$0D Low RPM Surge and rough VE table.

Hi folks, I have not been on in the past year or so, my 383 project got put on the back burner after Covid and recovering from other health issues, hope everyone is well. I am not going to back up on the other issue resolutions but in a nutshell I am pulling my hair out on a surging issue from about 1200 to 1600 rpm at part throttle. My VE table is also rough. I have started from scratch several times, used Dave W's WB02 table to tune, tuned open loop, tuned closed loop, used smoothing, changed injectors and tables still wind up looking the same. Disabled EGR, PE, DFCO etc. Can someone please look at this bin? The enclosed bin is closed loop with nothing disabled. At higher rpms everything runs great and even in PE mode, I just cant seem to kick this rough spot.

I appreciate any insight, would like to get this project behind me.

Often surging can be caused by Acceleration Enrichment (AE) being active at the wrong time. Maybe the parameters for the MAP Delta Difference for AE Active or the TPS Delta Difference for AE Active needs to be adjusted? Possibly a flat spot in the TPS sensor, or a faulty MAP sensor is setting AE active at the wrong time?

The TunerPro RT "dash" will show when AE is active. The TunerPro RT data log can be exported to an Excel spreadsheet to sort or filter when AE is active.

dave w

Thanks Dave. I did check my map and TPS voltages, they are smooth and in line of what they should be. I will look at a data log and see if I can find how AE is acting. Thanks for the suggestion.

Dave,
still struggling with this issue. I tweaked my VE table a little more, issue became a little less pronounced. AE or PE are not functional when this is occurring. My VE table has a huge trough in it at 2Krpm. I tried averaging the trough VE with the lower and higher rpms. If I continue to tune either WB02 or using BLM the smoothed table always continues to trend back to a trough. Attachment 16847

That's an odd looking VE table. It's common to see Valleys and Peaks in a VE tables. The VE table posted appears to have Valleys and Peaks outside of the "normal" range.

Typically, an engine at low RPM's and light engine load will require less fuel than an engine at high RPM's and heavy engine load. Residential driving at 25 MPH requires less fuel than towing a RV trailer at 70 MPH. Typically an engine will require more fuel as it quickly accelerates to 70 MPH than an engine cruising at 70 MPH.

Timing is another variable to throw into the mix. There's basically one rule for timing . . . give the engine a timing table it likes. The real "heartbeat" of tuning is timing table tuning.

dave w

As an experiment, try add or subtracting a few degrees of timing to the corresponding " VE Valley Cells" of the timing tables.

Too much idle timing and too lean at an idle will have these things surging every time.

That trough in the VE also points to something mechanical being off. I'd verify cam timing and check leakdown.

Thanks for the thoughts guys. I took a little more time to dig into this. Checked the cam timing, degree wheel and valve motions meet the spec sheet. Leakdown good, I needed to check this anyway, looks like the engine broke in well.

So in regards to timing, yes, was a good day! Dave I recall you suggesting and doing some research on a 98 vortec timing maps. I found that info and threw it in my spark table with some smoothing, note I don't have any added timing due to P.E. I have always been hesitant on too much timing based on the saying "it ran really good before it blew up"! I also think I was not advancing due to knock count activity and would appreciate some thoughts on from you. I am thinking most of these are erroneous, possibly some real.

I drove the vehicle after warming it up for about 1/2 hour, stayed below ~3500 rpm, the timing map really woke it up, low throttle opening and significant improvement in mileage. I got a total of 4550 counts. Reviewing the log in detail I found 599 instances of knock retard, 260 at 1 degree or more, 64 at 3 degrees or more, 2 at 22.5, 1 at 16, 1 at 40, I am thinking the higher values are erroneous data from the log and only occur at one discreet point, which is evident in the plot (attached). The high knock activity flag was present 24 times. Looking at the spark advance some of the values in the data skyrocket from 40-11548 degrees! I used the "wash and rinse" spreadsheet that I believe you put together, Dave, thank you. My timing table only advances up to about 36 degrees (attached), so anything larger is confusing to me.

In a nutshell it is a big step forward. I still need to check my VE tables and see if the "trough" has gotten better.
Thanks again for the thoughts.
Mark
Attachment 16848
Attachment 16849