puff of blue smoke at higher rpm decel

General engine tech -- Drag Racing to Circle Track

Moderator: Team

Post Reply
Belgian1979
Guru
Guru
Posts: 3708
Joined: Sat Mar 26, 2011 11:34 am
Location: Belgium - Koersel

Re: puff of blue smoke at higher rpm decel

Post by Belgian1979 » Tue Aug 01, 2017 9:47 am

naukkis79 wrote:
Belgian1979 wrote:It hunts severely when running stoich or leaner and even constantly starts missing. Some cams just don't let you do that
Get rid of closed-loop autotune, if you have problems with stoich AFR closed-loop is not usable either. Even with very mild stock cams std engines have almost zero ignition advance at light load to keep EGT high enough to keep lambdas alive. With high-overlap cam EGT recirculation with rich afr will certainly lower egt to point where false lean happens, and ecu corrects to very rich afr, which ruins engine incredibly fast.
0° advance at light load ? Seems counterintuitive to me. Engine will tend to run hot under those conditions as well.
Are you now referring to a NB O2 sensor or a WB O2. An WBO2 has it's own sensor heating.

Belgian1979
Guru
Guru
Posts: 3708
Joined: Sat Mar 26, 2011 11:34 am
Location: Belgium - Koersel

Re: puff of blue smoke at higher rpm decel

Post by Belgian1979 » Tue Aug 01, 2017 9:54 am

modok wrote:Looks to me that, when intake was designed, part load operation was not one of the criteria.
In fact the engine runs a lot better than with a Victor Jr type manifold which you usually see with these engines and an EFI system conversion.

What led you to this conclusion ?

User avatar
modok
Guru
Guru
Posts: 1720
Joined: Sun Jun 06, 2010 1:50 am

Re: puff of blue smoke at higher rpm decel

Post by modok » Tue Aug 01, 2017 8:10 pm

Wild guess. Was I wrong? :P
Glen Urban

Belgian1979
Guru
Guru
Posts: 3708
Joined: Sat Mar 26, 2011 11:34 am
Location: Belgium - Koersel

Re: puff of blue smoke at higher rpm decel

Post by Belgian1979 » Wed Aug 02, 2017 1:39 pm

modok wrote:Wild guess. Was I wrong? :P
yes

User avatar
modok
Guru
Guru
Posts: 1720
Joined: Sun Jun 06, 2010 1:50 am

Re: puff of blue smoke at higher rpm decel

Post by modok » Wed Aug 02, 2017 8:28 pm

Well I guess so, it's been two months sorry I forgot it's IR

Ok then why can't you cruise lean?
You can't blame the cam. Probably a problem elsewhere. Not a good load signal? throttles out of sync?
Glen Urban

User avatar
MadBill
Guru
Guru
Posts: 13445
Joined: Tue Nov 15, 2005 10:41 am
Location: The Great White North

Re: puff of blue smoke at higher rpm decel

Post by MadBill » Wed Aug 02, 2017 9:23 pm

Belgian1979 wrote:It hunts severely when running stoich or leaner and even constantly starts missing. Some cams just don't let you do that
Since we're touching on this topic, how much total spark advance is programmed in during light throttle cruise? Too little will cause surging; it needs as much as 50°+. Some mid-eighties GM vacuum cans were 30°...
Felix, qui potuit rerum cognscere causas.

Happy is he who can discover the cause of things.

Belgian1979
Guru
Guru
Posts: 3708
Joined: Sat Mar 26, 2011 11:34 am
Location: Belgium - Koersel

Re: puff of blue smoke at higher rpm decel

Post by Belgian1979 » Thu Aug 03, 2017 4:46 am

42-44°

naukkis79
Member
Member
Posts: 140
Joined: Tue Jul 29, 2014 5:14 am

Re: puff of blue smoke at higher rpm decel

Post by naukkis79 » Thu Aug 03, 2017 4:53 am

Belgian1979 wrote:
0° advance at light load ? Seems counterintuitive to me. Engine will tend to run hot under those conditions as well.
Are you now referring to a NB O2 sensor or a WB O2. An WBO2 has it's own sensor heating.
Stock NB sensors have heating too, but even with heating they are not accurate at very light loads if engine is tuned to best power. Stock ignition maps call for near zero load ~10 degreee timing which increases way over 40 degree when load increases. There is no way that WBO is accurate at richer than stoich, normal ignition timing and near zero load, it will show lean condition and ecu will richen up, and if ecu autotune has not sane limits if will go pig rich - and in such conditions it's not uncommon to stick oils rings in piston with a few thousand miles. And the result is smoking engine in decel.

