CEL after driving for 3-10 minutes, cannot pull code

[ParkerRocker]

I recently pulled my upper and lower intake (which required the removal of the valve covers) and replaced all the gaskets because i was leaking. Well THAT problem is fixed, and it ran perfect for about a week. Now my CEL comes on after driving for 3-10 minutes.

I tried to pull the codes and could not retrieve any, apparently this gets cleared when the engine goes off. and to my knowledge you cannot pull a code from a running engine.

I have heard that it could be the O2 censor, but I have a '92 and replaced the ONLY O2 censor a few months ago.

Ideas?

I ran out of washer fluid and forgot to connect the vacuum line to my TB but i fixed those and still get a CEL.

 

[Michiganbear]

you CAN pull codes from running engines, in fact, some tests require engine running.

if you cannot pull a code from a stopped engine (ignition must be in ON position), then you have a wiring problem, between the EEC test plug and the EEC.

Also, if any codes that are stored are being erased when ign is off, then there is a wiring problem (blown fuse, bad wiring, maybe even bad ign switch), as their is backup power directly from the batt to the EEC

 

[BrooklynBay]

Check the sticky threads in this link: http://www.explorerforum.com/forums/forumdisplay.php?f=114

 

[ParkerRocker]

well i pulled the codes today, KOER DTC 172: HEGO (HD2S) Sensor Fault/Lean.

So basically its the O2 sensor, that pisses me off, its brand new... GRRR. i think i still have the reciept, or at the very least the old 1.

Is there a way 2 test it?

EDIT: I recently replaced the fuel pressure regulator in my '92 with a regulator i pulled from a '95+ explorer with a 4.0L. I thought this was interchangeable, am I wrong? could this be causing the lean reading?

 

[MrShorty]

You only got a KOER 172? Was there an accompanying CM 172 (or similar O2 sensor code)? One common cause of a "false" KOER 172 is to perform the KOER test on a "cold" O2 sensor. O2 sensors don't function until they reach ~600 F, and the KOER test isn't long enough to heat up the sensor. So you have to preheat the O2 sensor immediately before the test by running the engine. Only you know if this is a possibility, but I'd suggest it as a place to start: make sure it's a real code and not something from operator error.

You can test an O2 sensor. there are a couple of ways. In vehicle, simply put a voltmeter on the signal wire (referenced to ground). You should get a voltage that varies from ~.1 V to ~1 V. Out of the vehicle, hook up a voltmeter across the signal and ground leads and point a propane torch flame at the sensor end. The hot, O2 poor environment of the flame should generate a signal.

How new is brand new? I once bought a house brand O2 sensor from a local parts store that died on me within ~ 2 months. You might have got a bad sensor out of the box.

 

[ParkerRocker]

Brand new is about 3 months old. And I had driven the car for about 20 minutes prior to running the test.
I might check the sensor. I also have my old 1 which i suspect might not be bad after all.

really my concern is the FPR, does anybody know if a FPR from a second gen is identical to the ones on a first gen?

 

[MrShorty]

I don't know if they are "identical". Early 2nd gens run a very similar fuel system to the 1st gens (continuously circulating and fuel pressure is regulated to about 40 psi), so if it fits without leaking, it should work. Later 2nd gens ('98 or '99+) used a returnless system, and it might even run at higher pressures (60 psi but I'm not sure). The main way that the FPR/fuel system would contribute to a lean code would be if the fuel pressure is too low.