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TheGrimMechanic · 09-16-2014, 12:25 PM

Yeah, I know. Haven't seen anyone here raving about the fuel economy improvements on their full size, gas fueled V-8 pickup. BUT, I think there some things I've discovered that apply to just about any internal combustion powered vehicle that I haven't read much about anywhere on this site.

I bought the F350 about 7 years ago with 126,000 miles on it. Its powered by a venerable 351 Windsor that was factory rated at 245hp. When I first bought it, I got about 10mpg city and 11mpg hwy. It had an intermittent check engine light that was traced back to a faulty O2 sensor and a cracked distributor cap. After changing the oil and doing a tune up (replacing cap, rotor, wires, plugs, PCV valve, etc.), my mileage improved ever so slightly to 10city/12hwy. Not impressive and still disappointed with how bad the mileage was. I would have expected this out of a 460 powered truck but not the 351. The F350 had decent gearing for mileage (3.55:1) but the automatic 4 speed overdrive E4OD tranny isn't known to be very efficient. The F350 is also a 4x4 but its a standard cab and the weight is fairly low for a full size pickup at 5,500lbs. Highway mileage, as expected, really took a dump above 65mph and this is something I can live with. No need to cruise at 75 in my old truck. All of the checks for mechanical faults were checked and nothing appeared to be defective; no exhaust leaks upstream of the O2 sensor, engine compression was good, no vacuum leaks, fuel pressure correct, etc.

One of the first mods I made was to repair a rusted out muffler. When I removed it, I looked at the cat and found that it had been gutted (or melted itself out) and wasn't functional. I replaced the exhaust from ahead of the non-functional cat with home-made 3" system and a Flowmaster muffler. Still not much difference in the fuel mileage. The next mod came about while trying to address a erratic idle problem. Idle speed was unsteady and erratic at times. This was traced back to an EGR valve that had a worn seat inside and wouldn't close completely at times. Decided to do a little experiment and block it off completely rather than replace it. Instantly gained 1mpg city and 2mpg hwy. Hmmmm.....
This got me thinking about why. After the EGR was blocked off, I noticed that I had some slight pinging at part throttle cruise. A good thing as far as fuel economy. I checked the timing and it was spot-on so just for safety's sake, I retarded it 2 degrees. Apparently, the ECM advanced the timing considerably when the EGR is open to make up for the slowed down rate of combustion caused by the diluted air/fuel charge. By blocking off the EGR, I got the free benefit of advanced ignition timing just where I needed it..... During part-throttle cruise.

More experiments.
The next on the list was the Air Injection Pump. The pump was beginning to make some noise and I've had these fail before. The vanes inside blow apart and the pumps seize, burning up the belt and leaving you stranded. So... off to the auto parts store and put on a shorted belt that bypassed the air pump. Holy Cow!!! Mileage jumped another 3mpg on the highway! Again, I needed to understand why and about the only thing I have been able to figure out is that the air pump was doing its job of pumping air into the exhaust and creating an artificially 'lean' state as far as the O2 sensor was concerned. The ECU responded by richening up the mixture. Now I can see a reason for this as far as emissions systems are concerned. In order for the catalyst to function, there has to be some air in the exhaust and some unburned fuel. If there wasn't, the cat wouldn't come up to temperature and it wouldn't do its job of taking excess air and using it to oxidize CO and unburned hydrocarbons in the exhaust. Brilliant engineering, "lets make an already fuel inefficient vehicle even worse so we can make the exhaust cleaner". Just out of curiosity, I checked the exhaust with an exhaust gas analyzer and found the CO was at 1% and hydrocarbons were around 60ppm. The exhaust was still VERY clean yet none of the emissions control devices were functional. If you take into account the fact that the F350 is burning 33% less fuel, then the real numbers of tailpipe emissions are even better that when the vehicle was new! The EPA numbers for fuel economy for my F350 were almost perfectly inline with what I was getting before I changed anything.

Well, to keep a long story short, I have since made a few other mods to the old F350; An MSD 6A ignition, a hotter thermostat, an adjustable fuel pressure regulator, a better quality fan clutch, replaced the crankshaft pulley with a smaller one (to reduce accessory drive speed), and did away with the stock cold air intake. Right now, I'm getting a consistent 14mpg in town and 17+ on the highway if I keep the speed at 65mph. And this is with 224,000 miles on the stock engine! When its due for a rebuild (I'm sure it'll go to 300,000) I'll make some other changes. More compression, regrind the crank to use smaller 351 Cleveland main bearings, low tension oil rings and gapless compression rings, and if it's in the budget a set of TFS twisted wedge heads. I'm pretty confident I can break 20mpg and also pick up another 75-100 hp.

