Air Fuel Ratio gauge and now have question?

[Gary Lewis]

Now holding the throttle steady on flat ground it was still bouncing around the above numbers is this some what normal?

If I should leave it where its at, average 13.5, what else could be done to get the MPG up more than the mid 14's I am getting now? Its not like I am burning rubber at each light, 300 six, 2.75 rear gear and T18 is not a speedster, I also have over drive so the RPM is not killer high at the 65-70 MPH maybe 1800 RPM?

Dave,

I am running an Air/Fuel Ratio gauge also, and it oscillates a bit like yours. If I'm running along on the hwy at very light load, it's in the 14.2-14.7 range, but it probably bounces overall between 13.5-15.0, but I can get it to hold relatively tightly around 14.5 +/- 0.3 or so. It runs around 12.5 at idle.

This is with the Holley 4160 4bbl 600CFM Vac secondaries. When we did the break-in on the dyno, we did bump the jet sizes up from the stock #66 to #68. If I recall correctly we were hitting upwards of 13.0 on the dyno pulls and he wanted to get it back down around 12.5, and the #68 jets worked.

He said at that time that I could probably put the #66 jets back in the truck for street use...assuming that one, I wasn't going to be doing heavy load redline pulls with it, and two, it wouldn't breath as freely on the truck as it did on the dyno with their longtube headers and basically no exhaust. Howver, the #68 jets seems to be OK. I was going to put the #66 back in to lean it out a little more to see if there was another MPG available, but the darn thing just works so nicely where it sits now, I figured it is best if I simply don't touch it at all.

And, after all that....with regards to my typical light load easy driving, I'm probably running on the idle jets anyway, and not the main jets, right?

PS: I should note that the truck did get better MPG with the large open element air cleaner installed. I didn't have the AFR gauge installed at the time, but the truck got a solid 2MPG more. I will have to try it this summer for a while and see what the AFR is with the open element air cleaner.

When I heard the pinging the AFR was around the 14.0 - 14.2 mark and after what Jim posted if I try to adjust AFR to mid 14's pinging may get worst.

But I may be able to get to the 14.5 and adjust the timing curve to stop the pinging but like you the motor runs so good I hate to start messing with it other than to stop the pinging.

It just hit me I think Gary posted what the AFR would be for 10% blend over real gas.

I have been looking at the AFR as real gas and not a blend so maybe I am ok AFR wise now?

If that is the case my MPG sucks at mid 14's!

I will do more adjusting to see what I can get out of her

Thanks

Dave ----

Yes, the "best" AFR for 10% ethanol blend is 14.04:1, not 14.7. So you may not be that far off.

But, I suspect that your pinging problem is due to having a vacuum advance can that was designed for EGR, which was meant to come in at high vacuum. But the exhaust gas slowed the flame front such that they had to give it a whole lot more advance, which they did with the vacuum can. So if you are running w/o EGR but with an EGR vacuum unit you have too much advance at high vacuum. And while you can determine when it comes in you can't change how much you get.

I don't know what the options are from Crane, but I'd be looking for a vacuum unit that gives less advance.

[ArdWrknTrk]

Now holding the throttle steady on flat ground it was still bouncing around the above numbers is this some what normal?

If I should leave it where its at, average 13.5, what else could be done to get the MPG up more than the mid 14's I am getting now? Its not like I am burning rubber at each light, 300 six, 2.75 rear gear and T18 is not a speedster, I also have over drive so the RPM is not killer high at the 65-70 MPH maybe 1800 RPM?

Dave,

I am running an Air/Fuel Ratio gauge also, and it oscillates a bit like yours. If I'm running along on the hwy at very light load, it's in the 14.2-14.7 range, but it probably bounces overall between 13.5-15.0, but I can get it to hold relatively tightly around 14.5 +/- 0.3 or so. It runs around 12.5 at idle.

This is with the Holley 4160 4bbl 600CFM Vac secondaries. When we did the break-in on the dyno, we did bump the jet sizes up from the stock #66 to #68. If I recall correctly we were hitting upwards of 13.0 on the dyno pulls and he wanted to get it back down around 12.5, and the #68 jets worked.

