Hanging revs
06-08-2006, 10:43 PM
#11
4th Gear Member
Join Date: Apr 2006
Location:
Posts: 1,313
RE: Hanging revs
Right. On older cars they had solinoids and other devices to keep the throttle plates from closing at high rpms and creating an over rich mixture. The main reason they claimed it existed was to protect the cats. On some cars it was called a catylist protection solinoid.
What we might be expiriencing is the modern equivilant of that feature.
However, the reason for the orginal feature was that with the throttle closed, with the engine at high rpms, it creates very high vaccume in the intake. This is a very strong signal at the carb. Even with the carb plates shut, the engine is pulling hard on the idle feed orifices and slots. Still richening the mixture. And since you cant shut the fuel off in that application, the easiest thing was to keep the throttle open a bit.
But in modern cars, all they have to do is shut off the injectors to kill the fuel. So I dont quite understand why there is a need to keep the engine speed hanging to protect the cat and decrease emmisions. Unless there are other emision problems created by suddenly shutting the throttle on the motor, which there may very well be.
What we might be expiriencing is the modern equivilant of that feature.
However, the reason for the orginal feature was that with the throttle closed, with the engine at high rpms, it creates very high vaccume in the intake. This is a very strong signal at the carb. Even with the carb plates shut, the engine is pulling hard on the idle feed orifices and slots. Still richening the mixture. And since you cant shut the fuel off in that application, the easiest thing was to keep the throttle open a bit.
But in modern cars, all they have to do is shut off the injectors to kill the fuel. So I dont quite understand why there is a need to keep the engine speed hanging to protect the cat and decrease emmisions. Unless there are other emision problems created by suddenly shutting the throttle on the motor, which there may very well be.
06-09-2006, 11:26 AM
#13
Thread Starter
Join Date: Jun 2006
Location: Front Royal, VA
Posts: 4
RE: Hanging revs
ORIGINAL: Scooter80
Well, on a GT the TPS is on the left side of the TB as you look from the front of the car. Dunno if a 6 is the same??
EDIT, ooh, just found a V6 diagram. The TPS on the 6 is on the Driver's side of the TB. Go Figure.
[IMG]local://upfiles/31863/EC0BFCFAFC1C41D9A4E0CD13121A5B61.jpg[/IMG]
Well, on a GT the TPS is on the left side of the TB as you look from the front of the car. Dunno if a 6 is the same??
EDIT, ooh, just found a V6 diagram. The TPS on the 6 is on the Driver's side of the TB. Go Figure.
[IMG]local://upfiles/31863/EC0BFCFAFC1C41D9A4E0CD13121A5B61.jpg[/IMG]
Just to clarify - I think there's talk about two types of hanging revs here. The 'standard' one is to reduce emissions from an over-rich fuel mixture going through. It sounds like this can be reduced through a canned tune. I believe that there is a second type (which I'm experiencing) which is probably due to a problem with the TPS - which also happens on other Ford vehicles including the Focus. Most likely to be experienced in a manual, when coasting to a stop in neutral. Rather than revs returning to idle, they will stay at the revs that you have been cruising at on that trip (so around 2000rpms if you've been on the freeway for a while). Revs only return to idle when the vehicle comes to a complete stop. I've sometimes experienced the revs dropping down to idle, then picking back up to 2000rpm, which I suppose is an interim condition with the TPS very confused!
Would be interested to hear if anyone else has had these 2nd types of symptoms - obviously you'd only tend to notice if you shift into neutral before stopping. Blackfoot, I agree with you that the service centre explanation is a bit unsatisfactory - I've become rather cynical of service centres in general and the skill is finding one you trust.
06-09-2006, 11:45 AM
#14
2nd Gear Member
Join Date: Mar 2006
Location:
Posts: 311
RE: Hanging revs
ORIGINAL: Speedy
Scooter - awesome, thanks a bunch for the diagram. Just what I was hoping for. Hopefully I'll get a chance to have a check later on.
Just to clarify - I think there's talk about two types of hanging revs here. The 'standard' one is to reduce emissions from an over-rich fuel mixture going through. It sounds like this can be reduced through a canned tune. I believe that there is a second type (which I'm experiencing) which is probably due to a problem with the TPS - which also happens on other Ford vehicles including the Focus. Most likely to be experienced in a manual, when coasting to a stop in neutral. Rather than revs returning to idle, they will stay at the revs that you have been cruising at on that trip (so around 2000rpms if you've been on the freeway for a while). Revs only return to idle when the vehicle comes to a complete stop. I've sometimes experienced the revs dropping down to idle, then picking back up to 2000rpm, which I suppose is an interim condition with the TPS very confused!
Would be interested to hear if anyone else has had these 2nd types of symptoms - obviously you'd only tend to notice if you shift into neutral before stopping. Blackfoot, I agree with you that the service centre explanation is a bit unsatisfactory - I've become rather cynical of service centres in general and the skill is finding one you trust.
ORIGINAL: Scooter80
Well, on a GT the TPS is on the left side of the TB as you look from the front of the car. Dunno if a 6 is the same??
