lawdash wrote:
Thanks Cobra, that does help. I have sporadic check engine light but the computer won't give up the code. Also getting some nice backfires and lots of sputtering. Climbing into higher elevations makes it worse. I think O2 sensor seems like the most likely culprit, would you agree?
When you say it won't give up the code, what do you mean? Do you mean unless the light is actually lit you can't pull the code? Or do you mean that you scan the code and it won't give a code number?
Is the chassis OBDI or OBDII? If it only has one O2, and no cat, then probably OBDI.
I'm not very familiar with Ford MH chassis, but I am intimately familiar with Ford Fuel Injection Controls in general.
An O2 sensor on the way out will not typically cause the symptoms you are describing. When O2's start going, the heated circuit is what usually goes first. This means that the O2 isn't preheated so it can start "switching" correctly. The other way an O2 will go bad is they stop "switching" due to age or contamination. When that happens, the vehicle will run off calculated tables.
Sounds more like an issue with:
1. Bad MAF unit (assuming it has one). Does your chassis have a Mass Air Flow? I'm guessing not. I'm thinking Ford never had a 460/MAF combo but my memory is a bit fuzzy on that.
2. Vacuum leak of some type. Is the backfiring occurring in the exhaust or in the intake?
3. Exhaust leak - believe it or not, an exhaust leak can give issues on fuel injected motors like you describe.
4. EGR valve stuck open - this is basically a giant vacuum leak.
Honestly, it's going to be a lot of guesswork until we can get a code pulled. You can throw parts at it, but it's like gambling. However, I will say that if it has the OEM/original O2 sensor(s) on it it, they are far past time for a change. I think the life expectancy on O2's degrades significantly after five years.
By the way, any time you install any new sensor on your vehicle, disconnect the battery for 30 minutes (in fact, disconnect the battery before you do any work on your car is good practice). The disconnect will clear all short and long term fuel trims and let the EEC relearn it's adaptive strategy.
In fact, before you replace ANY parts, lets try a little test: Disconnect your battery for 30 min and take it for a drive and report if it acts any better or not.
