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Questions about Timing and AFR's

CyberSniper said:
This is the base timing I pretty much always start with, assuming if it has a distributor it is at TDC, if I have nothing to start with, assuming it is a modern camshaft not terribly far advanced, and I left the PE adder alone.
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That's reasonable for everything in good order, but if there IS a distributor, that means that things are not ideal. The variability of mechanical timing components means you have to keep the timing a few more degrees less advanced to account for that variability.
 
Well, who the hell knows of the crank position related to when the spark bridges the gap when you have something spinning a camshaft that then spins the distributor all of which may be looser than a certifiable las vegas slot... that's why you tune and we have knock sensors.
 
OK, been able to confirm my issues aren't coming from the AFR settings. I've gone up and down substantially, and the issue (backfiring through the exhaust and no power) is not changed. So it's time to look at the ignition and the valvetrain. I want to know what heads I've got on this, so I'm going valvetrain first. Once I fix whatever it is, I'll be using this info to tune things correctly, I will start up a new thread then, but to answer the questions and offer one unexpected lesson here we go.
I can say with certainty that if your idle AFR is to low, the engine is going to surge. Not sure why, but anything lower than 15 casues the ECU to raise and lower the rpms between about 750-1000, like it's searching for a spot. I've got the idle set at 825. So if you're trying to fix a surging idle, try more fuel.

I'm running the ProCal software, although the only real use I've gotten from it is for the datalogging and graphing. I've been using the handheld to change most of the parameters since it's much more simple. The "dash" function on the ProCal is nice, also.

I will add a hose to the fuel pressure gauge and run it up so I can watch it under load. I'm using a frame mounted pump, so I'm not ideal from the standpoint that it's mounted above the tank, but so far it's seemed to keep up well.

Cam is very mild, just a step better than stock.

As far as I can tell, the timing with the light matches the advance shown on the computer. Hard to tell for sure,, but it's close.
 
I don't know anything about ProCal. Does it have a COT feature? If you ain't got dem dere catalytic converters turn it off. Also consider turning off DFCO to see what it does. Has it fully learned the IAC steps? Does it have a AFR target at idle and high vacuum?

For a fuel pressure gauge I have one of these I rigged up so I just need wires instead of a hose and usually strategically mount it under a windshield wiper blade:
and buy one of these so when I'm not using it I just plug the NPT port and remove the gauge/harness:
 
IAC steps are set first, once it's warm, you set the idle and then adjust the throttle body so that it's idling between 2-12 IAC steps. Yes, it has quite a few AFR targets in each area, WOT, Cruise, Idle based on RPM and MAP readings. It's apparently pretty sensitive. I leaned everything out and drove it for a week. Pulled a couple plugs, and you can see a difference just from changing from a 12.8 to a 14. Here's what the plugs look like now, with the old ones as a comparison:
IMG_1083.jpg
It will fill in the rest of the chart based on your input and driving. It does not, however modify the spark map once it's in, it merely goes off of a table like the ones provided above. And yes, that's how I have my pressure gauge hooked up, but I'm using a mechanical gauge. So I can extend a fuel line up so I can see it from inside while I'm driving. And yes, I've already made it a little more rich...at least I know something is really happening when I change the settings!
 
Still on this...trying to make sure the timing is correct now...for those of you who have done this, let me verify: I'm using a MSD 85501 locked out distributor. I don't have an adjustable rotor. To get my base timing of 13* I'm going to want to rotate the engine until it shows 13 on the balancer, then put the dizzy in as if I was putting it in TDC, correct? Obviously, I'm going to want to go around once so I'm back to the compression stroke.
 
No, if you have a locked-out distributor, the computer is controlling the timing. You set the distributor so the timing light readings match what the ECU is commanding. Then all timing is set in the ECU. Sometimes there's an offset setting in the ECU you can advance and subtract to make the timing match what you read manually, as an alternative to turning the distributor.

Here's the limitation of locked-out distributors: you have to have it adjusted so the rotor points at the distributor terminal throughout the range of timing you're using (the max and min numbers in your timing table). If it's not set right, it begins to misfire as you go above or below certain degrees BTDC. So if you get some breakup that seems RPM related, keep that in mind.
 
OK, so if I'm understanding this, that's the part where I lock the timing from the ECU at 30*, then adjust (rotate) the distributor until I'm getting 30* with the timing light, correct? Then I'm good, and the ECU will follow the spark map programmed into it/ although I may suffer a little arcing at the top and bottom or the rpm range, I should be good in the middle. Thanks for helping me out with this...I've watched so many videos and everyone has a different way of doing things...and I'm sure most of them aren't ideal. Also, it sounds like the "adjustable rotor" might be convenient, but is not something I need, correct?
 
Isn't there a procedure from FiTech? I don't understand why 30* is an important number. It seems like you could set it at any amount of advance, like idle the engine, read what the computer is commanding, turn the distributor until the two numbers match and lock it down. Keep in mind as you rotate the distributor the actual timing is changing, which will likely change the idle speed and commanded advance, so it may take a few iterations.

