Hey folks! I'm getting horrible fuel economy! No CEL 302, AOD, 3.08 gears with 31.50x10 tires, I'm getting 7.8mpgs. It had an upper intake leak so I resealed it aND fixed all the vacuum lines and I went from 4.3mpgs to the 7.8. I'm getting black soot on the tail pipe and it's definitely burning rich. It's an 89, if i cant figure it out I'm going to slap a carb on it!

 

You probably have a leaky injector or a bad fuel pressure regulator. Pull vacuum line off the regulator and make sure it's not spitting fuel out while running.

Do a fuel pressure test, then with the key off confirm that it hols that pressure. If not, there's a leaky injector.

Another way to test is with a downshift to 3000-3500 down a large hill...when downshifting and rpm that high, the injectors will not be energized, so if you get a stumble fumble sound/feel, you have a leaky injector.

You should also check codes anyway whether you have a cel or not.

 

When my '87 Bronco still had the 302, 3:55 gears with a C6 I consistently got 14 mpg combined city/hwy. Does it idle bad, stumble or anything? I wouldn't give up on FI just yet.

 

Doesn't matter, pull the codes and check fuel pressure while you're at it, and while you're under the hood also check that there isn't fuel leaking out of the FPR into the vacuum line.

With that gear ratio I'm not surprised, the computer probably rarely goes into closed loop because of the load the engine constantly sees. This truck needs 4.10 gears badly.

 

Its interesting to watch the PCM go from closed to open; happens alot more often than I expected if there's any head wind, hill, or weight in the truck. Granted, different truck, but I could use 4.10 as well due to 3.55 & 33" tires.

If the PCM doesn't think the engine ever warms up, it will stay in open loop too. Could this be a coolant temp sensor issue? Note: as I understand it, the gauge and PCM use different sensors for coolant temp, so don't assume it's fine bc the gauge says "normal".

 

Yep, when I had my old 5.0 truck I found it was a lot better in terms of fuel milage to lock out OD when traveling on twisty/rolling 2-lane highways, and that truck never had anything bigger than 31" tires with 3.55 gears. This change meant the motor was turning 2500rpm instead of about 1600rpm but milage jumped from about 12mpg to close to 20mpg. On big highways if there was a headwind the motor never went into closed loop at all. Moral of the story.. it doesn't pay to lug an EFI motor, and especially with the 5.0 which doesn't make any useful power below 2000rpm.

 

as said check for codes, also check that coolant temp sensor reading is fairly accurate with your scan tool they have an acceptable range that won't set a code but will kill mileage i.e engine is actually at operating temp but sensor is telling pcm it is only 50 degrees.Won't set a code because it is within parameters but will cause it to run rich.Also check map sensor they will cause this make sure the line is ok and hooked directly to intake vacuum. With a scanner check that while engine is running the map reading matches actual vacuum at idle and other driving conditions using vacuum gauge. The map acts like a power valve on a carb low vacuum it adds fuel. The coolant temp sensor performs the choke function of a carb adds fuel at low temps. The oxygen sensor fine tunes the mixture at cruise. Everything on a fuel injection engine has a correlation with a carbed engine look at the system you would suspect if a carbed engine was giving you the same symptoms. Also double check timing and ignition function.

 

Sorry for the delay in keeping y'all updated, I tried pulling the codes and found that the ECM wouldn't commence sequence codes. Did alot of research and figured out that the ECM is in limp mode, and that the ECM is indeed dead.