Low RPM High MAP Stutter

[XDR]

Doing some SD VE tuning and trying to figure out while around ~1200 RPM and 70-90 MAP the engine stutters. It looks like the o2 sensors are working, was my initial thought.

Engine is a 2001 5.3 installed in my Jeep.

Here is a short log, anytime the TPS was over ~30 it had the issue. I see alot of spark is pulled out, could that be the reasoning? If so, what would be the best solution?

Here are my log and tune for specific session.

STUTTER.hpl
VCM SD 1 BAR.hpt

Here is a longer log, it had the issue the last couple of minutes around the same RPM. All other areas don't have issue.

TEST LOG.hpl

[XDR]

So far I have tried loading the stock 5.3 spark maps and settings from the repository, no change. Also tried enable changing delta cyl air to 8.0 with no change.

What else could cause spark advance to drop?

Some more details on swap, it is a manual trans, VSS is not hooked up to PCM (Chrysler VSS, 3 wire iirc). Not sure if that would have a weird effect on this situation.

[XDR]

Watching the log and comparing it to my truck (lq4) I notice that the spark timing is reacting really weird. If you look at the log file, when off throttle spark is ~25*, as soon as tps is present it jumps to ~55* momentarily then drops significantly. It did this at all RPMs but is only noticeable at the lower rpm / high map like I said before. Been doing allot of searching and coming up with nothing. Also compared my trucks tune vs this tune and nothing stands out.

[Higgs Boson]

i can't see the tune on this computer but low rpm high load/map is called lugging the motor and it will knock easily if you have too much spark in it, this is why factory tables are negative there. so, if you have too much spark lead in those cells it is probably crying out in pain.

if you have a cam then it is also most likely advanced on the intake vs a stock cam creating even more cylinder pressure and needing even less spark lead.

are you logging knock? put the car in open loop and check your fueling with a wideband to make sure it's spot on instead of using trims, especially if you have long tubes, the sensor delay might also be wrong and they are inaccurate at low flow.

[XDR]

Stock internals and shorty headers. The spark spike was even without lugging the motor, stutter can only be felt during that time. I have loaded the stock spark maps and have been logging KR and BKR with both not showing anything during the spike/drop. I dont have a WB yet so can't do that.

Also, this "lugging" portion of the tune is important to the use of this engine. When in the rocks and slowly crawling over it is typically in these higher MAP ranges with low RPMs.


I got the spark I think to not drop, but it has an instant lead in to 50* advance, which is higher than the spark map for high and low octane.

i can't see the tune on this computer but low rpm high load/map is called lugging the motor and it will knock easily if you have too much spark in it, this is why factory tables are negative there. so, if you have too much spark lead in those cells it is probably crying out in pain.

if you have a cam then it is also most likely advanced on the intake vs a stock cam creating even more cylinder pressure and needing even less spark lead.

are you logging knock? put the car in open loop and check your fueling with a wideband to make sure it's spot on instead of using trims, especially if you have long tubes, the sensor delay might also be wrong and they are inaccurate at low flow.

[Higgs Boson]

you would be amazed what correct airflow values will do for your spark abnormalities. I would definitely recommend getting that in line first.

[XDR]

you would be amazed what correct airflow values will do for your spark abnormalities. I would definitely recommend getting that in line first.

Well the fuel trims are pretty close ~1% when its happening now. Some things I noted, seems to always be in FTC 14 when its happening, and it always pulls spark down to ~5. Cruise spark is around ~25 and off throttle it is around ~55.

Seems to happen at 1800 RPMs and below. I have PE disabled for now, so that's not messing with fuel and flooding it or anything.

So to me that sounds backwards, not 100% if it is, but you'd think you'd want more fuel and spark with more throttle.

[Higgs Boson]

Disable closed loop and run around in open loop to rule out your closed loop system. If your trims are within 1% in closed loop you should have no fueling issues in open loop and you can try to recreate the stumble.

[XDR]

Well I just checked my fuel rail pressure, key on ign off its at 48 PSI, and 52 PSI at idle. Also, I see minimal bleedoff after its turned off, 1 PSI every 30-60 seconds. I ordered a 255lph fuel pump to try out since I'm starting to thing its not in the tune.

[XDR]

Ended up being a bad Corvette style FPR....