Need help with JTEC issue - 1998 Dodge Ram 1500

[rich s]

As the title says, I need some JTEC help with my 1998 Dodge Ram. It's a Quad Cab 2wd Automatic that originally came with a 5.9Magnum.

In Dec of last year I swapped out the 5.9 magnum for a 408 stroker because the motor had 220k+ miles and was using a significant amount of oil.

The new motor is a 408 stroker block with factory heads. A 222deg (at .050) with .5xx lift camshaft with 32 lb injectors based on Holley's calculator for injector sizing.

The issue I am having is that, during coast and deceleration shortly after start-up, the Manifold Pressure will randomly spike to 90+ kpa from a normal 40-50kpa with no throttle input. At that point, the injectors are firing in excess of 15ms, the rpms drop and the engine stalls. Then when I go to restart it, the MAP pressure stays above 70kpa, the injectors are firing at 8ms and higher (3-4ms is about average for idle) and the engine just stumbles and sounds like crap.

I have to repeatedly turn the ignition off, wait and re-try to start the engine.... sometimes if it starts and it's running poorly with the erroneous sensed MAP pressure you can get the engine RPM to increase and all of a sudden the MAP pressure returns to normal and the engine runs normal.

This typically occurs after sitting overnight or when I am leaving work and the vehicle has been sitting for some time.

I have added grounding straps to everything possible (block to heads, block to chassis, block to battery, chassis to battery, ECU to block). The problem is not grounding.

I replaced the MAP sensor. The above happens with the new MAP sensor and the old MAP sensor. The crank position sensor (with new MOPAR unit), distributor pick-up coil with one from NAPA and the O2 sensor with a new Mopar unit. The engine when running idles smoother, but the mysterious Manifold Pressure spike still occurs.

I am beginning to wonder if the IAC valve is sticking causing MAP pressure to rise and create the issue.

I have attached two screen grab showings where the TPS voltage remains at 0.78v and the MAP pressure rises and maxes out at 95ish kpa, the injector pulse width increases and the rpm drops to zero.

I've also attached the entire log and the tune. If you go to the 3 minute and 26.5 second point in the log you will see where the MAP goes to 95kpa, the injector pulse width goes to 16ms and the TPS voltage is at .78 (closed throttle)

Any help or ideas would be most appreciated. This is becoming quite frustrating.

24-12-10 20-02-01.hpl

1998 Dodge Ram 12.9a.2024.hpt

43.6 kpa ----- hp tuner screen.jpg

95 kpa ----- hp tuner screen - 95 kpa.jpg

[LilSick]

in the 43 kpa pic the engine is idling at 800 rpm

95 kpa engine has stalled and is not running



nvrm... i looked at the log and yes, something is way wrong. why are your trims all over the place like that. O2 sensor voltage looks odd too

can you load this channel list and make another log?

you will have to add the wide band again

maybe try logging lambda rather than a/f too?

[rich s]

in the 43 kpa pic the engine is idling at 800 rpm

95 kpa engine has stalled and is not running

that is correct.

the channel list you sent is the same as the channel list I am logging?

[LilSick]

naw, there is an additional channel added

the O2 you are logging started off reading 5v ?

[rich s]

So, I was able to reset the adaptives and adjust the fueling so that the long term fuel trims are within +/- 5%.

I reduced/adjusted the cranking pulse width and enrich shot tables by 30% to account for the larger injectors (32 lb/hr vs OEM 19) and it starts easier, not perfect but MUCH easier.

It also drives nicely with repsectable Fuel trims and Lambda ratios.

The issue that still eludes me is the random stall after start-up .... approximately 2-3 minutes after start up.

A datalog is attached along with the revised tune

[hexdummy]

So, first recommendation, please make sure you are on the latest BETA and that polling interval says 0ms, reduce the amount of channels to maximize the datalogging speed. These computers are polled byte by byte so double the channels = half the logging speed. The log you shared has poor resolution. I've attached a channel config.

screencap JTEC polling interval.JPG

Based on what could be seen, I would say put a fuel pressure gauge on it and watch what it's doing when you start it up and when it acts up. The ecu appears to be doing everything it can to keep it running but both O2's are flatlined lean, pulse-width is not dropping so could very well be a fuel delivery issue. Have you made any changes to in in-tank fuel pump ? Also, the fact that you zeroed "closed loop enable delay" and set the temp threshold to 0 deg is not helping.

[rich s]

So, first recommendation, please make sure you are on the latest BETA and that polling interval says 0ms, reduce the amount of channels to maximize the datalogging speed. These computers are polled byte by byte so double the channels = half the logging speed. The log you shared has poor resolution. I've attached a channel config.

screencap JTEC polling interval.JPG

Based on what could be seen, I would say put a fuel pressure gauge on it and watch what it's doing when you start it up and when it acts up. The ecu appears to be doing everything it can to keep it running but both O2's are flatlined lean, pulse-width is not dropping so could very well be a fuel delivery issue. Have you made any changes to in in-tank fuel pump ? Also, the fact that you zeroed "closed loop enable delay" and set the temp threshold to 0 deg is not helping.

Thanks for the feedback. LilSick made the same recommendation regarding a fuel pressure gauge.

The pump in the tank is an aftermarket OEM replacement. A few years ago the OEM pump failed and we replaced it with a unit from Advanced Auto Parts.

I have a couple spare Walbro 274s from my Challenger. I would imagine that a 274 would be more than enough pump if the fuel pressure gauge shows issues?

[LilSick]

something starts happening at 1:55

20 secs before it dies

idle air valve opens about 20 numbers

lambda goes for 1.000 to 1.1 or so

[hexdummy]

A few more observations:

The IAC is all over the place and very high when idling. At idle you should have 20-30 steps, you may need to increase your minimum air flow, i.e. adjust the throttle stop.

Why did you rescale you map axis ?

Your long term fuel trims are -33 a majority of the time, -33 is the limit for long term fuel trims on a JTEC.

The fueling table needs some work, that could be your primary issue.

O2 seems very lazy, is it a NTK or Mopar sensor ? Is it new ? Have you extended the wires ? Do you have any exhaust leaks ?

Finally, again it is really hard to get a good idea of what's going on due to the slow sample rate. Your logging at about three times per second, the template I gave you should give you about ten times per second. If you reduce the channel count to five , it will log at nearly twenty hz.