To all,
I have a 1997 TransSport with the 3.4L with about 130,000Km on it and in good shape. The tranny is a 4-spd auto.
This past weekend I noticed a peculiar problem. When in 4th gear doing
80Km/H (about 50Mph) if you accelerate lightly so that the tranny stays in 4th the van will start chugging as if it is misfiring. If you hit the throttle to gear it down, or wait for the RPM to pass 2000 then the van pulls strongly. If you do nothing, it will "chug" 3 or 4 times until it passes 2000RPM and then accelerate smoothly.Similarly, when accelerating from a complete stop you can feel this same "chug", only once or twice though. It kind of feels like that sensation you get when your tires spin a bit when accelerating across those crosswalk lines when they are wet. Again, once you get over 2000 RPM the van pulls strongly. Also, if you let the van start to roll away before accelerating you don't get the "chug". Further, if you "granny" start you don't get it. You have to be about 1/8-ish on the throttle, any harder and it gets passed
2000 RPM too fast and you won't feel it.The mechanic and I initially thought plug wires, but they check out fine. We then tested the fuel pressure, fine. We flushed the engine and changed the oil and fuel filter. It still does the "chug" thing. No dash lights come on and there are no error codes in the computer (the mechanic scanned it).
Other points: the idle is fine, no strange sounds (clicking or otherwise). If you do a "brake stand" all is well. Fuel mileage hasn't changed noticeably. The van has never towed anything.
A tune up, along with plugs were done this spring even though there was nothing wrong. Did lower ball joints at the same time.
Right now I am thinking tranny with a slipping torque converter or something since it kind of feels like what a previous vehicle did when the clutch was slipping in a standard tranny. Tranny fluid smells and feels fine though.
Any other ideas out there?
Thanks Tim