4.0 wont rev over 1600 rpm


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Old 10-18-2009, 09:55 PM   #1
chip9399
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Default 4.0 wont rev over 1600 rpm

just got this jeep, new wires plugs,rotor cap. engine wont rev over 1600 rpm, even when driving, fuel pressure is 39psi, starts to stumble and backfire, 1990 cherokee any help would be appr, thanks alot chip


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Old 10-18-2009, 10:20 PM   #2
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clogged cat converter maybe??
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Old 10-18-2009, 11:07 PM   #3
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Quote:
Originally Posted by Lyon View Post
clogged cat converter maybe??
that might cause it to overheat though.
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Old 10-18-2009, 11:07 PM   #4
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my guess would be something fuel related. pump or something to that effect.
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Old 10-19-2009, 12:15 AM   #5
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intake too. somethings choking the engine. check your filter and make sure its flowing, check all your hoses to make sure nothings kinked, the pressure may be there but make sure the cylinders are getting fuel. injectors might be bad
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Old 10-19-2009, 05:57 AM   #6
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Default no cat

there was no cat converter when i bought it,
it smooths out at 1300 rpm then get worst as u up the rpm,
fuel press is ok
ill check the injectors
could it be one of the sensors? which one to check first
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Old 10-19-2009, 06:16 AM   #7
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Moved to the right section for ya

I'd check the TPS or CPS.
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Old 10-19-2009, 07:00 PM   #8
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Quote:
Originally Posted by 2000XJ View Post
Moved to the right section for ya

I'd check the TPS or CPS.
Money is on the TPS.
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Old 10-20-2009, 09:25 PM   #9
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Check the firing order. Since the tune up was just done maybe you have crossed wires. Spark plug gap could be closed on one as well. May have to pull them.
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Old 10-21-2009, 03:55 PM   #10
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still no luck, has a new cps and a new tps, checked the ignition modual and is good, it like the timing isnt advanceing as the rpm tries to gain? distributor???? help guys
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Old 10-25-2009, 08:37 PM   #11
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Any suggestions.....
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Old 10-25-2009, 08:44 PM   #12
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Did you try what I said? Go 3 up in the thread.
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Old 10-25-2009, 09:18 PM   #13
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WIRES ARE CORRECT, IT IDLES SMOTHLY, will check plug gap in am, i have tried another dist,o2 sensor,coil, will try another,pressure reg and different injectors tomarrow also, i have a thought.....what about ground on computer under dash,???
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Old 10-26-2009, 08:22 PM   #14
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ok, originally you said it stumbles and backfires. Now it runs smoothly? Which is it? What did you change to make it run better? You might have more than 1 problem. If you can find a computer ground under the dash, then go for it. Check it out or just run an alternate ground to see if you still have the same problem. This thing is a 1990. It has injectors or a throttle body? Ok, so you don't have a clogged cat because there isn't one, how about a resonator or muffler? Is the exhaust strong or weak at an idle and when hitting the gas? It's a long shot but could be the computer not sending voltage to one of your sensors. Maybe the map sensor or something. You'll need a voltmeter and check the voltage going to the sensors before you spend even more money you don't have to. Good luck.

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Old 10-27-2009, 04:08 PM   #15
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it run smothly up to 1500 rpm then stumbles badly,injectors,


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