I'm getting quite desperate to get some lower rpm, part throttle engine stumble/hesitation issues resolved. The custom tune was provided via email and multiple attempts to resolve the issue based on data logs and updates to the tune over email have failed. I have noticed some interesting patterns in the data logs, and I'm hoping someone might recognize how these odd patterns might be traced back to a problem in the tune that can be solved.
General description of the problem I experience: At certain engine speeds below 3000 rpm, with certain amounts of engine load (most noticeable in 1st gear, part throttle "normal" acceleration), the engine will briefly stumble/hesitate as I accelerate through a specific engine speed. It's worst with a freshly started cold engine, and can sometimes be severe enough to appear as if I'm a newbie stick-shift driver, rocking the Jeep with a bad shift.
Here's some clues in a screenshot of a data log (actual data log file attached to this post):
- log.png (34.85 KiB) Viewed 2722 times
2) Air charge data has sharp jumps in the data. This is unexpected to me. When air charge jumps, throttle position, manifold pressure, and engine speed data is all smooth. It appears to me that "air charge" has an error in its calculation, erring on the side of less air than reality at lower rpms, then at some threshold it jumps up to correct values at higher rpms. It seems that this would result in an incorrect amount of fuel to be injected to match the incorrect calculated amount of air. This would cause leaner-than-desired fuel mixture, which could explain the engine stumbling issues I experience at lower rpms. Does this point to an error in something like VE lookup tables (this is a speed density system, no MAF sensor)? This is not happening consistently at specific engine speeds, but seems to be dependent on a combination of engine speed and engine load.
3) Interestingly, the "p-ratio" (manifold pressure divided by barometric pressure) also follows the shape of the air charge data, jumping erratically. Is this a clue to anyone? The manifold pressure data is smooth, and barometric pressure obviously isn't jumping around, so how could the calculated p-ratio jump suddenly like that? What is in common between the calculation of p-ratio and air charge that would cause them to both have this same erratic jump?
I'm looking for any ideas anyone might have that I could forward to tuner for further investigation. I have also attached my original backup, and "last tune written" in case that's helpful. Thanks!