    Post subject: Reply with quote

Might try turning the ignition to run and let it sit for ::30 and see what happens. If it starts then on the first attempt to START might be the pump/pressure.
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saharatj98
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Joined: 22 Nov 2004
Location: Federal Way, Washington USA

PostPosted: Thu Nov 17, 2005 8:36 pm    Post subject: Reply with quote

yeah, but it always starts fine cold. Just warm it doesn't want to start on the first try. After maybe 10 minutes or more since it has been shut off it will do this. It's almost like the fuel pump does not come on with the first try which does not make any sense. You can hear the pump come on if you listen closely. Maybe it is a computer problem? Actually, I just thought of something..... What if the fly wheel had a missing tooth or something? Then maybe the crank sensor would get confused? That would be intermittent though and would not matter if it was hot or cold and I would think the starter may make noise on occassion and it does not..... A bad crank sensor should set a code too..... This is weird....... I guess I should add that the idle prob is only warm too, cold it idles perfect.... Today when I drove it home and parked in the garage the idle was stuck at 1000. I even threw it in gear and let the clutch out to drop it and it still came right back up. Shut it off a few times and then it was normal again....... I think I may have a computer prob that is not setting codes?
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ThePhantum
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PostPosted: Thu Nov 17, 2005 11:18 pm    Post subject: Reply with quote

That's what I think too....it's either the PCM or a sensor. When it's cold ithe PCM runs the engine off a specific set of parameters (it runs a richer fuel mixture for example). Once the engine hits operating temperature, it starts using sensor data, coupled with stored history to run the engine.

What I think has happened is that the PCM is used to receiving sensor inputs from bad O2 sensors/cat, lack of a tune up, etc. and it's made adjustments to compensate. Now it's gotten some maintenance, a tune up, new O2 sensors...but it is still working with old data and trying to compensate in the wrong direction for those changes.

That's why I said try disconnecting the battery for an hour or so. Some people say it forces the PCM to "learn the engine" again, but that not quite accurate. It's more like clearing the cache on on a PC...actually...it's exactly like that. It clears the history and, forces the PCM to build a new set of historical data over the next 200 miles or so miles. It just might clear up the problem.
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saharatj98
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Joined: 22 Nov 2004
Location: Federal Way, Washington USA

PostPosted: Wed Nov 30, 2005 7:25 pm    Post subject: Reply with quote

Thanks for all the help. I did dis connect the battery over the weekend a week ago. Still the same.... I wonder, if somehow the computer is confused. If the shift light is computer controlled then maybe the computer or a sensor is causing the computer to think backwards? That could be the warm idle, warm start and light problem all in one. It would be more than a throttle position sensor though. Somewhere the computer recognizes when the engine is under load or not and adjusts accordingly. The light should only come on when the engine is under very light load or coasting and never in 5th gear. It still never does light in 5th but it should not be lighting up under acceleration and never under light load as it does now. Jeeps share so many common maladies I was hoping someone else would have had the same problem and already found the answer?
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saharatj98
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Joined: 22 Nov 2004
Location: Federal Way, Washington USA

PostPosted: Mon Dec 19, 2005 6:06 pm    Post subject: Reply with quote

Back again..... I did some more investigating and out of curiousity I checked my timing... At idle is approximately around 8 pos and I thought it should be around zero. It's a 1997 and still has a distributor, but you can't turn it. This thing still did the rough idle when warm and the hard starting thing before I replaced the timing chain and gears which were worn a year ago when I first got it back..... Made noise at idle went away when revved ect. I thought this could be my culprit but it seems I can not adjust it. I also checked my plugs which I just replaced also about a year ago. #1 has carbon deposits and the rest are fine. Also compression is around 125 on the others and only about 95 on #1.... Burns no oil and the first few cranks it bumped up like the others so I am thinking I have a valve problem.... I remember when I just replaced the exhaust manifold all valve stems looked the same inside the ports though last month.... Ideas? I think that V8 swap might be sooner than expected. No reason why this engine should be having probs at 143k other than lack of maintenance... Love it....
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