Gas Mileage?

I'm not sure that this is a good idea. very extreme fire hazard.

I wouldn't try it either. I just replaced my Plenum & so I know there's no oil/gunk in there yet. For now I'm happy w/ my 13-17mpg.

I sprayed carb cleaner into my MAF then replaced the air filter tubing (on Cougar) and then started the car. I'd let it run for a bit revving to about 3k RPMs and blipping the throttle. You could see crud come out of the exhaust. I then took off my upper intake manifold (not a fun chore) and cleaned the intakes. They were nasty.
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I wouldn't spray carb cleaner in the plenum, but if your injectors are dirty enough to affect the spray pattern, fuel injector cleaner can improve your mileage & performance. The single best thing you can do for your gas mileage is to keep your right foot off the floorboard as much as possible. If you've modded your car, keeping it tuned with the air-fuel ratio as close to 14.7:1 most of the time helps too. I have seen my mileage drop from 19-20 to 13-14 by forcing it to run open loop @ 12:1 all of the time. It had more power, but the mileage wasn't worth it to me.

Check this out, I know it's for an explorer but it goes with this thread. (I did this to my 92 explorer with 220k miles because it was pinging like crazy and a friend did this to his and told me about it. The results were amazing, no more pinging, more power, and a little better gas mileage) I also ran a little bit of water (1/2 cup) through it at the end and it seemed to help more then the carb cleaner but you have to play with the throttle because the engine will want to die. Water is and old trick used with Carbs. Any way I though it would be of interest especially since it is a Ford TSB. I used Gummout liquid fuel injector cleaner in a bottle, not a spray.

Article No. 01-19-7 · ENGINE - 4.0L OHV - CARBON KNOCK ON ACCELERATION · NOISE - CARBON KNOCK ON ACCELERATION - VEHICLES EQUIPPED WITH 4.0L OHV ENGINE ONLY
Publication Date: SEPTEMBER 24, 2001

FORD: 1990-97 AEROSTAR 1990-2000 EXPLORER, RANGER
ISSUE:
Some vehicles equipped with the 4.0L OHV engine may exhibit an engine noise which may be perceived by the customer as a piston/connecting rod bearing knock. This carbon knock is heard only under load during the drive cycle. Carbon knock is a customer drive duty-cycle phenomenon that cannot be repaired with an engine exchange. This may be caused by carbon build-up within the combustion chamber.
ACTION:
Verify condition. If normal diagnostics fail to correct the condition, de-carbon the combustion chamber to help quiet the carbon knock noise. Refer to the following Service Procedure for details.
SERVICE PROCEDURE
1. Use Motorcraft Carburetor Tune-up Cleaner PM-3.
2. Carbon removal:
a. Disconnect canister purge line from throttle body.
b. Attach a vacuum line to the canister purge port.
c. At hot engine idle, allow the engine to ingest 1/2 to 2/3 of a can of Motorcraft Carburetor Tune-up Cleaner. Use caution not to ingest too quickly due to potential hydro-lock issues.
d. Shut engine off and allow it to soak for one hour.
e. Start engine, allow engine to ingest the remainder of the Motorcraft Carburetor Tune-up Cleaner.
f. Remove vacuum line and re-install canister purge line.
g. Road test vehicle at 3500 RPM for 2-3 miles.
h. Repeat above procedure two times for a total of three times.
i. Change oil and filter.
3. Review the customers' driving habits. The recommended drive cycle should include daily periods of engine operation above 3,000 RPM, such as a brisk acceleration from a stop position. This will break/burn the carbon off the piston head.
4. Use regular unleaded fuel, 87 Octane. Mid-grade and Premium fuels may increase the probability of carbon buildup, leading to a knock noise.

PART NUMBER PART NAME
PM-3 Motorcraft Carburetor Tune-up Cleaner
OTHER APPLICABLE ARTICLES:
NONE
WARRANTY STATUS:
Eligible Under The Provisions Of Bumper To Bumper Warranty Coverage
OPERATION DESCRIPTION TIME
011907A Remove Carbon From Combustion Chamber (Includes Time To Perform Procedure A Total Of Three Times) 1.6 Hrs.
DEALER CODING
BASIC PART NO. CONDITION CODE
6108 42
OASIS CODES:
497000, 615000, 702000, 702100