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Unread 02-05-2007, 05:32 PM   #1
rbluhm
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Problem with misfire on acceleration 98 4.0

I have a 98 cherokee 4.0 that misfires on acceleration. Now it does it only after I have run
the Jeep (warmed it up) then after it sets for about 2 hours or so usually after I take off
from the first stop sign, it lasts for about 10 seconds. After that it runs perfect. The Jeep dealership has, done the following: changed TP sensor, MAP sensor, oxygen sensor, coil, distributer cap, plugs, wires, air cleaner, they have done an engine combustion cleaning and it still does it. They have done a computer recording of it when it acts up and have told me that the map sensor reading shows a drop in vaccuum. They are now scratching their heads wondering what to do next. The Jeep runs perfectly otherwise. Any help would be greatly appreciated.

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Unread 02-05-2007, 05:41 PM   #2
bee guz
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Try tightening the intake maniflold, could be loose bolts, on the intake of the throttel body is loose, and sucking air, just a guess
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Unread 02-06-2007, 09:42 AM   #3
rbluhm
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98 cherokee 4.0 that misfires on acceleration

I had the dealership check the intake and throttel body for leak and they said that they were tight. any other ideas?
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Unread 02-09-2007, 08:51 AM   #4
rbluhm
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still a problem

My Jeep stopped doing it for 2 days after checking the intake being tight and throttle body being tight and fter 2 more combustion cleanings but now is doing
it again just as bad. My bill is getting huge and am ready to sell it but who's going to buy it like it is? Please help does anyone have an idea.
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Unread 02-09-2007, 05:38 PM   #5
balloo93
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Is the MAP seal on the TB tight? Is that the only code that is being thrown?

Have them remove the IAC (Idle Air Control) motor and clean the metering rod on it and the housing as well.

Maybe have them check the air temp sensor as well and make sure it is functioning properly.
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Unread 02-11-2007, 12:48 PM   #6
moroyoqui
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is it misfiring or a stumble? try checking the fuel system. let me know what is going on....
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Unread 02-11-2007, 06:11 PM   #7
rbluhm
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It sounds like it is backfiring. But the popping sound comes from under the hood.
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Unread 02-20-2007, 09:00 PM   #8
rbluhm
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not giving up

checked the MAP sensor seal looked good the dealership connected a fuel pressure guage and taped it to the hood hile I drove with and when it was doing its backfire thing the guage held steady so they are ruling out fuel problem. does anyone know if the coolant temperature sending unit could make things act up like this I am thinking of having them replace it for the heck of it.
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Unread 02-20-2007, 09:05 PM   #9
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forgot to say

forgot to say they changed the air temperature sensor too
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Unread 03-05-2007, 06:41 PM   #10
rbluhm
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TSB on 97 and 98 4.0

Just an update, I have found out that the was a technical service bulletin on my 98 4.0 which calls for heavier duty valve springs. It is a 3 hour job. I have had them replaced and it has been 2 days so far and all is well. Hope it continues.
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Unread 03-06-2007, 04:17 AM   #11
Rogo98Sport
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Quote:
Originally Posted by rbluhm
Just an update, I have found out that the was a technical service bulletin on my 98 4.0 which calls for heavier duty valve springs. It is a 3 hour job. I have had them replaced and it has been 2 days so far and all is well. Hope it continues.
Would You happen to have the TSB number??
I've been having the exact same symptoms with my 98 4.0
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Unread 03-06-2007, 06:31 AM   #12
jlmclean
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Hope the valve springs do the job but normally a weak spring would cause problems at higher rpm. I'm not saying that they are not the problem because a lot of times things don't work like you think they should. If the problem comes back, I'd check everything that has to do withe the fuel mixture, especially at low rpm. A lean condition will make an engine miss and sometimes backfire throught the intake. I don't think the TPS is adjustable on your engine but locate the specs for it and make sure you have the correct voltage at closed throttle. As I've found many times, just because you installed a new item, that dosen"t mean it's working up to specs. I don't think the manufacturers have high quality test anymore anyway. Especially China and Tiawan.
Good Luck and Post the results after you've driven it a couple more days.
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Unread 03-06-2007, 09:12 AM   #13
CJ7-Tim
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I am thinking heat soak and the fuel injector #3 heat shield TSB or the fuel pressure check valve on the fuel pump. Any problems with long crank times before starting? The gas in the fuel rail can vaporize and you get good old vapor lock (rough running) until you refill the fuel rail. Search the forum for these topics.
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Unread 03-06-2007, 01:14 PM   #14
Rogo98Sport
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Quote:
Originally Posted by jlmclean
Hope the valve springs do the job but normally a weak spring would cause problems at higher rpm. I'm not saying that they are not the problem because a lot of times things don't work like you think they should. If the problem comes back, I'd check everything that has to do withe the fuel mixture, especially at low rpm. A lean condition will make an engine miss and sometimes backfire throught the intake. I don't think the TPS is adjustable on your engine but locate the specs for it and make sure you have the correct voltage at closed throttle. As I've found many times, just because you installed a new item, that dosen"t mean it's working up to specs. I don't think the manufacturers have high quality test anymore anyway. Especially China and Tiawan.
Good Luck and Post the results after you've driven it a couple more days.
I get the same problem but the Jeep runs fine when I floor it thus eliminating the weak spring issue since it would most likely occur at WOT...
Could it be carbon buildup on exhaust valves??? I know 99+Grand Cherokees have a TSB on that.
I think my next step in trying to find out what the f... is wrong with this thing would be SeaFoam treatment...
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Unread 03-07-2007, 07:08 PM   #15
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Third day results

Tonight it did it again, backfire through intake. The temperature here in Wisconsin tonight is 10 degrees. For the last couple of days it did not do it and the temps were in the 30's and 40's. I cannot remember it do it any time the temps were above 40. The good news is the temperatures are getting warmer with spring coming but the bad news is that I have done all the work on it without solving the problem and if the temps get warm soon their will be no way to test the problem till next winter, if I still own it. I probably should have posted the fact earlier that the cold weather triggers it. With this info does it narrow down the things that may be causing it? Thanks
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