long cranking tbi....tuning fix?
06-19-2008, 08:02 PM
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long cranking tbi....tuning fix?
Car has always cranked quite a bit before firing up. After sometuning the problem wasnt any worse but its not any better either. I am pretty confident i haven't touched the value that has to do with this in tunerpro at all. I remember someone mentioning something about fixing this problem while tuning their setup but i cant find it anywhere. Any suggestions? '92 tbi by the way
06-20-2008, 09:00 AM
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Re: long cranking tbi....tuning fix?
This can be caused by a bad ECM (ECM isn't turning on the relay) or bad fuel pump relay. At key-on, engine-off the fuel pump should run for 2 seconds. If not then long crank times will occur.
The engine will need to be cranked until some oil pressure builds. This closes the oil pressure switch for the fuel pump relay bypass and turns on the pump.
RBob.
The engine will need to be cranked until some oil pressure builds. This closes the oil pressure switch for the fuel pump relay bypass and turns on the pump.
RBob.
06-20-2008, 09:04 AM
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Re: long cranking tbi....tuning fix?
This can be caused by a bad ECM (ECM isn't turning on the relay) or bad fuel pump relay. At key-on, engine-off the fuel pump should run for 2 seconds. If not then long crank times will occur.
The engine will need to be cranked until some oil pressure builds. This closes the oil pressure switch for the fuel pump relay bypass and turns on the pump.
RBob.
The engine will need to be cranked until some oil pressure builds. This closes the oil pressure switch for the fuel pump relay bypass and turns on the pump.
RBob.
06-20-2008, 04:41 PM
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Re: long cranking tbi....tuning fix?
ecm is brand new, so is the fuel pump relay, car runs great. I also hear the pump prime and i always let it prime first before cranking it
06-20-2008, 09:27 PM
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Re: long cranking tbi....tuning fix?
Well that doesn't help then. One thing that I need to mention is that 'long crank' times are relative. Long crank to one person is a not so long crank to another.
However, there are some other items that can contribute to long cranking. One is that it is inherent to how TBI works. At key off the manifold is run dry. At key-on you can't pump the throttle like a carb to add fuel. It takes some cranking to get fuel in the manifold.
Low fuel pressure and/or an incorrect CTS reading can make this worse.
What I usually do is to key-on, pause, crank briefly and pause. The crank to start. The brief crank puts some fuel in the manifold which needs to evaporate before it is of any use.
I've played with having AE active during engine not running (treat it like a carb with key-on, pump the the throttle). Along with a fuel pulse at key-on. Both allow instant start up. However, both can also cause flooding, so I didn't go with those functions.
Check the fuel pressure. Nine psi is minimal. Then see if the CTS is reading a tad high. Otherwise it just may be the nature of the beast.
RBob.
However, there are some other items that can contribute to long cranking. One is that it is inherent to how TBI works. At key off the manifold is run dry. At key-on you can't pump the throttle like a carb to add fuel. It takes some cranking to get fuel in the manifold.
Low fuel pressure and/or an incorrect CTS reading can make this worse.
What I usually do is to key-on, pause, crank briefly and pause. The crank to start. The brief crank puts some fuel in the manifold which needs to evaporate before it is of any use.
I've played with having AE active during engine not running (treat it like a carb with key-on, pump the the throttle). Along with a fuel pulse at key-on. Both allow instant start up. However, both can also cause flooding, so I didn't go with those functions.
Check the fuel pressure. Nine psi is minimal. Then see if the CTS is reading a tad high. Otherwise it just may be the nature of the beast.
RBob.
06-21-2008, 01:17 AM
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Re: long cranking tbi....tuning fix?
With the older ECMs, I had the same issue. It took about 6 seconds or so for the manifold to prime enough to get fuel into the cylinders. The ability for the computer to prime on cranking didnt come until the later PCMs. Those add a large shot of fuel for the first few DRPs for when you first start cranking to prime the manifold.
06-21-2008, 01:33 AM
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Re: long cranking tbi....tuning fix?