The distributor is installed just like any regular distributor, with the rotor pointing at #1 when the timing tab lines up. The smallest increment you can adjust rotor position is 1 tooth, which you would only do if there's some problem with running out of terminal. Of course then you would have to re-sync the computer with the tab.

The computer has no idea what the engine position is or which cylinder should fire next. It's just reading pulses from the pickup coil and based on the set up it interpolates between them to a calculated TDC. From there it fires the ignition coil when it calculates you're the desired number of degrees from another TDC.
 
The only reason I'm using 30* is because that's what the procedure from FITech says. Problem I'm having is there's at least three videos from FiTech on how to set up the timing control. and they are all different. Two of them use an adjustable rotor, the one that doesn't is outlined like above. What you're saying is confirmed by them, they are saying due to the fixed rotor, you're only going to be able to increase timing about 15-20* from what the base timing is. So I'm on my way out right now to go set this thing up and see what happens. I've got about 15* in base right now, and it was idling fine, but when I would blip the throttle, I'd backfire through the throttle body. Funny how I thought this was going to be easier than dialing in the GM TBI system.
 
It's possible that backfiring is the thing I was describing about the fixed rotor (it could also be bad valve timing/adjustment, etc.) I can't remember if I told the whole story about how I figured that out (https://ck5.com/forums/threads/i-go...-done-update-distributorless-ignition.181264/), but my big clue was that the engine began stumbling based only on advance and not load or RPM. When you're going beyond the terminal, the spark begins to choose the next one, since the hole without compression offers lower resistance. FWIW, my table goes from 3-55 degrees, but I'm not sure any of the regions are used that are above low 40's (I'd have to look back at old tables since I got rid of the dizzy in 2009, but I don't remember any major changes with the EDIS).

You could probably troubleshoot it with a timing light or spark plug tester to see if the spark is going away as the breakup occurs.

You do have options! The easiest thing I can think of is to make changes to whatever you're using to lock down what used to be the vacuum advance. Of course you can try marking the current distributor position, sending it back one tooth and re-syncing it there.
 
Leaving the base at 15 but pulling out a few degrees in the advance for the cruise settings has helped. Also, I rotated the dist. about 5* to the retard side. The idle is now smooth, no more backfirew when I rev it, and the spark on the handheld is where the spark on the timing light is at several rpm ranges. So it would seem we have done some good. Road test when I get home from work and hopefully the power has improved.
 
I just came across these old parts I had made to lock the distributor many years ago and thought of this thread. It seems obvious you could rotate the hole pattern for the mechanical advance to alter the rotor position. It also affects the pickup events, but that is easily adjusted for in the ECU. Likewise, the adjustment slot for the vac advance could be used.

20240502_110207.jpg
 
PROBLEM SOLVED:

Here's what was wrong....Still not sure what exactly changed, but it was a combo of things that caused my issue. I think it was mostly related to the exhaust leak, probably even a little bit when I had it dyno tuned. It got worse over time, causing the AFRs to continue to come down until I was running very rich. The timing was set too high. Maybe it was right for WOT, but for the type of driving I do, it was too advanced on the base at over 14*. Then, I tried to set the IAC steps and the idle stop screw up with the rich fuel and too much timing, and when I had it to where it would run between 0-10 IAC steps at idle, my idle wouldn't come down to below 900. I kept playing with it and got it to where it was completely fighting itself, backfiring, idle too fast, leaking exhaust, it was a mess.

Much like the IT guy always says at work, unplug and start over. I went back to the very beginning and started over with the engine setup menu, and the dist. at 0 lined up on TDC with the #1 cylinder. I set the idle up so the IAC's would be right at about 800. Once all that was done, then I started with 5* base advance on the dist. Which raised the idle speed, so I had to go back and dial all that in again. Once that was set, I started to drive it around, and it did better already.

Each time I'd set the timing, I'd check it with the light at idle and make sure it matched the computer's idea of what was happening. Then I'd lock the timing at 25* and verify it would stay there at several different rpm ranges to verify the computer was actually controlling the advance. Unlocked the timing and check it again to make sure it would advance with the different rpms.

From there, I gradually added in timing and readjusted the IAC and idle set screw until I couldn't get it to hold 800 and under 10 steps on the IAC. I figured that was enough base timing, so I went back a couple of degrees and ended up at about 9* for the base. Since the dist is locked and I can only get about 20* total advance out of it, that means that I'll be limited to about 30 total advance, but for a big block, I think that is enough...I rarely get over 2500 rpm. If I need more I'll have to look into an adjustable rotor or something so that I can get the trailing edge of the contact on the post at idle and the leading edge at my max advance. If I understand correctly, I can pick up maybe another 10* by doing that, but then that's it due to the locked out advance.

So far, it runs fine, starts and idles fine, no more backfiring or popping. Little gas smell, so I may be a bit rich, but I can play with the AFRs and keep checking plugs until I get that right. Seems a little sluggish in the middle of the MAP/RPM range, but much better than in was. I may just think that because I've been driving my other car more, and I forgot how much a 37" tire will take away from your acceleration. Thank you all for the help, hopefully this will help someone else. I'll post my AFR settings and spark settings when I get them dialed in so anyone else can use them as a starting point.
 
