Towncivilian

Adding to the fluid type concern above, you likely need to overfill the trans too. See this topic.

Be sure to change the diff and transfer fluids and regrease both driveshafts and maybe the front wheel bearings. Water entry is bad for lubricants. If you off-road often, cheaper conventional fluids changed at shorter intervals will save money over synthetic lubes.

Still, I'd fix the other codes first before diagnosing the knock sensor.

Short trips do not allow the engine to warm up to operating temperature. The engine runs richer, consuming more fuel and also contributing to more fuel dilution of the oil. If you primarily do short trips without allowing the engine to reach operating temperature, take it for a run on the highway weekly to get everything nice and hot to boil off any excess moisture build up. If you have 4WD, install manual locking hubs. Your 2002 does not have wires. It uses ignition coils, one on each spark plug. If you're around 105k miles and don't know whether they were replaced yet, replace them with new OEM ones. See here for a guide on spark plug replacement. Run a fuel system containing polyether amines (PEA) such as Chevron Techron, Gumout Regane, or Redline SI-1 for a couple tanks back to back to thoroughly clean the fuel system. PEA cleans without leaving behind its own deposits as other cleaners might. It's better to allow things to sit for a while and let the cleaner do its work instead of blowing through the entire tank during a highway drive. Air filter takes all of 5 minutes to replace. If it looks crazy dirty, replace it with a Wix/NAPA Gold or OEM one. Fuel filter ever been changed? If not, see here for a guide on changing it. Change to a synthetic 75W-90 in the differentials, this may improve average MPG slightly. Mobil 1 gear oil is great and can be had for very cheap at Advance Auto Parts if ordered online using discount codes then picked up in store.

P0325 as mentioned above is knock sensor. It does NOT necessarily indicate that the KS itself is malfunctioning; it could just be a side effect of another code. P0115 & P0125 are both the engine coolant temperature sensor. Check its resistance following EC-142. Replace if necessary. P0505 is the idle air control valve. Clean both it and the throttle body using throttle body cleaner spray. P0705 is the inhibitor switch for the transmission. Try following the component inspection procedure on page AT-90.

As far as I know there hasn't been any guides on removing the fuel tube and intake manifold. The FSM would be your best help here. It looks like there are a couple more gaskets - [14035] GASKET-MANIFOLD. If you want the exact part number you can PM me your VIN. If the fuel pressure regulator has to come off, there are O-rings which must be replaced and then lubricated with new engine oil prior to their installation.

Hell, if it's free, go for it!

KS is in the bottom center. If you are replacing your PCV valve, you need the rubber grommet that goes around it (11812-41B00 INSULATOR-). You can measure the resistance of the knock sensor at its terminals. See EC-327, step 4. EC-323 pictures the knock sensor's location.

You are wasting your money changing M1 so early. Change it at 5k minimum, or switch to conventional oil if you insist on wastefully short oil change intervals.

Today I changed my rear differential fluid. I used the 13mm Harbor Freight drain plug socket. It fit in quite well. I used a 1/2" to 3/8" adapter. The fill plug loosened off with a couple raps on a 24" breaker bar. The drain plug also loosened easily using a slightly shorter breaker bar (actually a broken torque wrench with its ratcheting mechanism still functional). I had no problems tightening the plugs either using a working, unabused torque wrench to 50 ft-lbs. The old fluid was Valvoline High Performance (white bottle) 80W-90 gear oil in use for approximately 11k miles. There was some fuzz on the drain plug magnet, but not a giant mushroom cloud. The fluid looked amber and clear when draining, but in the drain pan it looked greyish. 3 quarts of Mobil 1 75W-90 gear oil went in. I used the gear oil pump that fits in both quart and gallon jugs. It made the job significantly easier and cleaner, and I was done with the entire service in approximately 45 minutes.

All R50s have the RE4R01A transmission. 01-04 have the HD variant of this transmission. The bellhousing is different between the engines so a 01+ trans won't fit your 98. The part time transfer case is identical on 01+ to the 96-00 tcase I believe.

I was asking the OP.

Use any DOT 3, 4, or 5.1 fluid for both the brakes and the clutch fluid. Each has higher minimum wet & dry boiling points of the fluid than the previous. DOT 4 fluid is easily obtained in most parts stores. Out of curiosity, what will you be putting into the diffs & trans? What engine oil & filter do you run and what is your typical change interval?

No and no.

PSF is basically ATF without the friction modifiers which would obvioisly be useless in a power steering system. They are of similar viscosity and will mix fine in most vehicles. Honda PSF is proprietary, but I digress. ATF isn't chock full of detergents (not nearly as much as engine oil anyway) since transmissions don't need to deal with the combustion process and its byproducts, blow-by, intake air, etc like engine oils do. Hydraulic systems like clean fluid though so additional filtering is always a great idea.

FSM specifies Nissan PSF II and lists Dexron III as suitable. Synthetic ATF is the better choice.

Power steering fluid reservoir. Use synthetic ATF for better cold weather operation and lowered operating temperature of the P/S system. Use a turkey baster to siphon fluid from the reservoir. Your brake and clutch fluid appears dark. Have they ever been flushed/bled?

3M generally makes excellent products. I've never used this kit, but I wouldn't hesitate to do so. I saw this deal posted over at Bob Is The Oil Guy as well.

Can't find the breather in the 98 AT section, sorry.

Greased my driveshaft. The Harbor Freight grease gun I was using broke, so I bought a Plews grease gun from Walmart. It seems to be better quality so far and was easy to prime and remove from the grease fitting. I also switched to Valvoline DuraBlend grease (from SuperTech Moly-Lithium).

I would probably drain via the drain plug, drop the pan and change the strainer, button it back up, add a gallon of cheap Dex 3 fluid then use your preferred fluid via the cooler return line (entire transmission capacity + 2 to 4 quarts).

Nope. The instrument cluster is not electrically compatible either.

You should never need to replace an in-tank fuel filter unless you're replacing the fuel pump. Don't worry about it, just replace the in-line filter in the engine bay.

If your fuel filter looks ancient or you don't know when it's been last changed, change it! A partially restricted or clogged filter can put more strain on the fuel pump. Though I don't think this has anything to do with the humming, it's a good idea regardless.

There is a window limiter switch. Reset it if you haven't yet - instructions are in this post.