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I have a 99 Jeep Grand Cherokee with about 183,000 miles. Over the last couple of days it has developed a problem where when accelerating it will lose all engine power for about 5 seconds (rpms drop and and then regain power with a short burst of acceleration). It feels like it's running out of gas. I already replaced the air filter and fuel filter, those needed to be replaced anyway, but it didn't help.

Other than the power loss, it in general feels sluggish, like I'm constantly towing something. No check engine light. Any suggestions of things to check or other symptoms that I could look for that would help diagnose it?

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  • Which engine? Any oil consumption? Feb 19, 2012 at 21:16
  • In-line 6. I haven't noticed any oil consumption, I'm about 1000 miles into this old change and it's still at the top.
    – bmbaeb
    Feb 19, 2012 at 21:29
  • I'm noticing a little more of a trend with the problem. It seems as though it happens within the first mile and then it generally runs better, still feels heavy but it doesn't lose power. Doesn't seem dependent on the engine being warm or cold, it's happened both ways. Today I tried releasing the gas pedal and it seemed to recover faster.
    – bmbaeb
    Feb 20, 2012 at 16:46
  • Did you figure it out?
    – theUg
    Jan 26, 2013 at 20:31
  • Not yet, going to be looking into the EGR valve and the Idle Air Control next
    – bmbaeb
    May 30, 2013 at 15:01

6 Answers 6

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The 4.0L is generally a very robust engine so I think the problem is with the ancillaries. Here's what I would look at:

  • Fuel pressure. If the car feels like you're running out of gas, it might be that the fuel pump isn't supplying enough fuel or there's another problem with the fuel system like a leaking injector. Has the fuel mileage been suffering lately?
  • Check the ignition components like the distributor rotor and cap if it still has a distributor, leads and spark plugs. Especially the latter if they have more than 10k miles on them, plus they're the cheapest part to change :).
  • As PetroEkos suggested, check for vacuum leaks
  • Check the emissions equipment, you might want to change the PCV valve if it hasn't been changed recently.
  • If it runs rough when warming up and runs a lot better when it's up to operating temperature, I would check if all the ECU temperature sensors are working as expected. If the ECU thinks that the engine is warmer than it actually is, it'll inject less fuel than it needs during warmup.
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  • Thanks for the suggestions. Mileage has been rough, it's cold where I'm at so in winter mileage tends to drop but it seems like it's lower than it should be. I checked the spark plugs and readjusted the gap but I didn't check the rest of the ignition components, so I'll check those out. I don't remember the last time the PCV value was changed, I'll check that too and see if it's getting worn out.
    – bmbaeb
    Feb 20, 2012 at 16:40
  • What did the spark plugs look like? Sooty? Normal? Too white, as if the engine was running lean? Feb 20, 2012 at 16:52
  • Some black and a little white on the ends. I'm not an expert when it comes to engines but my dad thought they looked to be of normal wear.
    – bmbaeb
    Feb 20, 2012 at 17:03
  • 1
    The L-shaped electrode should be mostly white with current fuels but as long as it's not sooty I think the plugs sound OK. The whole thing also depends if you drive mostly short distances, if that's the case there's a good chance the plugs will have less white and more black on them. Feb 20, 2012 at 17:08
  • Thanks for the information. Sounds like it's more likely that it's something besides the plugs but I won't rule them out completely. I'll also check the ECU and see if it's malfunctioning.
    – bmbaeb
    Feb 20, 2012 at 17:16
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Does you engine have any vacuum leaks? They would affect your lower RPM power, and as soon as you lose that vacuum, the problem would seem to disappear.

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  • I'll give this a try later today.
    – bmbaeb
    Feb 20, 2012 at 14:45
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I had the same exact problem. It is the fuel injectors!!! Does the quick acceleration come followed by a clunk? I replaced them and problem totally gone on my 275,000 mile 97 xj

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  • if it is the injectors, did you replace all six of them ??? and if you didn't how did you find out which one was defective
    – user2676
    Jan 25, 2013 at 14:12
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Remove one injector wire at a time until you find the one that doesn't change the way it runs. Do it running

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It happened to me and it was the crank shaft positioning sensor but it also could be your cam shaft positioning sensor if it’s not the crankshaft one but mine was

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I have a 2000 cherokee with the 4.0. The engine hass less than 100k miles on it and runs perfect for the first hour. After that it doesnt seem to want to start, but after it does, I dont have enough power to get out of 1st gear. I let it set and cool and then it runs great again

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  • All electrical components face higher resistances when hot, so a failing ignition component might still work alright until it reaches a higher temperature . Also, if there is crack developing in an electrical component (e.g., coil pack), it will be worse when hot. So, when the engine is faltering, check each spark plug boot with an ignition tester to confirm the ignition's operation. Another possibility is a failing vacuum hose, which may work when cold but collapse when warm.
    – Carguy
    Jul 16, 2018 at 4:00

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