New to JTEC not new to tuning. Have JTEC questions

[rich s]

Hello I have a 1998 Dodge Ram 1500 that I just installed a new 6.7L/408cu in Magnum engine into.

[email protected]/.515 lift cam, 32 lb/hr injectors, long tube headers, Cat delete, 3" dual exhaust, orignial intake manifold, Flyin' Ryan ported throttle body.


As I said in the title, I'm new to JTEC, not new to tuning. I have a 2012 Dodge Challenger with a 426 cu in, Whipple supercharged Gen III Hemi that I tune. It runs low 10's in the 1/4 mile and I can drive it on the street. I have a good handle on NGC3 (I think that's the system) As a result I tend to think in terms of tuning the modern Challenger.

The questions I have are related to fueling. Spark seems pretty straight forward as I adjusted the spark timing long before the new engine install, so I have an understanding of that.

Questions I have:

What table/tables/etc affect or control closed loop fueling?
What table/tables/etc affect or control open loop fueling?
What controls/sets the closed loop AFR/FAR?
What controls/set the open loop AFR/FAR?

I've found the Open Loop/Base tables (EGR on and EGR off) but when I adjust those my results are not obvious to me and I'm not really sure when these are used.

Right now my plan is to force the ecu into open loop and use my wideband AFR gauge to try and adjust things like a carburetor.

I could use some help understanding the basic premise behind the operation of JTEC ecu's and help understanding which tables affect the fueling described in my questions above.

Any help is appreciated!

Rich

[Mully95]

This might shed some light on what your questions are. There are more Youtube vids that might help as well.

https://www.youtube.com/watch?v=Z7o_I21sBDI

[rich s]

thank you - watched that and a few others from the same guy.

[putts000]

I attached the JTEC manual from Chrysler. It explains all hardware and logic. It's a good read for anyone tuning anything. Cars today have added some complexity/features but they all still operate on the same basic principles since the 80s, inputs -> logic = outputs.

Chrysler dropped EGR when Jtec came out. Any tables listed as EGR ON do nothing, they are carried over from the SMEC/SBEC days. If the tables are there, mirror the EGR OFF table to the EGR ON table. Most when you go under the EGR ON table have no data listed or only one box filled in. There is no way to adjust the closed loop fuel AFR, it is fixed and will bounce around 14-15/afr. This should be fine for any engine running gas. These cars use a narrow band O2 sensor calibrated to stoich of gasoline/e10. The Open Loop/Base fuel map is the main map you will change. Under the O2 sensor tab is where you will set when closed loop happens based on rpm and temperature. Change the Closed loop coolant to 140F+ to start. Adjust idle up a bit to start. With higher duration cams the O2 sensor gets a bad reading at idle/low rpm.

Essentially the setup for Jtec and high duration cam will be running open loop at idle/-1200 rpm or so and WOT/low vacuum, and closed loop under normal driving. Setting the closed loop temp to the max of 376F will keep the car in open loop forever. If you have a wide band hooked up and graphed into the HP tuner software this is your best bet to get things in the ball park. Then lower the closed loop temp see where its' operating zone works best. The power enrichment and transient I don't touch unless I'm having a stumble/stutter when changing throttle quickly.

Also stock the Magnums run 32-35kPa at warm idle. So you will need to either move your all tables to compensate for where your idle vacuum sits vs stock. Or trial and error the MAP sensor scaling under the airflow tab. I've been doing a bit of both on big cam engines to keep the resolution better on all the tables.

[rich s]

putts000 thank you, the pdf is over and above!

your explanation is exactly was I was looking for and pretty much confirmed what I learned this week while working on the tune. I put it in constant open loop, datalogged my AEM wideband and adjusted the Base/Open Loop tables to get the AFR in the 12.5-15 range depending on what the MAP was. When I got the base tables to where I was happy, I adjusted the timing and then turned closed loop back on.

Because my new displacement is 410 and my cam is bigger than stock, I bumped the idle speed to 750ish and things got even better from there during decel - prior to that it would stall from time to time when coming to a stop. With the bigger displacement and cam, idle is at 45-49kPa. I pretty much got rid of the 13kPa row and rescaled the row axis for better resolution. The one thing that I did do that you say you didn't do is I lowered the threshold for WOT to 70kPa at the lower RPMs but left it the same at mid and higher rpm. I plan on towing my racecar with the truck and I felt I wanted it to go into WOT sooner to take advantage of the richer mixture (12.5-13 AFR) I tuned for.

