94 318 rough idle,bucks and drags when take off
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94 318 rough idle,bucks and drags when take off
My 94 ram has the 318, It only does this if it has set idling for about 7 or 8 min or if you drive really slow for about 200 yards.. it will try to die rpms go way down but never stalls. you can turn it off and crank it back up and it runs fine..check engine light doesnt come on...Thought it was the IAC. changed that helped some but still does it... what could it be...
Grand Champion
Joined: Apr 2010
Posts: 5,011
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From: Meeker, CO
Hmmm... I was all set to approach it as a high mileage engine that's getting too much oil in the cylinders, but you say that shutting it down and starting up fixes it. How long since that 02 sensor was changed?
Just in case, though, I'll ask: Is it using most of quart of oil every 3000 miles and the plugs gunk up with the thick carbon? If so, do compression and leak-down tests, and if they don't show bad rings or valves you may just need some new valve stem seals.
Just in case, though, I'll ask: Is it using most of quart of oil every 3000 miles and the plugs gunk up with the thick carbon? If so, do compression and leak-down tests, and if they don't show bad rings or valves you may just need some new valve stem seals.
Grand Champion
Joined: Apr 2010
Posts: 5,011
Likes: 6
From: Meeker, CO
Only 50k miles on the engine changes things. It shouldn't be loading up with carbon. How many miles on the chassis? How many on the 02 sensor?
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Grand Champion
Joined: Apr 2010
Posts: 5,011
Likes: 6
From: Meeker, CO
It'd be a good idea to get a code reader on there to see if it's got O2 sensor related codes in the pending queue. You'll have to get the reader on there not long after the symptom appears in order to catch it because if you wait too long the code will be cleared because the problem is intermittent.
A by-guess-and-by-golly test: Set up the failure conditions and when the engine starts stumbling, shift into neutral and rev the engine to 1500-2000RPM for about 15 seconds. If the symptom disappears when you close the throttle afterward and there's no smell of oil or unburnt fuel in the exhaust, the pre-cat O2 sensor is suspect.
Why I'm thinking in this direction: An old oxygen sensor that's on its way out will seem to work okay as long as it's good and hot, but when it cools it gives up values that indicate the engine is running rich, so the PCM compensates by driving the fuel:air ratio lean. When you rev the engine the greater quantity of hot exhaust gas flowing over the sensor warms it so it gives more accurate (more correctly "less inaccurate") values.
A good quality O2 sensor should last around 100k miles. If you know the pre-cat sensor that's in there is getting close to or has already passed that mark, then it'd be a good idea to replace it just because it's time to replace it and not even bother reading codes unless you're curious.
A by-guess-and-by-golly test: Set up the failure conditions and when the engine starts stumbling, shift into neutral and rev the engine to 1500-2000RPM for about 15 seconds. If the symptom disappears when you close the throttle afterward and there's no smell of oil or unburnt fuel in the exhaust, the pre-cat O2 sensor is suspect.
Why I'm thinking in this direction: An old oxygen sensor that's on its way out will seem to work okay as long as it's good and hot, but when it cools it gives up values that indicate the engine is running rich, so the PCM compensates by driving the fuel:air ratio lean. When you rev the engine the greater quantity of hot exhaust gas flowing over the sensor warms it so it gives more accurate (more correctly "less inaccurate") values.
A good quality O2 sensor should last around 100k miles. If you know the pre-cat sensor that's in there is getting close to or has already passed that mark, then it'd be a good idea to replace it just because it's time to replace it and not even bother reading codes unless you're curious.
