I have a question about A/F readings and a cam

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TrailBeast

TrailBeast

AKA Mopars4us on Youtube
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At idle my A/F reads way rich (like mid 10's) and it won't adjust out but figured it was because the idle of the cam lets a lot of unburned fuel into the pipes.
As soon as the throttle starts to open it goes right up into the mid to high 13's.
Is this the case, as I don't see how it could be much of anything else but I don't have much experience with performance cams.

My mouth is now in neutral and my ears are in gear:D

My Dad used to say "When you put your mouth in gear your ears go into neutral"
And "You don't learn anything when you leave your mouth running"
I didn't, and still don't talk much so I don't think he meant me specifically but just giving good advice overall. :D
RIP Dad.
 
TrailBeast said:
...it won't adjust out...
Click to expand...

Sounds more like the adjuster isn't doing it's job, which points the finger at something other than the cam. I'm guessing big cam, no air bleed for idle, the idle screw is adjusted too far and the t-slots are too far open. But that's just a guess since you haven't given us enough information to know better :D :p
 
Phreakish said:
Sounds more like the adjuster isn't doing it's job, which points the finger at something other than the cam. I'm guessing big cam, no air bleed for idle, the idle screw is adjusted too far and the t-slots are too far open. But that's just a guess since you haven't given us enough information to know better :D :p
Click to expand...

Thanks.
The cam is on a stock 9:1 Magnum with 318A closed chamber 62cc EQ heads.
214/224 @ .50 and 110 LSA
Timing is right at 23-24 intial with 11 mechanical on the distributor and all in @ 2,500 or so.
Vac advance is ported at the carb, and have 52 degrees max possible advance at light throttle.
87 pump fuel
Idle at 800 RPM with the butterflies fully closed and very likely no transition slot use at idle at all.

The idle mix makes a difference just not able to get the A/F ratio up to where it was with the old engine. (around 14:1)

It not a big deal, I just thought I would ask if that's why.

Thinking back on what AJ said about bringing the timing down and opening the idle farther is haunting me now. :D
 
AF is solely determined by the amount of fuel available to the intake tract. I bet if you opened up the brake booster or PCV hose to atmosphere you could get it to lean out. Even with a bit of cam, it shouldn't take a richer mixture to run well.

I'm assuming if you close the idle mix it'll die? I can't imagine not being able to get from 10 to 14 if the adjustment is working.. Unless it just begins to run poorly as you move toward 14..

The PO didn't have much info on the car when I bought it, but it's got a helluva lumpy idle for a 318, and RHS X heads and ~.550 lift. I've got my EFI set right now to idle with about 26 degrees of idle advance (effectively like running 14~16 degrees of initial with the vac can to manifold vacuum - which I'm a proponent of), 15.2 AFR and it works great. Maintains a steady 194 degrees at idle in 100F temps. I had started around 18 degrees at idle and 13.75 target AFR and it would slowly creep up to 206 in 90 degree temps. It wasn't a big deal either, but refining the idle really helped to keep things from heating more than they needed to. Back when it was still on a carb, I had a tough time getting from 10 to ~14 at idle as well, and just as tough a time keeping the plugs from giving me fits.
 
Are you using the same PCV valve? Do you know how much less vacuum at idle this one has compared to the LA engine? I bet a PCV with a little more bypass will do the trick.... Or your (power valve / metering rods) are not pulling down at idle.
 
Do you have control of the idle mixture screws?

That cam is small and should not throw the idle mixture into a tizzy!
 
Phreakish said:
AF is solely determined by the amount of fuel available to the intake tract. I bet if you opened up the brake booster or PCV hose to atmosphere you could get it to lean out. Even with a bit of cam, it shouldn't take a richer mixture to run well.

I'm assuming if you close the idle mix it'll die? I can't imagine not being able to get from 10 to 14 if the adjustment is working.. Unless it just begins to run poorly as you move toward 14..
QUOTE]
Yes, it'll die.
I probably should recalibrate my A/F gauge again just to make sure it's reading right but the engine runs like the gauge should be right.
I also checked plugs and they were nice and clean with slight tan tint at the tips so it can't be too far off.
It starts idling crappy way before I can get it anywhere near 14.



mguner said:
Are you using the same PCV valve? Do you know how much less vacuum at idle this one has compared to the LA engine? I bet a PCV with a little more bypass will do the trick.... Or your (power valve / metering rods) are not pulling down at idle.
Click to expand...
Using the same orifice limited PCV so it can pull very little there, and the engine vacuum is right about the same at 18-20.
That is one reason I didn't consider the metering rods, but maybe they are bouncing because of the cam lope.
I have the calibration kit and can try the next lighter springs if needed.
Any more thought on it now?

crackedback said:
Do you have control of the idle mixture screws?