Belgian1979
Guru
Guru
Posts: 3708
Joined: Sat Mar 26, 2011 11:34 am
Location: Belgium - Koersel

Re: puff of blue smoke at higher rpm decel

Post by Belgian1979 » Thu Aug 03, 2017 1:19 pm

Strange. This is the map of a 1995 stock SBC LT1.

Image

n2xlr8n
Expert
Expert
Posts: 508
Joined: Tue Jun 28, 2005 9:01 pm
Location: Bama

Re: puff of blue smoke at higher rpm decel

Post by n2xlr8n » Thu Aug 03, 2017 3:36 pm

I'd honestly like to see how it idled with a vacuum pump.
He who is in me is greater than he who is in the world.

Belgian1979
Guru
Guru
Posts: 3708
Joined: Sat Mar 26, 2011 11:34 am
Location: Belgium - Koersel

Re: puff of blue smoke at higher rpm decel

Post by Belgian1979 » Thu Aug 03, 2017 3:42 pm

n2xlr8n wrote:I'd honestly like to see how it idled with a vacuum pump.
Not sure I follow you here

n2xlr8n
Expert
Expert
Posts: 508
Joined: Tue Jun 28, 2005 9:01 pm
Location: Bama

Re: puff of blue smoke at higher rpm decel

Post by n2xlr8n » Thu Aug 03, 2017 3:53 pm

Belgian1979 wrote:
n2xlr8n wrote:I'd honestly like to see how it idled with a vacuum pump.
Not sure I follow you here
I've had some nasty cams idle better than I ever imagined after adding a vacuum pump. Both EFI and carb'd.

I'm not sure how your injected setup would differ, but it's worth a shot.
He who is in me is greater than he who is in the world.

Belgian1979
Guru
Guru
Posts: 3708
Joined: Sat Mar 26, 2011 11:34 am
Location: Belgium - Koersel

Re: puff of blue smoke at higher rpm decel

Post by Belgian1979 » Thu Aug 03, 2017 4:02 pm

n2xlr8n wrote:
Belgian1979 wrote:
n2xlr8n wrote:I'd honestly like to see how it idled with a vacuum pump.
Not sure I follow you here
I've had some nasty cams idle better than I ever imagined after adding a vacuum pump. Both EFI and carb'd.

I'm not sure how your injected setup would differ, but it's worth a shot.
To put the crankcase under low pressure...I don't see how this could influence the idle quality/cam combo but I might be wrong here.

Belgian1979
Guru
Guru
Posts: 3708
Joined: Sat Mar 26, 2011 11:34 am
Location: Belgium - Koersel

Re: puff of blue smoke at higher rpm decel

Post by Belgian1979 » Sun Jan 28, 2018 11:12 am

Coming back to this old thread of mine. I just recently acquired a smoke machine and connected it up to the engine. I see smoke coming out of each individual intake channel (ITB manifold). As said before I have a vacuum chamber underneath each runner connected with a small hole to the runners themselves. I couldn't quite see the source as the runner got filled up with smoke but due to fact that each and every runner smokes, I assume that at least this is not caused by an openstanding valve and smoke migrating up from the crankcase through the ring gaps and such.

The vacuum chamber (underneath the cross ram runners forming a 'v' have a SS plate that closes it towards the lifter valley. It is sealed up with blue silicone. I assume that it has failed. Would it be possible that oil migrates up into the lifter valley to create the issue ?

Thanks for the input.

Newold1
Guru
Guru
Posts: 1282
Joined: Fri Apr 08, 2016 9:50 am

Re: puff of blue smoke at higher rpm decel

Post by Newold1 » Sun Jan 28, 2018 4:34 pm

Absolutely!
A manifold vacuum even in your vacuum chamber under the manifold if it is leaking under vacuum will pull oil up from the lifter valley area and send it through those individual ports into the ITB inlet runners and burn it. When you are decelerating you will have maximum vacuum and thats when it would happen the strongest.

Is there a way to plug temporarily 7 of the 8 holes and then put some slight air pressure into that chamber with a hose and just pressure when you blow on it to see if it holds any pressure. If it has a leak into the valley it should bleed of and you might even hear the leak if its quiet enough.

Post Reply