While chasing detonation (detected but not audible knock) problems, I have made a number of runs and recorded data using my Auto X-Ray. Cutting the timing in the problem areas doesn't seem to help. It just makes a "boggy" area in the torque curve.

I remember reading that another way to attack knock is to richen the mixture. So on my last run, I made note of where Open Loop / Closed Loop and Learn Control Enabled / Disabled changes took place.

The ECM never left Closed Loop. But Learn Control went from Enabled, to Disabled, and back to Enabled as I slowly mashed the gas, held it, and released it during the run. My TPS went from .98 up to 3.17 and back. The breakover point is somewhere between 2.54 and 2.88 volts. Is this the flag that indicates when I am in "WOT" (also known as PE)?

Well, that's when I'm getting the knock retard! It's while Learn Control is disabled. Does this mean that cutting the timing is the wrong approach? Is it time to modify the "WOT" fuel tables? FWIW, the Rich/Lean flag indicates Rich while in PE, but if I am understanding this, it looks like it's not rich enough.

For my first attempt, I will double all of the values (the highest is only 16%) in the "WOT % Change to Fuel/Air vs RPM. Does this sound reasonable?

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'87 IROC 5.7l TPI - original owner!

 

I think your assumption of hitting the PE mode is correct. There is a table that relates %TPS to enable WOT vs RPM, that should be around 70%, so if your TPS volts was near 70% of your max TPS volts, you should be in PE. You should be rich, and O2 volts should be 850-950mV.

Are you sure you want to add more fuel during WOT conditions? I think previous posts indicated that adding fuel doesn't help a knock problem. There are 2 other tables I would look at first, that relate to WOT. One is "max knock retard in WOT vs RPM" and "spark advance in WOT vs RPM. I also would hit the knock sensor in WOT, so I cut back on my main spark advance table, in the high load areas from 1600-4000 rpm.

If you are using the ARAP tables for the AFR changes in WOT, you should be ok. I use them, and have not changed them. Not yet at least!! Hope this helps, good luck.

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Best ET 14.413 @95.57 without
pulling valve covers or manifolds.
Also with stock 2.77 rear end!!!

 

You have to prevent detonation some time before it's detected.
Adding fuel is often used, not just taking timing out.

Might try having the PE enabled earlier.

 

You've got me thinking...

The WOT spark advance table, is it in addition to the main advance table? Does it show how many degrees will be added to those in the main table at a given RPM? Another look at the data from this run suggests that this is the case. Once I crossed into PE, the spark advanced about 5* (about 5* got added). That's about how much is in the WOT table at that point.

If this is how the WOT spark table works, then it looks like that's the place to start, not in the main spark table or in PE fuel. Again, according to my last data run, I only detected knock while in PE.

What about (as an experiment) raising the threshold for PE to sorta defeat the WOT spark table? Or should I zero-out that table? If I no longer detect knock, then doesn't that tell me that I'm looking in the right place?

Generally, how do the main and WOT spark tables work together? I am more comfortable with working on spark tables than on fuel tables right now.

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'87 IROC 5.7l TPI - original owner!

 

What ID mask are you running?.

 

I think you got it right. That table of spark advance in WOT does add to the main spark advance table. I wouldn't change the threshold for PE, you want that to happen as planned. That table should be used for troubleshooting/tuning conditions.

You could play with that spark advance table in WOT. My values are all set to 1.1, except 0 at 400rpm. Set them all to 0, just for kicks. If your knock quiets down, then you are making progress. But don't forget your main spark advance table. If you are not too advanced to begin with, your are less likely to get "knock retard", when you nail the throttle.

One approach is to tune your part-throttle settings first, IE BLMs, INTs, MAF tables, mixture, etc. Then work the spark tables, then WOT conditons. Thats kind of what I am doing. I gots the part throttle stuff pretty good, now playing with the spark stuff. The spark advance changes seem to have made the most noticeable results with my ride. Plus you can play with highway mode and the TCC stuff as well.

Just so much to do!!!

