I have a '92 F-150 with 5.0 engine (2wd). The check engine light comes on when I am about 1/2 hour into a highway cruise and goes off when I go up an incline. It comes on again when cruising on a flat stretch and goes off again when I again climb a hill. The code I get is 172 (Heated Oxygen Sensor, Bank #1 Lean). Occasionally I get this code with an EGR code (334 or 328). It doesn't seem to affect driveability or give me worse gas mileage but is irritating. I don't want to start replacing parts (EGR valve, Oxygen sensor) if the problem lies elsewhere. Where do I look??

Thanks,

kwing.

 

Every few months, I have a similar problem on my '89 300, but exactly the opposite, and I've always fixed it by buying a new EVP sensor. When the problem exists, the CEL flashes randomly, and only in cooler weather (below 50º and warm engine) AND only when I'm accelerating hard or trying to pull a fairly steep hill. And yeah, mine never RAN any different, but the flashing light sure can be distracting! I've been known to head to the junkyard for an EVP (where I usually get it for free ), but since you seem to have oxygen sensor issues also, swapping out an EVP might not be the first avenue to take.

I know this post isn't helping you, most likely...just thought I'd share a similar problem and what I do to fix it.

Pat

 

I think the EGR and Oxygen Sensor are related as they have exhaust gases passing across them. If it was vacuum related I would have the problem as soon as I started driving. The CEL does not come on until at least 1/2 hour of highway speed. I checked the operation of the EGR valve and it is free and reacts to a vacuum. I'll check voltages/resistance today to find out more.

kwing.

 

Pull the codes. Then you'll have a better idea.

 

There is a good recent EGR thread, search and read.

 

My intermittent CEL stopped after I put in new spark plugs.

 

Here's the aforementioned EGR thread. Rather extensive , but worth reading it all.

https://www.ford-trucks.com/forums/s...d.php?t=299857



guzzler96

 

Yes, quite a long thread indeed but seems to point to suspect brittle vacuum lines. I've broken 2 of them before just taking the upper intake plenum off my 5.0 engine. I broke the yellow line (behind the manifold at a rubber hose leading to the exhaust) and the red line at the vacuum reservoir. I scarfed a couple of rubber inserts and put them back on. Where can you get colour coded vacuum hose at a not bad price??

kwing

 

Dealer doesn't have them, I asked and they said get black rubber. There is a post on here somewhere that I subscribed to where someone was mentioning color coded lines. I will see if I can find it and post later.



guzzler96

 

My '94 F350 w/351 did the same thing in high vacuum conditions and once I traced the brittle and cracked vacuum lines, issue went away. I had some extra tubing from an old set of auxiliary gauges and I used the clear line I had for the vacuum gauge to splice in where the hard plastic ones were shot. So far, no issues and no more CEL.

 

Here's the thread on the vacuum lines. Not much, J.C.Whitney and NAPA. Haven't looked in depth at these.

https://www.ford-trucks.com/forums/s...d.php?t=294593



guzzler96

 

I'll have a good look at those lines tomorrow and see what I find. I may just replace them all. I'll keep you posted on the results.

Thanks for all the info!!

kwing

 

Vip has repair kits for the pink lines.

 

hey MikeL. What is Vip?

And kwing. I had an intermittent CEL. Earlier in this post I said it went away with new spark plugs. I also replaced the distributor cap and rotor. The center terminal on the distributor cap was burnt and misshapen. I think the connector to it was loose and it was arcing a lot. When I pulled the wire off it black dust fell out. My truck starts and runs like a top now.

 

Thanks qman but I just completely rebuilt the engine, new pistons, reground crank, new bearings, rebuilt heads, new plugs, 8.8mm Accel wires, etc. I had this problem before the rebuild as well so I am suspecting vacuum lines or EGR or Oxygen sensor stuff. I'll start with the vacuum line to the EGR first and see how it goes. Note that I have cleaned the EGR valve with intake cleaner before and the problem seemed to go a way for a while but now it is back. I am miffed because it does not occur in town or on short highway trips. Only on longer trips. Like something is getting overheated and expanding or sticking, etc.

kwing