09-16-2014, 12:25 PM	#1 (permalink)
TheGrimMechanic EcoModding Lurker Join Date: Sep 2014 Location: Western Colorado Posts: 13 Thanks: 0 Thanked 2 Times in 2 Posts	Good F350 fuel economy? Yeah, I know. Haven't seen anyone here raving about the fuel economy improvements on their full size, gas fueled V-8 pickup. BUT, I think there some things I've discovered that apply to just about any internal combustion powered vehicle that I haven't read much about anywhere on this site. I bought the F350 about 7 years ago with 126,000 miles on it. Its powered by a venerable 351 Windsor that was factory rated at 245hp. When I first bought it, I got about 10mpg city and 11mpg hwy. It had an intermittent check engine light that was traced back to a faulty O2 sensor and a cracked distributor cap. After changing the oil and doing a tune up (replacing cap, rotor, wires, plugs, PCV valve, etc.), my mileage improved ever so slightly to 10city/12hwy. Not impressive and still disappointed with how bad the mileage was. I would have expected this out of a 460 powered truck but not the 351. The F350 had decent gearing for mileage (3.55:1) but the automatic 4 speed overdrive E4OD tranny isn't known to be very efficient. The F350 is also a 4x4 but its a standard cab and the weight is fairly low for a full size pickup at 5,500lbs. Highway mileage, as expected, really took a dump above 65mph and this is something I can live with. No need to cruise at 75 in my old truck. All of the checks for mechanical faults were checked and nothing appeared to be defective; no exhaust leaks upstream of the O2 sensor, engine compression was good, no vacuum leaks, fuel pressure correct, etc. One of the first mods I made was to repair a rusted out muffler. When I removed it, I looked at the cat and found that it had been gutted (or melted itself out) and wasn't functional. I replaced the exhaust from ahead of the non-functional cat with home-made 3" system and a Flowmaster muffler. Still not much difference in the fuel mileage. The next mod came about while trying to address a erratic idle problem. Idle speed was unsteady and erratic at times. This was traced back to an EGR valve that had a worn seat inside and wouldn't close completely at times. Decided to do a little experiment and block it off completely rather than replace it. Instantly gained 1mpg city and 2mpg hwy. Hmmmm..... This got me thinking about why. After the EGR was blocked off, I noticed that I had some slight pinging at part throttle cruise. A good thing as far as fuel economy. I checked the timing and it was spot-on so just for safety's sake, I retarded it 2 degrees. Apparently, the ECM advanced the timing considerably when the EGR is open to make up for the slowed down rate of combustion caused by the diluted air/fuel charge. By blocking off the EGR, I got the free benefit of advanced ignition timing just where I needed it..... During part-throttle cruise. More experiments. The next on the list was the Air Injection Pump. The pump was beginning to make some noise and I've had these fail before. The vanes inside blow apart and the pumps seize, burning up the belt and leaving you stranded. So... off to the auto parts store and put on a shorted belt that bypassed the air pump. Holy Cow!!! Mileage jumped another 3mpg on the highway! Again, I needed to understand why and about the only thing I have been able to figure out is that the air pump was doing its job of pumping air into the exhaust and creating an artificially 'lean' state as far as the O2 sensor was concerned. The ECU responded by richening up the mixture. Now I can see a reason for this as far as emissions systems are concerned. In order for the catalyst to function, there has to be some air in the exhaust and some unburned fuel. If there wasn't, the cat wouldn't come up to temperature and it wouldn't do its job of taking excess air and using it to oxidize CO and unburned hydrocarbons in the exhaust. Brilliant engineering, "lets make an already fuel inefficient vehicle even worse so we can make the exhaust cleaner". Just out of curiosity, I checked the exhaust with an exhaust gas analyzer and found the CO was at 1% and hydrocarbons were around 60ppm. The exhaust was still VERY clean yet none of the emissions control devices were functional. If you take into account the fact that the F350 is burning 33% less fuel, then the real numbers of tailpipe emissions are even better that when the vehicle was new! The EPA numbers for fuel economy for my F350 were almost perfectly inline with what I was getting before I changed anything. Well, to keep a long story short, I have since made a few other mods to the old F350; An MSD 6A ignition, a hotter thermostat, an adjustable fuel pressure regulator, a better quality fan clutch, replaced the crankshaft pulley with a smaller one (to reduce accessory drive speed), and did away with the stock cold air intake. Right now, I'm getting a consistent 14mpg in town and 17+ on the highway if I keep the speed at 65mph. And this is with 224,000 miles on the stock engine! When its due for a rebuild (I'm sure it'll go to 300,000) I'll make some other changes. More compression, regrind the crank to use smaller 351 Cleveland main bearings, low tension oil rings and gapless compression rings, and if it's in the budget a set of TFS twisted wedge heads. I'm pretty confident I can break 20mpg and also pick up another 75-100 hp.