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My combination is a Chevy crate long block SP350/357. It has iron Vortec heads with a hydraulic cam. AZSpeed large tube runners, ported plenum, 52mm throttle body, and long tube headers.
It uses a modified 6E mask running in Open Loop only with a MAF sensor.
The first issue I am having is on a WOT the AE does not seem to be sufficient and the motor leans out for a brief period. I have read many threads and tried adjusting the various AE parameters
without seeing any improvement in the initial lean spike. I also adjusted the PE at the low RPM end to try and reduce it but still no positive results.
The second issue is related to the main timing (PE timing is set to all zeros). If I put more than 15deg BTDC in the higher RPM/Load range than I get lots of knock.
Chevy states that this engine should run 32deg at 4000 RPM with a carburetor because that is what they sell as a complete engine but anything over 15deg with my TPI produces knock.
I saw in a recent thread that it was stated that limited advance could be run with the iron Vortec heads but that was a 11:1 compression engine.
I have a wide band on the engine and have attached a graph to show the WOT AFR as well as other parameters. I have a first pass compensation in the PE AFR for the MAF saturation effect
at higher RPMs.
This graph is with 15deg maximum advance.
Graph legend.
Red - Throttle position (excuse the unevenness my son was driving and was not used to the stiff pedal)
Blue - Requested AFR
Purple - LV8
Light Green - Wide band AFR
Light Blue - RPM
Gold - Knock retard
Couple things. First we need to see your fuel map.
1. Rather than put in craploads of AE, make sure the low rpm / high load areas of your fuel map has sufficient fuel in it. The engine will rapidly run through these areas of the map when you punch it and if they are lean you will get a lean spike.
2. You have way too little timing in it, leading to high EGT's. The lean mixture increases the problem driving the EGT's higher. Detonation causes the ECU to pull timing which further drives up EGT's...... the detonation just runs away from you at that point.
3. Detonation that results in severely retarded timing (too much authority being given to the knock control) will result in further detonation.
4. Detonation TENDS to want to continue. Especially if it's severe, till you lift the throttle.
5. Put the timing at a reasonable level suggested for this engine. If you get some detonation then pull a COUPLE of degrees. Don't go crazy, and don't give the ECU a ton of authority.
6. Get the fuel sorted FIRST. You need that AFR to drop right down to 12.5 under WOT. That lean spike is a BIG problem that can result in runaway detonation. Pulling timing will NOT stop it at that point as this just drives up EGT's and makes the problem worse in a hurry. Now you may find that you can run leaner than 12.5 in the end, but you should START there and only go leaner at WOT when experimentation shows this to be what the engine wants and it makes sufficiently more power by doing so to be worth it.
I have attached the fueling for AE and PE as shown below.
The original graph shows that the wide band AFR is running in the 12.5 - 12.6 range throughout WOT except for the initial lean spike even though the requested is a slightly leaner value. This seems to be a due to the MAF reading at the current ambient air temp.
I felt this was OK for the moment since it was richer rather than leaner than the requested AFR.
I did another run which I have not attached with the timing set to 22deg advance and there is heavy knock throughout the WOT event so I did try a moderate increase in timing which produced significantly more knock but the wide band AFR was still in the 12.5-12.6 range.
My goal was to do exactly what you stated and get the fueling correct which to me the 12.5-12.6 at WOT look OK minus the lean spike at the start of WOT so that is why I increased the timing to 22degs to test it but the engine did not like it.
Please clarify what you are asking for as this is a MAF system with 6E mask operating in Open Loop only I am not sure what you mean by main fuel MAP?
Are you asking for the Open Loop AFR with coolant temp and Open Loop AFR with load tables?
Here are those two tables if that is what you wanted.
Open Loop AFR with coolant temp and LV8
Last edited by Antimatter; Dec 21, 2019 at 02:24 PM.
Reason: Added tables.
