Question about the PCM, and ingnition timing
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Staging Lane
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Joined: Sep 2003
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From: Long Island, New York
Question about the PCM, and ingnition timing A friend of mine has a 1999 A4 Trans Am Convertible (triple white with an air lid, K&N filter and a Cold Air kit.) He recently purchased the car and we took it to be dynoed for the first time at a TT Performance Dyno Day. When he dynoed his car his max HP numbers were 265 and his max torque numbers were 298. I was interested to know why his numbers were so low and later found out that he had regular 87 octane gas in his car at the time the dyno pulls were made. Fast Forward to today, he recently sent his car to an east coast tuner to have QTP headers (1 3/4") installed and have his car tuned. He had the headers installed with whatever type of cats the QTPs come with. He also paid extra for the high velocity merge collectors. When he got his car back from the shop he said that it made a max power of 310 RWHP.
Thats the story up until now, so now I have some questions.
I have heard that when the computer sees knock retard for any reason it will go into a "Low Octane Park Table" and seriously pull timing. I was wondering if someone could verify the validity of this statement and if it is true would this be the cause of the extremely low intitial dyno numbers. The reason I ask this question is because I have a 98 SS with a very old heads and cam package (DRM Stage 1 heads and a 221/221 114 vette doctors cam) that has 2 degrees of knock retard all the way up and I dont see anything near the timing values indicated when I looked at the tune using LS1edit. My car also only dynoed 360 rwhp and 380 rwt with every bolt on besides on ls6 intake.
If I left anything out please let me know and I will post up any other information needed. Im hopeing one of you guys understands how the PCM works better than me as I would really appreciate any help.
Thanks in advance.
Rob
Thats the story up until now, so now I have some questions.
I have heard that when the computer sees knock retard for any reason it will go into a "Low Octane Park Table" and seriously pull timing. I was wondering if someone could verify the validity of this statement and if it is true would this be the cause of the extremely low intitial dyno numbers. The reason I ask this question is because I have a 98 SS with a very old heads and cam package (DRM Stage 1 heads and a 221/221 114 vette doctors cam) that has 2 degrees of knock retard all the way up and I dont see anything near the timing values indicated when I looked at the tune using LS1edit. My car also only dynoed 360 rwhp and 380 rwt with every bolt on besides on ls6 intake.
If I left anything out please let me know and I will post up any other information needed. Im hopeing one of you guys understands how the PCM works better than me as I would really appreciate any help.
Thanks in advance.
Rob
TECH Senior Member
Joined: Nov 2001
Posts: 7,036
Likes: 1
From: Lake Zurich, IL
There's a low and high octane spark table. The PCM over time learns which table to use... if it detects no knock it will learn more towards the high tables, but if there is knock it'll learn more towards the low.
It will go straight to low octane if it detects alot of knock, otherwise it'll hover between the two until it finally reaches the high octane timing advance
The 2* of retard I believe is a 98 issue
It will go straight to low octane if it detects alot of knock, otherwise it'll hover between the two until it finally reaches the high octane timing advance
The 2* of retard I believe is a 98 issue
He could also get a lot of knock retard from the K&N
crusting up the MAF. If you can log it, look at the PID
for (adaptive spark? not at my tuning laptop now) that
shows where, between the low & high octane, the car is
interpolating as well as current KR. The adaptive spark
is in a sense your knock history. Leanout from MAF
troubles will drive this toward zero and pull a lot of
timing out.
crusting up the MAF. If you can log it, look at the PID
for (adaptive spark? not at my tuning laptop now) that
shows where, between the low & high octane, the car is
interpolating as well as current KR. The adaptive spark
is in a sense your knock history. Leanout from MAF
troubles will drive this toward zero and pull a lot of
timing out.
