Dyno Run Running too Lean????? Graph attached

[1 Bad Snake]

Just got back from the dyno and my car is running an average of 14 A/F which is to lean. It is running this throughout the entire pull, it did dip down to about 13.8, but only once. Does anyone have any suggestions as to the possible culprit?

 

[Jason Heffner]

What mods do you have?

 

[Jack B]

The meaningful data is over 3000 rpm. The stock vipers seem to run in that 13.5 range. Both my Gen1 and Gen 2 ran approx 13.5 and started to slope down (richen) as the rpms climbed. Post your curve so we can see it.

 

[1 Bad Snake]

Unfortunately, I cannot scan the chart. The car is running right at 14.1 to 14.2 at 3000 and hits a best of 13.8 around 5200 rpms. This is somewhat consistent on all three pulls.

Jason,
I have headers, rockers, tubes and filters and 65mm throttle bodies and smaller pulley's. These are the mods that effect the power.

 

[Kurt 97 GTS]

Hey Dan,

I would sell that bucket and get a "real" Viper!!

 

[99 R/T 10]

What were your HP and TQ numbers? Gen I or Gen II?

Mike

 

[Jack B]

1 Bad Snake:

If it is Dynojet (Winpep), askyour shop for the file and email it to me. I have over 50 pulls on file I will compare it to mine and other some other vipers.

 

[Larry Macedo]

Do you know if the A/F reading was taken pre catalyst or post catalyst?

 

[1 Bad Snake]

Post Catalyst. I just went and dynoed again today and my A/F is worse. Our temp outside was 45 degrees and my best A/F was 14.3 just before 5800 RPM's. 3000 rpms started at 15 A/F and really didn't improve from there until about 4800 rpms. The result is a significant loss in HP and torque. My A/F reading is pretty straight accross no big peaks and valley's, starts at about 15.9 at idle and decreases from there to a best of 14.0 under full throttle.

 

[1 Bad Snake]

Here is a copy of the Dyno with A/F. The first run was a month ago, the last run was today as you can see my a/f was worse today. I changed plugs and checked wires, checked fuel filter, air filters, throttle cables and injectors all are fine. Please take a look and let me know if you see something to point me in a direction.

Dan

 

[Jack B]

The hp numbers are still not bad for Gen I. The torque numbers are a little low relative to the hp. The ten hp could easily be explained by dyno/car/temp variations.Remember max theoretical hp is at 14.7.

Check the fuel pressure at max hp. The fuel pressure pick up is on the rear of the drivers side fuel runner. You may have to take off the lower windshield fascia to attach the gauge. It should hold at 50-55 psi. If not look for an obstruction in either the fuel filter (easy to change) or the strainers in the tank (hard to get to)

 

[1 Bad Snake]

Thanks Jack,
I will try and check the fuel pressure this week. This was brought up in a conversation yesterday, and I am just looking for the right fuel pressure gauge. As far as the HP is concerned it was much hotter when I hit 411, and my torque number was over 500. As you can see my torque is way off, and with the addition of the rockers I should have gained more HP and Torque. Any other ideas would be appreciated.

Dan

 

[Jack B]

How about the wrong push rods or some out of adjustment rockers. I picked up a pressure gauge at NAPA. It has a 48" hose attached which makes it perfect.

I wouldn't look at the lean condition for the hp loss, your a/f is almost ideal for hp, although, not for reliability. I would also make sure the a/f sensor is a wideband and is installed in the forward O2 hole. The stock viper is going to run 13.5, you are a little high, but, that could be the variation in the sensor. You could also test compression or look for a bad/loose plug wire.

 

[99 R/T 10]

What brand of rockers did you install? Headers? TB's? There was a post awhile back that one individual picked up 40 RWHP with Rockers AND TB's. Don't know what to expect with just the rockers. I am going to add both in a couple of months with a before and after dyno to see results.
Mike

 

[phiebert]

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by Jack B:
Check the fuel pressure at max hp. The fuel pressure pick up is on the rear of the drivers side fuel runner. You may have to take off the lower windshield fascia to attach the gauge. It should hold at 50-55 psi. If not look for an obstruction in either the fuel filter (easy to change) or the strainers in the tank (hard to get to)

<HR></BLOCKQUOTE>

This interested me since I have a similar low HP (more like 342) and thinking maybe its the fuel pump. Pardon the stupid question but where is the filter and how easy is it to test the pressure?

 

[Jack B]

Simple - attach the pressure gauge and read at approx 4000 rpm, shut down, relieve the pressure into container and remove the gauge. Both my Gen 1 and Gen 2 read 50-55 psi @ 3000-5000 rpm's on a dyno. NAPA is good source for the gauge.

The Gen 1 pickup is behind the drivers fuel runner (back of valve cover under the cowl/fascia). Difficult but not impossible to attach without removing the fascia. The Gen 2 is on the passenger side fuel runner (valve cover inside/rear), that one is simple.