With the older ECMs, I had the same issue. It took about 6 seconds or so for the manifold to prime enough to get fuel into the cylinders. The ability for the computer to prime on cranking didnt come until the later PCMs. Those add a large shot of fuel for the first few DRPs for when you first start cranking to prime the manifold.
http://youtube.com/watch?v=FmS1m3zlqHo
I haven't been driving the van much and it sits alot. The current TPI setup running on the 7730 has a longer crank time than the TBI PCM did.
With TPI and the PCM, the engine would start cold after sitting for weeks with just a blip of the key.
http://s243.photobucket.com/albums/f...t=100_1261.flv
The 7730 takes about 3-4 seconds of cranking to fire up.
I had the PCM running a 3.1 TBI/ 4L60E combo in a S15 Jimmy too. Instant cold starts there too.
http://youtube.com/watch?v=gNVs-_RzwFo
Last edited by Fast355; 06-21-2008 at 01:41 AM.
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06-21-2008, 04:31 AM
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Re: long cranking tbi....tuning fix?
This can be caused by a bad ECM (ECM isn't turning on the relay) or bad fuel pump relay. At key-on, engine-off the fuel pump should run for 2 seconds. If not then long crank times will occur.
The engine will need to be cranked until some oil pressure builds. This closes the oil pressure switch for the fuel pump relay bypass and turns on the pump.
RBob.
The engine will need to be cranked until some oil pressure builds. This closes the oil pressure switch for the fuel pump relay bypass and turns on the pump.
RBob.
06-21-2008, 09:43 AM
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Re: long cranking tbi....tuning fix?
The oil pressure switch will turn on the fuel pump whenever the pressure is above 4 psi (or so). This can actually be checked on a cold engine. Start it, let it run for a few seconds, then key-off. The fuel pump can run for several seconds until the oil pressure drops (cold oil).
RBob.
06-22-2008, 06:26 PM
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Re: long cranking tbi....tuning fix?
Rbob yea i would its about..idk..5 seconds of cranking before she fires. I also notice that sometimes it even happens when the car is restarted after driving, but in most cases she fires right up. As far as fuel pressure goes its 13psi.
06-23-2008, 05:23 AM
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Re: long cranking tbi....tuning fix?
From a tuning standpoint, the '8746 has a Cranking AFR vs Coolant table. This table defines the AFR while cranking. There is also a cold cranking multiplier for this value. This table has a coolant threshold before it takes affect. Then the multiplier is based on engine vacuum. In ANLU the CTS needs to be below 14F for the table to be used.
Once the cranking AFR is created, the code will use either that value or the open loop AFR, whichever is richer.
I think for the Crank AFR multiplier vs Vac table, the first row is 80 KPa and the last 0 KPa.
It works by multiplying the AFR from the crank table by the value in the multiplier table, then dividing by 16. I haven't tested this portion on the bench, but it looks to be that at initial crank it is richer, then leans as the engine vacuum increases.
May be able to set up the calibration for an very rich inital crank AFR, then have is taper off to prevent flooding.
RBob.
Once the cranking AFR is created, the code will use either that value or the open loop AFR, whichever is richer.
Code:
LD256: FCB 241 ; cranking coolant threshold, -10c
;*==================================================
;* Crank Afr vs Coolant
;*
;* Afr During Crank
;*
;* Tbl = AFR * 10
;*==================================================
LD36F:
;----------------------------------
; AFR ; Deg c Cool
;----------------------------------
FCB 4 ; COLD
FCB 20 ; -7.0
FCB 25 ; 6.5
FCB 50 ; 16.0
FCB 64 ; 24.0
FCB 64 ; 31.0
FCB 64 ; 37.3
FCB 64 ; 43.7
FCB 64 ; 49.7
FCB 64 ; 56.5
FCB 64 ; 63.5
FCB 64 ; 71.5
FCB 64 ; 80.5
FCB 64 ; 92.0
FCB 80 ; 108.5
FCB 80 ; 138.5
FCB 64 ; HOT
;*==================================================
;* Cold Engine Crank AFR multiplier vs Vac
;*
;*
;* Cold crank AFR Mult for cts < -10c vs Vac
;*
;*==================================================
LD380:
;----------------------------------
; AFR mult ; Vac
;----------------------------------
FCB 13 ;
FCB 15 ;
FCB 16 ;
FCB 20 ;
FCB 30 ;
FCB 28 ;
FCB 26 ;
FCB 24 ;
FCB 22 ;
FCB 21 ;
FCB 15 ; It works by multiplying the AFR from the crank table by the value in the multiplier table, then dividing by 16. I haven't tested this portion on the bench, but it looks to be that at initial crank it is richer, then leans as the engine vacuum increases.
