Dyno issue with Vec2 and IAT

[2001 GTS]

Went to the dyno to try to tune the heads/cam and am running into issues.

The car won't take any fuel out above 5000rpm. The VEC2 ranged from +10 in the fuel load to a -50 without any change to the AF. (2.4ms added in the MS table from -3 to 0). With no change.

Called Joe Donovan and he said something about the IAT getting too hot, but the airbox after the pulls was not very warm.

Two back to back pulls netted a gain of 20rwhp from 3000-4000 for one pull but after 4k it was the same for both.

Does this sound like a IAT problem? Is there a speed density compensation?

 

[Joseph Dell]

Is this an old VEC2 or a new VEC3? PBJ is spot on about the IAT issue. although 2.4ms isn't hardly anything, playing with more might help. with the IATs, it confuses the VEC and was known to create a V-notch back in the day.

How many runs did you do and how long did you wait between them before this issue cropped up?

JD

 

[Schulmann]

I have had some very similar issues. I have some questions for you:

What year is your Viper ?
What boost do you run ?
How many dyno runs did you do when this issue occered ?
What was your head temperature ?


Backup in 2004, I had to use a very unconventionnal RPM/Fuel chart. Above 4000rpm I had to cut by nearly half the fuel. Sean was stunned by the graph. Later we found out that the issue was related to my PCM. I had to use a new 1996 PCM (It is on sale in the classifieds).


Yes the AIT is a little challanging after 10-15 dyno runs ... after 10 runs let the engin cool down a half an hour. You can lean out the AFR but your chart will be useless on the street. Tuning on dyno is not the best thing. The better is to have two WBO and tune the car on track or hwy. That give very accurate fuel and ignition charts.


Another issue that I encountered is that under intense heat the VEC2 is not working properly. Actually on one side of the car it stops from altering the fuel (slave or master I don't remember). It occures very suddenly. There is no way to reduce the fuel because the slave or master side is dead. The VEC2 will let the fuel and the ignition signals run through. So you Viper will run very rich (9-10 AFR) I noticed some sort of electronical interferences. We never managed to fix the issue. The possible corrections are: let the engin cool down for an hour. Plug your laptop into the VEC2's serial cable. Having the serial cable pluged into a laptop eased this issue in many situation.


When the Gen2 Viper engin gets very hot, strange things happen. I think one of the causes is the VERY poor grounding of the entire electrical system. I don't want to be harsh but the engineer who designed the old PCM must have missed a couple of classes at the University. I think there are a couple of ground loops between the 3-4 grounding points. I believe the engineer wanted to reduce the number of grounds to avoid ground loops but ended up having weak grounds and ground loops too. There must be a bad diod that lets the current/ground pass when it heats up.



Sometimes "soft industrial spying" is not a bad thing. If I was the Chrysler's president I would right away prevent Chrysler engineers from owning a Chrysler car. I would force them to own a Nissan, BMW or a Mercedes and would force them too to do the maintenance on their cars. Japon auto industry's strenght comes from the fact that many *** engineers owned/owns foreign cars. They learned things from these cars and improved them before implanting them on their products.

 

[2001 GTS]

This is a VEC2 with the latest VEC2 updates, but not with the VEC3 update

We did about 10runs the first run was around 14.0, so we richened it up and saw results after run 2 and 3. But after that, the a/f didn't move at all no matter what the change, just went rich after 5000.

There was only five minutes between each run.

No v-notch problem at any time.

But 2 runs had a weird miss so we took the timing advance out, so the last runs were with stock timing. No different results here either.

 

[Schulmann]

Your case looks very similar to my issues. Be very carefull not to blow up your engine. Dyno is tough on the mecanic.

• As a start call Sean Roe and ask his help. He stands and supports firmely his products. It is beyond your imagination how much he helped me.
• Try to change your PCM to an older one
• Have a look on your grounds
• Get a clean ground for the VEC2. Make a single ground for the VEC2 into the frame just below the brake's master cylinder. Don't use the PCM`s ground.
• Get a clean and stable +12V alimentation for the VEC2. Use the the source just beside the fuses.

 

[2001 GTS]

I have a Roe PCM on the car as well.

I'll be calling Sean tomorrow for sure.

But the additonal ground will be done right away.

Thanks,
Steve

 

[Sean Roe]

Went to the dyno to try to tune the heads/cam and am running into issues.

The car won't take any fuel out above 5000rpm. The VEC2 ranged from +10 in the fuel load to a -50 without any change to the AF. (2.4ms added in the MS table from -3 to 0). With no change.

Called Joe Donovan and he said something about the IAT getting too hot, but the airbox after the pulls was not very warm.

Two back to back pulls netted a gain of 20rwhp from 3000-4000 for one pull but after 4k it was the same for both.

Does this sound like a IAT problem? Is there a speed density compensation?

The only question I have is, did you log the runs with the VEC?
The log file will show you what is happening with the injector pulse and answer the question you have.
I suspect, being a heads and cam package, you may be using the stock MAP sensor for input and not have a value in the fuel load table at the vacuum area where the engine is running. If the Fuel load value is 1ms and you add 100%, you'll add 1 ms. If the value is 0 (due to vacuum increasing as the RPM rises with a heads / cam car), you'll change nothing.
The log file is the key to answering your question. The answer is a guess without it.

Regards,
Sean