tuning issues LQ4
tuning issues LQ4 Here is my combo,
lq4,ported 243 heads,228r 114 cam,fast LSXR intake and BBK 92 mm dbc TB with 411 PCM. Vintage Air AC
I have been to two tuners chasing stalling issues over the last two years and after every visit some things a better and some are worse.
At this point we are chasing a stall at idle or coming to a stop with AC on. RPM pulls down @ 125 rpm when compressor engages. Some times it functions flawlessly and other times it stalls. I have a PSI harness with a 12v input to ECM when the ac clutch engages. Both tuners are freaked out that they have no tuning control via ECM (both HP tuners and EFI live).I know on a Snap on scanner I can see AC request turn on and off with AC. Any body have ideas on this? is this totally normal? I read online that people run VA with not AC signal wire with no issues. My car has been a finicky PIA idle wise since the swap was completed.
lq4,ported 243 heads,228r 114 cam,fast LSXR intake and BBK 92 mm dbc TB with 411 PCM. Vintage Air AC
I have been to two tuners chasing stalling issues over the last two years and after every visit some things a better and some are worse.
At this point we are chasing a stall at idle or coming to a stop with AC on. RPM pulls down @ 125 rpm when compressor engages. Some times it functions flawlessly and other times it stalls. I have a PSI harness with a 12v input to ECM when the ac clutch engages. Both tuners are freaked out that they have no tuning control via ECM (both HP tuners and EFI live).I know on a Snap on scanner I can see AC request turn on and off with AC. Any body have ideas on this? is this totally normal? I read online that people run VA with not AC signal wire with no issues. My car has been a finicky PIA idle wise since the swap was completed.
Restricted User
Joined: Mar 2014
Posts: 7,192
Likes: 109
From: Ohio
There are settings in HPTuners you can change that will cause the engine to compensate for the AC being on.
Also, maybe you should increase timing in the idle underspeed section so that when it drops below idle it starts adding additional timing to prevent it from stalling?
Also, maybe you should increase timing in the idle underspeed section so that when it drops below idle it starts adding additional timing to prevent it from stalling?
TECH Addict
Joined: Aug 2005
Posts: 2,305
Likes: 126
From: Monroe,NY
The ecm also needs to see that the a/c system has pressure. On my swap i grounded the pin on ecm so when the a/c was turned and the signal request was given the idle bumped up. On my 1999 5.3 ecm i had to ground pin 55. Without that pin grounded or setup so it sees pressure nothing would happen when a/c was turned on.
On The Tree
Joined: Sep 2007
Posts: 196
Likes: 0
If you are killing the engine when A/C is kicked on I would assume your A/C system is overcharged and killing the thing. Ran into this a few times with customers in the past and that was the issue.
The A/C wire supplied (depending on where it goes) will only kick on the fan when +12V applied.
The A/C wire supplied (depending on where it goes) will only kick on the fan when +12V applied.
If you are killing the engine when A/C is kicked on I would assume your A/C system is overcharged and killing the thing. Ran into this a few times with customers in the past and that was the issue.
The A/C wire supplied (depending on where it goes) will only kick on the fan when +12V applied.
The A/C wire supplied (depending on where it goes) will only kick on the fan when +12V applied.
Well doubt its over charged as it has not been touched since the car was put together in 2014.Changed injectors( no flow data on originals) due to a random stall in reverse and retuned this July. Stall in reverse fixed end result was stalling with AC on. Idle speed was dropped from 900 to 800 at that time may have been part of the cause. He was saying it had no ac input to ecm/pcm so no data to adjust air volume when ac is on. Went to a different tuner closer to home Sunday said the same thing. Said if I could add pressure sensor or trick ecm/pcm to think there was one he could alter the air volume when ac is on.411 pcm pin 45 5v reference and in 14 from sensor. would it be possible to ad a resistor between these terminals to simulate AC on? Computer is set up for 2002 Camaro and I do have a 12 v input to pin 18 when AC is on.AC request shows up on snap on scanner when ac clutch engages, but on efi live or HP they see nothing for ac request. Talked to PSI and their opinion is the cam and intake are to "wild" for the simple on wire ac control to function. I set up a buddy's stock LS1 the same as mine and it does not stall when ac turns on, pulls down some and recovers
Last edited by Nova 404; Aug 30, 2016 at 08:22 PM.
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On The Tree
Joined: Sep 2007
Posts: 196
Likes: 0
Every harness that we sell and make has ZERO provisions for A/C control. We just provide A/C wiring as a convenience factor. I understand you are having an issue and would like the feature but it's not necessarily required. Our customers have only had issues when over charging on accident.
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when you hit the A/C clutch, it subtracts a little HP from the engine, and that slows the engine down a bit. Often computers have an A/C kick up function you might be familiar with.
Its just a vacuum leak. You can run a brake booster sized vacuum line into the car, and uncap it just before you turn on the A/C compressor for the same RPM raising effect. Likewise, you can steal any Idle control valve from any vehicle with a built in 12+ or G- activated "air leak A/C kickup valve" and weld/bolt that into your intake tube and use it with a switch as well. Or a custom output from the computer.
Lots of options for adding some air during idle, from manual to electric.
Its just a vacuum leak. You can run a brake booster sized vacuum line into the car, and uncap it just before you turn on the A/C compressor for the same RPM raising effect. Likewise, you can steal any Idle control valve from any vehicle with a built in 12+ or G- activated "air leak A/C kickup valve" and weld/bolt that into your intake tube and use it with a switch as well. Or a custom output from the computer.
Lots of options for adding some air during idle, from manual to electric.
TECH Regular
Joined: Jun 2012
Posts: 414
Likes: 5
From: SV, AZ
You're probably overcharged as others have said. Also your tuners should tune idle with AC on and blowing as your baseline. Basically build the AC air and spark requirements into the tune. It's not the best solution but it's a workable solution. I've had to do it a few times on cars where the shop didn't consult with me first and used a stand alone AC system.