CEL comes on, but no consistent pattern

[94stockexpl]

Hey all:

I'm having a problem with my 94.
The CEL comes on, but only after I've been highway driving for as much as 15 minutes. Never does it just running around town. Then it doesn't always stay on - sometimes on, sometimes off. I can't feel any difference in drivability or performance when it's on/off.

So far, I've cleaned the MAF, IAC, and changed air filter. I also disconnected battery to reset PCM. I then reconnected, drove some in town and a short trip at highway speeds( CEL did not come on, thought it was fixed !!); went back home, hooked up code reader and KOER showed 111, which is no faults.
Then last evening, took a 35 mile trip to ref a football game and it came back on about 20 miles into the trip. Crap! :thumbdwn:

I will be running another KOER on it, possibly yet this evening and will post results of that. Meanwhile, is there anything I should be checking or considering that might be contributing to the problem?

John

 

[CAHUNTERMAN]

You need to see what code was set when the light came on to really know what direction to look but I had the same symptoms in a 92 Probe and the code was for a lean condition detected. It ended up being the O2 sensor was acting up but only on the highway and over 70 MPH. Replaced the O2 sensor and solved the problem.

 

[boggs1227]

sounds like you need to check harness's all over the truck . the reason i say this is because my maf was replaced .the harness was only taken off maybe 2-3 times during the whole replacement process but it was enough to loosen the clips on the connector and make it not make contact and throw a cel (but yet it took months for this to happen compared to when the work was done on it ) . i could not figure what the hell it was till i found the connector .even tho it's on there and the clips look like they are grabbing ...their not ...so i had to tie wrap the connector on the maf and problem solved.


i would check the pcm again when the cel comes on but if it tells you 111 then i would still look around the truck in the most dirt filled areas for a loose connector ,because if it only comes on the goes off then that sounds like a loose wire and not a bad sensor .anyways it's free except your time and energy and may save you from spending money on a part that may be good .


luck

 

[94stockexpl]

Good ideas from both of you Thanks.

I did run codes a couple weeks ago and got 172, 173, 176, 177. I don't have my code reader book here with me, but those indicate either a lean or rich condition on each side (Bank) I think. At that time I wondered about a wire connection somewhere that feeds both O2 sensors, but did not have time then to start tracing and checking.
After I get codes, I'll post back.

 

[94stockexpl]

Read codes on it this evening earlier. Got a 111 again on KOER. Also ran KOEO and CM: KOEO was 539 (forgot I had defroster on this AM !!) and CM was 172 and 176. I assume the 172 and 176 caused the CEL to come on.
My code reader book's description of those codes is:
172 Oxygen sensor not switching-system is or was lean-Single, Right, or Rear HO2S
176 Oxygen sensor not switching-system is or was lean-Left or Front HO2S - Fuel Control

Can both sensors be (go) bad at the same time ? Or is something further up the wiring harness causing these codes? I seem to remember reading a thread a couple weeks ago about a similar code read that ended up not being O2 sensors, but I can't find it now.....

Thanks for any suggestions anyone might have.

 

[MrShorty]

Can both sensors go bad at the same time? Yes, both sensors can go bad at the same time. However, the chances of them both going bad at the same time aren't that high.

By the book, the first thing they suggest when you get O2 sensor codes (especially for both banks) is to check fuel pressure. A vacuum leak might also be at fault.

 

[94stockexpl]

OK
Gonna chase down a friend who has a fuel pressure guage set and check it, but thought I'd throw this out as well.
When I stopped to get fuel today, with a tank down to fumes almost, as I screwed off the fuel cap I heard what sounded like either suction or pressure being released. Can't say for sure which it was. Anyone run across this before?

Thanks all