May be able to set up the calibration for an very rich inital crank AFR, then have is taper off to prevent flooding.
RBob.
06-24-2008, 01:22 AM
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Re: long cranking tbi....tuning fix?
Probably not the problem, but I would usually have to give a 1-2 second crank for starting. I had a bad ignition control module in the Low RPM. Replaced it and car fired up and was running before I could let go of the key, even after sitting for a month. It's worth a check at least.
06-24-2008, 03:33 PM
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Re: long cranking tbi....tuning fix?
good call, i will take a look at that, i am pretty sure the original one is on there. and Rbob that table looks like it may be the answer if its even a problem
01-15-2014, 10:37 PM
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Re: long cranking tbi....tuning fix?
From a tuning standpoint, the '8746 has a Cranking AFR vs Coolant table. This table defines the AFR while cranking. There is also a cold cranking multiplier for this value. This table has a coolant threshold before it takes affect. Then the multiplier is based on engine vacuum. In ANLU the CTS needs to be below 14F for the table to be used.
Once the cranking AFR is created, the code will use either that value or the open loop AFR, whichever is richer.
I think for the Crank AFR multiplier vs Vac table, the first row is 80 KPa and the last 0 KPa.
It works by multiplying the AFR from the crank table by the value in the multiplier table, then dividing by 16. I haven't tested this portion on the bench, but it looks to be that at initial crank it is richer, then leans as the engine vacuum increases.
May be able to set up the calibration for an very rich inital crank AFR, then have is taper off to prevent flooding.
RBob.
Once the cranking AFR is created, the code will use either that value or the open loop AFR, whichever is richer.
Code:
LD256: FCB 241 ; cranking coolant threshold, -10c
;*==================================================
;* Crank Afr vs Coolant
;*
;* Afr During Crank
;*
;* Tbl = AFR * 10
;*==================================================
LD36F:
;----------------------------------
; AFR ; Deg c Cool
;----------------------------------
FCB 4 ; COLD
FCB 20 ; -7.0
FCB 25 ; 6.5
FCB 50 ; 16.0
FCB 64 ; 24.0
FCB 64 ; 31.0
FCB 64 ; 37.3
FCB 64 ; 43.7
FCB 64 ; 49.7
FCB 64 ; 56.5
FCB 64 ; 63.5
FCB 64 ; 71.5
FCB 64 ; 80.5
FCB 64 ; 92.0
FCB 80 ; 108.5
FCB 80 ; 138.5
FCB 64 ; HOT
;*==================================================
;* Cold Engine Crank AFR multiplier vs Vac
;*
;*
;* Cold crank AFR Mult for cts < -10c vs Vac
;*
;*==================================================
LD380:
;----------------------------------
; AFR mult ; Vac
;----------------------------------
FCB 13 ;
FCB 15 ;
FCB 16 ;
FCB 20 ;
FCB 30 ;
FCB 28 ;
FCB 26 ;
FCB 24 ;
FCB 22 ;
FCB 21 ;
FCB 15 ; It works by multiplying the AFR from the crank table by the value in the multiplier table, then dividing by 16. I haven't tested this portion on the bench, but it looks to be that at initial crank it is richer, then leans as the engine vacuum increases.
