What causes this?

[Silver03]

What causes this? I have had this tune forever and have never seen my car do this on the dyno. No matter what tweeks were made with the predator, all the runs take this same dip at 5500 RPM.

These runs were in 105* heat and about 6% humidity but IAT2 temps stayed under 150, which is where the tune is set to cut timing.

TIA

 

[SmokenGRA03]

To tune the car you need to tune the MAS AIR not the fuel!!!!!!!
What does the Mas Volts say? are you pushing 5.v????

 

[Silver03]

Nope, not even close, highest I saw was around 4.7V. TPS voltage stayed around 4.65 all the way through under WOT.

 

[Chonger]

If you peg the MAF sensor the car goes lean. That looks like classic belt slip to me. That explains the loss in power up top (drop in boost) and why the AFR goes rich up top.

What pulley set up are you running?

Are you running an idler pulley?

Have you datalogged boost on the dyno? I bet it takes a dump up top.

May want to get a new belt.

May want to use a smaller belt.

May want to get a new pulley.

 

[Silver03]

Thanks Chonger. This run shown is on a 2.93/4lb. Using an upper idler and the belt length puts the tensioner right where it is supposed to be. I was not aware that you could datalog boost, thats good to know, I'll take a look at that.

 

[Chonger]

2.93 upper with an idler should not slip. Is it a non slip pulley?

 

[Silver03]

Yep, BF non slip. I've had the pulleys for awhile and this is the third trip to the dyno with this combo. Again, never seen it do this before.

 

[Fast Willy]

If your pushing 5V on the mas air then your pegging your meter.

 

[Juiced-03]

If your pushing 5V on the mas air then your pegging your meter.

I doubt he would be pegging the MAF that early in the RPM range, especially on the Eaton. Maybe after 6000, but not before in my experience.

I would probably say belt slip, or maybe spark blowout?

 

[Silver03]

I doubt he would be pegging the MAF that early in the RPM range, especially on the Eaton. Maybe after 6000, but not before in my experience.

I would probably say belt slip, or maybe spark blowout?

Yep, only seeing about 4.7 volts max on the MAF. Good point on the spark blowout. Is there anyway to tell by inspecting the plugs if blowout is occurring?

 

[RJCobra]

Looks like belt slip. When the belt slips you get less boost and therefore less air, causing a dip in power and A/F ratio. I'm not sure spark blowout would cause the dip in the A/F

 

[orange2004cobra]

put in a set of new NGK TR6 plugs...
L.

 

[Steeda30]

I think it's belt slip, if you were pegging the MAF, the A/F would start tapering off on the lean side up top.

 

[imswheel]

You can monitor blow out by sharp spikes in A/F - everytime your plugs blow out it will go 'pig rich' as the unburned fuel blows thru - also look for fast little sooty puffs out the exhaust. (they can be hard to see) This will not typically throw a misfire code (p0300?) as the computer thinks it actually"sparked"

I vote that you have belt slip - maybe you have to long of a belt and that is why even with idlers it may be slipping.

Hope this helps.

Paul

 

[Silver03]

***Found the cause***

Cat Overtemp Protection is what was causing this. I knew it wasnt belt slip. :bash:

Thanks for the responses though, guys.

 

[RJCobra]

Cat Overtemp Protection is what was causing this. I knew it wasnt belt slip. :bash:

Thanks for the responses though, guys.

????

 

[RixSikcobra04]

deleted, didn't see that he found the cause. Most Excellent that he did!!