That cam is small and should not throw the idle mixture into a tizzy!
Click to expand...

Total control right to the point it runs like crap if open to far and dies if closed to far.
But still never comes into range as far as the gauge says, so it's odd.
If I can lean it till it almost dies you would think it would go beyond 14 on the gauge, and that's why I asked about the cam lope causing a real rich or unburned mixture at idle.
Click to expand...
 
"Total control right to the point it runs like crap if open to far and dies if closed to far.
But still never comes into range as far as the gauge says, so it's odd.
If I can lean it till it almost dies you would think it would go beyond 14 on the gauge, and that's why I asked about the cam lope causing a real rich or unburned mixture at idle."

What carb are you running Greg?
 
Calibration is most likely, then. What kind of gauge do you use? Some seem to have a reputation of not holding a calibration.

If all the signs check out though, run it! There's plenty of things that could throw off the lambda reading, like burning oil or contamination of some sort on the sensor, or even that you have one or more cylinders that are leaner than the average - meaning that the aggregate mixture needs to be richer to make up for the few lean cylinders. Personally, I'd grab an IR thermometer and check the collector or manifold runners and see if there's any major imbalance just to make sure. Could be something to do with the carb and not feeding both side equally (do you have a single or dual plane intake?).

Metering rod springs could be worth a check, but if you can kill it with the idle mix screws then they're probably not a major culprit. They're easy enough to swap though that I'd do it anyway to see if there's a difference.
 
Yea, the only place there seems to be an issue is at idle.
Right off idle everything seems to match up, like how it feels and runs compared to the gauge.
Every indication is that it's running near perfect except for the gauge at idle.
It's a dual plane 318/360 Performer intake, and I think I'll put the vac gauge on it at idle again and make sure of what that is before doing any changing on the springs, as I think it has the one step stiffer than stock in it right now. (It may very well be bouncing if the idle vacuum varies much) I remember it being pretty dog gone steady when I was setting the vacuum switch pressure for the lockup disengage of the trans.

Oh, the gauge is the Innovate LM2 wideband.
 
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TrailBeast said:
Yea, the only place there seems to be an issue is at idle.
Right off idle everything seems to match up, like how it feels and runs compared to the gauge.
Every indication is that it's running near perfect except for the gauge at idle.
It's a dual plane 318/360 Performer intake, and I think I'll put the vac gauge on it at idle again and make sure of what that is before doing any changing on the springs, as I think it has the one step stiffer than stock in it right now. (It may very well be bouncing if the idle vacuum varies much) I remember it being pretty dog gone steady when I was setting the vacuum switch pressure for the lockup disengage of the trans.

Oh, the gauge is the Innovate LM2 wideband.
Click to expand...

Yeah, the innovate ones are the ones I've read most of the stories about having to recalibrate often.

Being a dual plane, it's entirely possible one side has something 'up' at idle on just one side. Do you have a bung on both sides? Even with an X or H the gasses won't cross over a whole lot. It may just need a tweak to even things out, or one of the metering rods may not be seating.

My engine only idles with about 10" and with one step stiffer than stock the rods would bounce. With a smallish cam and 18-20", I don't see them bouncing much. Even if they did, it shouldn't affect things much at idle unless the T slot is too far open.
 
It's not the cam.

The cam in my 340 is 234/242 @ .050" with a 110 LSA and vacuum at idle is ~9". Advance at idle is 22*, all in mechanical is 35*. It will still idle at 14 on the AFR, I run the same Innovate wideband AF gauge too. I run a Holley 750 Ultra DP with mechanical secondaries.
 
Phreakish said:
Yeah, the innovate ones are the ones I've read most of the stories about having to recalibrate often.

Being a dual plane, it's entirely possible one side has something 'up' at idle on just one side. Do you have a bung on both sides? Even with an X or H the gasses won't cross over a whole lot. It may just need a tweak to even things out, or one of the metering rods may not be seating.