EDIT, ooh, just found a V6 diagram. The TPS on the 6 is on the Driver's side of the TB. Go Figure.
[IMG]local://upfiles/31863/EC0BFCFAFC1C41D9A4E0CD13121A5B61.jpg[/IMG]
Well, on a GT the TPS is on the left side of the TB as you look from the front of the car. Dunno if a 6 is the same??
EDIT, ooh, just found a V6 diagram. The TPS on the 6 is on the Driver's side of the TB. Go Figure.
[IMG]local://upfiles/31863/EC0BFCFAFC1C41D9A4E0CD13121A5B61.jpg[/IMG]
Just to clarify - I think there's talk about two types of hanging revs here. The 'standard' one is to reduce emissions from an over-rich fuel mixture going through. It sounds like this can be reduced through a canned tune. I believe that there is a second type (which I'm experiencing) which is probably due to a problem with the TPS - which also happens on other Ford vehicles including the Focus. Most likely to be experienced in a manual, when coasting to a stop in neutral. Rather than revs returning to idle, they will stay at the revs that you have been cruising at on that trip (so around 2000rpms if you've been on the freeway for a while). Revs only return to idle when the vehicle comes to a complete stop. I've sometimes experienced the revs dropping down to idle, then picking back up to 2000rpm, which I suppose is an interim condition with the TPS very confused!
Would be interested to hear if anyone else has had these 2nd types of symptoms - obviously you'd only tend to notice if you shift into neutral before stopping. Blackfoot, I agree with you that the service centre explanation is a bit unsatisfactory - I've become rather cynical of service centres in general and the skill is finding one you trust.
Would another symptom be a high idle upon cold start? Like 2500-3000 RPM's that stay there for like 10 seconds? Only happens when the car is dead cold and can be stopped by reversing out of the driveway. A short distance, but once all the way back and then into 1st, the idle has settled down. Weird. I called Procharger on it and they say its normal for a s/c'd car, but I am not believing that.
06-09-2006, 02:09 PM
#15
1st Gear Member
Join Date: Mar 2006
Location:
Posts: 109
RE: Hanging revs
My 98 F-150 does this. I know it's not a Mustang but it is a Ford with a 5 speed manual and a 4.6L V8. I always thought they left the revs hang while the vehicle is in motiion and the tranny in neutral so the tranny would be easier to put back into gear if you decided to.
06-09-2006, 04:01 PM
#17
2nd Gear Member
Join Date: Jun 2005
Location:
Posts: 271
RE: Hanging revs
Here's another data point:
I noticed the revs staying up nearly a year ago when I got my car, have complained about it multiple times, and the dealer says there is nothing they can do about it.
I've watched it closely and generally understand what it's going to do. I can be cruising down the road at 35 mph, gently nudge the shifter into neutral, and watch the revs stay at 1800 rpms until I come to a complete stop. Sometimes it's 1800, sometimes 1500, and sometimes 1200, but it stays up there until it detects that the car has come to a complete stop, then it drops right down to 800. If you wait long enough it will come down anyway. It seems to make a difference whether or not you push the clutch in when going into neutral, but only for how high the engine is running.
I find it especially annoying when heading downhill in the mountains and I can't get full engine braking for five seconds or more.
If anyone ever gets Ford to admit this is a problem and provide a fix for it, please let me know so I can get it fixed.
I noticed the revs staying up nearly a year ago when I got my car, have complained about it multiple times, and the dealer says there is nothing they can do about it.
I've watched it closely and generally understand what it's going to do. I can be cruising down the road at 35 mph, gently nudge the shifter into neutral, and watch the revs stay at 1800 rpms until I come to a complete stop. Sometimes it's 1800, sometimes 1500, and sometimes 1200, but it stays up there until it detects that the car has come to a complete stop, then it drops right down to 800. If you wait long enough it will come down anyway. It seems to make a difference whether or not you push the clutch in when going into neutral, but only for how high the engine is running.
I find it especially annoying when heading downhill in the mountains and I can't get full engine braking for five seconds or more.
If anyone ever gets Ford to admit this is a problem and provide a fix for it, please let me know so I can get it fixed.
06-10-2006, 05:35 PM
#18
2nd Gear Member
Join Date: Aug 2005
Location: Houston TX
Posts: 222
RE: Hanging revs
yeah, for the most part I think ppl are talking about the emissions deal. Really Really REALLY annoying if you miss a gear...
and I'm not sure if this is at all related but any of you who fixed the hanging idle with a tune...can you shift into first going any faster than 10 mph? I hate that I'm locked out of gear until I make a damn near complete stop. What if I'm at 20-25 in 2nd and want to downshift for a little fun. NOPE!
and I'm not sure if this is at all related but any of you who fixed the hanging idle with a tune...can you shift into first going any faster than 10 mph? I hate that I'm locked out of gear until I make a damn near complete stop. What if I'm at 20-25 in 2nd and want to downshift for a little fun. NOPE!
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