At the risk of opening a proverbial "can of worms" I want to put some information out here for those folks who may have difficulties understanding, accepting, repairing, or restoring certain parts of their 87-95 EEC-IV equipped trucks. The title of this thread harkens back to an ancient thread about emissions control equipment that ran the gamut from enthusiastic support to antagonistic argument. (Search for it using "fascination" as the keyword).

In the years since having begun that thread, I have spent far more time learning the intricacies of the EEC-IV engine management system than was probably ever required. However, since I have, I have come to grips with a few hard truths that many folks either can not or will not wrap their heads around.

Admittedly, I have spent time on other forums (yes, I know, FTE, I cheated on you but I had my reasons). In the course of trying to answer questions in those forums I had opportunity to put together a lengthy post detailing what parts of the EEC-IV system do what and WHY removing one or two of them simply will not be good for the engine/vehicle in the long run. As I said, I'm not doing this to start arguments or call anyone out. I post this as information with the sincerest hope that the reader(s) may glean from it, the FACTS that I have come to understand, accept, and deal with as a result of owning, driving, troubleshooting, and repairing vehicles so-equipped for the last 12 years or more.

Apologies for the length of this post...

EEC-IV: Some folks like to call it OBD-I but it was actually the fourth generation engine/emissions control system Ford engineered. Ford employed it in light trucks (1985 EFI-1995). The Thermactor system pushed fresh air into the heads just DOWNstream of the exhaust valves AND/OR into the exhaust pipe just UPstream of the catalytic converter. BOTH ports have a specific function and BOTH are indeed necessary because the EEC-IV computer USES them to control the engine's operational parameters and in so doing, reduce emissions output insofar as the system is capable.

Upstream of the catalytic converter: This port serves to introduce more oxygen into the exhaust stream to enable the OEM catalytic converter to achieve the necessary temperatures to burn-off the crud its supposed to burn off. (Adding fresh air/oxygen to hot exhaust gasses... its like opening a window in a house that was burning. The fire was out... but you just gave it a big deep breath of air). So, unless you have swapped a newer (more efficient) cat into the vehicle, the OEM cat will NOT function without the fresh air from the pump.

Downstream of the exhaust valves: This port serves to keep the HEGO (Heated Exhaust Gas Oxygen) sensor (O2 sensor) from getting a false "rich" reading before the engine fully warms up. The EGR is also closed at this point so ALL of the exhaust is headed down the pipe. This is the ONLY point in time that the Thermactor air is EVER used to "dilute" exhaust gasses. A cold engine needs more fuel and less air however, under normal operating temperatures, the fuel level is greatly reduced and the air level increased. So, until things warm up, the O2 sensor is going to get readings that are way over on the "rich" side of the ratio. Once warmed up, the EEC-IV computer shuts this air injection down so as to get accurate readings during normal operation.

TAB & TAD solenoids: The EEC-IV computer changes the flow of vacuum through the TAB (Thermactor Air Bypass) and TAD (Thermactor Air Diverter) solenoids (most frequently mounted near the ignition coil). These two electronic solenoids are nothing more than vacuum switches. They control the flow of vacuum to the Diverter Valve.

Diverter Valve: (behind the passenger cylinder head on the V8's) Redirects fresh air from the Thermactor Air Injection Pump (smog pump) between the ports in the cylinder heads and the port in the exhaust pipe. The EEC-IV computer controls this flow of air from the smog pump DURING engine operation based on temperature and throttle position.

This system is completely integrated and removing just one or two parts adversely affects engine operation. Even if the EEC-IV computer can compensate for the missing information, the LACK of this information causes the computer to alter the operational parameters of the engine... there is no way around this without rewriting the software in the EEC-IV computer. (And no, performance chips don't have the capacity to do this).

EGR: Exhaust Gas Recirculation is a system that is actually much older than any electronic control system. Early EGR was employed by some auto makers as far back as the late 1960's. This system uses a valve to allow a controlled amount of exhaust back through the intake in an effort to run unburned crud back through the combustion cycle to "try again" so to speak.

So, why does it matter if it isn't there? In older carburated systems, if the EGR was removed, you could simply retune the carburetor to adjust for the missing partial air/partial combustibles coming in through the intake. Simple enough. However, with a system like EEC-IV and other electronic engine control systems, if you just remove that flow of air & combustibles all together, you are taking away something that the computer was programmed to control and calculate. So imagine for a minute, that you suddenly removed a predetermined amount of air and fuel from your engine but you could make no adjustment to compensate for the loss. Well, Ford couldn't have that happen so they programmed the computer with options so it could still keep the engine running... not nearly as well as with the system functioning properly but the vehicle would run well enough to get you home. Since EGR is controlled by vacuum AND electronics the EEC-IV computer can "know" how much exhaust gas is recirculating and make fuel/air mixture adjustments accordingly. However, if the EGR is removed all together, the computer must "guess" and since it cannot control the EGR valve anymore, it spends a LOT of time trying to adjust spark timing and fuel/air mixture to compensate for the loss of exhaust gasses back through the engine. Remember the O2 sensor "knows" when the exhaust gasses are "rich" or "lean" and it snitches about 8 times per second. What you end up with, particularly in a gasoline engine, is a lot of erratic idle issues... is it any wonder?

The problem that we are dealing with is that Ford engineered these systems in such a way that IF some part DOES fail, the computer will keep the engine running "well enough" to still drive the vehicle but it will trigger the "Check Engine" light to warn the driver that even though the vehicle still APPEARS to be running properly, there is something amiss. Running this way for extended periods of time WILL eventually cause bigger problems unless its fixed. What folks who arbitrarily remove parts of the system FAIL to accept is the FACT that just because you remove or ignore the Check Engine light (or put tape over it...which is my personal favorite uneducated maneuver) does NOT mean the engine is "running fine" and further it means that whatever the EEC-IV computer is doing to compensate WILL cause other problems that WILL be worse in the long run. Remember the EEC-IV computer controls fuel-air ratio and spark timing along with shift points (E4OD only). Anyone who knows anything about internal combustion engines knows that these settings/adjustments are critical and failure to maintain them results in terrible problems if not immediately, then definitely over extended periods of time. When you are dealing with a vehicle where the ONLY way to be certain that these adjustments are correct is to make certain the on-board computer has ALL of the information it needs, maintaining ALL of the sources of that information becomes as critical as spark timing and fuel/air mixture. These are the FACTS.

 

I'm standing up and clapping!

 

As usual, great post. Thanks.

 

Great post. A lot of good info there.

Jim

 

Great write-up GS! Thanks, now I can see how it all works as one big system, not as independent parts.