My engine only idles with about 10" and with one step stiffer than stock the rods would bounce. With a smallish cam and 18-20", I don't see them bouncing much. Even if they did, it shouldn't affect things much at idle unless the T slot is too far open.
Click to expand...

The gauge was stable as a rock for two years, and the 318 was smooth as glass with that same carb.
Also, I can make changes with one idle circuit or the other and it changes to rich and lean both but doesn't get any better about the A/F than about the 10-11 I mentioned.
I can make it worse. :D
 
72bluNblu said:
It's not the cam.

The cam in my 340 is 234/242 @ .050" with a 110 LSA and vacuum at idle is ~9". Advance at idle is 22*, all in mechanical is 35*. It will still idle at 14 on the AFR, I run the same Innovate wideband AF gauge too. I run a Holley 750 Ultra DP with mechanical secondaries.
Click to expand...

Like I wanted to hear that. :D
Thank you for the info though, and I can consider other possible issue's.
 
It's not the cam.
IMO,Way too much initial for the size of cam.
See below.

Unless you are trying to idle it way too slow, or are running a singleplain.
Then the whole shebang can conspire to wreck the idle AFR

Well, I guess it could be the cam.
If the intake opens way too early, and,you are running a SP intake, and the idle is way to slow.
But none of that applies to you. You have a DP and idle at 800, and unless you installed the laziest cam in the world, the intake closing angle will be fine.
The tip off is when you said;" as soon as"..
But at 800 with the throttle closed, those pistons are sucking so hard they're about ready to suck the bowls dry right through the idle-ports.BaBaam!

Wait, is there an echo in here? Hello... ello.....elo..........looo...................lol!

Pull her back to 12* to 14*,close up the secondaries tight, and, you guessed it...................Set the T-port sync.
Rev her up to around 2400. Reset the mixture screws for highest rpm. Drop her back to idle. Use the T-port to add or subtract idle fuel to get a smooth idle. Adjust the secondary opening to drop the idle down to something like 550 to 650 in gear.Reset the transfer opening if you have to for smoothness; leave the mixture screws alone.
TB you know me, would I steer you wrong?
Ok truth; Thats how I set mine with a 223/230/110 cam; Did I mention it went 32mpgUS in O/D? heehee.
Oh yeah, All in by 2500..., Ima guessing you have a hi-stall,Or you might not get away with that on 87.
For very long.....
 
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Adjust the A/F ratio until it runs smooth, my guess is around 12.5:1. A larger cam gets 'choppy' with lean idles.. They like rich mixtures.

For example, My cam is 225 @ .050 and idles like a drag car at 14:1 and purrs like a kitten at 12.0.
 
TrailBeast said:
The gauge was stable as a rock for two years, and the 318 was smooth as glass with that same carb.
Also, I can make changes with one idle circuit or the other and it changes to rich and lean both but doesn't get any better about the A/F than about the 10-11 I mentioned.
I can make it worse. :D
Click to expand...

Then it's probably the mix, not the cam, and a lot to do with the timing. 20" is decent even for a stocker. I'd pull the initial down to 12-14, hook the v can to manifold vac and then try leaning it. Bigger cams may like more idle mix, but I'm willing to bet that they'll idle lean just fine with the timing set well enough.
 
I do seem to remember someone saying something about all this before, so who was that? :D

Ok, I'll play with it when I get a chance here,(maybe this eve) as I'm doing a few things at once right now and it's too hot out to mess with it right now anyway.
Thanks guys.
 
Yeah, I can pull my 230/237/110 down to 550 with the clutch, and it will idle around the parking lot by itself like that. 750 in neutral.14* initial timing, even down to 10*initial.( dial back timing device in the cab)

Ba-bupup,babupup, babupup, babupup, babupup............. .
That's the sound of 230@050@550rpm. .. .. .. .. 550/60=9.16 revolutions per second. At 4 shots per revolution, thats 36.6 shots per second.
Say it with me now; ba-bupup,babupupbabupupbabupup.......................
OK, now, a lil faster............

BTW; the location of the O2 in the collector can play a role in it's reading too; If it's too close to the merge....well you know.......I'm sure you know all that.
This is more of a problem with some of the cheaper headers with very short collectors.
One more time; ba-bupup,babupupbabupupbabupup.......
 
