I was getting an intermittent CEL while driving my '97 F-250 crew cab (460, E4OD, EEC IV (aka OBD1)) on the freeway with a load. When I checked codes I had:

• 111 for KOEO (system pass)
• 136 for CM (HEGO lean, left side) (edit: oops, was actually 172, HEGO lean right side, not that it makes a lot of difference, but it does line up with the thermactor right side)
• 311 for KOER (thermactor inoperative, right side)

I cleared codes and now I'm getting 111 (system pass) for CM. I figure I might need to replace the O2 sensor if the 136 (sorry, 172) comes back, but I want to address the 311 now.

I've tried to search for an answer, but most of what I've found seem to be fixed by repairing the vacuum lines. The pink line to the diverter valve on my truck was broken, so I replaced it (by the way, you can get 50' and 100' roles of nylon tubing, specifically intended for vacuum lines, from McMaster-Carr). But I'm still getting the code 311.

I pulled the vacuum line off the diverter valve and ran the KOER test. During that test I was able to feel vacuum at the end of the line at times during the test, so I would guess that the signal part of the system is OK.

I've looked over all of the plumbing. I don't see any obviously damaged or rusted out pipes or fittings.

Some of the threads I found searching say there should be two vacuum lines to the diverter valve, but I only see one fitting for one. One thread did seem to say that some trucks had two and some only had one, so I'm thinking that isn't a problem.

Does anybody have any suggestions for next trouble shooting steps?

 

Another question. Can anyone tell me where the two vacuum lines on the diverter valve solenoid go? I'm 95% sure that I've got them right (and I get the code 311 both ways, so I'm at least that sure that it isn't my problem). There was a pink vacuum line that went to the diverter valve and a black line that went to the vacuum canister. I replaced both with black tubing, and I didn't pay quite as close attention as I should have to which went where.

This first picture shows the solenoid near the back of the left valve cover, looking in over the master cylinder.


The second picture is a close-up of the solenoid hose connections. I'm pretty sure the pink line to the diverter valve was on top, and the black line to the canister was on the bottom. Can anybody confirm or correct?

 

Deleted, sorry I had 311 and 312 mixed up in my thinking.

 

A little more self-diagnosis and a new question.

I pulled the hose off the inlet to the diverter valve, the pipe coming up from the air pump. With the engine running there's a pretty solid flow of air coming out of that pipe. So it would seem that my air pump is good.

I reinstalled that hose and pulled the hose off the diverter valve output, the hose that goes back down to the exhaust. With vacuum on the signal line to the diverter valve air comes out of the outlet. When I remove the vacuum line from the diverter valve no air comes out of the outlet, but air does come out of the dump line. So it would seem that my diverter valve is working correctly as well.

So it must be something downstream from the diverter valve. The posts I've seen before on this suggest looking for rusted out or obviously broken pipes or hoses, but as I said before, everything downstream from this looks solid. Any suggestions on where / how to look beyond this?

And the new question. Code 311 is "Thermactor air system inoperative (right side)" while code 314 would be left side. Is there any significance to the fact that I only have a right side code? In other words, should I be focusing on where the diverter valve output "Y"s off to the right rather than the left? Or does the fact that my truck only has a single solenoid and a single vacuum line to the diverter valve mean I have a single system while other trucks have a dual system, and "311" doesn't specifically apply to one side or the other on my truck?

 

Thinking about it more, it almost seems certain to me that my truck doesn't know the difference between right and left thermactor performance. Originally the vacuum line to the diverter valve was broken, so I had no thermactor operation on either side, and it only showed the code 311, not the code 314. So it would seem that in this case code 311 is simply "thermactor air system inoperative" and is not specific to either side. Can anyone confirm or refute that?

I'm also wondering how the computer "knows" the thermactor system is inoperative. It must use a sensor to collect the information. The only sensor I can imagine that it's using is the "HEGO" sensor (Hot Exhaust Gas Oxygen sensor, called an "O2" sensor by everyone and everything except the code chart?). So could the code 311 hanging on be related to the CM code 136 I had before? I cleared that code and it hasn't come back yet. But could I have marginal O2 sensor that's now causing my code 311?

 

The true definition of Code 311 for your year/model truck is: Secondary Air Injection system is inoperative.

Therefore your hypothesis is correct.

 

During the KOER running test the computer will open and closes the A.I.R. control valve(s) and then look for the changes at the HEGO sensor(s). If it does not get what it think it should (change of temp) then it reports the error.

 

I know that a week ago the entire system was inoperative due to the broken vacuum line. But now with the vacuum lines replaced and everything seemingly in decent condition I'm still getting the 311 code on the KOER test. Could that be due to a bad HEGO sensor? I hate the "just throw new parts at it" method of trouble shooting, but particularly with the code 136 it stored earlier I'm thinking replacing the HEGO sensor(s) might be my nest step.

 

Got it!

I replaced the HEGO sensor (my truck has a single sensor in the Y pipe, right behind where the pipes coming down from the two manifolds meet). Now I've got code 111 (system pass) for KOEO, CM and KOER!

 

Glad to see you have this one resolved