Does anyone know what the reverse idle steps are used for?17FB8710-A6F7-4841-A641-A8CB80A1CE7F.jpg
Does anyone know what the reverse idle steps are used for?17FB8710-A6F7-4841-A641-A8CB80A1CE7F.jpg
Idle error vs. steps.
I'm learning and trying to fix an idle issue...can you elaborate more? this is a dodge jtec computer.
Idle error vs. steps, i.e. target idle = 800 , actual idle = 880, ecu will subtract 8 steps from the iac. In this function the left column is idle speed error, the right column is the amount of steps that will be subtracted . If you want to experiment just zero out the steps in this and the sibling table, when the engine is in idle control mode you will see that the steps will not move in response to idle speed error. This does not apply when the ecu is in off idle or other modes.
I set all reverse correction drive to zero, no help. I set all my idle timing tables the same and all main timing tables the same, no help. turned off DFCO, no help. I've tried 2 different IAC, TPS, MAP and VSS sensors with no help. Removed and plugged PCV valve, no help. Pulled a vacuum test on the brake booster, checks good. Checked all grounds and power at sensors, all check good. No check engine light. Truck runs down the road good but still has RPM drop when rolling and occasional stalling pushing in clutch and coming and coming to a stop. I'm at a loss. this is a new rebuilt 5.9 magnum engine with Edelbrock heads, stock injectors, stock intake and small custom roller cam 218/[email protected] 525/525 lift, 112 lobe separation installed +4 degrees. It shouldn,t be this difficult. Bad computer?
Post your log
The only way I can get it to stop stalling is to set my idle spark thresholds like the Mopar Performance 98 Grand Cherokee
here's my latest tune file and run file
Have you and how have you set you base or minimum air flow ?
I haven't. This was dyno tuned by a shop. It's a brand new engine. It was running really bad so I took it to have it dyno tuned. When I got it back it was running good enough to drive. Thats when I found out it was stalling and idle was dropping. I had already shelled out enough money to have it tuned. A friend had a MPVI2 tuner, so I thought I would try my hand at learning how to computer tune. Unfortunately there's no information out there on how to tune a JTEC computer. And that brings me to where I am today. This is a 5.9 magnum that was installed in a Jeep Wrangler. The computer is a junkyard computer, so it could be bad. o2, crank position and IAC are new Mopar sensors.
Last edited by Dwg86; 07-10-2022 at 05:18 PM.
They used a tailpipe o2 sensor to set fuel trims and I'm running cats (i have to be emission legal). I don't know if cats will mess up the A/F reading at the end of the tailpipe or not. So I installed an AEM a/f gauge. I had to adjust idle trims. They were so lean it wasn't registering on my gauge. looking at HP scanner, it was 18:1 AFR at idle. So I had to adjust the A/F some also. It seams theres not a lot to adjust on the JTEC platform
So, I realize you have been around in circles but start with the basics. It may not fix your drivability issues but if your minimum air flow is too low it certainly won?t help. You are looking for a slight drop in idle rpm when you completely seal the iac passage in the throttle body, make sure engine oil and coolant are up to full temps. You can pop out the plug for the set screw, lower the setting and recheck. If you have to open the throttle make sure to shut off the engine and cycle the key several times to move up the minimum throttle voltage, idle to off idle is only .04 volt delta at the tps.
Beyond that, make sure your mapping is good especially where it drops or hints when you are coming to stop.
Try contacting this guy , he's the only one I've seen talking about Jtec
https://www.youtube.com/watch?v=eFNuDmkhuQk
62 Biscayne 425/409 SS/D stock class car 10.60s
66 Dart 426CIG3 8.60@171 2750lbs Naturally asperated
04 Ram All Alum , 468Ci G3 10.50s @4800 lbs Naturally asperated
04 Rumble Bee, built 6.1 ,4000lbs 10.48 @ 129s MPH. Naturally asperated
05 Rumble Stock 5.7, 3.92s TUNE ONLY 13.94@98mph
Looking at your log and tune here is my suggestions to start with:
1. Change your log template to remove: battery volts, desired charging voltage, mil, add: vehicle speed, tps voltage, nv ratio if those are available.