He said at that time that I could probably put the #66 jets back in the truck for street use...assuming that one, I wasn't going to be doing heavy load redline pulls with it, and two, it wouldn't breath as freely on the truck as it did on the dyno with their longtube headers and basically no exhaust. Howver, the #68 jets seems to be OK. I was going to put the #66 back in to lean it out a little more to see if there was another MPG available, but the darn thing just works so nicely where it sits now, I figured it is best if I simply don't touch it at all.

And, after all that....with regards to my typical light load easy driving, I'm probably running on the idle jets anyway, and not the main jets, right?

PS: I should note that the truck did get better MPG with the large open element air cleaner installed. I didn't have the AFR gauge installed at the time, but the truck got a solid 2MPG more. I will have to try it this summer for a while and see what the AFR is with the open element air cleaner.

When I heard the pinging the AFR was around the 14.0 - 14.2 mark and after what Jim posted if I try to adjust AFR to mid 14's pinging may get worst.

But I may be able to get to the 14.5 and adjust the timing curve to stop the pinging but like you the motor runs so good I hate to start messing with it other than to stop the pinging.

It just hit me I think Gary posted what the AFR would be for 10% blend over real gas.

I have been looking at the AFR as real gas and not a blend so maybe I am ok AFR wise now?

If that is the case my MPG sucks at mid 14's!

I will do more adjusting to see what I can get out of her

Thanks

Dave ----

Limit stops affect mechanical advance.

Bending the spring tabs affect spring preload.

With no EGR you probably don't want the mechanical advance 'all in' until 3,600-4K

Go to Jegs.* Arrrgh!

Find the Crane advance for '68-80 Ford's and look in the listing for the instruction sheet link.

Print it and read it.

Go to Scotty's old pages and find the two pages of distributor recurve instructions.

Both will help you understand what you are doing.

[FuzzFace2]

Yes, the "best" AFR for 10% ethanol blend is 14.04:1, not 14.7. So you may not be that far off.

But, I suspect that your pinging problem is due to having a vacuum advance can that was designed for EGR, which was meant to come in at high vacuum. But the exhaust gas slowed the flame front such that they had to give it a whole lot more advance, which they did with the vacuum can. So if you are running w/o EGR but with an EGR vacuum unit you have too much advance at high vacuum. And while you can determine when it comes in you can't change how much you get.

I don't know what the options are from Crane, but I'd be looking for a vacuum unit that gives less advance.

Well if 14.04 for blend then I am not off all that much as you say.

I did 1 full turn of the rod / seat on the carb to get were I am at now and that was before I had the gauge. It did seam to help with a little more power and the motor ran smoother just nothing on the MPG front

As for the "while you can determine when it comes in you can't change how much you get." from what Jim is saying below I need to slow down the mechanical. I was all in by 2500 RPM so if I slow this down and / or limit it I would be changing the total.

My thinking is keep the vacuum to come in as it was, low vacuum, and install heavy springs so the mechanical will come in later. It is rare it get the RPM up to 3000 RPM, I shift between 2000 & 2300 RPM and maybe 2500 RPM but the truck does not shift well (NP435) at the higher RPMs.

Limit stops affect mechanical advance.

Bending the spring tabs affect spring preload.

With no EGR you probably don't want the mechanical advance 'all in' until 3,600-4K

Go to Kegs.

Find the Crane advance for '68-80 Ford's and look in the listing for the instruction sheet link.

Print it and read it.

Go to Scotty's old pages and find the two pages of distributor recurve instructions.

Both will help you understand what you are doing.

I will look up the information to get a better grip on this timing thing

So right now my mechanical is all in by 2500 RPM and as I posted above if I was to install heavy springs and return the vacuum can back to where it was that would limit the total timing, remember I have 46* BTDC @ 2500 RPM.

The vacuum timing would kick in as soon as the carb was off idle but the mechanical would not start to come in till say 2000 rpm.

Now this is just numbers I am throwing out and would be adjusted for best running and no pinging.

Remember I shift around 2000 RPM and cruse RPM is around the 1800 in OD in the high way and under 1400 RPM on back roads.

Or am I way off in my thinking before I read up on this

Dave ----

[Gary Lewis]

Yes, the "best" AFR for 10% ethanol blend is 14.04:1, not 14.7. So you may not be that far off.

