Dyno run...car too rich?

[MoparMan]

Got the car dyno'ed at our club's dyno day and the peak numbers were a little less than I expected. The car seems to be running very rich per the A/F plot. A dump of the params in the PCM shows that the PCM is adding 3% to 5% fuel across the board. Is this an issue that is arising from a bad sensor or such or will I have to correct it with a VEC2? BTW: the car has an Arrow rebuild on the engine, Belanger headers, no cats, Mopar Performance cat-back exhaust and smooth tubes/K&Ns.

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[Joseph Dell]

Will prob need a vec2 to correct. definitely a little rich, but not as bad as some. the stock PCM is pretty safe for all around the country (altitudes and weather). add a VEC2 and you can fine tune quite a bit. plus the VEC2 will let you add some timing...

just my .02...

JD

 

[Jack B]

WOT is open loop, the O2's are not active, therefore, it is not a sensor issue. How do you know what the PCM was doing - your reference to adding 3-5% fuel. What was the exact text description that led you to this conclusion. Is is possible you are referring to the adaptives?

The VEC2 can correct the a/f. You are about 10% too rich, therefore, the Vec would have to pull about 10% of the injector pulse, if you are at 15 mSec pulse, you would have to pull 1.5 mSec, that is a bunch.

Another issue is the way the hp drops off after it peaks, if you were still at wot the hp shouldn't drop that quickly. I would want to know if the operator partially pulled out of the run early. My car logs throttle position and several times the operator has unknowingly eased up on the throttle as he approaches his rpm cutoff. This would also force the car to appear richer than normal.

 

[Schulmann]

Yes it is really rich.
Your viper recalls mine, I had some similar issues.
The 2000 PCM is not the best one. I had to get a 96 pcm.
The 00 PCM might modify inversely the fuel pulses.
My Viper was running piggy rich too.
00 PCM might also add way too much fuel in certain conditions. Maybe a local Dodge/Viper dealer can reprogram your PCM. I know that some dealers have the righ software to do so.

Do you have cat sims ?
What was the intake's temperature during the run ?


Regardless the AFR, try to use a better fuel and check your plugs and ignition. Your torque curve should be smoother. It is too much uneven. It is maybe an ignition break down. 00PCM is notorious for this. Have a look on the Dyno chart under my pictures. Your chart should look as smooth as mine. You can also try to add some new grounds to your Viper. 00 PCM is weak regarding grounding. A good place is the MAP sensor's ground.

Before you install a VEC2 try to find the root cause of this trouble. The VEC2 will only hide it. This problem is too much strange to install right away a VEC2.

There is some work to be done before you push this Viper.

 

[plumcrazy]

definetely get the VEC2 from sean

 

[Jack B]

Schulman Said:

What was the intake's temperature during the run ?
Regardless the AFR, try to use a better fuel and check your plugs and ignition. Your torque curve should be smoother. It is too much uneven. It is maybe an ignition break down. 00PCM is notorious for this. Have a look on the Dyno chart under my pictures. Your chart should look as smooth as mine. You can also try to add some new grounds to your Viper. 00 PCM is weak regarding grounding. A good place is the MAP sensor's ground.

Before you install a VEC2 try to find the root cause of this trouble. The VEC2 will only hide it. This problem is too much strange to install right away a VEC2.

There is some work to be done before you push this Viper.

Lets not get carried away:

1. "What was the intake's temperature during the run ?" This is meaningless since the correction factor (SAE) will off set the temperature. Maybe more important is the coolant temperature.

2. The curve is not "as smooth as mine". There is nothing wrong with the curve itself, I can post dozens (perhaps hundreds) of curves that are similar from different cars. The only issue with the curve is the hp past 5300 and whether the operator pulled out before the end and killed the power. Turn your smoothing to 1 and see how it looks.

3. "It is maybe an ignition break down". There is also no indication of an ignition problem.

4. "This problem is too much strange", there is nothing strange about this curve.

In summary, the HP is close to where it should be and he will pick up a bit more by pulling fuel and adding timing just as JD said. The VEC is not a bandaid because there are no major problem displayed on this curve.

I wouldn't normally post contrary to a fellow viper brother, but, when someone asks for help he shouldn't get bad information.

The shepard cried wolf once too often and in the end no one would listen to him.

 

[MoparMan]

Thanks for all the responses.

Jack B - yes, those are the adaptives so they are not in effect at WOT but I thought that info might be useful anyway. Our Viper tech pulled those figures out with the scanner.

I don't think the operator bailed out early. the operator was Garth Weaver who is very familiar with dyno'ing Vipers. He's got a Viper shop here in town associated with Underground Racing, who just put the finishing touches on his mid 8 second twin turbo GTS. We were both a little surprised at the numbers the car put up and were expecting about another 10 to 15 rwhp. All in all, the top run translates to 503 flywheel hp (assuming a 15% parasitic loss through the drivetrain).

Also, the car has the O2 sims on it to keep it from throwing codes.

Sounds like the VEC2 is going to be the way to go. I just didn't want to jump in for a grand plus tuning until I was sure that there wasn't something else wrong with the car.

 

[Schulmann]

Schulman Said:

Lets not get carried away:
Agree with you however I have been in exactly the same situation ... I have just described what I have tried to do before concluding that I had a poor quality PCM on my viper.

1. "What was the intake's temperature during the run ?" This is meaningless since the correction factor (SAE) will off set the temperature. Maybe more important is the coolant temperature.
Coolant temp will stay the same if the cooling system is running perfectly. However the intake temp will go up from 110F to 170F during the dyno run.
That can induce the PCM in error. There is a bug in certain pcms. At higher intake temperature instead of removing fuel the pcm adds fuel.


2. The curve is not "as smooth as mine". There is nothing wrong with the curve itself, I can post dozens (perhaps hundreds) of curves that are similar from different cars. The only issue with the curve is the hp past 5300 and whether the operator pulled out before the end and killed the power. Turn your smoothing to 1 and see how it looks.
Unless the operator has Parkinson the curve should be smoother.

3. "It is maybe an ignition break down". There is also no indication of an ignition problem.
You are right I was guessing. On a NA Viper this might not be as visible as on a SC Viper. Mine had 100% same sympthoms so I guessed this Viper has the same troubles.

4. "This problem is too much strange", there is nothing strange about this curve.

In summary, the HP is close to where it should be and he will pick up a bit more by pulling fuel and adding timing just as JD said. The VEC is not a bandaid because there are no major problem displayed on this curve.

It is not major trouble but it is a trouble. Do you know why this Viper runs so rich ? I have tried to mask the issue too. Ended up having an abnormal ignition and fuel map. Finally I switched to a 96 PCM.

I wouldn't normally post contrary to a fellow viper brother, but, when someone asks for help he shouldn't get bad information.
There is nothing bad. It is good that you give your opinion. I like to read your advises. Usually you are right but in this cas, I think your diagnosis is not as accurate as usually

The shepard cried wolf once too often and in the end no one would listen to him.

 

[GTS Bruce]

Looks just right for your mods.Identical to mine.GTS Bruce

 

[Jack B]

Schulman:

see reply above from GTS Bruce.

We can now let MoparMan get his VEC and pick up another 20 hp.