May be able to set up the calibration for an very rich inital crank AFR, then have is taper off to prevent flooding.
RBob.
I know this thread is old, but I figured I'd continue it rather than start a new one since it contains the information I'm after.
I'm running an 8746 ECM $61 mask and a modified version of the ANLU chip.
Now that the cold weather has hit, my car floods when I try and start it. I'm also over 7000 feet, which doesn't help. The VE tables are tuned pretty well once the car gets to closed loop mode--I did that this summer--but startup, in particular cranking, is a problem. The tables that I figure are involved with this are:
Crank - AFR vs. Engine Temp
OpnLp - Open Loop AFR vs. Engine Temp
OpnLp - Open Loop AFR vs. Load
Choke - AFR vs. Coolant
My understanding is that the AFR in Open Loop is calculated by:
((OLAFR vs. Engine Temp) + (OLAFR vs. Load) - (Choke AFR vs. Coolant))
(I'm using the names of the tables in the .xdf for clarification)
Based on what you say above, the computer uses this value, or the value from the Crank - AFR vs. Engine Temp multiplied by the Cold Crank AFR vs. Coolant, whichever is richer.
I have leaned out my open loop tables based on the air density at 7000 feet, as using the formula above I come up with reasonable numbers. However, I am uncertain as to how to modify the Crank - AFR vs. Coolant table to fix this issue. Thus, my questions:
1. Is the multiplier table one decimal place off like the Crank - AFR vs. Coolant is? (i.e., the Crank - AFR vs. Coolant shows up as 0.4 in TunerPro, not 4; thus, is the multiplier actually 1.3 and not 13 in the first row of the multiplier table?)
2. How does one add the multiplier table as an .xdf parameter to the $61 mask in TunerPro? I'm confused as to how one identifies the starting address in hex, or if I'm even on the right track here. I'd prefer to edit these tables in TunerPro rather than try and hand edit a bin, as my assembly skills are non-existent.
Perhaps in simple terms, I'm having trouble translating what I'm seeing in the assembly. Any help or advice you have would be great, as I'd like to quit flooding my engine on startup. These 6 °F days are killing me.
01-16-2014, 11:11 AM
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Re: long cranking tbi....tuning fix?
The cranking AFR multiplier is only used when the temperature (CTS) is below this calibration parameter:
LD256: FCB 241 ; cranking coolant threshold, -10c
The -10c (14* F) is from ANLU, other BCC's can be different.
The use of the multiplier is as I described above. Take the crank AFR, multiply by the cranking multiplier, then divide by 16. So, at 6* F the cranking AFR is going to be about 1.0 (someplace between COLD & 19* F of the table), with the multiplier at 15 for 0 KPa vacuum:
(10 * 15) / 16 = 9.375 for an AFR of 9.4
As the engine cranks the vacuum will increase, changing the AFR.
The starting address of the crank multiplier table is: $380
Note that the open loop AFR table is versus vacuum, not load. Big difference. This one:
OpnLp - Open Loop AFR vs. Load
Should be:
OpnLp - Open Loop AFR vs. Vacuum
RBob.
LD256: FCB 241 ; cranking coolant threshold, -10c
The -10c (14* F) is from ANLU, other BCC's can be different.
The use of the multiplier is as I described above. Take the crank AFR, multiply by the cranking multiplier, then divide by 16. So, at 6* F the cranking AFR is going to be about 1.0 (someplace between COLD & 19* F of the table), with the multiplier at 15 for 0 KPa vacuum:
(10 * 15) / 16 = 9.375 for an AFR of 9.4
As the engine cranks the vacuum will increase, changing the AFR.
The starting address of the crank multiplier table is: $380
Note that the open loop AFR table is versus vacuum, not load. Big difference. This one:
OpnLp - Open Loop AFR vs. Load
Should be:
OpnLp - Open Loop AFR vs. Vacuum
RBob.
01-16-2014, 06:44 PM
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Re: long cranking tbi....tuning fix?
RBob, thanks for the (as always) timely and informative reply!
