High RPMs
Thread Starter
Melting Slicks
Joined: Jun 2012
Posts: 3,163
Likes: 6
From: Oceanside California
High RPMs
Ive read some threads and seen some charts now that show the approximate RPM the engine should be at with whatever gears are installed.
I have an A4 with 3.42's and I feel like my RPM's are way too high. Most people seem to be at 2000rpm at 65mph. I am at 2500 at 65mph. The freeway is killing me and I have to commute. To go 75 and barely stay with traffic I am at 3000rpm the whole way. I read so much about the gears before doing them and was satisfied when I knew it would only drop the economy by 2-3mpg. I am down from 31mpg on the freeway to 25 average.
Why is this happening?
The vehicle is in pristine condition and well maintained. No problems at all. I am mechanically inclined and have gone through everything on this car and done all maintenance items. So its not anything to do with how its running. The only change was the 3-rib 3.42 diff.
I have an A4 with 3.42's and I feel like my RPM's are way too high. Most people seem to be at 2000rpm at 65mph. I am at 2500 at 65mph. The freeway is killing me and I have to commute. To go 75 and barely stay with traffic I am at 3000rpm the whole way. I read so much about the gears before doing them and was satisfied when I knew it would only drop the economy by 2-3mpg. I am down from 31mpg on the freeway to 25 average.
Why is this happening?
The vehicle is in pristine condition and well maintained. No problems at all. I am mechanically inclined and have gone through everything on this car and done all maintenance items. So its not anything to do with how its running. The only change was the 3-rib 3.42 diff.
Safety Car
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From: Wisconsin
Race Director
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Thread Starter
Melting Slicks
Joined: Jun 2012
Posts: 3,163
Likes: 6
From: Oceanside California
I highly doubt the Ethanol has to do with how high my rpms are. But any info helps. Thanks.
Last edited by NukeC5; Sep 2, 2012 at 12:32 PM.
Thread Starter
Melting Slicks
Joined: Jun 2012
Posts: 3,163
Likes: 6
From: Oceanside California
Is it possible that the 3.42 diff I installed has 3.73's or 3.90's and I just didn't know it? That would be closer to the rpm on the chart I am at... I bought if form a guy that bought it from another guy and never used it. He didn't know much about it... maybe it was upgraded in the past. How do I find this out without removing it?
My car is tuned for 3.42's. Would the tuner have noticed that it was off?
My car is tuned for 3.42's. Would the tuner have noticed that it was off?
Thread Starter
Melting Slicks
Joined: Jun 2012
Posts: 3,163
Likes: 6
From: Oceanside California
Holy $hit, 4.10's are actually the closest to what I am getting rpm to mph wise. I'll be PO'd if I have that high of ratio behind my A4. Horrible fuel economy. But maybe that explains why I thought the acceleration increase was so insane even without a converter...
Am I on the right track checking into this? Or is there something else possibly going on?
Am I on the right track checking into this? Or is there something else possibly going on?
Last edited by NukeC5; Sep 2, 2012 at 02:03 PM.
Tech Contributor
Joined: Jan 2007
Posts: 19,450
Likes: 1,155
From: Dyer, IN
...of course it's possible. You purchased a 3rd hand differential, that NO ONE could vouch for the condition/contents, and installed it in your daily driver(sans inspection)......so you can't be too surprised with the outcome.
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Thread Starter
Melting Slicks
Joined: Jun 2012
Posts: 3,163
Likes: 6
From: Oceanside California
This is where I stop and wonder if its possible. How would it have been possible to tune if they were tuning for a 3.42 ratio? It shifts and drives perfect, and the shop hit it correctly on the first attempt at tuning it. So it seems like it would have been caught if the ratio was different.
All I know is that my economy went way further down than it was supposed to and I'm at around 500 more rpm at all speeds than I should be.
Last edited by NukeC5; Sep 2, 2012 at 01:46 PM.
Tech Contributor
Joined: Jan 2007
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From: Dyer, IN
If it is a higher gear, it slipped by the guy I bought it form, myself, the shop that inspected/installed it, and the tuner who corrected the shift points/tachometer. I know what I am looking at, and that it was a good diff, and the shop agreed when they inspected it. So no bad diff was installed into my daily driver. It has the GETRAG 3.42 badge on it, and its easy to assume that's what in it. Especially considering I paid $275.00 bucks for it. Thats extremely cheap for even a used stock 3-rib diff. No one considered that it was modified (It it is).
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From: Da U.P.
Just because the tuner flashed you for a 3.42 doesn't mean you have a 3.42. It also doesn't necessarily mean that everything is right. Have you verified your speedo with a GPS/smartphone to see if it's off?
Thread Starter
Melting Slicks
Joined: Jun 2012
Posts: 3,163
Likes: 6
From: Oceanside California
I would not call $275 cheap, that's a steal. So you are saying the shop physically pulled the cover, and inspected the internals before install? If not, the only way to compare (if you don't trust the speedo method..and don't want to pull the cover), is counting the ratio between driveshaft rotation to wheel rotation.
Basically if its 3.42 I should see close to 3 and a half turns. And 4.10 would be 4 turns right?
Last edited by NukeC5; Sep 2, 2012 at 01:51 PM.
Thread Starter
Melting Slicks
Joined: Jun 2012
Posts: 3,163
Likes: 6
From: Oceanside California
No, this whole thing just hit me this morning. I haven't tried anything yet. Ive been driving with this diff for three months now and thought I just needed to get used to it. But now Im finding it more and more strange that its acting the way it is.
