[Nailbender]

Well the exhaust stinks, maybe it smells rich? I'd descibe it as kinda a wet smell, not dry. When the car is started in garage, even when backed out immediately, the heavy exhaust smell hangs in the air forever. I thought it was just because there are no catalytic converters on it.

I'll have to see if I can physically get a scanner on the ECU. It's mounted on top of the heater box, behind the glove compartment.

These are the pics of it I have from working on the heater box.

View attachment 925748 View attachment 925749

Looks like reading codes was kind of tough back in the day! I skipped the early EFI days but maybe another forum member can help you out or try a fox body forum?

 

[cougar70]

You have a problem with the EFI system. Does it have stock fuel injectors and O2 sensors? Spark plugs and O2 sensors will foul if running rich. Running large amounts of unburned fuel through the engine is bad for it. Typically some things will be disabled by substituting resistors for sensors. It's simple to check OB1 codes, but not so simple without a check engine light.

 

[b_arrington]

You have a problem with the EFI system. Does it have stock fuel injectors and O2 sensors? Spark plugs and O2 sensors will foul if running rich. Running large amounts of unburned fuel through the engine is bad for it. Typically some things will be disabled by substituting resistors for sensors. It's simple to check OB1 codes, but not so simple without a check engine light.

Ugh, this isn't going to be fun to get any codes. There's no check engine light.

I should be able to pull an oxygen sensor or spark plug to inspect them though. I have no idea if it has stock injectors or O2 sensors since the upgrade wasn't done by me.

 

[tbrooks]

As Nailbender stated, I would look for the O2 sensor. My son had dual exhaust put on his 1986 F150 and the shop eliminated the O2 sensor. That caused a 30% decrease in his fuel mileage.

Hope you get it figured out.

TB

 

[awhtx]

Are you checking the mileage after running several full tanks of gas down to about 1/8 remaining. Trying to calculate gas mileage after driving 50 miles is useless.

 

[Nailbender]

Ugh, this isn't going to be fun to get any codes. There's no check engine light.

I should be able to pull an oxygen sensor or spark plug to inspect them though. I have no idea if it has stock injectors or O2 sensors since the upgrade wasn't done by me.

Looking at post #21 it would seem you could use a test light where the light tan wire is as a check engine light? This is assuming you have the connecters shown.

 

[b_arrington]

Are you checking the mileage after running several full tanks of gas down to about 1/8 remaining. Trying to calculate gas mileage after driving 50 miles is useless.

We checked when the gauge was about showing empty. Put in 13 gallons to fill, and noted the mileage since last fill up.

 

[b_arrington]

I just pulled one of the spark plugs. It looks pretty normal. Smelled a bit of fuel/oil.

 

[W427]

Approaching this with no idea where the fuel is going will be tough. You need some direction. Find clues and follow them.

I've diagnosed a fairly large number of "poor economy" cars, and have occasionally found fuel line pinholes, leaks and other places the fuel is going (sloshing out the wrong type fill cap!) besides through the engine. So first check is both running and not - any signs, smells, etc, of fuel.

Next is pulling codes. Post any reported. Then pulling all the spark plugs to inspect for proper color (light tan to white) and even across all cylinders. We can specify tests from there to dig in specific areas, but see what that much gets you. One thing at-a-time.

 

[Klutch]

I would suspect leaking fuel injectors. When they worn, fuel gets past them when they are in the closed position creating a very rich condition.

 

[spliffy007]

It's been quite a few years since I had a 90 5.0. But, I suggest cleaning the Mass Air Flow Meter (MAF) and check the Throttle Position Sensor (TPS). Don't use carb cleaner on the MAF, it will damage it. Use MAF cleaner from any auto store. The TPS adjustment (just takes a multimeter and screwdriver) should be easy to find in a manual or online.

 

[kb65]

Ck the odometer also just because the speedo is correct does not mean the odometer is correct.
The color of the injectors should tell you what they are. stock is 19lb unless it is a pretty wild build 19s should be fine. You might try to find a stock ecu.
I am running a 97 explorer motor with an AOD and 3.73 gears in a fox convert and the worst i have ever seen was 18 does 25 on the highway

 

[gwstang]

My first instinct would be to assume your son drives the car like I drove my first Mustang at 16 yrs old. Can you check the mileage with only you driving it?

Next I would look at how the car is tuned. That's a lot of fuel for a 5.0.

Exactly what I thought. The younger the kid = lesser the fuel mileage! I get around 24-25 on my 5.0 with an AOD transmission. OD makes a big difference. I drive spirited too, well at least for an old fart!

 

[gwstang]

Could be an injector or two is stuck open? Just throwing it out there. Get one of those stethoscope things from harbor freight and listen to each one for clicking on/off. It's easy and I have done this before. Good way to find a dead injector too. No clicky = no worky.

 

[Nailbender]

On my dedicated autocross car I do better than 10 mpg and it's trailered and only raced! This is an EFI issue. No clue what sensors necessary to make the car run properly are even installed and hooked up. I would start with a fresh set of plugs and O2 sensors assuming everything else is in order..

 

[gwstang]

Ck the odometer also just because the speedo is correct does not mean the odometer is correct.
The color of the injectors should tell you what they are. stock is 19lb unless it is a pretty wild build 19s should be fine. You might try to find a stock ecu.
I am running a 97 explorer motor with an AOD and 3.73 gears in a fox convert and the worst i have ever seen was 18 does 25 on the highway

He can use a speedometer app, to tell how fast he is going.

 

[W427]

Have to find and confirm the source first, or you're chasing your tail. 101 suggestions or ideas, and 100 or so are not it. Much quicker and cheaper to diagnose and fix exactly what's wrong. Just sayin'.

 

[ZOW]

Start by checking the tread depth on the rear tires from time to time.

If it seems to be going down precipitously, you have your answer.

 

[JohnnyK]

I measured my consumption driving around town and I was getting 7-10 with EEC-IV. I'm also getting the same with PF4. WB (and now PF4 software) confirms all is good.

As I mentioned in the last thread about this, it's because I'm driving like a dick, with 3.55 gears. Tell him to go cruise on the highway and it will probably go up by 20.

 

[DonP]

Pulling codes is easy peasy. If you didn't wire in the CEL (Check Engine Light) you can use a test light and do as the YT video linked by cougar70. KASTAR 273A is just that with printed instructions and cute little bag to keep it in.