Need help getting my 396 to idle good
Thread Starter
Registered User
Joined: Aug 2000
Posts: 53
From: Victoria, TX
Need help getting my 396 to idle good
I posted this message on the LT1_edit list but decided to post here also.
My motor is a solid roller 396. Cam has around 248 intake/252 exhaust duration with around .620 lift. I am having a hard time making it idle. I have basically tried two things.
First, I tried the open loop idle. Change to WOT table to 0 at 800 - 1600 RPMs. If I got this right this should allow me to tune the idle with the PE tables... The thing is when the motor is at idle the
short term fuel trims go SCARRY lean (like 190 yipes). So tried to jack up the PE readings around the 1200 RPMS. Made a little difference Short term fuel trims stay around 170. Still very bad though. I maxed out the PE table around 1200 rpms but still only managed short term BLMS around 170. Also, as I watch the BLMS go lean the motor started to idel quit well but the fuel trim reading got me scared. Side note... The KPA is around 50 and the IAC count is around 35 ish. These are good numbers if I remember correctly.
Second think I tried was to switch off the open loop idle mode. While the car was in open loop it surged between 1200 and 1600 to 170O rpms. When switching the closed loop the car starts to idle better. Hardly no surge at all. IN fact pretty acceptable to me. As with the open loop mode the IAC and KPA values are good. However, as before the short term fuel trims go scary lean and after a minute of this the PCM switchs back to open loop (and back to the crappy surging idle).
I need help! Somebody throw me a bone. Please.
thanks
------------------
Allen Brotze
95 firebird
LT1 edit, 58 mm
AFRd 396,TNT nitrous,
58MM TB,6AL,Turbo 400, !cat,!cags,!egr,CAI, CSI electric waterpump
1 3/4 Hooker LTs
Mufflex exhuast
LCR's, Moser 12 bolt, Torque arm.
"Speed kills so you won't get hurt if you drive a Ford."
My motor is a solid roller 396. Cam has around 248 intake/252 exhaust duration with around .620 lift. I am having a hard time making it idle. I have basically tried two things.
First, I tried the open loop idle. Change to WOT table to 0 at 800 - 1600 RPMs. If I got this right this should allow me to tune the idle with the PE tables... The thing is when the motor is at idle the
short term fuel trims go SCARRY lean (like 190 yipes). So tried to jack up the PE readings around the 1200 RPMS. Made a little difference Short term fuel trims stay around 170. Still very bad though. I maxed out the PE table around 1200 rpms but still only managed short term BLMS around 170. Also, as I watch the BLMS go lean the motor started to idel quit well but the fuel trim reading got me scared. Side note... The KPA is around 50 and the IAC count is around 35 ish. These are good numbers if I remember correctly.
Second think I tried was to switch off the open loop idle mode. While the car was in open loop it surged between 1200 and 1600 to 170O rpms. When switching the closed loop the car starts to idle better. Hardly no surge at all. IN fact pretty acceptable to me. As with the open loop mode the IAC and KPA values are good. However, as before the short term fuel trims go scary lean and after a minute of this the PCM switchs back to open loop (and back to the crappy surging idle).
I need help! Somebody throw me a bone. Please.
thanks
------------------
Allen Brotze
95 firebird
LT1 edit, 58 mm
AFRd 396,TNT nitrous,
58MM TB,6AL,Turbo 400, !cat,!cags,!egr,CAI, CSI electric waterpump
1 3/4 Hooker LTs
Mufflex exhuast
LCR's, Moser 12 bolt, Torque arm.
"Speed kills so you won't get hurt if you drive a Ford."
Registered User
Joined: Sep 1999
Posts: 69
From: Ashburn, VA
I have a similar problem (396 LT1, 236/242/112 hydro cam) with idle and low-RPM operation.
I think the combination of big cam and short intake runners leads to intake reversion and uneven fuel distribution from one cylinder to the next. The O2 sensors see only the unburnt O2, so both banks appear lean, when actually they both have some cylinders rich and others lean. In fact, when I pulled off my headers last time, some of the tubes were black with carbon, while others were perfectly clean inside, so this idea is not completely without merit.
My temporary solution is to run open loop all the time (not PE idle, that's even worse). First, I drove around in closed loop, logging everything, then I put the data into Excel and graphed RPM vs MAP. Based on where my engine was spending most of its time, I then set the BLM boundaries to 1500, 2000, 2500 RPM and 50, 60, 70 MAP. I then drove around, still in closed loop, and logged everything again. I ran the data through my spreadsheet (another sheet that calculates average BLM per cell), and looked at the BLM's, ignoring the under-2000 RPM stuff, then tweaked the injector constant, and kept re-testing and tweaking until these BLMs were close to 128. Then I set it up for open loop and tweaked the AFR table a little. I checked the plugs a couple times to ensure that it's not running TOO rich or lean.
This got me close, the car runs well, but I am going to take these headers off again in a couple weeks and get EGT sensor bungs welded in... that way I can properly tune the cylinder balance tables on the dyno. I'm hoping by equalizing the cylinders I can clean up the idle as well as eliminate some low-RPM surge I'm feeling (when the TCC is locked), and maybe run closed loop again.
Anyway, take all this with a grain of salt, I don't have everything working yet, but I think I'm on the right track.
I think the combination of big cam and short intake runners leads to intake reversion and uneven fuel distribution from one cylinder to the next. The O2 sensors see only the unburnt O2, so both banks appear lean, when actually they both have some cylinders rich and others lean. In fact, when I pulled off my headers last time, some of the tubes were black with carbon, while others were perfectly clean inside, so this idea is not completely without merit.
My temporary solution is to run open loop all the time (not PE idle, that's even worse). First, I drove around in closed loop, logging everything, then I put the data into Excel and graphed RPM vs MAP. Based on where my engine was spending most of its time, I then set the BLM boundaries to 1500, 2000, 2500 RPM and 50, 60, 70 MAP. I then drove around, still in closed loop, and logged everything again. I ran the data through my spreadsheet (another sheet that calculates average BLM per cell), and looked at the BLM's, ignoring the under-2000 RPM stuff, then tweaked the injector constant, and kept re-testing and tweaking until these BLMs were close to 128. Then I set it up for open loop and tweaked the AFR table a little. I checked the plugs a couple times to ensure that it's not running TOO rich or lean.
This got me close, the car runs well, but I am going to take these headers off again in a couple weeks and get EGT sensor bungs welded in... that way I can properly tune the cylinder balance tables on the dyno. I'm hoping by equalizing the cylinders I can clean up the idle as well as eliminate some low-RPM surge I'm feeling (when the TCC is locked), and maybe run closed loop again.
Anyway, take all this with a grain of salt, I don't have everything working yet, but I think I'm on the right track.
Registered User
Joined: Feb 2001
Posts: 6
From: milford oh us
Go into your timing tables at the idle kpa(you stated yours is 50), and make sure your timing is about 17-20 deg. Sounds like some timing issues. The base maps are WAY off with a large cam, esp at idle. I have a similar cam with a little more lift/dur and it idles about like a cc306 no surge.
------------------
2000'
rocharged 95m6 ta 11.28@125
2001' : Ditched the Blower-Added Self ported heads
11.72@117.2
2002': ditched it all for a N/A 396 solid roller and a 4l80e
580hp/482tq- ECM rpm limited numbers
------------------
2000'
rocharged 95m6 ta 11.28@1252001' : Ditched the Blower-Added Self ported heads
11.72@117.2
2002': ditched it all for a N/A 396 solid roller and a 4l80e
580hp/482tq- ECM rpm limited numbers
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