I have a mass air 5.0 HO (it's actually an '86 HO with a Ford Racing mass air conversion kit). A while back I installed an Explorer intake. The Explorer intake has no provision for the air temperature sensor from my existing setup, so I plumbed the sensor into the air intake elbow between the mass air meter and the throttle body. That's where it is located on many later model applications, but is there any issue with that location on a mass air HO? I'm asking because I have a strange drivability issue involving ignition timing that started around the time of the upgrade. The computer controlled timing is very erratic, and after a few minutes of running, it goes into limp mode. I know that one of the many sensors the computer reads for timing output is the air temp sensor, and that's the only one that changed positions during the upgrade (which the upgrade may be purely coincidental to this problem, I don't know).

I initially read the codes which showed o2 sensors lean (it's running a little rich), and TAB TAD solenoid codes. I had some spare NOS parts, so I went ahead and replaced the TAB and TAD solenoids, the o2's, and I replaced the o2 harness for good measure. Problem and codes still persist. Any ideas?

 

On the factory equipped mass air trucks, the intake temp sensor is located on the air filter housing. I don't see how it could make that much difference if it is installed in the tube instead.

 

Yes the sensor location is a problem, the mustang computer you are using is programmed to see a range of intake air temps that are closer to the engine operating temps so it will interpret the numbers it is seeing now as out of range. remove the lower intake and drill and tap a runner to install the sensor.

 

I guess that's the next thing to do. I'd be very happy if that solved the problem, but I wonder if that sensor being slightly out of range would cause the amount of trouble I'm having?

 

What happens when it goes into "limp mode".. I'm assuming you mean open loop? And how are you determining it does that? What are the exact stored code numbers?

 

I can see the temperature in the actual intake being different than in the tube or air box. I would be warmer there. I have seen several people with modified setups that have just placed it in the tube, since they had no provision for it. I haven't heard of any of them having problems though.

 

It's been a few weeks since I've worked on it, and I've apparently misplaced the paper I wrote the codes on so I'll have to read them again when I get a chance.

The symptoms are like clockwork. At start up, regardless of engine temperature and not touching the throttle, it runs fairly smooth at normal idle for approximately 1 minute. Then suddenly the RPM will begin to bounce around erratically for a bit (as I believe the ignition timing is hunting. The IAC is not causing the RPM changes) before settling between 300 and 600 RPM for approximately 1 to 2 minutes (it is not drivable during this time). Then suddenly it bounces back up and smooths out at 800 to 1000 RPM and is drivable and fairly consistent for the rest of the running duration, although it is very under powered (I assume this is limp mode?). Occasionally, after having the battery disconnected for a long period of time, the truck runs perfectly at startup and is very powerful for the entire first driving duration. However, if I turn the key off and restart the truck, it goes back to running poorly with the symptoms described above and will repeat those symptoms at every startup like clockwork.

 

Yes, that's why I put it there...I haven't heard of any issues either.

 

I highly doubt IAT sensor would cause those sort of issues. You could find out by just unplugging it. Sounds more to me like a wiring problem, failing sensor, or a failing PCM.

I'd start by pulling the codes, including KOER codes. Make sure the engine is fully warmed up.