Hi All,

Since buying my 89 302 4X4, it has been running extremely rich. I am getting terrible mpg.
I tried to glean as much info as I could from the net, as I was somewhat interested in learning more on the sensor heirarchy when it comes to the EEC and fuel management (fordfuelinjection.com was a huge assest and an invaluable website). As I see it, the ECT sensor and the HEGO are the 2 prime sensors in warm/hot running fuel curves. I know the ACT has a part to play, but from an "eyes burning because she's running too rich" perspective, the engine coolant and O2 sensor play the major roles. I have tested the ECT according to Haynes and it checks out ok, same as the HEGO.
If I am in fact correct, and my theory is sound, should I just R and R one at a time to comfirm?
Now, I have made a couple of assumptions, being my fuel system is in good shape pressure wise and I do not have any leaking injectors. I say my system is in good shape pressure wise because I have checked using my buddy's MotorVac and it was a respectable 35-40 psi. I doubt I have leaking injectors due to the easy starting of the truck. It fires right up, every time, hot or cold on the first try. I do not have any fabled characteristic leaky injector symptoms.

Any ideas or suggestions?

Dan

 

Have you pulled codes?
Have you checked to see if all EEC systems are actually functioning or have some been disabled by some previous owner?
Does fuel pressure remain constant with load (try gage on while driving) and pull vacuum hose to see if there is any fuel smell in hose or evidence of fuel in hose to pressure regulator.
Just some thoughts.

 

Yes, I have pulled the codes KOEO. I got 11, 15, 43 (?), and 44 (?). #15 concerns me, but not to the extent that ROM failure would cause the old girl to run rich. I really doubt it is an EEC issue, as I have experienced the same rich running condition with another EEC I tried last month. #43 and 44 are CM codes, #43 being very interesting as I rarely (if ever) drive at WOT.
I have removed the air pump and bypassed the engine coolant to the throttle body. Recently I changed the t-stat and blew out the heater core. I doubt if that would make a difference.
I will run the codes again tomorrow using my buddy's proper reader and see what that brings to the table.

Dan

 

What have you done with the rest of the air injection system? Have you removed the plumbing and diverter valves? Did you plug the heads? Did you cap the vacuum lines?

 

The vacuum lines were looped together, the rest of the system was left 'as is'.

 

That's a problem. It's sucking fresh air into the exhaust and diluting the A/F ratio just upstream of the O2 sensor, the computer then adds more fuel to compensate. You need to remove these tubes and plug the heads and exhaust.

 

Alright, I ran a scanner on the truck again today and got the following:
KOEO
11
KOER
12-Cannot control RPM during ER Self-Test high RPM check.
25-Knock not sensed during dynamic test.
41-HEGO switching detected always lean

As well, I determined that the PO plugged the heads (I only say this because the steel tubes from the old thermactor valves that ran to the heads were broken off) and the rest of the air pump crap I removed today was just left there. I plugged the vacuum lines (X2 in number). The truck never had the cat when I bought it.

So, #41 seems to be the code of concern. If the sensor is always detecting lean, no wonder I am running rich. Should I stop my troubleshooting now and just buy another O2 sensor.....or are the plugs in the back of the heads leaking, drawing in ambient air, causing the exhaust to always indicate lean at the HEGO? If the plugs were leaking, wouldn't I get an exhaust leak sound?

Where should I go from here?

Dan

 

I ran the codes today, as mentioned in my previous post. The fuel regulator is still shiny new (with no evidence of leaks). I do not have a fuel pressure gauge, although your suggestion has merit. Thanks for that.

Dan