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AJ/FormS said:
Yeah, I can pull my 230/237/110 down to 550 with the clutch, and it will idle around the parking lot by itself like that. 750 in neutral.14* initial timing, even down to 10*initial.( dial back timing device in the cab)

Ba-bupup,babupup, babupup, babupup, babupup............. .
That's the sound of 230@050@550rpm. .. .. .. .. 550/60=9.16 revolutions per second. At 4 shots per revolution, thats 36.6 shots per second.
Say it with me now; ba-bupup,babupupbabupupbabupup.......................
OK, now, a lil faster............

BTW; the location of the O2 in the collector can play a role in it's reading too; If it's too close to the merge....well you know.......I'm sure you know all that.
This is more of a problem with some of the cheaper headers with very short collectors.
One more time; ba-bupup,babupupbabupupbabupup.......
Click to expand...

I think you are having a little too much fun with this, and in more ways than one. LOL
 
340 six pack. 11.3 to 11.5 at idle. Cam 550 solid lifter. 13 to 13.5 at 3000 to 3500 rpm. Full wot 10.5. First off I have to run 10% ethonal gas. So your afr has to be richened up to at least 13 to 13.5. Idle is at 900 rpms. Aem afr gauges in both sides. So does cam have affect on afr. Absolutely on tuning the carb.
 
My son's 340 cam is about identical to that (212/220 @ .050")and we have no problem getting the idle mixture into the high 13's or mid 14's..... not even trying anything special. We have the same AFR meter. With real AFR's in the 10's, your engine should be on the verge of blowing black smoke, and it will smell very obviously rich.... getting into the eye-burning range and blackening the plugs. Is it indeed very black in the pipes, and very rich smelling?

If not, then for some reason the O2 in the exhaust is on the low side for some reason under idle conditions. An AFR meter is really not measuring AFR directly; it is measuring free oxygen left in the exhaust after combustion, is ASSUMING very complete combustion of the fuel, and then interpreting the free oxygen % in the exhaust as an AFR in the intake. EGR will make O2 in the exhaust low...but probably not directly the case here.

Easy to see if the high initial advance is the culprit. BTW how high is your idle vacuum? If overly high for the cam, then perhaps it could be pulling more spent gases up into the intake at overlap, and acting like an EGR system. Things move pretty slowly at idle and the time is there so that could happen.
 
AJ/FormS said:
Yeah, I can pull my 230/237/110 down to 550 with the clutch, and it will idle around the parking lot by itself like that. 750 in neutral.14* initial timing, even down to 10*initial.( dial back timing device in the cab)

Ba-bupup,babupup, babupup, babupup, babupup............. .
That's the sound of 230@050@550rpm. .. .. .. .. 550/60=9.16 revolutions per second. At 4 shots per revolution, thats 36.6 shots per second.
Say it with me now; ba-bupup,babupupbabupupbabupup.......................
OK, now, a lil faster............

BTW; the location of the O2 in the collector can play a role in it's reading too; If it's too close to the merge....well you know.......I'm sure you know all that.
This is more of a problem with some of the cheaper headers with very short collectors.
One more time; ba-bupup,babupupbabupupbabupup.......
Click to expand...


Where's the dang (bow to someone) emotiflippincon? Oh, I guess this will have to do:drama::thankyou:
18 degrees at 800RPM and 13.8 -14.5 average.
Not so sure how I like that it sounds a little more labored than it did, but I suppose I'll get used to it (or just richen it up a little maybe around 13.5 and let it go)
It never crossed my mind that you would steer me wrong by the way :D
Sorry you had to say it twice, eh :D

Thanks for all the suggestions and tips guys.
 
Interesting.... and very good info. Now that I think of it, my son's similar cam sometimes reads a tad rich on idle, without changing anything.....so thanks for bring this up. I doubt that your AFR was really as low as the gauge indicated in this situation unless you had heavy soot in the pipes and a gassy smell out of the pipes. If the pipes were clean and the exhaust smelled clean at idle before, then it was likely a non-issue. Kinda like AFR being off when the enigne is cold....

Perhaps this is really why some newer EFI cars have IAC valves on them (idle air compensators): makes the computer not go nuts with a false AFR reading with a tightly closed throttle at idle or decel.
 
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