Shifting early, loss of power?
05-16-2009, 09:17 AM
#1
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Join Date: Jul 2005
Posts: 1,783
Shifting early, loss of power?
I recently noticed my car seems to be a little low on power. One reason being it shifts at 45 mph instead of 55 mph like it use to. I scanned it last night and this is what checked out.
-O2 sensors swing back and forth between .1 and .9 fairly rapidly
-BLM cell # 16
-BLM content 137 (idle) and 124 (load), 128 in open loop and first started
-TPS is at zero for idle, moves accordingly
-IAC went between 34-42 at idle depending on when I gave it gas
-Knock counts did not move, stayed at the same number the whole time
-Spark advance jumped from 18-20 degrees
The transmission was brand new (not rebuilt) nearly 4 years ago, and still shifts firm/quickly like it should. Even at WOT the shift is firm and does not lag past 6k RPM. The engine does have 205k on the stock engine (no cam, heads, etc). Has anyone had an issue like this before, and what was the problem? I'm going to check the TV cable, and look for manifold leaks, but I am kind of at a loss for what it could be. Frank from PerformaBuild Transmissions thinks it is more of a PCM/electrical problem.
-O2 sensors swing back and forth between .1 and .9 fairly rapidly
-BLM cell # 16
-BLM content 137 (idle) and 124 (load), 128 in open loop and first started
-TPS is at zero for idle, moves accordingly
-IAC went between 34-42 at idle depending on when I gave it gas
-Knock counts did not move, stayed at the same number the whole time
-Spark advance jumped from 18-20 degrees
The transmission was brand new (not rebuilt) nearly 4 years ago, and still shifts firm/quickly like it should. Even at WOT the shift is firm and does not lag past 6k RPM. The engine does have 205k on the stock engine (no cam, heads, etc). Has anyone had an issue like this before, and what was the problem? I'm going to check the TV cable, and look for manifold leaks, but I am kind of at a loss for what it could be. Frank from PerformaBuild Transmissions thinks it is more of a PCM/electrical problem.
05-16-2009, 10:04 AM
#2
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Join Date: Nov 1998
Location: Hell was full so they sent me to NJ
Posts: 70,677
-O2 sensors swing back and forth between .1 and .9 fairly rapidly - exactly what they are supposed to do
-BLM cell # 16 - indicates throttle was closed and it was idling
-BLM content 137 (idle) and 124 (load), 128 in open loop and first started - BLM's are always 128 in open loop.... can't be any other way. At idle, its adding 7% extra fuel to prevent it from running lean. But you have only indicated "BLM" and not whether it is for the right or left bank. You have to look at both banks and determine if they are close to the same. What "Cell" was it in when you indicate "load"? There are 15 different cells for load, each with a left and right BLM, plus two "synthetic" cells for open loop fueling and decel.
-TPS is at zero for idle, moves accordingly - Hopefully, you mean the TPP (= throttle position percent) was "0". The TPS (= throttle sensor voltage) should be in the range of 0.20-0.90V, with 0.67V the typical value for a stock TB.
-IAC went between 34-42 at idle depending on when I gave it gas - IAC count, if taken at idle, is normal. What it does when you move the throttle is not important, because once you move the TPS above 1.00V, it is not longer controlling idle, it is usually opening up to prvent the engine from stalling if the throttle blade is suddenly closed.
-Knock counts did not move, stayed at the same number the whole time - Normal. Knock count is not related to the knock sensor. It is a simple numerical field that incerments when the PCM sees operating conditions that MAY contribute to knock. It takes no action based on knock counts, unless the knock sensor has recently caused the PCM to retard timing. You shouldn't seen any change in knock counts at idle.
-Spark advance jumped from 18-20 degrees - Normal. As the RPM change slightly, the point the PCM is looking up on the timing table moves slightly, resulting in minor changes to the iginition advance.
Scanning the engine at idle is not really going to tell you why its down on power, or why its not shiftig at the correct MPH. To possibly find a problem under those conditions, you have to scan the PCM under those conditions.
I'm going to check the TV cable - Your 94 (4L60E) doesn't have a TV cable. Shifting at WOT is controlled by the PCM, based mostly on MPH.