 

If you're getting knock retard at WOT then definitely start by pulling timing out of the PE spark table. I went ahead and zereod out PE spark and make all changes soley in the main spark table. I haven't found a need to have different PE and non-PE commanded advance values for a given LV8 and RPM point since I only operate in the high LV8 and RPM region of the table when in PE.

What's the knock sensor doing to the timing when you're experiencing the "boggy" feeling? Even with advance of only 24-28 degs in PE I'm running just as quick by the stopwatch compared to the previous vendor PROM that ran 34-38 degs advance. In the case of the vendor PROM, the knock sensor would never allow the actual spark command to come close to the requested values of 34-38 except above 4500 RPM.

 

$6E APYU base calibration.



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'87 IROC 5.7l TPI - original owner!

 

I chased a detonation problem in an '89 IROC with a 5.7 TPI for two years Finally Jim Formato suggested that the MAF could be giving a skewed value so I changed that out and the problem disapeared. I don't know what your situation is but that was an expensive lesson for me.

 

Do you have a TPS problem or did you not get your foot to the floor? You should be seeing over 4 volts at WOT on a 165...


GregF
87 IROC

 

I would like to pursue this, but I don't know what you're talking about. Could you please elaborate?



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'87 IROC 5.7l TPI - original owner!

 

I didn't have my foot to the floor. I never do full throttle runs (at least not until I get this detonation problem solved). All of my runs are from about 55mph in 4th and mashing the gas for a downshift into 3rd just like I was making a semi-agressive pass on a two lane road.



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'87 IROC 5.7l TPI - original owner!

 

There is a definite trend, here. For some reason, knock is detected immediately upon downshift into 3rd. It doesn't seem to matter what I change, this happens. I've removed "added" PE timing, removed main timing, and added PE fuel, all without result. It even occurs if I'm in PE before the downshift. Once it downshifts, the ECM takes out a ton of timing (up to 16 degrees!). As the car accelerates after the downshift (constant LV8), the retard gradually goes away.

Looking at my data, the decay rate roughly matches that in the table. It's impossible to see if the attack rate matches because it's sooooo much faster. If the initial knock incident is false, or only lasts one or two engine revolutions, it would seem that modifying the attack and recovery rates are a good place to look for a solution.

Please give me some guidance on how much I should/can modify these values. I'm thinking of doubling or tripling the recovery rates. That wouldn't get rid of the "bog", though -- it would only shorten it. Instead of taking three seconds to restore the spark, I could cut that to one (by tripling the recovery rate), for example. It looks like cutting the attack rate will "eliminate" it. But should I halve it? Divide it by five? ten? In 500ms, it's retarding the spark by as much as 16 degrees. Is setting the maximum retard to a very low number (say 1) an effective way to "bypass" the ESC in order to listen for audible knock?

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'87 IROC 5.7l TPI - original owner!

 

Try doing a WOT run from a 15 MPH roll. You won't hurt anything since you're still using the stock knock sensor parameters. I think you're going to find a different knock profile than from your usual 55 MPH roll. I've ALWAYS seen the knock sensor going off on the 2-3 shift no matter what PROM I'm running (stock or otherwise). I consistently see an even higher magnitude of knock counts during WOT runs from a 40-50 MPH cruise. BTW, I drop from 4th to 2nd when punching it at 55 MPH.

Setting the max knock retard in PE to zero or a small number does effectively disable it. But that's not necessarily what you want. Just because you can't hear knock doesn't mean it's not occurring; it's just more severe when audible.

There's more than one strategy you can try. My latest efforts assume that incrementing knock counts are in fact real knock events that need to be attenuated. I retain the stock attack rate and max knock retard values to squelch the knock. I then add timing back in as quickly as possible. I've had good luck with increasing the recovery rate from 61% to just over 220% and will probably try even higher numbers. I recognize the assumptions I've made relative to the validity of the sensor counts but feel this conservative approach is appropriate for a newbie like me.

I'm sure there are many other strategies, disabling the sensor via the retard limits being one of them. Timing curve and octane become critical factors. Hopefully someone else can provide their experiences/recommendations.