Need help diagnosing an issue

I am going to do my best to explain the "issue" I am encountering so please bear with me. For the past few months, I have noticed that when attempting to hold a consistent RPM while driving, it sounds like and feels like the vehicle is sputtering. In other words, it almost seems like the throttle body is constantly opening and closing because I can feel and hear the power coming and going. The ebb and flow is very minuscule, but still certainly noticeable. I have not received any CEL's and the car is certainly still drive-able but this "issue" has me concerned. Does anyone have any thoughts on what this could be? I appreciate any thoughts you all can provide.

Vehicle: 2013 GT500 with PP
Mod List:
· 10% OD Pulley
· ThumpRacing Belt Tensioner
· Dual 65mm TB
· 127mm JLT Carbon Fiber CAI
· MRT O/R catless H-Pipe
· 3.73 Gears
· MGW Short Throw Shifter
· NGK TR6 SparkPlugs
· Lund Tune
· KB Competition BAP (e85 capable)
· ID1000 Injectors
· ARH 1 7/8Headers with O/R H-Pipe (catless)
· 2.4 Upper Pulley
· 90mm Idler
· BMR Adjustable Upper Control Arm/Mount
· BMR Adjustable Panhard Bar/Support Rod
· BMR Single Adjustable Lower Control Arms/Relocation Brackets
· Eibach Pro Kit Lowering Springs

Have you watched your air fuel ratio while this is happening to see if its going crazy?

Fox&Cobra said:

Have you watched your air fuel ratio while this is happening to see if its going crazy?

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No I have not. I do not have an A/F gauge but isn't their a built-in gauge in the vehicle information center?

Yes there is i watch mine pretty often it is in the gauge selection of the cluster. That will give you some more insight as to whats going on it could be an o2 sensor going bad mine would do what your talking about and i replaced an o2 sensor and it fixed it also when the weather broke from cold to warm it was much worse tho, you would have to let it warm up before driving it.

had water down a spark plug hole letting it ark off instead of through the plug, car still ran decent till it went to closed loop for the computer then it did basically the same thing, this was on a 04 cobra but worth mentioning in case the motor has been washed recently ---- it never set a CEL so it took me a little while to figure out what was going on

Fox&Cobra said:

Yes there is i watch mine pretty often it is in the gauge selection of the cluster. That will give you some more insight as to whats going on it could be an o2 sensor going bad mine would do what your talking about and i replaced an o2 sensor and it fixed it also when the weather broke from cold to warm it was much worse tho, you would have to let it warm up before driving it.

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Great suggestion. I will get it out of the garage when I get home from work and take it on a drive and monitor the built-in AF gauge to see if it is also showing the ebb and flow I feel. To your point, when I don't allow it 5 minutes to warm up after having sit for a while, the throttle volatility is much worse. I will take also take a look at the o2 sensors. Pardon my ignorance, but on my Jeep I know the tuner I use traditionally turns off the o2 sensors on catless pipes. My H-Pipe is catless, so would the o2 sensors still be enabled?

beau t said:

had water down a spark plug hole letting it ark off instead of through the plug, car still ran decent till it went to closed loop for the computer then it did basically the same thing, this was on a 04 cobra but worth mentioning in case the motor has been washed recently ---- it never set a CEL so it took me a little while to figure out what was going on

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Great suggestion, I change my plugs every 2500 miles or 3 months (usually happens to be 3 months since it's a garage queen) so based on the last time I changed them, this could certainly be an issue. I will check them out as well. Thank you.

I also have a catless offroad x pipe and custom dyno tunes and they are using the built in 02 sensors and they arent turned off in mine

Have you talked to the tuner? They may have a data log file they will want you to run to see what is going on.

You change spark plugs every 3 months?

Could be the gap. Check to make sure its in specification. Mine was doing a little bit of the same. My Air-fuel was around 13.9-14.2 at steady state. My plugs were 2 years old so I changed them and that seemed to solve the problem. Even though you changed the plugs, thats not to say that you might have a "bad" or marginal one. Sometimes a different brand or type might cause grief.

Fox&Cobra said:

I also have a catless offroad x pipe and custom dyno tunes and they are using the built in 02 sensors and they arent turned off in mine

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Great thanks for confirming.

Catmonkey said:

Have you talked to the tuner? They may have a data log file they will want you to run to see what is going on.

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That is going to be my next step. I didn't want to bug Jon Lund too early on in the process in case I could triage the issue without him.

72MachOne99GT said:

You change spark plugs every 3 months?

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That is correct. With running e85, I want to be very careful about performing routine maintenance (oil, filter and plug changes). Is it overkill, sure, but I prefer to be risk averse.

Robot_trainer said:

Could be the gap. Check to make sure its in specification. Mine was doing a little bit of the same. My Air-fuel was around 13.9-14.2 at steady state. My plugs were 2 years old so I changed them and that seemed to solve the problem. Even though you changed the plugs, thats not to say that you might have a "bad" or marginal one. Sometimes a different brand or type might cause grief.

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Yeah that is all a great point. I have consistently used the NGK TR6 plugs gapped at .030. I will double check the gapping this afternoon to make sure.

4 o2 sensors.

The o2 sensors they turn off are after the cats and just check for proper cat operation. The o2s you need to worry about are before the cats and help tell the engine how much fuel to use.

jps043 said:

Great suggestion. I will get it out of the garage when I get home from work and take it on a drive and monitor the built-in AF gauge to see if it is also showing the ebb and flow I feel. To your point, when I don't allow it 5 minutes to warm up after having sit for a while, the throttle volatility is much worse. I will take also take a look at the o2 sensors. Pardon my ignorance, but on my Jeep I know the tuner I use traditionally turns off the o2 sensors on catless pipes. My H-Pipe is catless, so would the o2 sensors still be enabled?



Great suggestion, I change my plugs every 2500 miles or 3 months (usually happens to be 3 months since it's a garage queen) so based on the last time I changed them, this could certainly be an issue. I will check them out as well. Thank you.

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check for vacuum leaks... if the line going to the bypass valve leaks periodically that cause surging.

Throttle body sensors?

MAF dirty?

Also... how do Older plugs wear if the electrodes are ok and they look good? Just wondering how plugs go bad just because they're old.