-BLM cell # 16 - indicates throttle was closed and it was idling
-BLM content 137 (idle) and 124 (load), 128 in open loop and first started - BLM's are always 128 in open loop.... can't be any other way. At idle, its adding 7% extra fuel to prevent it from running lean. But you have only indicated "BLM" and not whether it is for the right or left bank. You have to look at both banks and determine if they are close to the same. What "Cell" was it in when you indicate "load"? There are 15 different cells for load, each with a left and right BLM, plus two "synthetic" cells for open loop fueling and decel.
-TPS is at zero for idle, moves accordingly - Hopefully, you mean the TPP (= throttle position percent) was "0". The TPS (= throttle sensor voltage) should be in the range of 0.20-0.90V, with 0.67V the typical value for a stock TB.
-IAC went between 34-42 at idle depending on when I gave it gas - IAC count, if taken at idle, is normal. What it does when you move the throttle is not important, because once you move the TPS above 1.00V, it is not longer controlling idle, it is usually opening up to prvent the engine from stalling if the throttle blade is suddenly closed.
-Knock counts did not move, stayed at the same number the whole time - Normal. Knock count is not related to the knock sensor. It is a simple numerical field that incerments when the PCM sees operating conditions that MAY contribute to knock. It takes no action based on knock counts, unless the knock sensor has recently caused the PCM to retard timing. You shouldn't seen any change in knock counts at idle.
-Spark advance jumped from 18-20 degrees - Normal. As the RPM change slightly, the point the PCM is looking up on the timing table moves slightly, resulting in minor changes to the iginition advance.
Scanning the engine at idle is not really going to tell you why its down on power, or why its not shiftig at the correct MPH. To possibly find a problem under those conditions, you have to scan the PCM under those conditions.
I'm going to check the TV cable - Your 94 (4L60E) doesn't have a TV cable. Shifting at WOT is controlled by the PCM, based mostly on MPH.
05-16-2009, 10:38 AM
#3
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Join Date: Jul 2005
Posts: 1,783
Took it for a spirited drive and checked out what happened under WOT and slight load.
What "Cell" was it in when you indicate "load"?
The cell # is 6 at WOT, and the left bank is 122-126, right bank is 124-128. BLM content was at 120-124.
Hopefully, you mean the TPP (= throttle position percent) was "0".
Yes, did not know what to call it but yes that is what I meant.
Your 94 (4L60E) doesn't have a TV cable.
Cool, saves me some time
Under WOT spark advance jumps to 38-42 degrees. Hoping that's also normal.
A couple things I noticed this time was
1) the IAC was at 27 after driving it, and did not want to go any higher/lower. If that's a big deal or not, I'm not sure.
2) the MPH reading I was getting from the scanner and my speedometer were off. The scanner reported 55 mph when my speedo said 51-52 mph. Same went for when speedo said 30 mph, scanner said 32-33 mph. Don't know if that's a big deal, but at 55, 5 mph is the difference between a ticket to some police.
Is the speed sensor in the tailshaft of the transmission, and could that have an effect on my shifting?
What "Cell" was it in when you indicate "load"?
The cell # is 6 at WOT, and the left bank is 122-126, right bank is 124-128. BLM content was at 120-124.
Hopefully, you mean the TPP (= throttle position percent) was "0".
Yes, did not know what to call it but yes that is what I meant.
Your 94 (4L60E) doesn't have a TV cable.
Cool, saves me some time
Under WOT spark advance jumps to 38-42 degrees. Hoping that's also normal.
A couple things I noticed this time was
1) the IAC was at 27 after driving it, and did not want to go any higher/lower. If that's a big deal or not, I'm not sure.
2) the MPH reading I was getting from the scanner and my speedometer were off. The scanner reported 55 mph when my speedo said 51-52 mph. Same went for when speedo said 30 mph, scanner said 32-33 mph. Don't know if that's a big deal, but at 55, 5 mph is the difference between a ticket to some police.
Is the speed sensor in the tailshaft of the transmission, and could that have an effect on my shifting?
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