But, I suspect that your pinging problem is due to having a vacuum advance can that was designed for EGR, which was meant to come in at high vacuum. But the exhaust gas slowed the flame front such that they had to give it a whole lot more advance, which they did with the vacuum can. So if you are running w/o EGR but with an EGR vacuum unit you have too much advance at high vacuum. And while you can determine when it comes in you can't change how much you get.

I don't know what the options are from Crane, but I'd be looking for a vacuum unit that gives less advance.

Well if 14.04 for blend then I am not off all that much as you say.

I did 1 full turn of the rod / seat on the carb to get were I am at now and that was before I had the gauge. It did seam to help with a little more power and the motor ran smoother just nothing on the MPG front

As for the "while you can determine when it comes in you can't change how much you get." from what Jim is saying below I need to slow down the mechanical. I was all in by 2500 RPM so if I slow this down and / or limit it I would be changing the total.

My thinking is keep the vacuum to come in as it was, low vacuum, and install heavy springs so the mechanical will come in later. It is rare it get the RPM up to 3000 RPM, I shift between 2000 & 2300 RPM and maybe 2500 RPM but the truck does not shift well (NP435) at the higher RPMs.

Limit stops affect mechanical advance.

Bending the spring tabs affect spring preload.

With no EGR you probably don't want the mechanical advance 'all in' until 3,600-4K

Go to Kegs.

Find the Crane advance for '68-80 Ford's and look in the listing for the instruction sheet link.

Print it and read it.

Go to Scotty's old pages and find the two pages of distributor recurve instructions.

Both will help you understand what you are doing.

I will look up the information to get a better grip on this timing thing

So right now my mechanical is all in by 2500 RPM and as I posted above if I was to install heavy springs and return the vacuum can back to where it was that would limit the total timing, remember I have 46* BTDC @ 2500 RPM.

The vacuum timing would kick in as soon as the carb was off idle but the mechanical would not start to come in till say 2000 rpm.

Now this is just numbers I am throwing out and would be adjusted for best running and no pinging.

Remember I shift around 2000 RPM and cruse RPM is around the 1800 in OD in the high way and under 1400 RPM on back roads.

Or am I way off in my thinking before I read up on this

Dave ----

I am NOT a guru on this, so take what I'm saying with a pound of salt. But I didn't think they changed the static nor mechanical/centrifugal timing all that much for EGR vs non-EGR. That the real change was done in the vacuum advance because it was only at high vacuum that the exhaust gas came in.

In other words, when you are accelerating hard the EGR will be off and the vacuum low so you are mostly getting your timing from the static + mechanical. So they left that alone and just dialed in lots of advance via the vacuum can.

Again, that is my very limited understanding and may well be wrong.

[ArdWrknTrk]

Yes, the "best" AFR for 10% ethanol blend is 14.04:1, not 14.7. So you may not be that far off.

But, I suspect that your pinging problem is due to having a vacuum advance can that was designed for EGR, which was meant to come in at high vacuum. But the exhaust gas slowed the flame front such that they had to give it a whole lot more advance, which they did with the vacuum can. So if you are running w/o EGR but with an EGR vacuum unit you have too much advance at high vacuum. And while you can determine when it comes in you can't change how much you get.

I don't know what the options are from Crane, but I'd be looking for a vacuum unit that gives less advance.

Well if 14.04 for blend then I am not off all that much as you say.

I did 1 full turn of the rod / seat on the carb to get were I am at now and that was before I had the gauge. It did seam to help with a little more power and the motor ran smoother just nothing on the MPG front

As for the "while you can determine when it comes in you can't change how much you get." from what Jim is saying below I need to slow down the mechanical. I was all in by 2500 RPM so if I slow this down and / or limit it I would be changing the total.

My thinking is keep the vacuum to come in as it was, low vacuum, and install heavy springs so the mechanical will come in later. It is rare it get the RPM up to 3000 RPM, I shift between 2000 & 2300 RPM and maybe 2500 RPM but the truck does not shift well (NP435) at the higher RPMs.

Limit stops affect mechanical advance.

Bending the spring tabs affect spring preload.

With no EGR you probably don't want the mechanical advance 'all in' until 3,600-4K

Go to Kegs.

Find the Crane advance for '68-80 Ford's and look in the listing for the instruction sheet link.

Print it and read it.

Go to Scotty's old pages and find the two pages of distributor recurve instructions.

Both will help you understand what you are doing.