In your original post, you said that the values for the vacuum in the multiplier table went from 80 kPa down to 0 kPa. Starting at the top with 80 kPa and decrementing by 10 kPa each time hits zero two entries before the bottom.
So does this table actually start at 100 kPa of vacuum and decrement by 10 (such as in the table below), or does it go from 80 to 0 with a non-integer decrement? I would guess the former, but I am asking because I would rather get this right the first time.
Just so that I understand this, if, for example, we were to crank at a coolant temp of 24 °C (a value from the crank table of 64), and have say 20 kPa of vacuum (a value of 22 from the multiplier table, I'm guessing), we would have:
(64 * 22) / 16 = 88 for an AFR of 88. This seems unusually lean to me. Is this correct, or am I missing something here? Maybe this value is meant to be abnormally lean so that the richer Open Loop table is used instead? Or perhaps I'm screwing up the vacuum values in the table?
Thanks once again for all your help. This is going to be a huge help in getting my car starting reliably at high altitude and low temperatures!
Thanks as well for the clarification of load vs. vacuum. I had assumed that the titles on the xdf parameters were correct, but since they are erroneous, I will fix them tonight in TunerPro. And thanks as well for the starting address in the code. I will try and make a new parameter for the multiplier table and see how it turns out.
In your original post, you said that the values for the vacuum in the multiplier table went from 80 kPa down to 0 kPa. Starting at the top with 80 kPa and decrementing by 10 kPa each time hits zero two entries before the bottom.
Code:
AFR mult Vac (kPa)
13 80
15 70
16 60
20 50
30 40
28 30
26 20
24 10
22 0
21 ?
15 ? Code:
AFR mult Vac (kPa)
13 100
15 90
16 80
20 70
30 60
28 50
26 40
24 30
22 20
21 10
15 0 (64 * 22) / 16 = 88 for an AFR of 88. This seems unusually lean to me. Is this correct, or am I missing something here? Maybe this value is meant to be abnormally lean so that the richer Open Loop table is used instead? Or perhaps I'm screwing up the vacuum values in the table?
Thanks once again for all your help. This is going to be a huge help in getting my car starting reliably at high altitude and low temperatures!
Thanks as well for the clarification of load vs. vacuum. I had assumed that the titles on the xdf parameters were correct, but since they are erroneous, I will fix them tonight in TunerPro. And thanks as well for the starting address in the code. I will try and make a new parameter for the multiplier table and see how it turns out.
01-18-2014, 12:03 PM
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Re: long cranking tbi....tuning fix?
"I think for the Crank AFR multiplier vs Vac table, the first row is 80 KPa and the last 0 KPa."
Code:
AFR mult Vac (kPa)
13 50
15 45
16 40
20 35
30 30
28 25
26 20
24 15
22 10
21 5
15 0 (64 * 22) / 16 = 88 for an AFR of 88. This seems unusually lean to me. Is this correct, or am I missing something here? Maybe this value is meant to be abnormally lean so that the richer Open Loop table is used instead? Or perhaps I'm screwing up the vacuum values in the table?
RBob.
01-19-2014, 09:56 PM
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Re: long cranking tbi....tuning fix?
Thanks again, RBob! Sorry about my careless paraphrasing; I forgot to include the "think" part of your statement.
Are all the AFRs divided by 10? I ask because, if you use the example:
In this case, we didn't divide by 10; if we did, we'd have an AFR of 0.94, which is insanely rich. Maybe that's normal for this temperature, but it seems overly rich to me. Based on the formula:
((Crank AFR * Crank Multiplier) / 16 ) / 10 = AFR during Crank (if temp < -10 °C)
I have come up with the following table (for ease of viewing). In it, we see the 8.8 AFR that seems pretty reasonable, but now the low values are extremely rich. Does this look right? (I am assuming this is MAP measured vacuum)
Question 2: If this table is only used when the coolant temp is below -10 °C, why does the crank table have higher temperature ranges? Is it because code is shared between the BCCs that have different temperature cutoff values and thus they have the full table in the ANLU as well even though it is not used?
