I wanted to post this because this site has always been a big help when I have a problem. I always find it more helpful when somebody reports the fix for their problem, so I wanted to do this.

I have been having several small but annoying problems with my 2000 ford Excursion (6.8 V10 4X4), and as it turns out a single bad part was the cause. I bought the truck in 2008 when I moved from San Diego to Akron, Ohio (no jokes please). Since then I have just driven it and just ignored these nagging problems until recently. My "check engine" light would light up once and awhile (insufficient egr and one time something else), but it would turn off by itself and not reappear for months. I had Autozone read the code one time and they said was nothing to worry about, and reset it or something. It passed both ohio and Ca smog checks.

The first problem that I noticed was that the engine idled high and pinged when towing while using 87 octane gas. I found the pinging would improve with 89 octane and go away entirely if I used 92 octane, so that’s what I did. Normal driving would not usually produce any pinging. In fact, I towed a car over the Grand Tetons using high octane, and did not have any problems. Also I averaged 12.5 mpg towing, which I was happy with.

The second problem was when hot starting. When starting hot, the engine would surge to well over 1,200 RP. Whenever the transmission was shifted into drive or reverse, the engine would suddenly stall out. The only cure was to let it idle for about 30 seconds or so, then it would usually go into gear without stalling. When starting cold this was never an issue.

The third and most important issue after I moved to Georgia, was that that the AC worked intermittently after the vehicle warmed up. When the engine warmed up, the AC would begin to blow warm air when the vehicle was idling, like in traffic or at a light. While just cruising down the highway, the AC worked well.

I discovered the problem really while working to fix the pinging. While searching this site, I found that the DPFE sensors were problematic. So I replaced mine but it did not fix the pinging issue.

Because I was not getting a consistent check engine light and did not trust AutoZone diagnoses, I bought an Innova 3140. While reading the live data stream, I noticed a problem with the ECT (Engine coolant temperature) reading. This sensor would read correctly until the engine warmed past 135 degrees or so, then it would all of the sudden read –55deg. While cruising down the road it would either read 135 or oscillate between that and –55 deg. When stopped at a light it was pegged at –55. When it would read 135 the AC would pump out cold air, but shut off when it showed –55.

I found out (the hard way) that what the innova tool calls “ect” was actually the engine cylinder head temperature sensor. On the 6.8 V10, it was located on drivers side cylinder head in the lifter valley. I had to remove the alternator to get a ¾” wrench on it. As it turns out though, the sensor itself was OK, but I replaced it anyway.

The real problem was in the wiring harness that attached to the sensor. Somehow the circuit was broken there, and only at high temps. I traced the break in the circuit to the molded plastic end that snaps to the sensor itself.

I replaced the one wire and all three problems are now cured, the pinging has stopped, it no longer stalls when starting hot and, most importantly, the AC now works all of the time. I still don't know why having a temperature oscillate between -55 and 135 Deg F would have not thrown a code, but I am sure glad I bought the engine diagnosis tool that had the live data stream, or I would have never figured it out.

 

Glad you took the time to post your fix. How much did you pay for the Innova 3140?