1998 ram 2500 JTEC PCM timing help

[jonfrabitoy]

Good afternoon,
I have a 1998 Ram 2500 w/5.9 L gasser. The truck has the JTEC PCM, no external TCM, w/46RE trans. I bought the MPVI2 system from HP Tuners to specifically tune this truck. I have succeeded reading and editing the base code. However, there is not a lot of resolution in this controller. For instance, there is no VE table map to edit, there is a spark table map where RPM vs MAP exists, the total spark advance in degrees populates the table. And there is an injector pulse time table map where RPM vs. MAP populated with injector pulse times. My question: how can I dial in a new cam? Where the cam card information is not adjustable by just tuning? These magnum engines have a puny cam, just adding 0.050? and 10 degrees more duration is all I am after? A 467/487 lift @ 0.050? and 208/214 duration with 114 LSA. Ill Try to answer this myself, my engineering background tells me to delay the hysteresis of the injectors from 448 us to lets say 248us, it will energize later than stock, and lengthen the pulse width for the longer duration? Then advance the timing a few degrees until AFR is acceptable? Am I on the right track here? No much in the JTEC to change?

[3barboost]

do you have a wideband ?
and yes the jtec seems pretty simple but due to the simplicity it is actually very bloody complicated
you will likely find loads of corrections in power enrichment etc

you need to get a wideband, log the afr and then you can start, dont just start changign variables around unless you know what the effect will be
since their is no maf sensor, the cam should move the load to the "right" or "down" in the tables and you will then find you touching different values than you were in stock

log it log it log it
then plot the results and see where AFR is not optimum, get AFR optimum, then start with timing

[jonfrabitoy]

do you have a wideband ?
and yes the jtec seems pretty simple but due to the simplicity it is actually very bloody complicated
you will likely find loads of corrections in power enrichment etc

you need to get a wideband, log the afr and then you can start, dont just start changing variables around unless you know what the effect will be
since their is no maf sensor, the cam should move the load to the "right" or "down" in the tables and you will then find you touching different values than you were in stock

log it log it log it
then plot the results and see where AFR is not optimum, get AFR optimum, then start with timing

I agree to what you are saying its excellent advice. I don't have the latest version, the +2 module or a sniffer yet. instead i thought i might make a bunch of calculations to see if i could figure this out first. the JTEC controller is very nice, and if I just wanted to tune a little and smooth things out, it would be fine. but i need more, change the mechanical in the engine.

Greg Banish wrote an excellent text on engine management and tuning, according to fact, the injectors need to be energized prior to delivering fuel at steady state or consistent flow and volume and pressure. this is hysteresis. the dodge engineers included this feature in the JTEC, where for the 23 lb/hr. stock injectors, the default value entered from the factory is 492 us. so the injectors need a running start to energize prior to injecting fuel at the exact time in the cycle.

then the MAP vs. RPM table contains the length of time that the injector delivers fuel for that RPM/MAP set point which can be 68,900 us and that corresponding RPM. if the exhaust closes at 245 degrees of crankshaft rotation, in that cycle, the injector will energize shortly after that and inject fuel on the surface of the intake valve prior to it opening.

how can i change that? by delaying the hysteresis of the injector offset? that is still not going to change when the machine code in the JTEC turns on the injector. if i change the cam timing and open the valves for a longer duration, if the machine code is the same, the injector might deliver fuel too soon, how can we change that, if you can not change the machine code?

is this the issue?

[jonfrabitoy]

I was told by a repair house, that the JTEC PCM was an analog device, it does not learn or self program like the new stuff. So i found a deep Chrysler article on the operation of the JTEC controller for training technicians.

it operates on the speed density algorithm, where the controller looks at the sensor inputs, matches the voltage signals to in order, the MAP sensor table 1st, then it looks at the TPS, then it looks at the ECT then the IAT then the sensed batt voltage and then the O2 sensors, it multiplies all of the values and coefficients in all the tables to come up with a value that should be within +/- 5% of actual in closed loop mode.

in open loop mode it has long term and short term tables to pull from in fail-safe mode or default mode. in the event an O2 sensor fails, it just operates at the last known ST table.

Still, i realize there is no way to add functionality to the controller, i was hoping someone might have found a way to make bigger cams work, perhaps our friends idea of incorporating a sniffer to tune AFR is the best approach, and hope the controller has enough bandwidth to dial in the cam?

at 800 rpm, the intake valve opens 13.33 times, the event lasts 75 ms each time, and its portion of the whole 360 degree cycle is 56/360 degrees. so the controller is programed after the 448 us energize period at some degree of the camshaft rotation. maybe that does not change even with a larger longer duration camshaft, since they should have the same center line?? lots of deep thought here? any ideas friends?

[jonfrabitoy]

I thought i might add someone else's tuning experience to this discovery process, this article helped me learn a little more about the PCM. this article was taken from HPacademy FAQ forum, and is interesting.

"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."

This is all good, but there is still something that bothers me. I can change the spark event, retard and advance, but i can not see how to change the injector spray time in the cycle, and perhaps the JTEC will adjust with the spark table. but somewhere, in the machine code, the initial timing of 12 degrees advanced and injectors triggering on the 350ms after exhaust valve closure is hard programmed into the machine code. maybe there is some bandwidth here, ill assume a mild cam can be dialed in. ill try, thanks for listening.

[duster360]

This is my first time looking at a JTEC and its goofy for sure but all the important bits are there.

Base tables for Spark and Fuel and then a bunch of scalar multipliers as modifiers for this and that.

[duster360]

This is all good, but there is still something that bothers me. I can change the spark event, retard and advance, but i can not see how to change the injector spray time in the cycle, and perhaps the JTEC will adjust with the spark table. but somewhere, in the machine code, the initial timing of 12 degrees advanced and injectors triggering on the 350ms after exhaust valve closure is hard programmed into the machine code. maybe there is some bandwidth here, ill assume a mild cam can be dialed in. ill try, thanks for listening.

The Start and/or End of injection is not tunable. Its nothing you need to be concerned with as long as you're not trying to use +220lb/hr injectors on a 4cly running pump gas.

[duster360]

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.

Never try to correct non-sensical data. Take it as a red flag not to touch it. 99.9% of the time its a HpT PCM mapping error that only they can fix. Forcing it to makes sense to you, can, at worse, brick the PCM

Also, i rarely if ever, have to touch any sort of "Air Enrichment Factor table based on IAT" regardless of how radical of tune. PV=NRT doesnt change much regardless of setup.

[duster360]

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.

If holding the throttle open a tad is helpful and reducing Hot Crank IPW didnt do much, you need to give it more AIR. Open the AIS... A LOT

35706 - Idle Speed Adj Startup Position

[jonfrabitoy]

i actually think i figured this out. i hand calculated it the hard way, and then confirmed my solution with Mr. banishes second book. attached is my spreadsheet. the real issue i was chasing, the machine code for injector initialization, 0-720 degrees, where is it? second, can the injectors deliver enough fuel at 5500 rpm, the injector has 22 milliseconds to do so, without resting?? going to buy a wide band to, i built a MAP from scratch. attached. if someone has installed the factory original R/T cam P4532635, superseded to P5155565, and have generated a good set of tables or maps, would appreciate some sharing. I have one of these brand new camshafts, although i am certain the restrictive throttle body will have to go as well to get the most out of breathing a little.VE Map from Scratch.xlsx