I only recommend this mod if you live in a climate that is primarily HOT!
This mod richens up the overall mixture and WILL drop your gas milage in colder climes and/or during the winter! I lost 2 mpg during the winter and got it back when it warmed up!
If you're really adventurous, you could figure out the cold / warm / hot resistance on this thing and make a resistance box that will accomplish the same thing without relocating the M.A.T.
If ya do that - write it up & send it in to update this article.
A quick and easy way to pick up a few horsepower is to move your manifold air temperature sensor (M.A.T.) off the manifold and away from the heat generated by the engine. This is done in order to fool the computer into thinking the motor is getting cooler intake air and coaxing a slightly richer fuel mixture out of it.
You'll most likely have 90% of what ya need laying around already so your total cost for this project should be well under $5.00. The only specialty item you'll need is a threaded brass plug from your local hardware store's plumbing department that cost me less than a dollar. You'll need this in order to plug the sensor's old intake manifold location.
First ya need to locate your M.A.T. sensor. In it's stock location, the M.A.T. is located on the intake manifold at this location on one of the rear intake runners.
(*Note! - I have my brake booster line running into the stock MAT location for reasons unrelated to this tech article! You'll have to plug this port after relocation.)
Disconnect the sensor's connector. You'll need to gently lift the connector's tab up to clear the little tab lock in order to slide them apart. Inspect the connectors for oxidation & crud. Clean with electrical contact cleaner if needed & apply dielectric grease to the pins.
Using an open end wrench, remove the M.A.T. sensor from the intake runner.
Inspect the sensor for carbon/goo/tar-like crud deposits. Take it outside and clean it up with carburetor cleaner. *Note! - If the sensor was thickly coated and a lot of crud came off with the cleaner be aware that (on older XJ's with EGR valves) this can be a sign of a faulty EGR valve. Another bad EGR confirmation is stalling at stops and/or spitting through the throttle body under acceleration. Please see engine diagnostics.
Now ya need to determine the mounting location on the air tube. Look at the final picture below for a suggestion. Note that the location does not interfere with any hoses or the filter and flex tube connection. Mark a location that won't interfere and be easy to drill using your drill press or hand drill. After marking, disconnect all hoses and air filter from the air tube and remove the air tube from the vehicle. In the case of my Rusty's Air Tube, it is held on with one bolt located where the old air box was.
Now, using a small steel punch, strike a small dimple dead center where you want the M.A.T. sensor to be on the air tube. Select a drill bit that is -SLIGHTLY- smaller than the sensor's threads. Err on the side of caution since you can always make holes bigger but it's tough to shrink one! (Hey! Watch those jokes! )
Using either your drill press or hand drill, carefully drill straight in on the mark previously made on the air tube. Deburr with a rat tail file.
Select a tap that matches the sensor's threads EXACTLY. Don't do this on the vehicle as you will have metal shavings INSIDE your air tube when this is over that MUST BE CLEANED OUT or you risk CRITICAL ENGINE DAMAGE! Clamp air tube in a vice. You can wrap it in cloth, or use plywood on the vice's jaws to prevent scarring. Insert the tap in it's proper handle and using some 3-in-1 oil CAREFULLY begin threading the hole for the sensor. You'll have to work slowly, backing out often to clear out shavings. Use plenty of oil to help ease the cutting process. Once you've finished threading the hole, deburr the inner and outer surface of the air tube being careful to avoid damaging your newly threaded hole. Test fit and remove sensor. Clean up air tube with some carb cleaner and then with some glass cleaner. Dry it off and touch up with spray paint as needed.
Reinstall air tube and connect flex tube to verify air tube is where it needs to be. Tighten air tube down snug.
Test fit sensor and measure from new location to sensor's connection to engine wiring harness. Measure with a tape measure following along a logical, OUT OF THE WAY path so ya won't have to move it later to do other service work. Do NOT run wires in a straight line and be sure to leave plenty of slack to allow for engine movement in relation to body mounted air tube.
Remove sensor again and clip M.A.T. sensor's wires mid way between sensor and it's connector. Using a soldering iron and rosin core solder (for electrical connections), extend each wire until both are to the proper length for connection. Just keep track of which wire is which or extend one at a time. (This didn't matter on my 1990 XJ, the M.A.T. sensor is just a varistor in series with this circuit.) Use some teflon tape and fully install the M.A.T. sensor in it's new location. Reconnect the sensor to the engine wiring harness, wrap the wires with wire loom and zip tie into place.
Here's the final location.
Clean up yer mess! You're done!
*Note! - Stay away from crimp connectors as much as possible,
especially on engine sensor connections under the hood. You're asking for
engine performance trouble later on due to poor input from sensor circuits to
the computer with crimp connectors. If ya do use one, pull off the insulator
and solder the connection after crimping, then shrink wrap or tape it up.
Use heat shrink tubing where possible although with soldered connections you should be fine with electrical tape.
After cleaning with Electric Contact Cleaner, Dielectric grease should be used on every plug type connector you have. NAPA carries both.
If you have pics of your own repairs or can suggest other methods - please contribute your ideas (and pictures) to this article!
October 11, 2006