Thanks again for the PDF and explanation.... it confirms a lot!

I do have a bit of work to do on start up. Not when cold and not when hot..... I guess you would call it warm.... after it's run and driven and sits but is not completely cold and not at operating temp, starting it can be a little bit of a challenge.

[bee44850]

putts000 thank you for the pdf

[putts000]

Some tips on the timing. The WOT modifier I always zero out and add that into the base table. The "Warm Spark" table is what it runs on warm restarts only, based on the settings below the table. I usually drop that table down a few degrees across the board vs base to eliminate any detonation issues from hot soaking. The duration is how long it runs on the warm table before switching back to the base. I usually set it to 58.9 seconds(1 minute). The rest should be easily understood. The magnum heads don't need anywhere near the advance the old LA did. I run max 28 degrees in at 3200rpm with stock compression.

If you need to give it throttle to get it started under the Idle-airflow page you can adjust where the IAC starting position is warm or cold. The correction tables will change the amount of extra throttle it blips in for a second as soon as it sees D/R is selected. Rather then going from park to drive and the engine dropping down and then the PCM reacting. Under the fuel-general tab the prime shot is one injector pulse when the key is first rolled on. Cranking is obvious. I usually add more and more to both of these the bigger the cam gets. Setting fuel sync to 2-4 advance with a higher end scan tool can help idle/low rpm drivability.

I've ran across a few stock Jtec files I pulled having more or less tables/options available then others. If you come across this make a ticket with HP tuners support, upload both files and tell them what tables your missing and they will add them to your Vin. Always run the BETA version of their software. The official version is always missing tables for me vs the beta version.

Screenshot (1).png
Does your oxygen sensor page have all 4 options like in the picture?

[putts000]

Here is the read from the stock 5.9L Mopar Performance PCM. I think they suggested 93 octane. Use it as another JTEC to compare to.

[rich s]

Some tips on the timing. The WOT modifier I always zero out and add that into the base table. The "Warm Spark" table is what it runs on warm restarts only, based on the settings below the table. I usually drop that table down a few degrees across the board vs base to eliminate any detonation issues from hot soaking. The duration is how long it runs on the warm table before switching back to the base. I usually set it to 58.9 seconds(1 minute). The rest should be easily understood. The magnum heads don't need anywhere near the advance the old LA did. I run max 28 degrees in at 3200rpm with stock compression.

If you need to give it throttle to get it started under the Idle-airflow page you can adjust where the IAC starting position is warm or cold. The correction tables will change the amount of extra throttle it blips in for a second as soon as it sees D/R is selected. Rather then going from park to drive and the engine dropping down and then the PCM reacting. Under the fuel-general tab the prime shot is one injector pulse when the key is first rolled on. Cranking is obvious. I usually add more and more to both of these the bigger the cam gets. Setting fuel sync to 2-4 advance with a higher end scan tool can help idle/low rpm drivability.

I've ran across a few stock Jtec files I pulled having more or less tables/options available then others. If you come across this make a ticket with HP tuners support, upload both files and tell them what tables your missing and they will add them to your Vin. Always run the BETA version of their software. The official version is always missing tables for me vs the beta version.

Does your oxygen sensor page have all 4 options like in the picture?

Good information, thank you. I will play with it some more this weekend.

My o2 sensor page only has 2 options, not the 4 like you show.

[jbliss15]

subscribing for more JTEC info that might come up

[joefus25]

I am wondering if you found a solution to the "warm" start issues you were having? I have had the same issues for a couple years but I have still not worked that part out yet. I am also wondering what you have come up with for timing map. I have a 410 magnum motor that is 10.6:1 with edelbrock heads and I have had a heck of a time finding a good spark map (also, unable to get it on a dyno still). Would anyone consider peeking at mine or vice versa?

Also, does anyone know how to calculate injector duty cycle off of these PCM's? I have a hard time trying to figure if my injectors are big enough or not??

(99 Dodge Dakota Jtec+)