Alright guys, My gas mileage is an insult to hondas everywhere. I get about 150 miles to the TANK, yes TANK. I have no CEL codes, I put in a new FITV, IACV, spark plugs, and cleaned the cap towers inside the distributor, oil change, royal purple oil, transmission flush, new fuel filter, new tires. I had bad gas mileage before and after these changes.

A mechanic said it was probably my MAP sensor going out. I bought a map sensor $100+, and it turns out, my motor doesn't even have a map sensor (from my honda mech) He said something about it's a OBD0 motor and the intake manifold was something else. Maybe i got that backwards... What exactly adjusts the fuel/air ratio on a motor that has no MAP or MAF? I can smell i'm running pretty rich sometimes.

My wires are in good condition with little resistance. I get a bright blue spark at the plug. The plugs are gapped correctly, and are all in good condition. Fuel pressure is where it should be. Alignment is good too.

Can't seem to figure this one out. Oxy sensor could be bad, but i've had plenty of cars that have had them go out, and it NEVER causes a drop in fuel economy of FIFTY PERCENT, like i have here. It's been like this since I bought it. This is driving me nuts.

Any help would be GREATLY appreciated. Thanks.


Oh yeah. It's a 1994 civic DX, SOHC, non-vtec. 115k miles.

 

pictures

 

The CEL is not on? Does it come on as the bulb test when you turn the key on but don't start? Repair any CEL code oroblems before expecting your Civic to run properly. Any misfiring at all?

Your MAP sensor is the little black box on top of the throttle body. Download and read the service manual as I think there is a procedure to test it with a voltmeter before you buy a new one. Used one from junkyard should be OK as they very seldom go bad.

Check the spark timing. This really kills mileage without turning on CEL or causing rough running.

Also disconnect fuel injectors one at a time to make sure you're not running on 3 cylinders. The little vacuum hose on the top of the fuel pressure regulator needs to be connected to the manifold.

 

The CEL comes on as a self-test when the vehicle is started, then goes out after a second. I don't have a map sensor. I know it's weird, but it's not on the firewall, or on top on the TB. Look at my pictures. It's not there. It's like a manifold from a '91 got slapped on my car. No misfiring at all. I don't have a timing light to check the timing at this point. I bought one, brand new,(map sensor) thinking it was the problem. The car has low power too. I live in colorado, near pike's peak. The car struggles to go up slight inclines without a running start. It won't break 40mph with the pedal to the floor, trying to go up a hill. DRINKS gas like you wouldn't believe.

 

You need a MAP sensor. All fuel injected Civics prior to 2001 have one. (those later models have a MAF sensor, and also distributorless ignition, which clearly you don't have).

Apparently you have something that is not stock, and not set up correctly. The pictures were too small for me to see clearly. Perhaps the next step in this detective job would be to find and identify the ECU.

 

here you go. NO map sensor. what the heck is going on...

 

I have a hunch that this is a 1991 civic engine, dropped into a 1994 chassis.

If this is the case, what meters fuel/air ratio besides the O2 sensor in a 1991?

 

What is your engine type number (found on the front of the block where the engine meets the transmission)?

Also which ECU do you have? If I were putting a 1991 engine into a 1994 chassis, I'd have just kept all the intake and control systems from the 1994. The 1994 manifolds will bolt exactly to a 1991 engine. Depending on what you have it may be most practical to get your car to that state.

I think in your third picture in post #6, that empty hose nipple on the top front of the throttle body is supposed to lead to the MAP sensor.

 

On my car my mileage went to 16 mpg, cat converter was bad-no CEL.

 

yes, i have no map sensor. Its not there, not on the firewall, as i have shown in pictures, and not on the TB. Where the hell is it?