My 427 SOHC Build..... Finally the time has come!

[cobracammer]

Hey Guys.  Out on the first cruise.  Getting a popping noise ( mini backgire) while holding cruising speed.  Any ideas?  Target AF ratio holds at the settings  around 13.5  14 when I throttle up.  Not sure what to do and dont want to break anything

Parked at a tire kingdom right now.  Help  lol

[jayb]

Target A/F should be 12.5-13 when you are significantly accelerating on the throttle.  Popping could be a lean condition.

[cobracammer]

Checked settings: currently idle is 13.5

Cruise is 14.0

WOT is 12.8

These are the current settings in the ECU

Should I adjust anything?  Also i can now alter Accel fuel  currently at -2  ?

I took this video really quick on the way home from the alignment shop.  Toward the end, you can see all the values fairly clearly.  Thoughts?

http://youtu.be/tL0XVt9bh-g

[My427stang]

Well a pop in the exhaust could be a lean misfire, could be a rich condition firing in the exhaust, could be a header leak, could be an ignition issue.

If you think it is EFI related, adjust your cruse target to 13.5, see what it does.  Then 14.5, see what it does, if no change either way, it's not the tune, if worse one way and better another than it tells you what to do next.  However, if you do consider going leaner than 14.5 on cruise, be careful

Sounded real nice to me though, I didn't hear the popping and it didn't look too lean.

[cobracammer]

Hey Ross.  I dont know why, but I have accel fuel at -2.  Maybe I should adjust this feature first?  Or should I start with the targets first?

[WConley]

+1 on the lean misfire.  It matches the symptoms you're describing - light load cruise stumbling / popping.  You should notice it too when you coast down in gear with the throttle closed.

I don't know if bumping your accel fuel will affect the steady-state map.  It shouldn't, but a lot of these EFI systems have strange interactions in the settings.

Looks like you need to fatten it up a bit in the light load mid-rpm range of the map.  The popping won'[t hurt anything in the meantime...

[My427stang]

I agree with Bill, unless you are bogging like a bad accel pump, I'd be looking at cruise mixture not accel fuel

Remember, the O2 sensor reads at best a bank of cylinders or sometimes all 8, so even though you may have 14.0 as a target, individual cylinders could be leaner.  It's easy enough to try changing cruise ratio to 13.8 and see what it does

Keep in mind, what you see may not be the actual mixture, O2 sensors can be funky. Additionally, if there is any alcohol in the mix, stoich values change, so E10 likes .6 lower or so at 14.1, and the more corn squeezins in the mix, the richer you need to command.  Just use the number as a starting point to return to if something doesn't work

[cobracammer]

Just full disclosure, it pops and hessitates to when I throttle up ( in 4 th and 5th gear) 
Might need to adjust WOT too?

[My427stang]

If you floor it and it bogs, then backfires, then you likely need to increase your acceleration fuel.  If it's always got some sort of pop or backfire in different degrees, I would be looking at the ignition (cap, rotor, wires, plugs)

[cobracammer]

They are more likestumbles and heasitations, small pops.... not really backfires.  It feels like not enough gas ( not smoking at all and doesnt really smell like unburnt fuel.

What should I setthe targets to ( all) as a starting point?  Sorry for all the questions

[My427stang]

Make one change at a time from where you are, and write down exactly where you are now and what you do for each change

If it were mine, I would do the cruise first, just drive it steady and go .5 richer (13.5)  than where it is now.  If at 13.5 it runs well, go to 13.7, then try again

When done and happy with steady cruise, do your acceleration fuel.  Don't do two steps at a time, and always write down what you did.

Also, always do your tests at full operating temp. 

[cobracammer]

Ok perfect!  Thanks again.  Exciting.  Got it aligned today.  Rides smooth.  Stays cool 185 degrees while cruising.  No rattles or glitches.  Just the Fuel issues.  I have cars and coffee this weekend about 10 miles away.  Might take it over just for some giggles  LOL  Also gives me a chance to test these fuel changes one at a time

[cobracammer]

Hey Guys,

Just a thought (while I am sitting here at work.)  Would those mini pops and hesitations (Actually when you listen to the youtube video, when I drop the camera to take it out of gear, you can hear the sounds I am talking about) be due to the PCV valve?  I know there was talk of "detonation", but I was not sure if this sounded like a detonation issue to you guys?  Wanted to ask this before adjusting the Air Fuel Targets.


Also, I was originally told by the FAST efi tech to adjust the Accel Fuel (which was originally at "0") because on my first drive around the block, there was the same sort of rough hesitation (minus the pops) getting up through 1st gear.  He thought it sounded like too much fuel, so had me adjust the Accel fuel to a negative number ( I think we settled at -2).  Could this also possibly be a lack of fuel too?  That would be funny.

Will take a notepad, write down all my current values.  Then I will try making the adjustment to the cruise A/F ration suggested (13.5).  Go a few miles down the open road (I have a 10 Mile stretch that the speed limit is about 65 mph with no lights).  I can then stop at the end, make note of what the difference was in the values and the handling, and make another pass back home (10 miles or so) with another small change in AF ratio.  Once we get this dialed in, We can work on WOT.  I thin idle is fine (once warmed up to operating temperature) since it idles nicely at 950-1000RPM and there is no un-burnt fuel or smoke currently coming from the tailpipe.

[My427stang]

I doubt it'd be the PCV, however, if it was slightly lean, it could be slightly leaner now.

I didn't hear them and Youtube is blocked at work, but I will crank it up.  Typically detonation would be under a load not decel.

[cobracammer]

Thanks Ross.  Hard to explain.  It seemed to happen intermittently in Cruising (holding at about 2200 PRM) and happens a lot during acceleration.... This is why I thought it was prob. lack of fuel.  I stomp on the gas and it doesn't go anywhere.  Just stumbles and pops.  Like you said, I will work on Cruise first and then when that's good, Ill report back and we can move on to WOT.

From reading online, very few people stay at the factory set A/F Targets.  Since this engine is a bit of a beast, its most definitely going to like some tweaking.  :0)