My truck ran great last year, and I was getting 18mpg on the freeway. Then it started running bad. I've replaced every sensor and the whole EGR valve on my engine and have taken it to 4 different mechanics. Everyone says "it runs great". However, I took an old ECT sensor and plugged it into the ECT lead for the computer and let it hang off the front of the engine (so it would read a much lower engine temp). As I expected, the thing ran great and I've been getting better mileage. However, the problem is that I don't know what else to check/replace to fix this? Any ideas. I may replace the computer as a last resort, but I'm hoping the problem may be elsewhere... Help..!
Thanks,
- "Nealio"

= Aaron K. Neal - 1991 F150 4X4 4.9L I6 =

 

Do this. Disconnect your battery and let the truck sit like this for 30 minutes. This way the computer will loose power and when you reconnect it, it will have to relearn the air/fuel mixtures again. See if they helps out.

 

I've disconnected from the battery a few times. However, its been sitting for a week (alternator caught fire) without a battery so when I put the new alt in tonight I will see if it runs better.
Thanks,
- Nealio
= Aaron K. Neal - 1991 F150 4X4 4.9L I6 =

 

The O2 sensor is showing a .9volt signal voltage which equates to "way too rich". However I know this isn't true. When the O2 is connected it runs horrible, but when disconnected it runs pretty good. The sensor is a Bosch unit and is only 10 months old. What are the odds that it was bad out of the box?? What else could cause the O2 sens to read this high of voltage..?
- Nealio
= Aaron K. Neal - 1991 F150 4X4 4.9L I6 =

 

A cracked exhaust manifold or a bad gasket could be letting air into the exhaust and giving a false reading.

Garrett
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