Rough running

[Billy Mild]

I did some further testing today. I know the exact scenario that my issue is coming up.

If I run the engine in the 3000+ RPM range and decide to slow down with the car in gear, when it drops below 3000 RPM I start to hear some pops and burble from the exhaust. If I let the car get to the 2000 RPM range then give it a little gas or try to accelerate my car stumbles or hesitates. I got this on the datalog today. It doesn't always do this stumble, but it does more often than not.

This happened using both ECM's. So it might be a sensor OR the tune itself. I did notice that when the INT number is down around 60's when this stumble occurs. If I go WOT it clears right now. Its only for partial throttle.

https://1drv.ms/f/s!AmLeM5vTSQEttmNJ9qMuJUA4Qpyk

Above is my OneDrive link to my folder with both datalog files. If anyone could review them it would be very helpful.

Is it worth looking into my tune as a possible cause?

[LGAFF]

Do you have secondaries removed?

[Billy Mild]

No they are intact and should be working correctly. The car makes good power when at WOT.

My only mods are Haibeck Tune for headers and antiback fire mode turned on, Longtube headers, C6Z06 cats and borla axleback with an X pipe.

[XfireZ51]

On decel, the MAP goes very low, somewhere around 25-30kPa. This is where the fueling is at that point. Although DFCO is disabled and the injectors are still providing fuel, once u crack the throttle the motor takes a huge gulp of air due to the high vacuum. This causes the fueling to go lean (INT LOW) and must be overcome with a pumpshot (AE) particulalrly at small increments of throttle opening i.e. 5-10%. When mods have been made to the motor allowing additional air, fueling should be modified in these areas of the VE table and possibly the AE. Could play w timing also.

[Billy Mild]

Originally Posted by XfireZ51

On decel, the MAP goes very low, somewhere around 25-30kPa. This is where the fueling is at that point. Although DFCO is disabled and the injectors are still providing fuel, once u crack the throttle the motor takes a huge gulp of air due to the high vacuum. This causes the fueling to go lean (INT LOW) and must be overcome with a pumpshot (AE) particulalrly at small increments of throttle opening i.e. 5-10%. When mods have been made to the motor allowing additional air, fueling should be modified in these areas of the VE table and possibly the AE. Could play w timing also.

Did you take a look at my most recent datalogs?

I have emailed Marc Haibeck about this to get his take. He mentioned that the car was going VERY LEAN and then it tries to compensate by moving the INT numbers to the extreme rich side.

So does this come down to a tuning issue on the PROM?

EVERYONE THANK YOU FOR THE HELP. I'm getting closer to a resolution.

[XfireZ51]

Originally Posted by Billy Mild

Did you take a look at my most recent datalogs?

I have emailed Marc Haibeck about this to get his take. He mentioned that the car was going VERY LEAN and then it tries to compensate by moving the INT numbers to the extreme rich side.

So does this come down to a tuning issue on the PROM?

EVERYONE THANK YOU FOR THE HELP. I'm getting closer to a resolution.

Didn't look at the most recent logs. Ur description sounds pretty typical. If u tuned carbs, u would recognize the symptoms.
As Marc suggests, the INT is trying to overcome the lean condition but it can't react quick enough. That's why the AE is used. How ever, like all fueling its based on the VE table. IOW, u adjust VE in the Decel area so it doesn't go as
lean as it does, then tweak the AE to compensate for the rest.

[BigJohn]

Originally Posted by LGAFF

Do you have secondaries removed?

Happy Birthday!

[Hib Halverson]

1) Dont' assume you have a problem with calibration (the chip) unless the problem you have has always existed. If it has NOT always existed, then it's not a cal problem.

2) I could only see two posts where the actual block learn (LTFT in modern terms) or integrator (STFT) were posted. STFT can be difficult to use for initial diagnosis of a problem but LTFT can be quite revealing. In each of those posts, the block learn has been below 128 which means, as Marc has suggested, the engine controls are reacting to a rich AFR in closed loop by "taking fuel out", i.e.: shortening pulse width to lean the AFR back to stoic.

3) First thing I'd do is swap the O2s side-to-side. If the problem stays then it's something causing that side of the engine to run rich. If the problem moves, replace the O2s.

4) So...what could make one side of the motor run rich? Bad injectors could do it and, based on your earlier discussion of your fuel pressure results and that the FP bled down after ten seconds, I'd suggest you pull all 16 injectors send them to RCEngineering in California and have them cleaned then flow tested. If you have bad injectors and want to replace them with really good injectors, ask RC about the LT5 injectors they sold me and many other Zroners. I had a set of RCs in my 95, Barney. They were installed in 1997 and were in the engine when I sold it in April of 2016. In that 19 years in service, I never had a problem with an RC injector.

[Billy Mild]

Originally Posted by Hib Halverson

1) Dont' assume you have a problem with calibration (the chip) unless the problem you have has always existed. If it has NOT always existed, then it's not a cal problem.

2) I could only see two posts where the actual block learn (LTFT in modern terms) or integrator (STFT) were posted. STFT can be difficult to use for initial diagnosis of a problem but LTFT can be quite revealing. In each of those posts, the block learn has been below 128 which means, as Marc has suggested, the engine controls are reacting to a rich AFR in closed loop by "taking fuel out", i.e.: shortening pulse width to lean the AFR back to stoic.

3) First thing I'd do is swap the O2s side-to-side. If the problem stays then it's something causing that side of the engine to run rich. If the problem moves, replace the O2s.

4) So...what could make one side of the motor run rich? Bad injectors could do it and, based on your earlier discussion of your fuel pressure results and that the FP bled down after ten seconds, I'd suggest you pull all 16 injectors send them to RCEngineering in California and have them cleaned then flow tested. If you have bad injectors and want to replace them with really good injectors, ask RC about the LT5 injectors they sold me and many other Zroners. I had a set of RCs in my 95, Barney. They were installed in 1997 and were in the engine when I sold it in April of 2016. In that 19 years in service, I never had a problem with an RC injector.

1. This stumble after a decel is a new issue. Never had that before. It for some reason feels like its the computer or Tune causing it.

2. I am going to get another datalog to really show the issue.

3. The O2 sensors are new, but are a "Standard" Brand from Rockauto. I have suspected these as well as a possible cause. Normally an engine will just run rich when an O2 sensor is bad.

4. I replaced fuel injectors with Accell brand injectors about 3 years ago. They are the model that Marc recommends on his site. At this time I also did plugs, wires, and fuel filter. I also at that time fixed any vacuum leaks that I could. Just recently I replaced the Spark Plugs again. Do you think I need to send out my 3 year old injectors? According to the FSM if the fuel pump tests show bleed off the pump needs to be replaced.

[Billy Mild]

I will try swapping the O2 sensors around this weekend.

I have been running ethanol free fuel 90% of the time.