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"Sluggish" 4.0 Explorer

4.0 V6 year 2000 Explorer (UK) In certain condidtions my Explorer suffers from 'sluggish' accelleration which can be quite alarming (and dangerous) when pulling out into traffic and nothing much happens when I stomp on the gas... From a standing start everything seems fairly normal - in comparison to the '98 Ex I had before this one, anyway. The problem arises from a low speed rolling start. A typical scenario is in a line of traffic at a level or slightly downhill junction or intersection. Traffic enters the main road fairly regularly so the line keeps moving at approx 5mph. I get to the head of the line still trundling along at less than 10mph, see a gap in the traffic and stomp on the gas expecting to unleash the 200+ horses hiding under the hood. Not much happens! The revs go up a bit and there is some acceleration and I can hear the motor 'trying' and sense a small amount of torque converter slip. The impression at this point is like being in a high gear (I suspect it's 3rd). Eventually after what seems like an age but is probably 5 or 6 seconds, the truck 'realises' that I want it to 'go' and it changes down a gear and starts to accelerate and then changes down another gear and really takes off like I wanted it to do in the first place.

OK, that was problem #1

Problem #2 may well be linked. When maintaining a steady speed (any speed as long as it's constant) between approx 50mph and 80mph I get an intermittent misfire. It's like a momentary cut out, not like a single sparkplug going off for a moment. I suspect something like a throttle position sensor might be at fault as the feeling is pretty much like when the throttle position sensor went bad on a car I had a few years ago.

Has anybody got any idea where I should start looking? (apart from in the rear view mirror when I've just pulled into traffic...) Oh! and don't suggest booking it into a Ford dealer! Ford dealers here in the UK know absolutely nothing about Explorers :(

TIA Simon H

Reply to
Simon H
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Prob #1 sounds like transmission. What happens when you shift manually, i.e. at the stop be un "L", then looking at the rpms and engine sound shift to "2", and ..... you get he idea.

Prob #2 is your "ck engine" light on? Look at your plugs and wires.

Reply to
mike

Thanks for the reply. No CEL. Plugs were replaced at 40k miles - no difference. Plug wires look and 'seem' OK. I'll try the 'manual' method tomorrow, but it's not gonna be a true test as on the 5 speed auto box position '1' = 1st gear, pos '2' = 3rd, 'D' = 1,2,3 or 4 (or 5) I'd be interested to know what system has replaced the kickdown mechanism on earlier auto trannys? I think the truck 'doesn't realise' that I want it to GO when I stomp on the gas - it seems to just wait around for the gearbox to go through it's torque sensing routine and shift down the gears one by one. If I 'stomp on the gas' at , say, 30 or 40mph the truck behaves just like you'd expect and it will accelerate hard up to 100mph without any problems (apart from the traffic cops) - it's just the take off from a low speed rolling 'start' that's an issue.

Cheers Simon H

Reply to
Simon H

Electronic transmissions don't need 'kickdown', modulators, or any other round-about tricks to sense throttle input and engine load. Instead of having their own hydraulic 'brain', they are controlled directly by the PCM (engine computer). That box knows as much as can be known about what your engine is doing, how fast you are moving, what the temperature on the moon is at the moment, etc, etc. Well, a bit of exaggeration, but you got the idea. All that works as long as the sensors are functioning correctly. But typically when they don't, the CEL turns on.

The sluggish acceleration sounds like a transmission problem, but it could easily be ignition. If this vehicle still has ignition wires (not coil-on-plug) I would start there. They are notoriously difficult to test without an oscilloscope and known to fail, sometimes very early. It's probably a safe bet to replace them on 6 year old vehicle, just as a precaution. Taking a look at the plugs couldn't hurt either.

Reply to
Happy Traveler

intersection.

Since you don't seem to say what you've checked besides the throttle position sensor let me ask: did you check the air filter and fuel filter? Have you checked the mass airflow sensor? What about the spark plug wires? To me it sounds like a transmission problem but I'd check those things first. Check the vacuum lines too.

intermittent

Reply to
Ulysses
5 or 6 years ago Ford issued an update to the PCM in my '97 4.0L SOHC Explorer for the same symtoms you have described. Per Ford, the issue could be experienced when coming to a stop when traveling at a speed of 45-55 MPH. If you rapidly step on the gas, the transmission can get stuck in 3rd gear causing a "percieved lack of acceleration". Well I wasn't percieving anything, it left me stranded in the middle of the intersection more times than I can remember while I waited for normal acceleration to resume. Once they updated my PCM though I have not experienced the issue since.

Alpine

Reply to
Robert Eberhardt

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