GEN 4 Vipers running 10.4 AFR above 4000rpm ?

[Schulmann]

We had a dyno session day in our club this morning. One of the thing that stunned us was the really rich AFR on the GEN4 Vipers above 4000rpm. For some unknown reason the AFR drops from 13 to 10.4 suddenly at 4000rpm causing the engine to loose 50hp. We were expecting 540rwhp and got 490 rwhp.
I will try to get a dyno chart. Anybody knows what causes this probleme ?

It makes me remember my old 2000 when the AFR suddenly dropped due to ignition issues above 5000rpm.

We had two Vipers with this problem. On the third one the dyno master has stopped the session because the engine was hesitating too much at 4000rpm.

What is going on in the GEN4 VENON control at 4000rpm ?

 

[mjorgensen Woodhouse]

Some of this is protection in the program. What gas is in the car? Old/New octane? If there is heat and a little knock detected that PCM will throw a bunch of fuel at it and remove timing to remedy. Also when this happens it will only release the added fuel after a little driving without seeing the condition again.

 

[Schulmann]

Very good guess !!! The issue might be fuel quality related.
I didn't think about. But running 10.3 can also ruin the engine.
The engin was not at all running smooth above 5000rpm.
It was hesitating way too much between full power and no power at all.

The guy who drove away from the dyno because the ignition broke down didn't have any issue before and after the dyno ....

 

[gofastr]

What kind of gas are you running? I'm using Chevron with no problems above 4000.

 

[SilveRT8]

What kind of gas are you running? I'm using Chevron with no problems above 4000.

It was my car on the Dyno, I had half a tank of 91 oct, so I filled it with 94 oct and ran about 60 miles before going to the Dyno.
I will scan the Dyno sheet and post it.

 

[SilveRT8]

Here is the Dyno sheet of my totally Stock 2008 Roadster with 5780 km on it.
On the first pass, it got 511 hp and 480 tq with the standard air filter, AFR got as low as 10.3.
On this posted run I added the K&N air filter and got 514.5 hp and 476.9 tq as shown here. Temp was about 65F and very humid, gas was a half/half mix of 91 and 94 oct.
Look at how the torque curve goes up and down. Dyno smoothing was maxed at 5

You must be registered for see images

Here is the same car on the same Dyno last Oct, all stock with 2900 km on the clock. Temp was cooler and dry, gas was 94 oct, it made a best of 557 hp and 502 tq (2 runs shown on the graph) Note that AFR did not drop below 11.

You must be registered for see images attach

What caused this 40+ loss in HP ?

 

[mjorgensen Woodhouse]

I still say it is bad gas, makes tq then the timing gets pulled causing the A/F to drop and power to plummet. Run that junk out and another tank of good stuff. Then fill up and go back, I bet you get the numbers back. Mixing fuel is not that easy as they don't really mix and you could be getting some good then a spike of bad then the ECU reacts to save the motor causing these swings.

 

[SilveRT8]

I still say it is bad gas, makes tq then the timing gets pulled causing the A/F to drop and power to plummet. Run that junk out and another tank of good stuff. Then fill up and go back, I bet you get the numbers back. Mixing fuel is not that easy as they don't really mix and you could be getting some good then a spike of bad then the ECU reacts to save the motor causing these swings.

Thanks for the tip Mark, I will go back on 94 oct only and then again with the "Mopar race Controller" I just ordered from you.

 

[HI-NOS-Viper]

Those spikes do look pretty bad. If not bad gas maybe the injectors are dirty. Might be worth taking a look at.

 

[SilveRT8]

Those spikes do look pretty bad. If not bad gas maybe the injectors are dirty. Might be worth taking a look at.

The car only has 5780 km on it, or 3580 miles.
Never ran on an empty tank to avoid picking-up dirt from the bottom of the tank, could it still be the injectors?

 

[mjorgensen Woodhouse]

See the Engineers responses on the Grail trail post you did. Some of the same info I have provided in the past since they are the source lol. There are also some great comments about the dynos effect.

 

[SRT09]

Does anyone have a dyno sheet with AFR's with a Gen running not in a "knock" limp mode?