2000 Ranger spark knock

In about 2003 I purchased a 2000 Ranger (3.0 V6 “Flex Fuel”, AT, AC, pwr everything). I later figured out that the seller had a tank full of premium gas in it because it ran just fine. But when I filled it up with the recommended regular grade fuel, it spark-knocked under any slight load. If the load was increased the knock went away, but since light load is the normal driving situation, it knocks almost all the time. Mid-grade fuel solves the problem, but it just sticks in my craw to have to buy mid-grade for a 6 cyl, especially when the manufacturer recommends regular.

Ford says the amount of spark knock is not excessive which just irritates me further (don’t get me started on them) and says there’s nothing to be done. Reminds me of my crappy Chevette way back when.

Electronic diagnostics do not indicate any problems. Some time back, I had EGR errors and failed inspection. I got all that straightened out, but the pre-ignition problem was unchanged.

I have a theory though. My theory is that, being a flex-fuel vehicle, it is configured not to run optimally on either gasoline or 85 ethanol (or whatever it is) but at some compromise. I have a problem with my own theory though, because the onboard computer ought to be taking care of that.

I’ve blown money on “decarbonizing the top end” - I knew it was smoke and mirrors when I agreed to it - no improvement.

Has anybody had a similar experience that they’ve been able to resolve.

Did the dealer re-program the ECU for lower octane?

The majority of spark knock problems are caused by an EGR system fault; some of which may leave no codes.

You state you had EGR errors, failed inspection, and got it all straightened out.
What errors were there and define the “straightend out” part of this.

That’s the first I’ve ever heard of such. Certainly the dealer didn’t mention it as a possibility. What else can you tell me about this?

Hard to remember, it’s been a while, but I could dig out the receipts and check. But it seems to me that it was a sensor, O2 maybe - or CO, and replacing that sensor cleared the error. I had also replaced the easier part myself, the EGR valve I believe, but that didn’t clear the error.

I don’t know much about the 3.0 flex fuel but the 4.0 has a pressure sensor that determines when and how long the EGR will open. Ford came out with a new sensor to replace the failing one. If you engine has one, it would be connected to 2 hoses which come from the exhaust pipe and is quite accesible under the hood. Price where I live is $75.00.