I will look up the information to get a better grip on this timing thing

So right now my mechanical is all in by 2500 RPM and as I posted above if I was to install heavy springs and return the vacuum can back to where it was that would limit the total timing, remember I have 46* BTDC @ 2500 RPM.

The vacuum timing would kick in as soon as the carb was off idle but the mechanical would not start to come in till say 2000 rpm.

Now this is just numbers I am throwing out and would be adjusted for best running and no pinging.

Remember I shift around 2000 RPM and cruse RPM is around the 1800 in OD in the high way and under 1400 RPM on back roads.

Or am I way off in my thinking before I read up on this

Dave ----

Dave, if your "Redline" is 3k, then you're fine with the springs you have (and you may not ever have to limit mechanical)

BUT, if you want more vacuum advance then you might have to trade some spring for vacuum.

Gary is correct!

Also note that Ford set all these DSII trucks up with manifold vacuum to the dizzy.

So it was all the way there when the throttle was completely closed.

Autoincorrect screwed my post up.

Go to Jegs and get the instructions.

You need to complete 'A', before you can address 'B', and so on...

You cannot fix a spring issue with vacuum, or vice versa.

But you don't say what exact conditions cause your pinging*, so I can't help until you better define the problem.

If you're only concerned with leaning out the carb, re-install the EGR and you'll be fine.

[FuzzFace2]

Dave, if your "Redline" is 3k, then you're fine with the springs you have (and you may not ever have to limit mechanical)

BUT, if you want more vacuum advance then you might have to trade some spring for vacuum.

Gary is correct!

Also note that Ford set all these DSII trucks up with manifold vacuum to the dizzy.

So it was all the way there when the throttle was completely closed.

Autoincorrect screwed my post up.

Go to Jegs and get the instructions.

You need to complete 'A', before you can address 'B', and so on...

You cannot fix a spring issue with vacuum, or vice versa.

But you don't say what exact conditions cause your pinging*, so I can't help until you better define the problem.

If you're only concerned with leaning out the carb, re-install the EGR and you'll be fine.

Took truck to work this morning and have an update but on phone so hard to type it out.

Will do when home on pc.

Dave ----

[ArdWrknTrk]

Took truck to work this morning and have an update but on phone so hard to type it out.

Will do when home on pc.

Dave ----

I was trying to use talk to text to reply to Staci yesterday.

It just wasn't having Jon Kaase.

I gave up and used his initials.

[Sac79]

I was trying to use talk to text to reply to Staci yesterday.

It just wasn't having Jon Kaase.

I gave up and used his initials.

Dave, you can ignore my post in your project thread... I'm following along here with interest!

[FuzzFace2]

I was trying to use talk to text to reply to Staci yesterday.

It just wasn't having Jon Kaase.

I gave up and used his initials.

Ok, Think Jim said something about the EGR may help with the pinging.

Well I cant hook it back up. A freeze plug was installed in the intake under the EGR plate, a plug where the tube would connect but nothing for the tube to connect on the exh. pipe side as I am running EFI exh. manifolds.

I must have gone the wrong way with the vacuum can adjustment it had the death rattle really bad all the time at speed. I had to pull off the first exit 10 miles from when I got on, road work so no place to pull over. I pulled the vacuum hose off the dist. and not being able to find anything on the ground at 1amI left it open.

No more rattle and it seam to run pretty good.

AFR was about 14.0 but I don't know if that is the open hose or change in timing?

I could not find anything before I left work to plug the hose so it was left open for the ride home.

I did find it odd that the AFR was about 14.0 going to work OAT was 61*f

On the way home the AFR was high 14's to low 15's with OAT of 48*f.

Normal driving keeping the RPM shift points to 2000 the truck felt good but I had to run her out a bit getting on the high way and it was a dog with no vacuum advance or was it just running that lean?

Someone wanted to know what the AFR was at WOT. From 65 MPH It went so lean the gauge went ----

only when it got up to about 75 - 80 MPH did I start to see any numbers, 16's & 17's.

It did have a little "miss" every now & then getting up to that speed.

Going to read up on re-curving the dist. as I feel this has to be under control first then the AFR.

Dave ----

[FuzzFace2]

Dave, you can ignore my post in your project thread... I'm following along here with interest!

I should do a link in the project thread pointing to here

thanks'

Dave ----