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Blue85 said:
Isn't there a procedure from FiTech? I don't understand why 30* is an important number. It seems like you could set it at any amount of advance, like idle the engine, read what the computer is commanding, turn the distributor until the two numbers match and lock it down. Keep in mind as you rotate the distributor the actual timing is changing, which will likely change the idle speed and commanded advance, so it may take a few iterations.

The distributor is installed just like any regular distributor, with the rotor pointing at #1 when the timing tab lines up. The smallest increment you can adjust rotor position is 1 tooth, which you would only do if there's some problem with running out of terminal. Of course then you would have to re-sync the computer with the tab.

The computer has no idea what the engine position is or which cylinder should fire next. It's just reading pulses from the pickup coil and based on the set up it interpolates between them to a calculated TDC. From there it fires the ignition coil when it calculates you're the desired number of degrees from another TDC.
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If I'm understanding this all the issue comes about with the amount of time it's taking the computer to analyze all this and tell the coil to spark, right? Because it has to know if you're on the way up or down, and then send the signal to the CDI box, to to the other components and do it all in time to make the spark arrive at the plug at the right time. So it's actually giving the spark command at about 40 btdc, which equates to an actual spark at 15-20 btdc. It has to read, calculate and send the spark, and that all takes time, right?
 
It only works because the speed of the engine can't change instantaneously. The computer is timing the pulses from the pickup coil to calculate speed (4 pulses per revolution) and it calculates position based on the information you gave it when you matched the timing marks to the software setting. The amount of advance is a similar phase shift within the period. It knows that the next spark event is x ms/degrees away, so it starts charging the coil at the firing time minus the dwell time and turns it off at the firing time.

A dial-back timing light is doing a similar trick of phase shifting where the output pulse happens vs the input pulse, it's just a simpler circuit.
 
Great example with the dial back timing light...that makes perfect sense. Since I'm not running this at the limits of performance, I think just lining up the trailing edge of the rotor tip with the leading edge of the cap contact at the 10 degrees base timing should be sufficient. That would give me 10 plus 25, maybe even 30 degrees of additional. I don't see a need for an adjustable rotor at this point, I've got a cam that's just a little better than stock and I don't wind the engine up, so it seems 30+ degrees should be fine.

On to what I started out with a week or two ago: AFR's . When I'm reading the AFR , I'm seeing how rich or lean the mix that was just burned was, correct. So I want to keep that under 14.7. If it starts to go over, that means I'm not giving the engine the fuel it needs, correct? So for each of the MAP/RPM readings, I want to set it up so the AFR's don't read above 14.7, correct. And under hard acceleration on a heavy load, I probably want them in the 14.7 or so range, right? Once those points are set, then I just drive around until the unit learns how much fuel it should be sending to keep the AFR's in the entered ranges, correct? Or if there's an easier way to set them up, please let me know...I have three settings for acceleration modes, two for "cruise mode" and three for a high load slow speed AFR. Maybe like a 14.9 for the low MAP higher speed mode, but everything else 14.7 or lower, correct?
 
When I look up pictures of Go EFI 600 (30002), I see a wideband oxygen sensor, so we'll assume that's what you have. The controller is varying the amount of oxygen it creates to get the narrowband sensor to switch, therefore telling you how much oxygen is present after combustion. If there is excess oxygen, the mixture is lean - not enough fuel to burn all of the air. If oxygen is low, the mixture is rich - not enough air to burn all of the fuel.

Stoich is a fine place to start for everything except acceleration. You really want to be rich at high load and WOT or the engine will ping. Probably something in the range of high 12's - mid 13's. Peak torque is at 13-13.5, but richer is safer. Most of these engines want to idle richer than stoich, as well. You could try 13.5 and play with it from there to see what's smooth.
 
I'm not sure there is a gas engine made that doesn't "cross over" from rich to lean. The computer does it's best to achieve whatever is set as it's target AFR...again, back in the day that was 14.7:1 at light load/cruise/closed loop idle, but with ethanol and so on, that's not really right anymore, and was also all the old narrowband sensors were accurate at. The wideband O2 sensors enable a better understanding of fueling under all conditions, so are vastly better.

As you suspect, the O2 sensor is looking at combustion byproducts. So it's always lagging behind what is actually going on with the engine. O2 sensor distance from the cylinders and exhaust flow (headers vs manifolds) is probably being compensated for somewhere in the programming of what you are running.

I just Googled lean cruise AFR, and I'm seeing all sorts of numbers. From 15.5 to 18. I know it increases cylinder temp to run lean, but thus far I've not seen any reliable way to determine what is so lean that pistons are in danger. It's possible that if in a narrow enough window (of the cruise/low load AFR), Normal cruise conditions might get it to bounce back and forth from super lean to rich frequently enough to prevent cylinder temps going hotter and hotter.

Here's one example of mixture ratio suggestions I ran across https://www.safrtool.com/SAFR-AFR-values.asp
 
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