Sorry I wasn't thinking MAF..... you need to increase airflow in your MAF table between (looks like about) 1800 and 3600 rpm. You can see it goes lean again on your shift when it drops into that range of the MAF table. You need to change it such that lower voltage indicates higher airflow.... need to know what the voltage is at those RPM.
Have you changed the intake plumbing before/after the MAF? If it's not 110% stock then it needs to be re-scaled.
What happens when you roll into throttle to go wot? Whats afr do if you try hold 60-70% throttle and 3000-4000 ish rpm? What lv8 is pe mode engaging?
does engine feel any different with 22 vs 15 deg? Are you sure its not false knock? I have seen alot of false knock before. Knock retard doesnt show anything being pulled but knock counts will rise. Sometimes the knock sensor can do weird things and may need desensitized or lower the attack rates. Or disable it and tune on dyno, power will tell you where best timing is
theres no reason that thing shouldnt be in the higher 20’s low 30’s range imo
Also maybe your pe enrich vs rpm should not taper off between 2800 and 3200 where that thing is making peak torque. It should take the most fuel there and the pe enrich curve may actually end up following the shape of your dyno tq curve. By 4500 or so afr has come down to commanded but you are well past peak torque by then and likely dont need near as much fuel. So my guess is it mayy want alot more pe enrich at the 2400-3600 ranges
Yeah but he's got a 16:1 lean spike at 3000 rpm with it to the rug..... need to fix that. That's likely going to detonate and it tends to just keep going till you lift. Get the AFR's under control with the MAF tables then if there's a stumble or something go attack the AE. The PE tapering in the peak areas does look odd. Definitely try flattening out that trough.
The intake plumbing is stock before the MAF and after the MAF up to the 52mm throttle body. Front and rear screens are removed on the MAF and I did do some rescaling on the MAF so I will look at where you suggested and adjust.
Rolling into the WOT the lean spike at the beginning does not occur. The PE is enabled with LV8 above 50. Subjectively 22deg seem stronger that 15deg.
It could be false knock and like you said it makes no sense that it cannot take more advance but I wanted to make sure the fueling is correct before I start desensitizing the knock sensor as I do not want to destroy this new engine.
Looking at the above curve the actual AFR once you are in second gear just to eliminate the effects of the lean out when you trounce the throttle is between 12.6 to 12.7. Do you think it should be richer than that?
Right now the PE is set to 11.5 AFR up to 2000 RPM so do you think this should be richer and extend further up?
What is the root cause of the lean out when you trounce the throttle as I mentioned earlier it is not there when you roll into WOT and at least the changes I have made to AE do nothing?
Do you have a higher-than-stock stall speed on your converter? Getting up against it could require substantially more AE. I had a similar problem with my 3000 stall converter and had to add about 200% more AE before I got it under control.
No my torque converter is stock but what parameters in the AE section did you alter to get 200% more? I read many posts on adjusting the AE which in theory does not seem like it should be that difficult but the final results when the threads ended were not conclusive that any improvement was gained.
I did find one thread here where specific numbers and in some cases large changes were stated and success was claimed but those values still did not produce a positive result for me.
In the above graph there is an initial lean spike when the throttle is hit and than a longer lean period as the RPMs climb until everything catches up and then the AFR is more like expected.
As I stated before that does not occur when you roll into WOT so it does seem like an AE issue but maybe something else is going on.
I manually calculated the injector pulse width from the log data just prior to applying WOT and then during the lean event right after WOT started and the pulse widths I calculated match up within a few hundred microseconds of what was recorded in the data log. So I cannot see where there is any additional AE pulse width being applied although there should be unless I am missing something here.
The term asynchronous is used to describe the AE injector pulses so does that literally mean that the AE pulses of the injector are truly asynchronous from the normal cylinder injector pulses and are only linked to the AE event triggers?
If that is the case I am guessing they will not show up in the data log because the ECM does not send that data out in the serial stream.
Last edited by Antimatter; Dec 22, 2019 at 01:25 PM.
Reason: Added statement on manual pulse width calculation
