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Old 04-21-2011, 10:07 AM   #1
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Missing and bucking

I'm hoping this is just a simple tune up but when I slow down in 3rd or 4th gear and the rpm's get low say to take a turn. It's starts missing until I get the rpm's back up to say 2000 then it's pretty good. Any suggestions? Thanks

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Old 04-21-2011, 11:22 AM   #2
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Hard to say since you don't say what model or engine or anything and you haven't filled out your profile, but mine was doing similar things and it turned out to be the fuel pump going bad. First thing I would do is test the fuel pressure (assuming your Jeep is fuel-injected).

I applied the shotgun approach to my problem and replaced a bunch of stuff before testing the fuel pump because changing the fuel pump is a PITA and frankly I didn't want to do it. I learned the hard way that you can change out everything under the sun but if the fuel pump is going bad the only thing that is going to fix it is a new fuel pump.

Save yourself some time and at least rule out the fuel pump before you do anything else. Learn from other's mistakes, you don't have time (or in the case of a Jeep owner - the money) to make them all yourself.

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Old 04-21-2011, 11:32 AM   #3
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Sorry my bad! 1998 4.0 manual. Thanks for the input
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Old 04-21-2011, 12:58 PM   #4
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My '99 TJ 4.0L (114,500 miles) started doing the same the same thing about two weeks ago. Was roughly 500 miles from home and in the rain on the interstate. Called my regular mechanic after the check engine light came on. He said that it sounded like the throttle body sensor. Had that replaced once I limped home. Check engine light is gone, but it is still kinda jumpy on acceleration in 3rd and 4th gear. Going up a decent grade and kind of long incline on the highway at 60mph I lose 5-7 mph until I crest and then all is well. I replaced the spark plugs prior to all of this with Bosch Platinum2 plugs. I also have a K&N filter that was on her when I bought her last month. Any suggestions?
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Old 04-21-2011, 04:22 PM   #5
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Quote:
Originally Posted by Bubbabuzz View Post
My '99 TJ 4.0L (114,500 miles) started doing the same the same thing about two weeks ago. Was roughly 500 miles from home and in the rain on the interstate. Called my regular mechanic after the check engine light came on. He said that it sounded like the throttle body sensor. Had that replaced once I limped home. Check engine light is gone, but it is still kinda jumpy on acceleration in 3rd and 4th gear. Going up a decent grade and kind of long incline on the highway at 60mph I lose 5-7 mph until I crest and then all is well. I replaced the spark plugs prior to all of this with Bosch Platinum2 plugs. I also have a K&N filter that was on her when I bought her last month. Any suggestions?
I read somewhere on another forum that Jeeps don't like anything but standard plugs. I doubt that's your problem but I thought I would pass it along. If you haven't checked the fuel pressure I would start with that and rule out fuel pump issues. As someone else said on here: "Ask me how I know..."
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Old 04-22-2011, 07:44 AM   #6
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I had heard that about the standard plugs too. After I had purchased and installed the bosch platinum2's.This may be a dumb question, but how would I go about checking the fuel pressure? Any particular place to buy the fuel pump or will any parts house do? I've got a feeling I'll be dropping the tank here soon to replace mine.
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Old 04-22-2011, 08:07 AM   #7
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Quote:
Originally Posted by Bubbabuzz
I had heard that about the standard plugs too. After I had purchased and installed the bosch platinum2's.This may be a dumb question, but how would I go about checking the fuel pressure? Any particular place to buy the fuel pump or will any parts house do? I've got a feeling I'll be dropping the tank here soon to replace mine.
You'll need a fuel pressure gauge - Harbor Freight has some cheap ones or you can usually borrow one (with a deposit) from Autozone. There is a valve with a cap on the fuel rail (it looks like an A/C fitting) - I think I heard it called a Schrader valve. You remove the cap and hook up the fuel pressure gauge to it them start the Jeep and check the pressure. My 93 YJ 4.0 is supposed to run around 31psi at idle. I would think yours should be about the same. Search on the forum for a better description and more info- I am sure someone's done a more thorough job of describing the process.

As for where to buy the pump, I bought mine at Autozone (it's an Airtex) and its working fine - for now.

If you don't have the Hayes or Chiltons manual for your Jeep I would highly recommend you getting it. I have both for mine and they are a tremendous help. Holler back if I have confused you.
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Old 04-22-2011, 08:11 AM   #8
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You've seen several comments on Bosch plugs causing that problem, but you still want to replace other things instead of taking advice?

Why would someone ignore advice, then ask for advice?

What does the underhood label on your Jeep say about what plugs to use? That's just advice from the factory.
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Old 04-22-2011, 08:20 AM   #9
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it calls for copper plugs. when i first got mine i checked the plugs and did a tune up. basic autolite plugs are making it run better than the new splitfires that were in it prior.
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Old 04-22-2011, 09:22 AM   #10
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I've never seen the factory underhood label say copper plugs or Autolites. That's purely assumption.

The label give SPECIFIC MAKES, NUMBERS AND THE GAP TO USE.

Wouldn't ya think the people that designed the engine and heads knew what they intended it to use rather than the ex-McDonald's onion slicer at the parts house?

Just because it runs good in a Yugo or lawn mower doesn't mean it will in other engines.

It's like saying some Barbeque sauce has sugar in it - so use it on your Wheaties.
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Old 04-22-2011, 12:27 PM   #11
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while i didnt say that autolites were the recommended plug from the factory, i did point out that even generic copper plugs were better than the wrong expensive plugs. here is a quote from you rrich saying basically the same thing i said, except recommending champions. most jeepers recommended champions but as you probably know, the old favorite truck plug is no longer in production. as for autolites, i have a 4-cylinder engine, paying twice as much for plugs isnt going to make it go any faster or run better. it is what it is.

"Use plain old Champions - use what the underhood label calls out or what the parts house computer says - except don't go by what Autochina says - their computer is wrong!

Avoid the gimmick plugs, splits, plats or any and all of the
trick plugs.
Gap them at .035."

i guess this leaves what? copper plugs?
i see a lot of posts on this forum about using what is recommended under the hood, why doesnt someone just say what is recommended instead of acting like that? many older vehicles might not have that label anymore so help the poor guy out if you have the knowledge, otherwise dont be down on others trying to help. unless someone has facts about what is right, the best that can be offered is experience because opinions are useless.
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Old 04-22-2011, 01:11 PM   #12
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Simple - If it works for you - don't fix it!

Some older, or repainted vehicles no longer have the underhood label. A quick call to a dealership usually results in what they use successfully, unless it's a real old or or no longer made vehicle. Finding out what the best plug for a 1937 Vauxhaul wouldn't be easy.

The OP said he had a problem - the same problem that so many have experienced with Bosch plugs. I was trying to save him from all the work and expense of replacing a fuel pump when it's very likely the problem stems from the Bosch plugs, even if they are new.

Plain old plugs may not last near forever, but they seem to work the best over all the "trick" and performance plugs.

Someone recommended getting and using a fuel pressure gauge before arbitrarily replacing the fuel pump too. That too would be a good move.

"""""i see a lot of posts on this forum about using what is recommended under the hood, why doesnt someone just say what is recommended instead of acting like that?"""""
It would be nice - but the recommended plugs on the labels have changed over the years, 4 cyl, 6 cyl, emission equipment also varies from state to state. The label on THAT PARTICULAR VEHICLE is the best way to get the right ones.

"""""the best that can be offered is experience because opinions are useless. """""
That's my opinion - based on many years of experience owning repair shops.

If it isn't broken -- don't fix it!

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