After swapping my TFI I cleared codes and drove the truck for 5 days.

MPG is still horrible (9-12) but CEL didn't come on until today. That's when I got the code reader back out.

Cylinder Balance Test- 10 - Cyl #1 has a problem (I have not repeated test to verify)

KOER
172 HEGO sensor fault / lean (I replaced O2 last fall, 10K ago)
213 SPOUT circuit open
538 Insufficient RPM change during dynamic response test

KOEO
522 Not in park / netrual (I didn't push the clutch in)
553 Air Management Circuit 2 failure
565 Canister Purge Solenoid circuit fault

CM
212 Loss of ignition diagnostic monitor signal / spout circuit grounded

I have have some of these codes before (553, 565, 213) but nobody has helped me figure out the problem, despite posting them several times.

Any help appreciated, I'm really sick of the MPG, I might as well be driving a lifted truck with a decent size engine for the same fuel cost. My last 300 got 17 MPG regularly

 

I would like some more information on your engine and computer.
You talk about an Cylinder Balance Test. How are you doing that with a 91 truck?
To do the Cylinder Balance Test it needs to be a SFI/MAF fuel system so it can turn one injector off at a time.
So what year computer and engine harness do you have?
And what are they off of?

OR

Do you have an engine test setup to do this with a MFI/MAP injection system?

You also have a code 212 Loss of ignition diagnostic monitor signal and if you do have the SFI/MAF system from a later truck you might have the wrong ICM in the truck (a gray one when you need a black one).

You may also have a missing SPOUT shorting bar (jumper) or bad SPOUT wire or a bad plug at either end (code 213).

The 172 could be a bad wire or plug also.

Do you still have the Canister Purge Solenoid and wiring (565)?

Do you still have the A.I.R. solenoids hooked up (553)?

If you did change to a later model computer and harness there could be a miss match in the harness to the computer.

 

I bought a code reader and it shows cyl balance test for anything with EEC-IV.

The spout plug is in. Its hard to trace the wiring since everything is in a loom. Where do the 2 yellow wires end up at?

My first problem is I have no idea what these are! I hate emissions, old diesels are SO much simpler to work on.
Anyway, today on the way home it started missing pretty bad but the CEL never came on. I pulled codes and got nothing new.

 

I take it your talking about the Yellow wires on the fuel pum and PCM Power relays. They end up at the battery side of the starter solenoid going through a fuse link there.


The Canister Purge Solenoid is in the vapor hose half way between the throttle body and vapor carbon canister.
Image:


The A.I.R. solenoids are just behind the EGR solenoid and the EGR solenoid is just behind the Ignition Coil.

 

I have a 300 so the A.I.R. solenoids are probly in a different spot.

I knew there was a canister there, just never knew what it was called.
I will see if I can get time to check it out tomorrow night.

 

The A.I.R. TAD solenoid is at location A-7 in 151-01 below.
The EGR solenoid is at location A-8 in 151-01 below.


The A.I.R. TAB solenoid is at location A-5 in 151-02 below.
The Canister Purge Solenoid is at location C-1 in 151-02 below.


/

 

If you have the original engine and computer in there, a '91 should only show 2-digit codes, not 3-digit. In which case, you're on a wild goose chase with the codes you posted.

Jason

 

I do not think this is possible with bank injection.



The only way would be for the computer to match information from the IDM & Signature PIP and that could only tell that the coil did not fire the plug on a certain cylinder. Not sure if this information is available to be picked out of the computer.



The 1991 F-series computer does not have the ability to stop one cylinder from firing and as far as I know that is the way a cylinder balance test is done.

 

My 1991 F-150 (since sold) gave three-digit codes.

 

Back when I checked codes with the CEL light and a paper clip everyone told me there was no way a '91 could have 3 digit codes. I bought a code reader and guess what I get? 3 Digit codes! Maybe it was a late '91 thing, I don't know.

It's raining pretty heavy so it doesn't look like I'll be getting to it tonight.

 

What kind of code reader do you have?

 

I got one at mills fleet farm on sale for $30. Its for Ford OBDI only. Lot easier than watching the CEL blink. I know its cheap and maybe the balance test doesn't apply for my truck but it still works great as a code reader.

 

Does it have a brand name or model number?

 

Will check it out and report back.
Anyway, took a quick peek and found the vacuum line from the C.P.S. wasn't hooked up at the canister. I put it back on.
What problems would it cause without that?

I'm going to check out the AIR and EGR solenoids and wiring today.

 

That could cause rough idles and the feeling you are missing a vacuum leak can also cause your engine to run lean, throw EGR codes, and cause allot of other things. I am just tracing all of my vacuum lines now and replacing them what a head ache with all those lines. good luck.