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Issues with tuning a JTEC PCM with HP Tuners

Practical Reflash Tuning

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Discussion and questions related to the course Practical Reflash Tuning

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I am tuning a 5.9L Magnum engine swap into a 1997 Dodge Dakota. The truck was originally a V6, but Dodge had a 5.2L V8 option in 1997. In 1998 they added the 5.9L as an option, but changed the PCM (ECU) architecture such that a 1998 ECU won't run the gauges in a 1997 vehicle. Therefore I am using a 1997 5.2L PCM and reflash tuning it for the 5.9, which has a big cam for good measure. This is a speed density ECU that normally runs closed loop except at WOT. As the ECU can adapt ±33% on the fuel trims, I initially used a STFT + LTFT histogram to get the fuel table adjusted into the ballpark. As expected the engine ran rich at low MAP due to the cam and lean at high MAP due to the increased displacement and cam. I then got an open loop histogram of wideband Lambda to tweak the fuel table and address WOT tuning. The fuel table is now good and the engine runs very well once it has warmed up and after heat soak has dissipated.

A hot start after heat soaking requires a long crank, which I have not resolved. It appears to be related to high intake air temperatures due to the heat soak. Starting a short time after a hot shutdown is no problem. The engine has headers so the engine bay does get hot. I have tried reducing crank and prime pw at high ECT, with no effect. I am nervous about moving too far on this table since it works fine when the engine is hot, just not when it is heat soaked.

There is an Air Enrichment Factor table based on IAT. This is where things get interesting. It ranges from IAT 82°C to 191°C with the factor ranging from 1.1758 to 1.0000 over those temperatures. This temperature range is not plausible or useful. If those numbers were °F, they would make sense, and the factors would correlate reasonably with the equivalent table in a 5.9L ECU. In other words, I think Dodge screwed up with this table due to a unit conversion error and never got around to fixing it. Or are these labels a resourse sourced from HP Tuners, and maybe the table is fine but that resource is wrong?

HP tuners allows editing the row axis labels on a table, so I have tried putting corrected temperature values into the table. When I do this uploading the tune fails. I am guessing that the table headers cannot be changed, and when a change is detected the tune is flagged as invalid. Anyone got experience with altering the range of a table, or have any suggestions?

I don't think that the Air Enrichment Factor applies to cranking PW, so it isn't a fix for the long crank, I question if this ECU can properly account for IAT variations, if that table is so far out. I suspect it makes do with fuel trims. Any thoughts on this?

Further to editing the row headers in the air enrichment table with HP Tuners VCM Editor: I am not sure what was causing the flashing error previously, but I have managed to get the air enrichment table row headers changed, flashed, and working. Right clicking on the table provides the option of opening an edit window for the row or column headers.

Putting rational values in this table (i.e. the values from the stock 5.9 L ECU) changes my tune because this table is now active instead of being stuck on one value. A single scaling change to the entire base fuel table has gotten me pretty close to right, which confirms the air enrichment table is now working as intended.

Reverse engineering the air enrichment table shows that these are just about exactly half the density change due to temperature change implied by the ideal gas law. I am unclear as to why the full change wouldn't apply, but I am sticking with these values for now.

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