I'm sick...think my car is developing "The Stumble"
07-15-2017, 03:56 PM
#91
Rennlist Member
One of mine threw a code and I replaced it. The other one did not throw a code, still had the stumble, and then I replaced the other one . Both of them within a two month timeframe. For only $150, I would do them both so you know they are both reading the same and on the same schedule.
Last edited by ChicagoSpeed996; 07-15-2017 at 10:15 PM.
07-15-2017, 10:14 PM
#92
Rennlist Member
Day 3 update. Over 80 miles. No cough no stumble. There is still the feeling of the cam changeover sometimes but no 2500 rpm cough/stumble at all.
Who is the next guinea pig?
Who is the next guinea pig?
07-16-2017, 09:43 AM
#93
Burning Brakes
07-16-2017, 09:49 AM
#94
Rennlist Member
07-16-2017, 09:54 AM
#95
Rennlist Member
Observation:
Removed my Cobb AV3 tune - map 93 last week as I sold the unit and will be selling my car ('16 C2). While I did not have the stumble before as has been described for years, the introduction of power is nowhere as smooth without the tune. I would not call it a stumble, but it is clearly different and not in a good way.
If you have some fortitude, purchase the Cobb tune for $1295, if it does not work to fix the stumble you can resell it for a $1000 or keep it. The engine will run a lot smoother. Alternatively, scan the RL Parts forum, they are offered for sale from time to time.
Removed my Cobb AV3 tune - map 93 last week as I sold the unit and will be selling my car ('16 C2). While I did not have the stumble before as has been described for years, the introduction of power is nowhere as smooth without the tune. I would not call it a stumble, but it is clearly different and not in a good way.
If you have some fortitude, purchase the Cobb tune for $1295, if it does not work to fix the stumble you can resell it for a $1000 or keep it. The engine will run a lot smoother. Alternatively, scan the RL Parts forum, they are offered for sale from time to time.
07-17-2017, 09:38 AM
#96
Rennlist Member
Day 4 and 5 updates. Two cold starts, at the beginning of each day. Typically the stumble would be present during called operation and as well as warm operation. But could be quite severe during called operation. Both days the stumble was not present. Covered over 110 miles and the two days.
07-17-2017, 09:41 AM
#97
Rennlist Member
Observation:
Removed my Cobb AV3 tune - map 93 last week as I sold the unit and will be selling my car ('16 C2). While I did not have the stumble before as has been described for years, the introduction of power is nowhere as smooth without the tune. I would not call it a stumble, but it is clearly different and not in a good way.
If you have some fortitude, purchase the Cobb tune for $1295, if it does not work to fix the stumble you can resell it for a $1000 or keep it. The engine will run a lot smoother. Alternatively, scan the RL Parts forum, they are offered for sale from time to time.
Removed my Cobb AV3 tune - map 93 last week as I sold the unit and will be selling my car ('16 C2). While I did not have the stumble before as has been described for years, the introduction of power is nowhere as smooth without the tune. I would not call it a stumble, but it is clearly different and not in a good way.
If you have some fortitude, purchase the Cobb tune for $1295, if it does not work to fix the stumble you can resell it for a $1000 or keep it. The engine will run a lot smoother. Alternatively, scan the RL Parts forum, they are offered for sale from time to time.
Just for another data point. I also have a tune and the stumble was present with the tune. Changing the oxygen sensors for less than $250 got rid of the stumble so far.
07-17-2017, 11:24 AM
#98
okay, new to the 991. I had a chip in my 964 that definatly changed the rev limter etc. Just looked on the Cob web site and if I read their peak HP gains correctly they are saying peak gaines on an S model are on 93 octane gas 400 HP x Max: +9.75% HP = an additional 39 HP. Is this real, has anyone independent dyno'd ? If it is real, that is a real cheap performance gain.
