94 3.0 running rich

[Guanfy]

Hello all, back again with another question about my B3000. I've been fighting with my truck running rich for several months now. Most of the time the check engine light stays off but it will flash on for 10 seconds or so then turn back off. When I pull codes they are codes like 173/177/188, all engine mix rich codes. I've replaced the 02 sensors with OEM bosch, checked for vacuum leaks and not found any and validated my fuel system. Injectors are brand new 19lb injectors. Air filter is not that dirty and I just replaced the MAF tonight. Doing that has made the check engine light more frequent and now the ECU is throwing a 173/177/188 codes all at the same time. I've also replaced the IAT for grins and giggles and that didn't really seem to change anything.

The only wrinkle to this is I know my cat is shot. honeycomb is loose inside and rattles around, but I don't think I have any back pressure issues.

Truck starts fine, idles roughly but it idles and is 100% drivable. However I'm only getting around 20mpg on a good day and its always smelling rich. It's driving me crazy. Anyone have any suggestions?

 

[Uncle Gump]

20 mpg's doesn't sound that unreasonable. What about ECT? Fuel pressure within spec?

Also with a broken catalytic convertor... it will smell rich.

 

[Guanfy]

Brand new motorcraft ECT and the fuel pressure should be good. Last time I checked it was around 35psi which is in spec. If the engine is running fine but the engine is throwing codes because the injector pulse width is to narrow I'm fine with that. I just want to make sure that I'm not missing something.

 

[Guanfy]

So I was inspecting the air intake system and found that most likely some air would have been leaking out from around the air filter. I fixed that. Also found that the air intake pipe that goes from the MAF to the throttle body is missing chunks of plastic on the throttle body end. The owner before me probably used an entire roll of duct tape to seal it but I tore all that off and I've been using epoxy to fix the cracks. Sure would be nice to get one in better shape though.

 

[Guanfy]

I may have solved this tonight. After some heavy duty research I figured out the silver disc with vacuum ports inside the air box is what ford calls a Cold Weather Modulator(CWM). Essentially it is a bimetal one way check valve that is use to actuate the air flapper located inside the snorkel. When the engine is cold, the flapper stays in an open position, allowing air warmed by the exhaust manifold to enter the air box and warm the truck up faster. A choke/emission device if you will. However, it is vacuum powered and it is one way. If you happen to have the vacuum source and destination lines backwards, the flapper never moves even after the one way valve closes due to an increase in the temp of the air coming into the engine. This sends overly heated, less dense air into the engine. That in turn forces the ECU to trim past pre-established limits and triggers a rich mix code. I found a post on the explorer forum detailing how these vacuum lines are supposed to be installed. I had them backwards. Switching them and fixing a small vacuum leak at that location seems to have resolved the issue. It's a hot, muggy night here in North Florida in the upper 70's and the truck did not throw a code after driving for nearly an hour at highway speeds. Also cleaned some decent goo out of the PCV valve so I'm sure that helped. The real test will be highway driving while the ambient air temp is in the 90's.

As a semi-related aside, vacuum gauges are awesome. Everybody should have one. You can learn a ton about the health of an engine from hooking one up. Using one let me rule out backpressure issues from a broken cat (engine vacuum was fine at 3k rpm) and any major vacuum leaks, which eventually led me to the CWM. Now to track down the ignition issue that is causing a little bit of stumble at idle..

 

[Guanfy]

Also if anyone is looking for the air intake tube that goes from the MAF to the throttle body for a '94 vulcan 3.0, here's a link: Ford Resonator Tube Assembly

Bimetallic one way check valve for air box: Air Charge Temp Sensor

 

[Guanfy]

So as a follow up.. while everything I talked about this in thread was a probable contributor, the fact the PCV valve was quite gummed up is the most likely stinker. I've cleaned it but not yet had a chance to start and run the trust since. I'll report back in to see if that cleared up all the rich codes.

 

[Guanfy]

So... this was a self-inflicted wound. Turns out you can't use 19lb injectors with this engine, too much for it to adjust for. I installed some reman 14lb injectors last night and did a test run, no codes. Providing it stays that way then problem solved. Now if I could just get the ABS light to turn off...