dyno results and A/F ratio anomally

[valentine_viper]

I dyno'd my '04 Viper today. Conditions were 75 degrees, 29% humidity, 30.01 barametric pressure at 65 feet above sea level. Car is 100% stock right down to the air filters. This was on a Dynojet.

Peak rwhp was 442 and torque was 482.

The numbers were good, but we did find a surprising anomally in the A/F ratio. Between 3000 and 3600 rpm, the A/F when very lean (although not quite lean enough to be dangerous) and then went fat for the rest of the run. The lean spot caused the torque to dip by 80 lb ft and the hp to take a similar dip. After that, the curves were smooth as would be expected. I understand that these are tuned from the factory to run rich in order to keep the cats running cool (good for longevity, bad for power), but don't think the dip is normal. We made 4 pulls and the dip was consistent through all of them. Surprisingly, I don't really feel this when I'm driving. The car does seem a little soft on the bottom end, but you can't feel a dip or stumble. I did get a couple of backfires the other night while doing some spirited driving. Perhaps becuase of the lean spot?

Has anyone else encountered this?

May send the computer to DC Performance for a reflash.

 

[Viper X]

Good idea on the re-flash. This doens't sound good. DC will do a good job for you.

Dan

 

[Dave T (BADVENM)]

I believe that there is a "natural" dip in the curve and as you say smooths out thereafter. My '04 SRT Ram did/does the same thing. The DC flash will remove this portion of the curve...lessening the threat of the lean condition.

 

[Joseph Dell]

Check to make sure that the _dip_ isn't a misfire. when the car misfires (especially a consisten misfire, ala the VEC2, for example) it will be reflected in erratic A/F readings.

Of course, that shouldn't happen on a stock car...

JD

 

[ViperGMC]

Talk to me about the VEC2 misfire???? I would like to hear more

 

[Joseph Dell]

do a search, for sure. But there is, basically, an issue where at somewhere between 4800 and 5400 rpm the car would misfire. It was always blamed on other things, but it turned out the problem is the VEC2. Some cars have never gotten out of the problem, even when replacing the PCM. Worse, the problem would be intermittent. Sometimes only when the car is hot. Other times at random intervals.

Some fixes have been noted as:
- install a resistor on the IAT signal
- replace stock PCM (especially 2000-2002)

But they don't always work. there are some cars that have _never_ gotten rid of the problem.

The "blame" for the problem has been passed to many things, but ultimately there is an issue w/ the VEC2 that sometimes rears its ugly head.

Try the SEARCH button for more info... lots and lots...

PM me for more info if you like.

Personally, I like tuning on the VEC2. Sometimes it is hard to trust, though...

JD

 

[plumcrazy]

valentine_viper, buy a VEC2