AUJP $8D Idle Limiter - Code Question
10-22-2012 | 01:14 PM
#1
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From: Montgomery, AL
Car: 84 El Camino
Engine: 360 TPI
Transmission: 700R4
Axle/Gears: 3.42 + Truetrac, Moser 28 Spline
AUJP $8D Idle Limiter - Code Question
Need some help from the gurus who know the AUJP code or from someone with an ECM bench. Sorry for the long post, but some detail needed.
In summary, at idle in Park, my logs are consistently reporting ‘Desired Idle RPM’ values that differ from those set in the ‘Idle Engine Speed .vs. Temp’ table (table below):
Deg F---RPM
...
68-------950
90-------900
111------850
133------800
154------750
...
For example, a cold start-up log in Park at 80*F, shows ’Desired Idle RPM’ at 800 (and Actual RPM is approx. 800). Everything stays that way until 133*F is reached and then Desired and Actual RPM start gradually declining to 750 as per the table. But that’s not what the table says should happen. It says Actual start-up (and Desired) RPM at 80*F should be between 900 and 950 RPM and then decline from there, but they’re not doing that!
So on a lark, changed the ‘Idle Limiter’ values in the AUJP code at addresses 0x426C and 0x4270 from 40hex (800 RPM) to 50hex (1000 RPM) in accordance with this thread: https://www.thirdgen.org/forums/diy-...ter-730-a.html
Bingo -- Immediately upon startup at 80*F in Park, the log reported ‘Desired Idle Speed’ at 925, and car idles at 925. What??? According to the link and all my research, the addresses changed are supposed to affect in-gear idle only. My first thought was that the ECM didn’t know the car was in Park, but that’s not the case because idle increases by 100 RPM when going from gear to Park/Neutral, which is the value set in ‘Idle engine speed in P/N added to base’.
For the life of me with these results and observations, it looks like something in the AUJP code is restricting idle to 800 RPM regardless of whether in gear or P/N. But then that seems illogical because it would render the ‘Idle Engine Speed .vs. Temp’ table useless at cold temps where RPMs are set > 800.
Any thoughts or ideas on this anomaly? Could bin changes to not restrict idle to BLM cell 4, disabling AIR and CCP, or defeating EGR cause this?
In summary, at idle in Park, my logs are consistently reporting ‘Desired Idle RPM’ values that differ from those set in the ‘Idle Engine Speed .vs. Temp’ table (table below):
Deg F---RPM
...
68-------950
90-------900
111------850
133------800
154------750
...
For example, a cold start-up log in Park at 80*F, shows ’Desired Idle RPM’ at 800 (and Actual RPM is approx. 800). Everything stays that way until 133*F is reached and then Desired and Actual RPM start gradually declining to 750 as per the table. But that’s not what the table says should happen. It says Actual start-up (and Desired) RPM at 80*F should be between 900 and 950 RPM and then decline from there, but they’re not doing that!
So on a lark, changed the ‘Idle Limiter’ values in the AUJP code at addresses 0x426C and 0x4270 from 40hex (800 RPM) to 50hex (1000 RPM) in accordance with this thread: https://www.thirdgen.org/forums/diy-...ter-730-a.html
Bingo -- Immediately upon startup at 80*F in Park, the log reported ‘Desired Idle Speed’ at 925, and car idles at 925. What??? According to the link and all my research, the addresses changed are supposed to affect in-gear idle only. My first thought was that the ECM didn’t know the car was in Park, but that’s not the case because idle increases by 100 RPM when going from gear to Park/Neutral, which is the value set in ‘Idle engine speed in P/N added to base’.
For the life of me with these results and observations, it looks like something in the AUJP code is restricting idle to 800 RPM regardless of whether in gear or P/N. But then that seems illogical because it would render the ‘Idle Engine Speed .vs. Temp’ table useless at cold temps where RPMs are set > 800.
Any thoughts or ideas on this anomaly? Could bin changes to not restrict idle to BLM cell 4, disabling AIR and CCP, or defeating EGR cause this?
10-22-2012 | 01:41 PM
#2
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From: Chasing Electrons
Car: check
Engine: check
Transmission: check
Re: AUJP $8D Idle Limiter - Code Question
Your best bet is to check the P/N input status to the ECM. It is in the FMD status byte of the ALDL stream.