Question 3: I think I see where the assembly code calls for the $380 address; I was curious how you could tell the vacuum pressures? I was unable to discern this from the hac that is posted on the web. This may be a whole different can of worms, and I am only curious, so please disregard this if it's out of scope / annoying.
Thanks yet again in advance. I am sorry for the overly-long posts, but in the hopes of others being able to learn from my ignorance, I am trying to be detailed and exact with my questions.
Are all the AFRs divided by 10? I ask because, if you use the example:
The use of the multiplier is as I described above. Take the crank AFR, multiply by the cranking multiplier, then divide by 16. So, at 6* F the cranking AFR is going to be about 1.0 (someplace between COLD & 19* F of the table), with the multiplier at 15 for 0 KPa vacuum:
(10 * 15) / 16 = 9.375 for an AFR of 9.4
(10 * 15) / 16 = 9.375 for an AFR of 9.4
((Crank AFR * Crank Multiplier) / 16 ) / 10 = AFR during Crank (if temp < -10 °C)
I have come up with the following table (for ease of viewing). In it, we see the 8.8 AFR that seems pretty reasonable, but now the low values are extremely rich. Does this look right? (I am assuming this is MAP measured vacuum)
Code:
MAP Vac. (kPa) Temp °C 0 5 10 15 20 25 30 35 40 45 50 COLD 0.4 0.5 0.6 0.6 0.7 0.7 0.8 0.5 0.4 0.4 0.3 -7 1.9 2.6 2.8 3.0 3.3 3.5 3.8 2.5 2.0 1.9 1.6 6.5 2.3 3.3 3.4 3.8 4.1 4.4 4.7 3.1 2.5 2.3 2.0 16 4.7 6.6 6.9 7.5 8.1 8.8 9.4 6.3 5.0 4.7 4.1 24 6.0 8.4 8.8 9.6 10.4 11.2 12.0 8.0 6.4 6.0 5.2 31 6.0 8.4 8.8 9.6 10.4 11.2 12.0 8.0 6.4 6.0 5.2 37.3 6.0 8.4 8.8 9.6 10.4 11.2 12.0 8.0 6.4 6.0 5.2 43.7 6.0 8.4 8.8 9.6 10.4 11.2 12.0 8.0 6.4 6.0 5.2 49.7 6.0 8.4 8.8 9.6 10.4 11.2 12.0 8.0 6.4 6.0 5.2 56.5 6.0 8.4 8.8 9.6 10.4 11.2 12.0 8.0 6.4 6.0 5.2 63.5 6.0 8.4 8.8 9.6 10.4 11.2 12.0 8.0 6.4 6.0 5.2 71.5 6.0 8.4 8.8 9.6 10.4 11.2 12.0 8.0 6.4 6.0 5.2 80.5 6.0 8.4 8.8 9.6 10.4 11.2 12.0 8.0 6.4 6.0 5.2 92 6.0 8.4 8.8 9.6 10.4 11.2 12.0 8.0 6.4 6.0 5.2 108.5 7.5 10.5 11.0 12.0 13.0 14.0 15.0 10.0 8.0 7.5 6.5 138.5 7.5 10.5 11.0 12.0 13.0 14.0 15.0 10.0 8.0 7.5 6.5 HOT 6.0 8.4 8.8 9.6 10.4 11.2 12.0 8.0 6.4 6.0 5.2
Question 3: I think I see where the assembly code calls for the $380 address; I was curious how you could tell the vacuum pressures? I was unable to discern this from the hac that is posted on the web. This may be a whole different can of worms, and I am only curious, so please disregard this if it's out of scope / annoying.
Thanks yet again in advance. I am sorry for the overly-long posts, but in the hopes of others being able to learn from my ignorance, I am trying to be detailed and exact with my questions.
01-20-2014, 01:18 PM
#19
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Re: long cranking tbi....tuning fix?
Yes, that value should have been 0.9 AFR.
Not really, most of that fuel won't evaporate. It will go right out the exhaust.
