Hello:

The computer on the 86GT says it is running lean. Gives codes 41 and 91. Here's the story so far.

In March I replaced the injectors with a rebuilt and tested factory set. I replaced the under body fuel lines, both supply and return. I cleaned out the other hard lines on the engine including the fuel rail. I also installed a new fuel filter. Finally I installed a new pressure regulator. It is visibly shorter than the factory unit I removed. I kept it just in case. Both are Ford parts. Actually Bosch but with the Ford part number.

I replaced all this as the car had over 225,000 miles on it at the time. Car runs better, has more power, and sounds better.

I even resealed the air box as it was loose and made sure the air tube was tight at the throttle.

I checked the Thermactor system and it is functioning properly. All the lines and hoses are tight and there are no leaks. That includes the metal tubes that attach to the back of the engine and the line down to the cats.

I checked fuel pressure and here are the results:

KOEO. Cycled the key on and off three times. Pressure= 38.5 psi.
Engine running (ER). Idle for about two minutes. Pressure= 33 psi.
Engine off, key off, then key on. Pressure= 37.5 psi.
Key off, waited one minute. Checked residual. Pressure= 37 psi.

No smell of fuel anywhere, especially at the regulator. Pulled the vacuum line and checked. Looks good. No leaks anywhere.

After a test drive of about five minutes, I ran the KOEO and ER tests again.
KOEO= Pass code 11.
ER gave codes 41 and 91, nothing else. Ran the cylinder balance test. Code 90= Pass.

Unless the new regulator is the problem, I'm stumped. Perhaps a mystery vacuum leak somewhere.
Any ideas? They are most appreciated.
Thanks.
PS- Can't load photos now. Looks like the factory pressure regulator I removed has part number E3EE-9C968-AA. The new one has F4CE-9C968-AA. Motorcraft number CM4764, which is listed as correct for my car.