Little code help, some guidance

[Cobra_Dusten]

Car is throwing codes 41 and 91.

I know from this post
http://forums.stangnet.com/788958-code-41-running-rich-brake-booster.html

that i should start with 02 voltage, and then wiring harness and then vacuum leaks. here is my issue. In that thread it says to pull the plastic cover off of the ECM. Does it just clip off, or is there a secret to it? My cage is in the way down there, and i have sort of limited space and i dont want to break anything. In the morning, i am going to do a quick carb cleaner vacuum leak test with the engine cold and see if i find anything.

what confuses me about the codes is they aren't being thrown at a specific time(full throttle, during idle) they just appear after i've been driving for a while.

I'm leaning towards a vacuum leak as this started when i installed the new motor. I've traced out all my vacuum lines. The car has no egr is it possbile something from the removal of that(it was gone when i got the car) could be uncapped and causing the leak? Thanks in advance.

 

[jrichker]

There is no easy way to find vacuum leaks. It is a time consuming job that requires close inspection of each and very hose and connection.


Small vacuum leaks may not show much change using a vacuum gauge. The range of "good readings" varies so much from engine to engine that it may be difficult to detect small leaks. Average readings seem to run 16"-18" inches at idle and 18"-21" at 1000 RPM. The only sure comparison is a reading taken when your car was performing at its best through all the RPM ranges and what it is doing now. Use one of the spare ports on the vacuum tree that is mounted on the firewall near the windshield wiper motor to connect the vacuum gauge.

Use a squirt can of motor oil to squirt around the mating surfaces of the manifold & TB. The oil will be sucked into the leaking area and the engine will change speed.
Avoid using flammable substitutes for the oil such as propane or throttle body cleaner. Flash fires can occur due to the heat and possible electrical sparks. Fire is an excellent hair removal agent, and no eyebrows is not cool...

The vacuum line plumbing is old and brittle on many of these cars, so replacing the lines with new hose is a good plan. The common 1/8” and ¼” vacuum hose works well and isn’t expensive.

Look for broken vacuum connections, damaged vacuum lines and hoses (don't forget the PVC valve and brake booster hoses). Check the brake booster and the rubber grommet that hold the vacuum check valve for damage.

Diagram courtesy of Tmoss & Stang&2birds

See the following website for some help from Tmoss (diagram designer) & Stang&2Birds (website host) for help on 88-95 wiring Mustang FAQ - Engine Information Everyone should bookmark this site.

Ignition switch wiring
http://www.veryuseful.com/mustang/tech/engine/images/IgnitionSwitchWiring.gif

Fuel, alternator, A/C and ignition wiring
http://www.veryuseful.com/mustang/tech/engine/images/fuel-alt-links-ign-ac.gif

Complete computer, actuator & sensor wiring diagram for 88-91 Mass Air Mustangs
http://www.veryuseful.com/mustang/tech/engine/images/88-91_5.0_EEC_Wiring_Diagram.gif

Vacuum diagram 89-93 Mustangs
http://www.veryuseful.com/mustang/tech/engine/images/mustangFoxFordVacuumDiagram.jpg

HVAC vacuum diagram
http://www.veryuseful.com/mustang/tech/engine/images/Mustang_AC_heat_vacuum_controls.gif

TFI module differences & pinout
http://www.veryuseful.com/mustang/tech/engine/images/TFI_5.0_comparison.gif

Fuse box layout
http://www.veryuseful.com/mustang/tech/engine/images/MustangFuseBox.gif