First things first: '86 F150, 300 I6, 4 spd MT, 2 WD used mostly for hauling small livestock, feed, hay and the occasional camping/canoe trip.

The stock emissions have been gutted and the MPG's are crap. I went through all this a few days ago in another post and am working to diagnose and fix the various problems.

What I'm curious about is if modifying the ignition/fuel systems with either a DS2 system and/or another carb and/or anything else will approach or exceed the original efficiency while keeping the power of the engine relatively equivalent. Did the Ford engineers achieve maximum efficiency given the emissions constraints placed upon them?

Any advice or observations are appreciated.

Dan

 

The above is also assuming reasonable cost as well. I'm sure with bottomless pockets a lot of things are possible, but 'm really talking about what a person could do in their own shop.

Dan

 

From what I understand of your situation you have a truck that had EEC on it and disabled it w/o converting to DS-II. If that is the case your power and MPG will be awful as you are locked into "limp home mode". The ignition is locked at 10 BTDC AND, if the computer still has control over the carb, the air/fuel ratio is very rich.

With a computerized system there is no half way. Either everything is there and working properly, which will give the best MPG, or you have to convert to non-computerized.

 

Gary, you understand correctly. My problem seems to be a relatively common one.

I understand that there are no "tweaks" to be done to the computer system. I guess what I'm really getting at is what are the main benefits of going to a DS2 system other than saving the costs of replacing defective sensors, valves, etc associated with the EEC? The DS2 is in some ways simpler in that adjustments are made mechanically and by vacuum rather than electronic solenoids, etc. But is it possible to get the same efficiency (as measured in MPG's) in a DS2 system as Ford originally got with the EEC-IV?

Thanks.

Dan

 

If we had precise ways to measure the MPG under controlled situations I think the EEC system would win. But, not in a big way. And it is a tough system to maintain, and you will have to do it yourself as the people who know how to do it have retired and hung up their wrenches. However, there are people on here that can help you with it as several maintain their own.

So, I would suggest that you go to DS-II instead of trying to put the emissions stuff back on. I'm not even sure you would need to change the carb out. Some seem to get along fine with the feedback carb, although with the feedback system disconnected, but others find the engine runs rich and change. However, you change the distributor without changing the carb and see what you think.

 

Oh, I missed the "simpler" part. The DS-II approach means you no longer are using the myriad of relays, sensors, vacuum switches, miles of wiring and vacuum hose, etc. yes, it is far, far simpler. But, it works well.

 

On your basic question, no, the EEC system will win as far as efficiency. It was a intermediate step before they went to fuel injection. The computer can make many calculations much faster from the sensors monitoring temp, engine load, throttle position, etc. and adjust the fuel delivery and timing much more precisely.

But like Gary mentioned, this system is old, parts are getting hard to find, and most every truck you run into has had stuff taken off it. The most efficient way to get the truck running correctly is to convert it back to the previous system they used, which is simpler and parts are more readily available.

So all these conversions are just to keep the truck running the "best we can" juggling costs and hassle. If you have a working EEC system it's always better to keep it as long as you can.

 

I have a 68 F350 with a 300 six and a dirt simple carburetor. I use it for trips to the dump, all short runs and lots of idling time so I can use the hoist. I have not kept track of fuel mileage, but I can assure you it is not very good.

I used to have a 92 Bronco with a 300 six and the full on multi point fuel injection. It got around 15 mpg. Many years ago, I had a Ford van with a carbureted 300 six and if memory serves correctly, mileage was in the mid teens.

So, did the Ford engineers get it right? Of course they did. I had a discussion with a GM engineer years ago and he confided that there were power and mileage gains to be had by leaning out the calibration, but for the public, you must assume that someone is going to pull a 10,000 lb trailer with a 4 cylinder and keeping the mixture rich would reduce warranty claims. Of course emissions must be satisfied and all those sensors allow you to tune increasingly close to the curve in all driving conditions. It is still a growing science and that is why the engine controls are becoming increasingly complex.

Some innovations, like the feedback carburetor, may be best forgotten and you would be wise to take a step forward, or a step back. Have you considered going to the later model fuel injection? Lots of work, yes, but the driveability of the engine is greatly improved.

 

As I see it the big advantages of EEC IV are...
1: The computer can control the timing better, thus better power, performance and gas mileage.
2: Another big one is a working EGR system, I miss this one as the EGR is a very good thing to have.

The computer controlled Carb is just to lower the emission numbers slightly. I have done emission testing 3 ways, computer controlled, limp home mode and manual control of the feed back Carb solenoid. The gas mileage doesn't improve any when the computer is controlling the Carb.

Jim

 

I learned to drive on an '81 Bronco with a 300 and 4 spd OD tranny and I used to get 23-25 MPG consistently on the highway. Granted, the vehicle was only a couple of years old when I drove it (it was my dad's) and I'm comparing it to an almost 30 year old truck now. Even the EPA gas mileage charts list my truck as having 23 MPG when new. I understand that driving conditions will alter that.

I briefly thought about going fuel injection but the longer I thought about it the more expensive it got. Fuel pump, exhaust mani, intakes, computer, etc etc...It would be a fun challenge but I can't have my truck down that long and my wife would kill me.

 

Jim, how did you manually control the feedback solenoid? Put a rheostat on it - assuming it's controlled by variable voltage?

 

I designed and built a variable frequency and pulse width generator which could replace the missing computer supplied voltage signal to the feedback solenoid on the carburetor. The idea was to be able to dial in the mixture at cruise based on the O2 sensor.

While everyone seems to think the feedback carburetor runs very rich at cruise it really doesn't. I never did use this because at around 60-65 mph the engine goes lean anyway.

I did install a hand-held push button switch for manual control. Used it for 2 months to drive it full lean at 35-45 mph. After a 2 month average it didn't improve my gas mileage.

I did use the push button control to pass emission testing, both idle and with the back wheels on the load drums. Without this I was just a hair over the limit. The reduction was slight, but enough to pass.

Jim

 

How was the gas mileage in limp-home mode?

 

When I first got the truck the EEC IV was fully functional and I got about 15 mpg
EEC IV in limp home mode was about 11-12 mpg

Current MPG 15 in the summer 14 in the winter.

My point was, for me to change to a non feedback carb won't increase my gas mileage any with my current setup. Increasing my MPG is my only motivation.

Jim

 

Thanks. I wasn't suggesting any change but was just curious how bad limp-home was. You answered my question.