TPS or Transmission?
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Senior User
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TPS or Transmission?
I posted a thread a while ago but didn't hear anything back...Trying again.
When coasting and then accelerating (trying to change lanes to pass quickly), the truck hesitates...it increases in rpms, then quickly decreases, then increases steadily. It's almost like it shifts into overdrive right as I press the gas. Not sure if it's the TPS or the Transmission.
I've tested voltage on the TPS as someone presses the gas smoothly, and I can't tell if the volts are smooth at first, because the numbers change so fast. Any ideas? I don't want to replace the TPS if it's the tranny or something else.
1998 F150 5.4 4x4
Thanks.
When coasting and then accelerating (trying to change lanes to pass quickly), the truck hesitates...it increases in rpms, then quickly decreases, then increases steadily. It's almost like it shifts into overdrive right as I press the gas. Not sure if it's the TPS or the Transmission.
I've tested voltage on the TPS as someone presses the gas smoothly, and I can't tell if the volts are smooth at first, because the numbers change so fast. Any ideas? I don't want to replace the TPS if it's the tranny or something else.
1998 F150 5.4 4x4
Thanks.
Hotshot
Joined: Jul 2005
Posts: 11,931
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maybe i dont get the question, but when you stomp on the throttle, the transmission down shifts and the RPM goes up. Truck accelerates untill you reach a certain RPM depending on how far you got your foot into it.. Then the transmission shifts up one gear and the RMP drops about 1000 rpm. THen you slowly increase RPM and truck speed increases.. sounds o.k. to me, unless your saying the timing of the situation is off.
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I'll try to make it more clear...when I stomp on the accelerator, the rpms increase about 1000 and then almost immediately they decrease about 1000, then the truck accelerates normally. It's the initial hesitation.
I hope that makes more sense.
I hope that makes more sense.
Lead Driver
Joined: Sep 2006
Posts: 7,907
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I suspect you are not discribing the issue accuratly.
If the truck begins to miss under light throttle after coasting, you have a faulty coil that is not a hard fault.
Reason: Under light throttle in OD the EGR operated, the fuel is cut back and timing is advanced making the mixture very lean.
If a coil has shorted turns, it is low on voltage output and can't fire the lean mix so the cylinder misses until you give it a large amount of throttle causing the system to shut off the EGR and revert back to a richer mix the coil still has enough voltage to fire so the issue clears and never sets a code or CEL lamp.
Which one is the small problem to determine due to the absence of a code.
This problem is a huge pain for a lot of owners because of it's complexity and suttle way it shows it'self.
If the truck begins to miss under light throttle after coasting, you have a faulty coil that is not a hard fault.
Reason: Under light throttle in OD the EGR operated, the fuel is cut back and timing is advanced making the mixture very lean.
If a coil has shorted turns, it is low on voltage output and can't fire the lean mix so the cylinder misses until you give it a large amount of throttle causing the system to shut off the EGR and revert back to a richer mix the coil still has enough voltage to fire so the issue clears and never sets a code or CEL lamp.
Which one is the small problem to determine due to the absence of a code.
This problem is a huge pain for a lot of owners because of it's complexity and suttle way it shows it'self.
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It's difficult to explain because it happens so fast, but it is noticeable and getting annoying. What you said makes sense, but is there a way to test all of the coils without having to buy all new ones? I replaced one of the coils not too long ago, but the CEL came on so I knew which one to replace.
Senior User
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I know what you're saying but I'm not sure either. Mine does something similar. With mine you can barely touch the accelerator and the truck down shifts momentarily and the shifts back into high.
When testing the tps you should have .5 to 1v. with
closed throttle. When the throttle is open it should
range from about 4.5 to 5 volts steadily increasing.
Mine however, works just the opposite. Starts high
and goes to low. I haven't found anyone who can explain that sufficiently. I've been told that you should only use the ground in that tps plug when
testing. Good Luck.
When testing the tps you should have .5 to 1v. with
closed throttle. When the throttle is open it should
range from about 4.5 to 5 volts steadily increasing.
Mine however, works just the opposite. Starts high
and goes to low. I haven't found anyone who can explain that sufficiently. I've been told that you should only use the ground in that tps plug when
testing. Good Luck.
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Senior User
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Probably not a cop but you can have someone sit
in the cab and put the truck in reverse while holding
the break bring the rpms up slightly. You unplug each cop and listen for changes in rpms. No change means a bad cop probably. If you hear a change it's
okay. If no change could also mean a bad plug.
in the cab and put the truck in reverse while holding
the break bring the rpms up slightly. You unplug each cop and listen for changes in rpms. No change means a bad cop probably. If you hear a change it's
okay. If no change could also mean a bad plug.
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From: Stockton Ca.
Both the TPS and COP are Motorcraft branded, not Ford captive parts. Check your local parts stores, if they don't carry Motorcraft they should be able to order it for you in Motorcraft brand.
Check prices and do your shopping, but when it comes to any component that feeds info to the PCM I'd recommend Motorcraft or Ford parts.
Check prices and do your shopping, but when it comes to any component that feeds info to the PCM I'd recommend Motorcraft or Ford parts.
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