2. Your idle steps are high at idle, as I noted you want to adjust the minimum air flow by closing the set screw until you have a slight rpm drop when the idle air passage is fully blocked. You can also use the indicated idle steps via HPT logger, shoot for around 10-20 steps at idle. To do this, get the truck good and hot, full coolant and oil temps, shut if off, disconnect the battery for 30 seconds, immediately re-start the truck then adjust the throttle to get to that step range. I try to start high then work down so you don't have to deal with re-setting the tps.
3. The fuel mapping could use some additional refinement, there are areas where the fueling is off by more than 20%. That's good that you have the wideband installed, but you can't use it for adjusting areas that are normally run in closed loop unless you disable you ltft and stft then reset the fuel trims (battery disconnect).
There's a TSB I found that the computer I'm using is affected by. It has something to do with lost idle steps and stalling. The TSB gives a software update it needs to have. I don't believe my computer has the update because it doesn't have the sticker on it, and my local dealer says they can't update anymore (maybe one of these computer repair places has the update). So, I ordered an ECM off Ebay that has the update. It was only $150. I'll have to buy another credit to tune it. JTEC's only require 1 credit to tune. I'll be $200.00 in this new computer (including 1 credit) so that's not bad. I'll download the tune off of it and apply it to my computer, and then I can sell my computer. I can download my fuel and spark table to the new computer and see if it's a computer problem.
When I was adjusting the idle A/F, I kept adding fuel with little affect to the A/F ratio. When I looked at LTFT the computer kept pulling fuel. The more fuel I added the higher the negative LTFT's kept going so I stopped. My idle fuel trims are still a little lean (better than it was) but it's just at idle with no load. I was adjusting fuel trims without turning off STLT and LTFT. I didn't know I had to do that. Where do I turn off LTFT and STFT?
The only way I see to disable closed loop would be to set the ECT so high that it never goes into closed loop. If you look at the HP editor for the JTEC, its very basic. It doesn't have a lot of stuff like the other platforms have.
There's another tuner that's supposed to be good with JTEC, but when I asked him a few questions to see if he thought my computer was bad or if this is something he has seen before and if adjusting the tune would correct it (I didn't want to waste his time trying to tune a bad computer). He stated he didn't give out free trouble shooting. OK, I get that. So then I asked how many hours I get for his email tuning procedure. I didn't want to drop another $1000.00 before I knew what I was buying. Also, his website said I needed "MPVI2+ PRO required for custom tuning. I asked if I needed that since I was able to datalog and write tunes with a MPVI2 and I already have bought a credit to tune, or if he required the pro version to tune, and no more replies. I don't know asked too many questions? Who knows, but I'll get it figured out.Originally Posted by rays04gtx
Last edited by Dwg86; 07-12-2022 at 12:47 PM.
Please check your PM's.
that's one of the things that bums me out about the "mopar" community......... ..FWIW , I searched through the tune repository and there's nothing for the Pre-03s I called a friend of mine ,and he said he hasn't dived into the older stuff yet.
62 Biscayne 425/409 SS/D stock class car 10.60s
66 Dart 426CIG3 8.60@171 2750lbs Naturally asperated
04 Ram All Alum , 468Ci G3 10.50s @4800 lbs Naturally asperated
04 Rumble Bee, built 6.1 ,4000lbs 10.48 @ 129s MPH. Naturally asperated
05 Rumble Stock 5.7, 3.92s TUNE ONLY 13.94@98mph
I don't mind paying a man for his time. especially if its his business, but I want to be sure I know what I'm purchasing (I feel I've been burned once). Thanks for checking with your friend on info. I do appreciate you trying to help.
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