Why does the map sensor drastically change at idle?
Why does the map sensor drastically change at idle? Combo:
418
13-1
PRC 237 heads
254/260 Hyd cam
Super Vic/dominator tb
Cold start motor is idling nicely about 900-1000 until about mid 130* ECT
Map is mid 80
Timing is solid 29*
IAC is 175 (I know a little high)
Then all of a sudden, no changes, map goes to high 30, timing goes to mid 30* rpm shoots up to 2,500.
I try commanding less timing in hopes to get it to come down. Try moving IAC to 0 through VCM controls. I can't find any vacuum leaks using brake cleaner and carb cleaner. I have verified IAC is working.
It does it every time. Looking for ideas and other things to look at.
418
13-1
PRC 237 heads
254/260 Hyd cam
Super Vic/dominator tb
Cold start motor is idling nicely about 900-1000 until about mid 130* ECT
Map is mid 80
Timing is solid 29*
IAC is 175 (I know a little high)
Then all of a sudden, no changes, map goes to high 30, timing goes to mid 30* rpm shoots up to 2,500.
I try commanding less timing in hopes to get it to come down. Try moving IAC to 0 through VCM controls. I can't find any vacuum leaks using brake cleaner and carb cleaner. I have verified IAC is working.
It does it every time. Looking for ideas and other things to look at.
MAP readings of 80~ are not normal at idle, they should be more like 30-40
If you have a faulty MAP or wiring, you will have trouble tuning it, because fueling and spark changes a lot from idle to WOT MAP values.
First you must make sure your MAP is reading good. Key open, engine not running, MAP should be the same as atmospheric pressure (BARO). From 80 to 100 KPa depending on altitude.
Engine running, MAP should be from 30 to 60 for big cams.
If these are not your typical values, you have a problem.
If you have a faulty MAP or wiring, you will have trouble tuning it, because fueling and spark changes a lot from idle to WOT MAP values.
First you must make sure your MAP is reading good. Key open, engine not running, MAP should be the same as atmospheric pressure (BARO). From 80 to 100 KPa depending on altitude.
Engine running, MAP should be from 30 to 60 for big cams.
If these are not your typical values, you have a problem.
For those of you that have HP tuners, here are the logs: http://www.hptuners.com/forum/showthread.php?t=39622
This also explains a lot of what I have tried.
This is a Custom OS which is a 1 bar Open loop SD tune. No MAF, no STFT's, No LTFT's, no Narrow band O2's. I have OL completely shut off.
I tried swapping the MAP, no change.
Regardless of what a MAP should read at idle, it does not explain why with no changes it suddenly changes. It doesn't matter on temp either. I just played with it drilling the TB holes bigger. does it at 130*, 165* 180*.. There is no method to it's madness
At least that I can see.
This also explains a lot of what I have tried.
This is a Custom OS which is a 1 bar Open loop SD tune. No MAF, no STFT's, No LTFT's, no Narrow band O2's. I have OL completely shut off.
I tried swapping the MAP, no change.
Regardless of what a MAP should read at idle, it does not explain why with no changes it suddenly changes. It doesn't matter on temp either. I just played with it drilling the TB holes bigger. does it at 130*, 165* 180*.. There is no method to it's madness
At least that I can see. Trending Topics
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That sounds like you've got a "switched" air leak. Maybe
something like the EVAP or AIR system (hacked? hose
come off?). Might disconnect and plug climate control
stuff, all the accessory vacuum taps for that matter.
something like the EVAP or AIR system (hacked? hose
come off?). Might disconnect and plug climate control
stuff, all the accessory vacuum taps for that matter.
Jimmy, thanks for the suggestion, but, this is a 63 chevy c10 swap. No emissions, no ac, bare bones set up. I can't think of a switched air leak. I tried doucing my 2 stages of n20 to see if they were the issue but no leak there either. I am super puzzled.
If I were a betting man (and I'm not) I would say it's probably not mechanical. I would bet the vacuum readings you're seeing in your MAP sensor in the scanner, are not reflective of the actual vacuum present.
Sounds like computer, wiring,sensor issue. The kpa should be 70-80 kpa at idle.
I do know that setup can be a bitch to idle right but by the sounds of it the car is still trying to go closed loop.
I do know that setup can be a bitch to idle right but by the sounds of it the car is still trying to go closed loop.
Ok, here is what I am going to put back in along with draining the tank and filling it up with 91. I figure I will get the part throttle driveability stuff done on 91 since round trip for E85 is almost 100 miles from my house.
I figure with 8.7 DCR i definately want to keep my foot out of it and reduce high end timing (stock is pretty low already at 19* anything >.88).
Open for comments suggestions before I give this a go.
This is for the most part stock settings in my custom 1 Bar SD tune. Non stock settings:
AIR is set to 285*
Idle: 1000rpm <90* and 900rpm >90*
VE:
400 * .6
800 * .8
1200 * .9
1600 and above @ MAP of 90-105 was multiplied by 1.2
Injector flow data
Closed loop ECT vs. IAT moved to 280*
Closed loop proportional > Airflow mode table was multiplied by .78
LTFT's are disabled and Min set to 280*, Max to 284*
PE Throttle Pedal is 50% @ 1,600 and above
PE EQ is at 1.176 accross the board
Enrichment Ramp is at 4
PE RPM Delay is at 1,600
COT Disabled
Stock high octane table coppied in to the low table
All Spark correction tables AFR, IAT, ECT, CAT, MISC are whiped out or adjusted
AC Bump TQ is disabled
Spark Retard is left how I had it, which is different from stock. IE Burst is disabled, General decay rate is reduced
Torque Management is completely disabled
I figure with 8.7 DCR i definately want to keep my foot out of it and reduce high end timing (stock is pretty low already at 19* anything >.88).
Open for comments suggestions before I give this a go.
This is for the most part stock settings in my custom 1 Bar SD tune. Non stock settings:
AIR is set to 285*
Idle: 1000rpm <90* and 900rpm >90*
VE:
400 * .6
800 * .8
1200 * .9
1600 and above @ MAP of 90-105 was multiplied by 1.2
Injector flow data
Closed loop ECT vs. IAT moved to 280*
Closed loop proportional > Airflow mode table was multiplied by .78
LTFT's are disabled and Min set to 280*, Max to 284*
PE Throttle Pedal is 50% @ 1,600 and above
PE EQ is at 1.176 accross the board
Enrichment Ramp is at 4
PE RPM Delay is at 1,600
COT Disabled
Stock high octane table coppied in to the low table
All Spark correction tables AFR, IAT, ECT, CAT, MISC are whiped out or adjusted
AC Bump TQ is disabled
Spark Retard is left how I had it, which is different from stock. IE Burst is disabled, General decay rate is reduced
Torque Management is completely disabled
