Hi, Wondered if anyone experienced a serious stumble when accelerating from a stop after a 100 mile drive on the highway. I've had 2- 2001 Sport-Tracs (I love 'em) that have darn near caused a bad situation when I tried to pull out into traffic after a stop after having run for an hour on the freeway. The truck starts to accelerate, then stumbles (like it died) for a couple of seconds, then picks up again. Scared the pants off me! It doesn't happen every time, and I think it only happens on hot days. This is the 400 V6...150K miles, new plugs, and otherwise runs flawlessly. I'd sure like to fix that problem...any suggestions?

 

I'm not aware of a 400 ci (or 6.5 - 6.6 L) V6, so I'll assume you meant the stock 4L SOHC V6.

My first suggestion would be to check the fuel pressure with the engine running. If it's on the low end, then consider changing the fuel filter. Actually, you should consider changing the fuel filter if that hasn't been done recently anyway. I'm guessing that the 2001 Sport Trac is similar to my 2000 Mountaineer V8 with the fuel filter behind the driver's side wheel well liner.

Another item to check would be the spark plugs and spark plug wires to make sure they are in good condition and connected well. You mention you have new plugs. Were those replaced just prior to this issue, or as an attempt to fix this issue? Since it sounds like you plan to keep the truck awhile, it may be in your best interest to go ahead and change the plug wires anyway.

A vacuum leak would be pretty typical for the V6, but would usually cause a rough idle as well. You mention yours otherwise runs flawlessly.

Oh, another item to try would be to clean the MAF sensor with MAF sensor cleaner, then pull the intake air tube off the throttle body and clean the throttle body of carbon.

If none of those items work, or to narrow down which of these items to really consider, you could datalog the fuel trims and oxygen sensor voltages to see if it appears that the truck is running rich or lean when it acts up.

-Rod