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Old 09-02-2013, 08:32 AM   #1
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Help!

I recently bought a 98 TJ 4 cylinder, when I initially test drove it, all was good, it had a 1/4 tank of gas, so I filled it up with 87 unleaded. Literally minutes after filling up the guy I bought it from text me and said to use premium gas and to not buy at the store I bought it from.

So I had bad, low grade fuel, and it was sputtering bad when at low RPMs. So I got it down to right under 1/4 tank, and gave it a tune up (plugs, wires, rotor, and dist cap, changed oil and filter). After this it was still sputtering, not idling worth a crap.

So we put some B12 Chemtool in it, and then it died. After reading about the Chemtool, I obviously used too much (the whole can). It would turn over and backfire some, but thats it.

So we got 10 gallons of premium gas and filled the jeep full, and still nothing, would turn over and backfire randomly, but nothing else.

What can I do?!?!??!?

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Old 09-02-2013, 08:55 AM   #2
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If the engine won't run properly on the octane level it was designed for, 87 octane, something is wrong with the engine. Ask the guy you bought it from if he installed one of those computer chips which can raise its octane requirement.

And 87 is not "low grade" fuel, its quality is as good as 91 octane... the only difference is the octane level.

I'd first clean the throttle body with an aerosol can of Throttle Body Cleaner, spray it into the throttle body with the engine running. Spraying into the throttle body with the engine at idle RPMs can make the engine stall but that is ok, that is a sign the cleaner is getting into a part of the throttle body called the Idle Air Controlller which is what controls the engine's idle RPMs.... the IAC is the engine's sole source of air at idle RPMs so if it's not clean & not letting enough air into the engine at idle, the engine won't run well.

How does the engine run when you hold it at higher RPMs with the gas pedal?

It's ok to raise the engine RPMs a tad at times while spraying the Throttle Body Cleaner into the throttle body but the more cleaner you can get into the engine without also holding the RPMs up with the throttle linkage, the more cleaner that will make its way into the Idle Air Controller.
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Old 09-02-2013, 09:04 AM   #3
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No he did not install the chip. And yeah that makes sense about the fact that it should run on 87.

When holding down the gas pedal and giving it higher RPMs it is fine. And if you hold it at a higher RPM, and ease off of it, it idles ok. If you turn on the A/C while idling it will usually die.

It it the worst when taking off or making a turn and dropping into 1st at lower rpms.

And right now the thing will not start at all.
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Old 09-02-2013, 09:41 AM   #4
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It won't start even if you hold the accelerator pedal down a tad?

If not, try this... cycle the ignition switch 5-6 times... on-off-on... so the fuel pump can run 5-6 times before you try starting the engine. After you've cycled the ignition switch on-off-on those 5-6 times, try starting it & see what happens.
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Old 09-02-2013, 10:27 AM   #5
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I am going to try that. Also checking fuel PSI, what should it be?
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Old 09-02-2013, 10:28 AM   #6
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Fuel pressure should be 49 psi +/- a few lbs. either way.
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Old 09-02-2013, 11:11 AM   #7
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Ok fuel psi is good. I tried what you suggested and nothing. Fuel pump is kicking on and getting fuel to tbi.
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Old 09-02-2013, 01:06 PM   #8
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Well it was the dist rotor. I replaced it with the old one and now its starting right up.

But it's still sputtering at take off. When you start it up it'll bust right off, but if you give it a little accelerator it initially bogs down, and it doesn't matter if you give it a little or a lot of accelerator, it still sputters/bogs down, but it will eventually level out. It also does it when shifting from 1st to 2nd.

I dunno what else to do other than pull the fuel filter and check it. But I know it's getting gas to TBI.
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Old 07-31-2014, 12:39 PM   #9
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Coil?

I would go through the TBI cleaning process as described in the previous post. You probably loosened up some stuff with the Chemtool and it needs to finish cleaning. What RPM is it idling at? Also, mine did something similar awhile back then completely died. It was the coil.
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Old 07-31-2014, 02:30 PM   #10
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Don't think any TJ ever had a TBI as that stands for throttle bottle injector or injection and all TJ as far as I know have injectors in the intake manifold not the throttle body so how the hell should you be getting fuel to the TBI the throttle body should be and stay dry as a bone as it is upstream from the injectors

Do you have some hybrid setup with a non TJ engine or am I missing somthing

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b12 , backfire , fuel , tune up

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