Is there a way to test my trucks computer? The reason I ask is because I have had my 85 F150 5.0 since 95 or so and I've always had weird codes. Most problematic over the past few years has been a rich running condition that I can't seem to correct. I've put in a few new O2 sensors, but it doesn't help. I get an O2 reading at the sensors connector and at the sensors wire right as it enters the EEC computer.

BTW, mileage has dropped from 17-19 to 8-13.

 

I've heard rumors of this being possible, call up some nearby auto parts stores and ask them if they can do it.

 

My Haynes manual describes some basic electrical tests one can perform on the EEC-IV computer, and the '86 Electrical and Vacuum Troubleshooting Manual says "Refer to the Engine/Emissions Diagnosis Manual and Technical Service Bulletins for complete EEC-IV test procedures using special Rotunda test equipment".

Unfortunately I don't have those specialized documents. But unless I'm mistaken, the same EEC-IV computer was used for some years to control ignition and fuel mixture in later fuel-injected trucks from 1987 onward.

So you might actually have more luck asking this question in the '87-'96 trucks forum. Those folks probably have to deal with the EEC-IV more than folks here. Many people in this forum took their EEC-IV computer behind the barn and shot it, replacing it with the Duraspark II or other ignition control system and a conventional carburetor.

 

The idea of asking in the 87-96 is a good one!

Yeah, the EEC IV stuff started appearing in 1985 and I believe it was late 80s or early 90s before everything had been fully transitioned.

I don't have that book (nor any TSBs) either. TSBs can be found online but aren't gonna be enough to help with this.

I'm sure some Ford dealers had the Rotunda® test equipment to do this, I'm hoping that, by this time (30 years later) that some decent auto parts stores have the Binford® 1000 generic variant.

Yes, this was used until I think it was 1996 when the OBD II stuff came out.

However, there were several different variations of the settings, what Ford called Calibration Codes. It's not like you can just take any computer that physically plugs in and expect it to work for your vehicle.

To the OP, I'd take the cover off and look for leaking or swelled capacitors, something like below:

Leaking caps:


Swelled caps:







This is actually more of a problem IMHO with today's cheaply-made electronics than it was 30 years ago when things were better made (again, IMHO).

In any event, I'd open it up and peer inside.

 

You can also find a lot of information on the EEC-IV (and other variants) computer, including pin-outs, etc. at this website: fordfuelinjection.com

A lot of useful information on that website. It may even have testing information, although I'm not sure of that.

 

One simple way to "test" your computer in situ is to check your base timing and timing advance (with engine warmed up to operating temperature). With the Spout disconnected your timing as tested with a timing light should be about 10 Deg BTDC (or whatever your sticker indicates). With the Spout re-connected, you can then see if timing advances with engine speed. If timing advances with engine speed, then you know your computer is advancing the timing and thus is not locked into "limp-home mode" with a fixed timing advance. Based on your mpg decline I suspect your computer might be locked in "limp-home mode", here is a link to a discussion here that might be useful: https://www.ford-trucks.com/forums/1...ck-system.html

 

I did take a look inside for swelled caps. There were only 3 or 4 electrolytic caps and they actually looked really good. I've had tons of bad caps problems in computers, DVD/CD players and music equipment.

I guess I need to do the timing check again to verify, but it has recently been verified that the timing was 10BTDC with the spout disconnected and that it was advancing when reconnected.

Codes tell me a 'lean condition' always for the last few years. I'll pull the O2 sensor and the little ceramic looking tip will be shattered. I replace with a new one, then I will still pull a "lean condition" code. I have checked and verified continuity from the sensor to the computer.

Is it possible to be locked in a "limp" mode on the air/fuel ratio only? Possibly still having the dist. advance feature?

 

Hmmm - a lean condition coupled with reduced mpg seems kind of contradictory. Are there any other symptoms that indicate you are actually running lean? Shattered O2 sensor tip might indicate overly lean running - high heat from lean conditions could maybe cause the ceramic tip to break? Do spark plugs look "lean"?

Question: after you replace the O2 sensor, do you then erase the computer's long-term memory? I believe you are supposed to.

If memory serves, it is possible to measure the current signal coming from the O2 sensor to see if it is in the normal range. I think it is a very low voltage, maybe 0-3V.

 

I'd put it on an exhaust sniffer.

 

The Bosch brand O2 sensor with OEM plug attachment is more expensive, but supposedly as close to OEM as is available.

To answer your earlier question - I don't think the computer sensing what it interprets as a lean condition would send the ignition timing into limp-home mode.

 

This computer has the oxygen sensor and uses this for feedback to adjust the air/fuel mixture. You already know this, but this can cause some difficult troubleshooting. You are naturally going straight to the oxygen sensor to find the problem, but the oxygen sensor could be reacting to another problem upstream.

Your truck is speed density. It looks at the vacuum level of the engine(MAP sensor), throttle position, rpm, etc. and then calculates how much fuel to deliver to the engine(how long to activate the injectors). After the engine is warmed up, the computer then looks at the oxygen sensor and "tweaks" the injector on time to adjust the air/fuel ratio. If you have a large vacuum leak somewhere, this is uncontrolled air entering the engine. On a normal carbed "dumb" engine, this would cause the engine to run rough with a higher than normal idle. On your computer controlled "smart" engine, the oxygen sensor says "hey, this mixture is lean we need more fuel". The computer says "ok", and adds more fuel. This ruins your fuel mileage. If the vacuum leak is large enough, the oxygen sensor still tells the computer "hey we are still running lean". If it keeps doing this for a long period of time, the computer then says "I don't believe you anymore, you must have a problem" and throws a "always lean" code for the oxygen sensor.

A common problem with some of the fuel injected 302's was a gasket leak on the intake plenum between the plenum and the intake manifold. It also has some hidden vacuum lines underneath the plenum at the rear, and I would also check the EGR valve, they can get a piece of carbon in them and get stuck open.

 

Kevin,
I sent you a pm.

 

There is a guy on the TwEECer group on Yahoo that has built a breadboard to allow him to test his EEC system and modify it before going to the Bonneville salt flats. I'm sure it can be done. Archion and I spent almost a year chasing various gremlins in his 86 F150. A lot of it revolved around aftermarket vs OEM Motorcraft parts. We found that the aftermarket TPS was reading high compared to the Motorcraft. This would cause the EGR control solenoid to "chatter" and a rolling erratic idle. A breakout box is your best diagnostic aid along with an analog multimeter so you can do "sweep" tests on some sensors.

 

Update. I threw a freshly charged battery in the 85 F150 and went for a spin. Wouldn't you know it, no codes. Well, at least no emissions light except at startup when I actually should see it. I'll go ahead and pull some codes in a day or two and maybe check the timing to make sure it is being controlled. I might even fill it up a drive it to work a time or two to get an idea of the mileage.

Grubbworm, Sparta is where my wife is from. Small world. Her family is still scattered all about the area. I'll be in touch.

 

Kevin, my wife's family's name in Sparta is Clouse, and there are too many to name here.