Yes & no for the table being correct. Recall that the multiplier table isn't used if the CTS is above 14* F. The value will be directly from the cranking AFR versus CTS table.
Because there are warm & hot starts.
Vacuum is calculated in the ECM by subtracting the current MAP value from the barometric value. As for the conversion from the ECM value to KPa, there is a series of standard conversions that GM used.
RBob.
Based on the formula:
((Crank AFR * Crank Multiplier) / 16 ) / 10 = AFR during Crank (if temp < -10 °C)
I have come up with the following table (for ease of viewing). In it, we see the 8.8 AFR that seems pretty reasonable, but now the low values are extremely rich. Does this look right? (I am assuming this is MAP measured vacuum)
((Crank AFR * Crank Multiplier) / 16 ) / 10 = AFR during Crank (if temp < -10 °C)
I have come up with the following table (for ease of viewing). In it, we see the 8.8 AFR that seems pretty reasonable, but now the low values are extremely rich. Does this look right? (I am assuming this is MAP measured vacuum)
Code:
MAP Vac. (kPa) Temp °C 0 5 10 15 20 25 30 35 40 45 50 COLD 0.4 0.5 0.6 0.6 0.7 0.7 0.8 0.5 0.4 0.4 0.3 -7 1.9 2.6 2.8 3.0 3.3 3.5 3.8 2.5 2.0 1.9 1.6 6.5 2.3 3.3 3.4 3.8 4.1 4.4 4.7 3.1 2.5 2.3 2.0 16 4.7 6.6 6.9 7.5 8.1 8.8 9.4 6.3 5.0 4.7 4.1 24 6.0 8.4 8.8 9.6 10.4 11.2 12.0 8.0 6.4 6.0 5.2 31 6.0 8.4 8.8 9.6 10.4 11.2 12.0 8.0 6.4 6.0 5.2 37.3 6.0 8.4 8.8 9.6 10.4 11.2 12.0 8.0 6.4 6.0 5.2 43.7 6.0 8.4 8.8 9.6 10.4 11.2 12.0 8.0 6.4 6.0 5.2 49.7 6.0 8.4 8.8 9.6 10.4 11.2 12.0 8.0 6.4 6.0 5.2 56.5 6.0 8.4 8.8 9.6 10.4 11.2 12.0 8.0 6.4 6.0 5.2 63.5 6.0 8.4 8.8 9.6 10.4 11.2 12.0 8.0 6.4 6.0 5.2 71.5 6.0 8.4 8.8 9.6 10.4 11.2 12.0 8.0 6.4 6.0 5.2 80.5 6.0 8.4 8.8 9.6 10.4 11.2 12.0 8.0 6.4 6.0 5.2 92 6.0 8.4 8.8 9.6 10.4 11.2 12.0 8.0 6.4 6.0 5.2 108.5 7.5 10.5 11.0 12.0 13.0 14.0 15.0 10.0 8.0 7.5 6.5 138.5 7.5 10.5 11.0 12.0 13.0 14.0 15.0 10.0 8.0 7.5 6.5 HOT 6.0 8.4 8.8 9.6 10.4 11.2 12.0 8.0 6.4 6.0 5.2
Question 2: If this table is only used when the coolant temp is below -10 °C, why does the crank table have higher temperature ranges? Is it because code is shared between the BCCs that have different temperature cutoff values and thus they have the full table in the ANLU as well even though it is not used?
Question 3: I think I see where the assembly code calls for the $380 address; I was curious how you could tell the vacuum pressures? I was unable to discern this from the hac that is posted on the web. This may be a whole different can of worms, and I am only curious, so please disregard this if it's out of scope / annoying.
RBob.
01-21-2014, 10:20 AM
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Re: long cranking tbi....tuning fix?
Ah ha! The light has gone on! (Sometimes I need to beat something into my brain). I think I have it now.
So really, because the volatility of the gasoline at -10 °C is so low, the fuel injectors are just trying to saturate the air with gas by commanding an AFR of 0.9, not actually trying to achieve a true AFR of 0.9? This makes a lot more sense.
