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Old 01-10-2014, 06:27 PM   #1
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engine running rough

so yesterday i drove my jeep and when i started it up it ran a little rough, on start up it was at 1200 rpm give or take and then went down to a 1000 and stayed. whats with this ?? i checked the oil and its low and time for an oil change, i haven't changed the oil sense i bought it in june so i don't know what oil he was using so can i just put a synthetic in it ? and with that what weight of oil and what kind is the best ? thanks

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Old 01-10-2014, 10:53 PM   #2
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10W-30 is fine in these old engines and synthetic or not no issues. Oil has nothing to do with running rough.

When you get a high idle and then rough running it is a sign of a possible vacuum leak.

Check all the rubber hoses they get old and crack.

You may have a leak also at the power brake booster hose or fitting check closely that on you should be able to hear.

You can spray something like carb cleaner in the areas of the hoses and if you see a rise in idle speed you have a vacuum leak but be careful it may also catch fire.

Once you have fixed any leaks or bad hoses then see what it does.

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Old 01-11-2014, 01:02 AM   #3
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Quote:
Originally Posted by jokerchief462 View Post
10W-30 is fine in these old engines and synthetic or not no issues. Oil has nothing to do with running rough.

When you get a high idle and then rough running it is a sign of a possible vacuum leak.

Check all the rubber hoses they get old and crack.

You may have a leak also at the power brake booster hose or fitting check closely that on you should be able to hear.

You can spray something like carb cleaner in the areas of the hoses and if you see a rise in idle speed you have a vacuum leak but be careful it may also catch fire.

Once you have fixed any leaks or bad hoses then see what it does.
okay and where do the vacuum hoses start ??
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Old 01-11-2014, 01:03 AM   #4
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and when i do the oil change, i don't know if he ran synthetic or normal so it doesn't matter if i run a synthetic and it mixing with what ever is left in the motor when i change it ?
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Old 01-11-2014, 10:17 AM   #5
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Even if you put in synthetic and the previous owner used regular oil, there should only be a little residual amount left over. You could always buy the cheapest stuff, run it for a few hundred miles, and then change it again with your preferred type. Get a useless Fram oil filter to put in for your "cleansing" and then get yourself a good K&N filter when you put in the good oil.

K&N HP-2007 - K&N Wrench Off Oil Filter for 87-90 Jeep® Wrangler YJ, Cherokee XJ & Comanche MJ with 2.5L I-4 or 4.0L & 4.2L I-6 Cylinder Engines - Quadratec
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Old 01-11-2014, 10:20 AM   #6
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I've had my car AND my motorcycle do that and, surprisingly enough, they both stopped doing it when I stopped using gas from AM/PM gas stations. I use 76 stations now and both run like a charm. Go figure. Bad gas messed them both up. All of my motorcycle riding buddies have had similar experiences at AM/PM gas stations. They'll now use 76 or Chevron and occasionally 7-11. You might also run some Sea Foam through. Get a can at the auto store and pour it in with a refill and it'll clean your system up a bit. Good stuff!!!
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Old 01-11-2014, 01:12 PM   #7
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thanks man

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