Carrera S 3.8L (Non X51)
Stage1 91:
+5.15% HP, +5.83% TQ
Max: +7.48% HP, +7.33% TQ
Stage1 93:
+7.32% HP, +8.74% TQ
Max: +9.75% HP, +9.84% TQ
Carrera S 3.8L (Non X51)
Stage1 91:
+5.15% HP, +5.83% TQ
Max: +7.48% HP, +7.33% TQ
Stage1 93:
+7.32% HP, +8.74% TQ
Max: +9.75% HP, +9.84% TQ
07-17-2017, 12:27 PM
#99
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okay, new to the 991. I had a chip in my 964 that definatly changed the rev limter etc. Just looked on the Cob web site and if I read their peak HP gains correctly they are saying peak gaines on an S model are on 93 octane gas 400 HP x Max: +9.75% HP = an additional 39 HP. Is this real, has anyone independent dyno'd ? If it is real, that is a real cheap performance gain.
Carrera S 3.8L (Non X51)
Stage1 91:
+5.15% HP, +5.83% TQ
Max: +7.48% HP, +7.33% TQ
Stage1 93:
+7.32% HP, +8.74% TQ
Max: +9.75% HP, +9.84% TQ
Carrera S 3.8L (Non X51)
Stage1 91:
+5.15% HP, +5.83% TQ
Max: +7.48% HP, +7.33% TQ
Stage1 93:
+7.32% HP, +8.74% TQ
Max: +9.75% HP, +9.84% TQ
Looks like there may be a little confusion on Peak/Max gains. Peak gains are where the car makes the most HP/TQ to the wheels at a single RPM point in the dyno graph. So, you need to look at the graph, see where the car made the most horsepower/tq to the wheels on the stock run and then add 7.32% HP and 8.74%tq to the wheels at that specific RPM point.
Max gains are where there was the largest gain over the entire dyno run- for example- a car may make peak horsepower at 6800 RPM and only gain 4whp there- but below the curve at say 3500RPM we were able to gain significantly more, say 20whp. This is where your max gain% is relevant.
Bottom line- it's also why answering the question of "how much do I gain" with a single number, though it's what we all want/expect, isn't the entire story as it's much more relevant to look at the entire dyno curve and see where the gains are made.
Thanks!
~Jared
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07-17-2017, 12:41 PM
#100
07-17-2017, 12:55 PM
#101
ok, so no to be thick here but is the claim then 400 stock HP + the 7.32 or 28.29 HP being gained only at a single point in the dyno but is not like bolting on something that gives you an extra 29 HP (think powerkit, etc). Has there been any real world testing with zero to 60 or quarter performance measurements ?
Looks like there may be a little confusion on Peak/Max gains. Peak gains are where the car makes the most HP/TQ to the wheels at a single RPM point in the dyno graph. So, you need to look at the graph, see where the car made the most horsepower/tq to the wheels on the stock run and then add 7.32% HP and 8.74%tq to the wheels at that specific RPM point.
Max gains are where there was the largest gain over the entire dyno run- for example- a car may make peak horsepower at 6800 RPM and only gain 4whp there- but below the curve at say 3500RPM we were able to gain significantly more, say 20whp. This is where your max gain% is relevant.
Bottom line- it's also why answering the question of "how much do I gain" with a single number, though it's what we all want/expect, isn't the entire story as it's much more relevant to look at the entire dyno curve and see where the gains are made.
Thanks!
~Jared
Max gains are where there was the largest gain over the entire dyno run- for example- a car may make peak horsepower at 6800 RPM and only gain 4whp there- but below the curve at say 3500RPM we were able to gain significantly more, say 20whp. This is where your max gain% is relevant.
Bottom line- it's also why answering the question of "how much do I gain" with a single number, though it's what we all want/expect, isn't the entire story as it's much more relevant to look at the entire dyno curve and see where the gains are made.
Thanks!
~Jared
07-17-2017, 01:34 PM
#102
Rennlist Member
Alright, pfan! the next guinea pig. How about you stealth boy? With three data points (plus the previous one I read somewhere) that makes a line on a graph! This is SWAG science at it best! Look out, I'm about to do science!!
07-17-2017, 01:40 PM
#103
Rennlist Member
07-17-2017, 03:12 PM
#104
Burning Brakes
I intend to after I have let my fuel treatment run its course. I do not want too many variables changing at once. This is science, after all.