ka24de 97 altima cylinder misfire #'s 3 & 4

[lsvteksol]

I bought this car about a week ago and the engine runs very rough at idle, but only after it warms up. I was told by the guy that sold me the car that is was a headgasket but my heat still works and I'm not losing any coolant. When the MAF is unplugged it runs fine. When the AC is on it runs a little better. I also had the check engine light read and it was (MAF, Knock Sensor, and cylinders 3/4 misfire). I assume it's knocking because of the misfire, so what could it be??? I don't think it's a head gasket. Imput from an experienced mechanic would be greatly appreciated. Thank you!

[lsvteksol]

can anyone help me with this? Please

[5upra]

Does it perform like supposed to under acceleration? for now a new maf would help. how much diagnosis are you willing to do? could be a HG, O2, or maf problem.

[OldmanPurdy]

A headgasket is a compression leak so if you unscrew your coolant resivior (when its cold!!) and start the engine up you should see bubbles coming to the surface of the resivior if ithe gasket is blown. Check that even though it sounds like its fine, after that I would check the maf sensor since they are a common problem on Ka24de's and a faulty one can give a rough idle which results in misfires which can result in triggering the knock sensor. Also when the maf is unplugged it runs in failsafe mode where it bypasses the maf so if it runs well there like you say it does then that is probally the problem. A brand new one is around $200-$300 so try and get used or better yet borrow on from a friend to see if it works before buying one.

[OperationZ]

Probably your inake manifold gasket, we're replace one right now and this is the second job i've seen have this problem.

Joe

[driftingmy240sx]

use carb cleaner and spray the intake gasket if the rpms change when you spray it you know the intake gasket is at fault. this is very common for the 2.4 altimas

[NISTECH]

Like the last 2 posters said, intake gasket. Spray right behind the throttle body where the intake manifold meets the head. What you will find when you pull the intake is the #4 cyl portion of the gasket has been sucked upward from the bottom of the port. Very Very common on the altima. You do not need to seperate the upper intake plentium from the lower intake manifold to do this. However you need to remove the PVC baffle from the front cover toward the fire wall to give clearance to the water pipe dropping down from the intake manifold. You will also need to detatch the p/s pump from the block and head and push it back to give additional clearance.Even after doing this it is still going to be a bear to get to all the intake bolts.

[driftingmy240sx]

nistech, email me at [email protected], i have a little trick to avoid all that water pipe removal.

[3Q Jay]

.....and.... while the intake is off i would definitly change the knock sensor (can't get any easier access), replace the pcv valve (you will see what a pain it is to do it later), and not least, replace all the water hoses on the backside of the block/underside of plenum. there is one 5/8 inch dia water hose near the pcv hose that is next to impossible (but not impossible, as i learned my first time) to do with the intake mounted to head.

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