Hi there looking for help with my 89 F250 with 351w and C6 auto. Has 4:10 gears and truck is in great shape.

I have done a lot of research and tried to fix my extremely low gas mileage. I get 5-6 easy driving, 50-55 miles an hour country roads.

What's been replaced is...

Plugs, wires, cap, rotor, coil, throttle position sensor, idle air control valve, fuel pressure regulator, air and fuel filter

The truck is definitely burning rich. You can smell raw fuel and basically see it coming out of the exhaust. I'm not sure where to go from here. I was going to check the timing and I bought a ford engine code reader. The reader said everything checked out ok for the key on engine off test. For the key on engine running test it said I need to check timing first.

Any thoughts or ideas would be great. I'm looking to try to get maybe 10-12 mpg. Seems reasonable from what I read. I have read about swaping engines with a 300 6 that will bolt up to my C6. Hoping that is a last resort! I don't need power, it's a farm truck and I bought the truck for it's condition and aluminum service body.

Thanks in advance!

 

How much PSI are you getting at the fuel rail?

 

Definitely need to rent or buy a fuel pressure tester.

Quick check to see if the FPR is a problem is to pull the vacuum line off and see if there is any fuel coming out.
Also, with the vacuum line removed, engine off, turn key to ON position, and see if fuel comes out then.

 

FPR has already been replaced......perhaps the OP got a bad one out of the box??

 

and yes ... 10-12 mpg is totally reasonable for your truck.

 

Totally forgot that he did!!! Doh!!

Well, checking fuel psi is a good start though. Only other idea for rich condition is ACT, ECT, O2 sensor. O2 "should" throw CEL though if not properly working.

 

Ok sorry for the newb question can you tell me what the ETC is? I replaced the atc.

Also to check pressure at fuel rail is it best to have a shop test it and check timing at the same time? If fuel pressure is too high, what is the correct fix?

Thanks

 

Also, previous owner put headers, cat, and full exhaust on truck and seems like O2 sensor had been replaced. Maybe worth replacing anyway?

 

ECT is engine coolant temperature switch located on drivers side engine block.

 

Hi everyone

Update on what's going on. Went to an older ford mechanic who knows a lot about these trucks. He checked fuel rail pressure, engine compression, adjusted timing, plugged obd1 computer to it, and said all sensors mentioned above have recently been changed. He did say though that my egr tube has a leak in it and thought maybe that would be causing it to be too rich. Checked all that and only charged me $25, I thought that was pretty fair. Still getting 6 mpg tops though.

Talked to a relative and said he had an old 85 ford out behind the barn with a non efi 300 i6. Said the truck is shot but motor is still good. Said I could have it for free. What's everyone think if I was to put that engine in place of the 351? I don't need power, not hauling anything besides my tools. Current motor still likes to stall out or idle roughly when I slow down to stop too.

Thanks

 

Is this a dual tank truck? If so do both tanks work?

 

Just a single tank. I'm guessing 20 gallons or so? Everytime I fill up I put in about 18 gallons and it's on E

 

My 94 with a 351W was getting about 9 mpg when my dad gave it to me. I noticed a small increase with everything I did such as oil, plugs, plug wires, rotor, distributor cap along with air, oil and fuel filters. The second biggest gain I saw was replacing the front callipers, rotors and brake pads in concert with the rear drums and brake shoes. I gained a full 2 or 3 mpg so I had something in the brake system dragging. It was not enough to create any noticeable heat though. I was still not where I thought it should be and, after lots of help from FTE, I finally checked and adjusted the timing. My truck went from a best of 18 highway mpg (Canadian gallons) to 20.1 highway mpg on a recent 2000 plus Kilometre trip.

As I learned, one needs to check everything. Getting 12 to 15 mpg US with the 351W is certainly attainable for our trucks.

 

I had thought about the brakes too. I know the front brake (rotors calipers ad pads) have all been replaced in the front. I guess I'm not sure about the rear. Everything else I believe has been replaced on it as far as I can see. Even the Ford mechanic thought it was running tip top shape. It still skips a little and sometimes wants to stall when I stop.

Next thing I'm going to try is remove all transmission fluid and replace with some Type F ATF. I read that could help too. I just cant understand why else I'm getting only 5 mpg.

 

Mine was running just great too. It started very well and ran just fine. However, it was frying my plug wires and that eventually led me to check the timing. I have to climb a 20 Km hill to get home from town and my exhaust was getting so hot it was burning my plug wires, even a set of Ford 9mm racing wires. Since I reset the timing I haven't had any issues with the plug wires. As a bonus I have a bit more power now too.

FWIW about two years after my front rotors were replaced I noticed my truck pulling to the left. I checked and the passenger rotor had seized. I replaced it this summer and haven't had any more issues there either. Nowadays new parts no longer mean "quality" parts.

With the skipping issue check to ensure all of your plug wires are solidly connected. On the 300 I6 VACUUM, VACUUM, VACUUM!!! Make absolutely sure all of your vacuum lines are perfect and have solid connections. Especially the underside of the "coffee can" It can rust out without being obvious.