94 F350 460 e4od. No smog equipment. Headman EGR Headers.Hollow cat.
I had a post a couple months back about the O2 sensor connector melting and my repair, but I did not want to tag back in that one since I feel I’m chasing something else.
When the connector melted on the Y pipe my kid had to limp truck home. Ran like crap, no power, back firing would not go more than 10mph. I disconnected melted connector and truck ran ok, rich but no longer in “limp mode”
I cannot get the truck to run right still after testing and making repairs. I took it for a test and it ran great, but after 10 min it lost power and ran exactly like when the O2 sensor connector melted. The computer also retarted the timing about 10’ from 10’btdc.
Right now after resetting timing the truck idles good in gear, D and R, but in P, or N it drops to 500 and wants to stall. Power is down when punching it in drive.
This is what I have done so far. Pulled codes
1. 334 koeo and keor. Egr closed valve voltage high. Vacuum tested egr and voltage, both tested good.
2. Replaced plugs. Old ones were very black, not wet.Wires are separated and not touching.
3.Compression test, all good.
4 reset timing to 10’btdc. When moving dizzy and getting close to base timing the truck would idle and sound great. You could really here it clean out.
5. New O2 sensor and continuity checked wiring in the loom
6. Fuel pressure all good, continuous, running, wot and unplugging regulator were all right in spec.
I dont know what to check next. Truck ran great before connector melting. I’m not sure what to check next.

 

What is the voltage signal on the O2 sensor? With it plugged in.

 

That I haven’t checked. I just bench tested it with a torch and my meter after rewiring it.
I have not tested it back in the exhaust. Should I probe the rear of the connector at operating temp?
what readings should I be looking for? Same as bench/torch test?

 

could be the ecm popped a capacitor.

 

O2 sensors will send out a voltage based on the oxygen differential between the outside air and the exhaust. Should be between .1-.9v. If it is reading 0V, the sensor circuit is probably shorted.

 

^^^ Yes ^^^
You need to backprobe the O2 sensor for the fluctuating / switching voltage and see where it's at
Start with what 1 Butcher said above
You can do it
You can also pull pids out of that 1994 with a NGS on it's OBD1 system

 

Got it, Thanks

 

Thank You.

 

Explain "can't get her right"
Meted sensor generally just means a blown fuse for a O2 sensor heater circuit
I take it the truck runs like puke? What codes? What's the fuel pressure and does it hold?
the 334 code might be the problem if the EGR valve is nor fully closed
Generally, that code is just a EVP sensor malfunction
In your case, I'd run through those pinpoint tests for that code in the PCED and verify the integrity of the valve

 

It’s low on power when in gear. It hesitates when punching it in Drive or Reverse. Idle drops to around 600-800 in Park, but in gear it idles steady right around 1000. Put in Neutral or Park and idle drops.
no spike in fuel pressure. 34 at idle and 40 with vacuum line off regulator. 39 koeo with pump jumped to run continuously.
I could not find a seperate fuse for the O2 sensor in any diagrams, so I went thru every fuse and checked them all.
Is there fuse for the O2 sensor? Where would it be?
I’m have not had a chance to voltage test the sensors with the truck running yet. I did ohm bench test them and the were both at 5.0.

 

There is no heater fuse on the old ones for the O2 sensors
Your TP voltage is around .8v at idle?
If the truck runs, all the sensors should have the reference voltage like the TP sensor
You wrote that backwards about the idles at 600 in park and 1000 in drive?
If you disconnect the IAC, does it fall on its face? (idle at 550 and just about die)
Low on power, have you checked the base time (ignition timing at 10 degrees with the spout plug out)
Left side hood hinge by the ignition module is where that spout plug is at
For the lack of power, I'd verify the timing is spot on 10 degrees, then clean the injectors through the rail and clean the throttle plate

 

I wrote that right lol, weird… Yeah it idles great in D and R with foot on break. Nice and steady at 1000. Put in P or N, drops to 600-700.
Timing 10’ btdc with spout out. Haven’t gone back to see what computer set it too.
when setting timing to 10’bdtc you can really here the engine clean out and sounds great.
work has been crazy so I haven’t worked on her since vacuum and voltage testing the egr.

 

Maybe the processor does not know the difference between drive and park, like if the transmission range sensor was no good
Those all needed a new connector and a new style TR sensor back in the day if one failed
For you, with a 1994, it is difficult to check the status of the TR sensor without a Ford NGS scan tool