RBob.
RBob.
10-23-2012 | 10:26 AM
#3
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From: Montgomery, AL
Car: 84 El Camino
Engine: 360 TPI
Transmission: 700R4
Axle/Gears: 3.42 + Truetrac, Moser 28 Spline
Re: AUJP $8D Idle Limiter - Code Question
10-23-2012 | 11:21 AM
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From: Chasing Electrons
Car: check
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Transmission: check
Re: AUJP $8D Idle Limiter - Code Question
Can check the pin via an DVM, P/N is 0 volts. With a drive gear being close to IGN+ volts.
It is better to check the P/N status that the ECM has:
That is byte #56 of the data stream, bit 0 has the input status.
RBob.
It is better to check the P/N status that the ECM has:
Code:
; 56 FMDBYTE1 BIT STATUS WORD ; 0 PARK/NEUTRAL SWITCH (1 = DRIVE)
RBob.
10-23-2012 | 03:26 PM
#5
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Senior Member
Joined: Jun 2010
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From: Montgomery, AL
Car: 84 El Camino
Engine: 360 TPI
Transmission: 700R4
Axle/Gears: 3.42 + Truetrac, Moser 28 Spline
Re: AUJP $8D Idle Limiter - Code Question
Can check the pin via an DVM, P/N is 0 volts. With a drive gear being close to IGN+ volts.
It is better to check the P/N status that the ECM has:
That is byte #56 of the data stream, bit 0 has the input status.
RBob.
It is better to check the P/N status that the ECM has:
Code:
; 56 FMDBYTE1 BIT STATUS WORD ; 0 PARK/NEUTRAL SWITCH (1 = DRIVE)
RBob.
In Gear? = bit zero of Diagnostic Data Stream byte 56 (byte 55 zero-based)
if False (0) = No (in P/N), if True (1) = Yes
If the bitmask is correct (would appreciate your review), the ECM is reporting the car is always in gear (bit 0 = 1). This is with key on, engine off, and also with engine running and does not change regardless of what gear the car is in (Park to 1st).
If the bitmask is incorrect, then I’ve got more work to do. But if correct, clearly the ECM doesn't know it's in P/N. So seems the next thing is to check Pin D16.
Don’t want to fry the ECM, so would the test be?
- Key on, engine off
- In a gear other than P/N to expect approx. 12v
- DVM +, to ECM Pin D16
- DVM –, to ground
Really appreciate the help!
10-25-2012 | 07:34 AM
#6
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From: Chasing Electrons
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Re: AUJP $8D Idle Limiter - Code Question
In an ADS file the index starts at the value 1. So it would be byte 56. I don't know if this was changed with ADX files.
Checking the input at the ECM is as you mention. Easy to use the ECM case as the ground point.
RBob.
Checking the input at the ECM is as you mention. Easy to use the ECM case as the ground point.
RBob.
10-25-2012 | 11:33 AM
#7
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From: Browns Town
Car: 86 Monte SS (730,$8D,G3,AP,4K,S_V4)
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Re: AUJP $8D Idle Limiter - Code Question
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10-25-2012 | 12:25 PM
#8
Thread Starter
Senior Member
Joined: Jun 2010
Posts: 577
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From: Montgomery, AL
Car: 84 El Camino
Engine: 360 TPI
Transmission: 700R4
Axle/Gears: 3.42 + Truetrac, Moser 28 Spline
Re: AUJP $8D Idle Limiter - Code Question
Well, the Bitmask didn’t lie. ECM was not seeing P/N switch because the ECM pin at D16 had a broken retaining tang, apparently causing it to slide out when the 16-pin ECM connector was pushed in.
Thanks for all the help. And BTW, the bytes are zero-based in the TPro .adx file, for once the faulty pin at D16 was replaced; P/N was properly reported by the bitmask using byte #55 decimal.
Jp - P/N or in-gear is reported key on, engine off and engine running .
Thanks for all the help. And BTW, the bytes are zero-based in the TPro .adx file, for once the faulty pin at D16 was replaced; P/N was properly reported by the bitmask using byte #55 decimal.
Jp - P/N or in-gear is reported key on, engine off and engine running .
Last edited by 84Elky; 10-25-2012 at 01:08 PM. Reason: Addition
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