Le Mans Master
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St. Jude Donor '13-'14-'15
Ok sound like your TQ converter is NOT engaging-- On my 3.42 A4 with stock tires my speedo reads 2200 RPM at 70 ( GPS verified as well)
Did you have done or did yourself a speedo correction and a shift point correction when intalling the 3.42's ?? IF so you DO NOT do a speedo correction on ant C5 on a gear change--period !! could be why your TCC is not engaing---You do however need to do a "shift point" correction in your ECM
depending on the gears you previously had the correction should be as follows:
If you had 3.15 gears you should make a - 8.5% shift point correction
If you had 2.73 gears " " ' a - 25% " " "
Try driving on a flat road with no traffic-- from a dead stop with light throttle count the shifts---You should feel 4 shifts the last one being the TCC locking--- Someimes however the 3-4 shift and the TCC lockup will happen very close or even at the same time so it's hard to tell---Another way is while it is in 4th gear if the TCC if unlocked when you punch the throttle the engine will rev up more ( maybe 300-500 RPM's) feels loose----but if it is locked it will rev up very little maybe only 100-200 RPM-- feels connected/locked
Did you have done or did yourself a speedo correction and a shift point correction when intalling the 3.42's ?? IF so you DO NOT do a speedo correction on ant C5 on a gear change--period !! could be why your TCC is not engaing---You do however need to do a "shift point" correction in your ECM
depending on the gears you previously had the correction should be as follows:
If you had 3.15 gears you should make a - 8.5% shift point correction
If you had 2.73 gears " " ' a - 25% " " "
Try driving on a flat road with no traffic-- from a dead stop with light throttle count the shifts---You should feel 4 shifts the last one being the TCC locking--- Someimes however the 3-4 shift and the TCC lockup will happen very close or even at the same time so it's hard to tell---Another way is while it is in 4th gear if the TCC if unlocked when you punch the throttle the engine will rev up more ( maybe 300-500 RPM's) feels loose----but if it is locked it will rev up very little maybe only 100-200 RPM-- feels connected/locked
Tech Contributor
Joined: Jan 2007
Posts: 19,450
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From: Dyer, IN
So I could lift the rear end, mark the converter or whatever is visible, put it in neutral and turn the wheels watching the mark for how many times that mark spins from one full rotation of the wheels?
Basically if its 3.42 I should see close to 3 and a half turns. And 4.10 would be 4 turns right?
Basically if its 3.42 I should see close to 3 and a half turns. And 4.10 would be 4 turns right?
Thread Starter
Melting Slicks
Joined: Jun 2012
Posts: 3,163
Likes: 6
From: Oceanside California
Ok sound like your TQ converter is NOT engaging-- On my 3.42 A4 with stock tires my speedo reads 2200 RPM at 70 ( GPS verified as well)
Did you have done or did yourself a speedo correction and a shift point correction when intalling the 3.42's ?? IF so you DO NOT do a speedo correction on ant C5 on a gear change--period !! could be why your TCC is not engaing---You do however need to do a "shift point" correction in your ECM
depending on the gears you previously had the correction should be as follows:
If you had 3.15 gears you should make a - 8.5% shift point correction
If you had 2.73 gears " " ' a - 25% " " "
Try driving on a flat road with no traffic-- from a dead stop with light throttle count the shifts---You should feel 4 shifts the last one being the TCC locking--- Someimes however the 3-4 shift and the TCC lockup will happen very close or even at the same time so it's hard to tell---Another way is while it is in 4th gear if the TCC if unlocked when you punch the throttle the engine will rev up more ( maybe 300-500 RPM's) feels loose----but if it is locked it will rev up very little maybe only 100-200 RPM-- feels connected/locked
Did you have done or did yourself a speedo correction and a shift point correction when intalling the 3.42's ?? IF so you DO NOT do a speedo correction on ant C5 on a gear change--period !! could be why your TCC is not engaing---You do however need to do a "shift point" correction in your ECM
depending on the gears you previously had the correction should be as follows:
If you had 3.15 gears you should make a - 8.5% shift point correction
If you had 2.73 gears " " ' a - 25% " " "
Try driving on a flat road with no traffic-- from a dead stop with light throttle count the shifts---You should feel 4 shifts the last one being the TCC locking--- Someimes however the 3-4 shift and the TCC lockup will happen very close or even at the same time so it's hard to tell---Another way is while it is in 4th gear if the TCC if unlocked when you punch the throttle the engine will rev up more ( maybe 300-500 RPM's) feels loose----but if it is locked it will rev up very little maybe only 100-200 RPM-- feels connected/locked
I took the car to Cunningham Motorsports near me to have the shift points tuned. I think thats all they did. They specialize in corvettes. So I doubt they changed the speedo if it wasn't needed.
I will give them a call tomorrow to explain what I think is going on and see what they say. Ill ask about a speedo change and if they did one too.
Last edited by NukeC5; Sep 2, 2012 at 02:14 PM.
Thread Starter
Melting Slicks
Joined: Jun 2012
Posts: 3,163
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From: Oceanside California
Burning Brakes
Joined: Oct 2004
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From: Florence SC
So I could lift the rear end, mark the converter or whatever is visible, put it in neutral and turn the wheels watching the mark for how many times that mark spins from one full rotation of the wheels?
Basically if its 3.42 I should see close to 3 and a half turns. And 4.10 would be 4 turns right?
Basically if its 3.42 I should see close to 3 and a half turns. And 4.10 would be 4 turns right?
Drifting
Joined: Jul 2001
Posts: 1,312
Likes: 2
From: Lake Havasu City AZ
Can the back diff cover be pulled and the gear teeth counted? I don't know the number difference between the two sets but I am sure someone here does.
Ex San O Nuke
Mike V
Ex San O Nuke
Mike V
Last edited by MikeV; Sep 3, 2012 at 12:53 PM.