And, the corrected table of AFR during cranking (since the multiplier table is not used above -10 °C):
Thus, in summary:
The 8746 uses the Crank - AFR vs. coolant temp to determine the AFR during cranking. This table, at -10 °C or below (~ 14 °F) is multiplied by the Crank - AFR multiplier table. Whereas at -9 °C or higher the Crank AFR is determined without regard to vacuum, at -10 °C or below, the Crank AFR is multiplied by a constant based on vacuum (as measured by barometric pressure - MAP).
The AFR itself is calculated by taking the value directly (divided by 10) from the Crank - AFR vs. coolant temp table at -9 °C or above or, at -10 °C or below by:
((Crank AFR vs. Coolant Temp) * (Crank AFR multiplier vs. vacuum)) / 160 = AFR
Thanks a bunch for all your help! Hopefully others will benefit from this as well (probably members in Minnesota and other wonderfully cold places).
Not really, most of that fuel won't evaporate. It will go right out the exhaust.
And, the corrected table of AFR during cranking (since the multiplier table is not used above -10 °C):
Code:
AFR Vacuum (kPa) Temp °C 0 5 10 15 20 25 30 35 40 45 50 COLD 0.4 0.5 0.6 0.6 0.7 0.7 0.8 0.5 0.4 0.4 0.3 -7 2 2 2 2 2 2 2 2 2 2 2 6.5 2.5 2.5 2.5 2.5 2.5 2.5 2.5 2.5 2.5 2.5 2.5 16 5 5 5 5 5 5 5 5 5 5 5 24 6.4 6.4 6.4 6.4 6.4 6.4 6.4 6.4 6.4 6.4 6.4 31 6.4 6.4 6.4 6.4 6.4 6.4 6.4 6.4 6.4 6.4 6.4 37.3 6.4 6.4 6.4 6.4 6.4 6.4 6.4 6.4 6.4 6.4 6.4 43.7 6.4 6.4 6.4 6.4 6.4 6.4 6.4 6.4 6.4 6.4 6.4 49.7 6.4 6.4 6.4 6.4 6.4 6.4 6.4 6.4 6.4 6.4 6.4 56.5 6.4 6.4 6.4 6.4 6.4 6.4 6.4 6.4 6.4 6.4 6.4 63.5 6.4 6.4 6.4 6.4 6.4 6.4 6.4 6.4 6.4 6.4 6.4 71.5 6.4 6.4 6.4 6.4 6.4 6.4 6.4 6.4 6.4 6.4 6.4 80.5 6.4 6.4 6.4 6.4 6.4 6.4 6.4 6.4 6.4 6.4 6.4 92 6.4 6.4 6.4 6.4 6.4 6.4 6.4 6.4 6.4 6.4 6.4 108.5 8 8 8 8 8 8 8 8 8 8 8 138.5 8 8 8 8 8 8 8 8 8 8 8 HOT 6.4 6.4 6.4 6.4 6.4 6.4 6.4 6.4 6.4 6.4 6.4
The 8746 uses the Crank - AFR vs. coolant temp to determine the AFR during cranking. This table, at -10 °C or below (~ 14 °F) is multiplied by the Crank - AFR multiplier table. Whereas at -9 °C or higher the Crank AFR is determined without regard to vacuum, at -10 °C or below, the Crank AFR is multiplied by a constant based on vacuum (as measured by barometric pressure - MAP).
The AFR itself is calculated by taking the value directly (divided by 10) from the Crank - AFR vs. coolant temp table at -9 °C or above or, at -10 °C or below by:
((Crank AFR vs. Coolant Temp) * (Crank AFR multiplier vs. vacuum)) / 160 = AFR
Thanks a bunch for all your help! Hopefully others will benefit from this as well (probably members in Minnesota and other wonderfully cold places).
Last edited by hmx; 01-21-2014 at 11:54 AM. Reason: Fixed mistake
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