V Notch Displayed

[Jack B]

The two curves are a stock Gen 1 (red) and a modified NA Gen 2 (blue). I have over 15 similar pulls that show the same notch. The curve below shows a 100 hp notch. That is the max I have seen. The typical notch is more like 20-50 hp and typically falls between 4000 and 5500 rpm's.

I can say this, the notch absolutely disappears when stock timing is used over 3500. If anyone posts comments relating to timing please give the absolute value over stock where the notch appeared or disappeared. All the cars where I have seen the notch have had 94 octane in the tank.

What is totally baffling is the inability of the four cars in my knowledge base to run at all on the Roe generic enhanced program that Sean supplies with the VEC2. Sean has been more than helpful and is trying to solve this issue, therefore, there is no reason to believe he is anything but honest as it relates to this problem. The VEC2 is an extremely useful tool, this problem has to be solved.

 

[KenH]

Looks like you also have a similar, but smaller event at about 2200RPM.

Do you feel that the momentary lean condition that occurs during the event is actually an overly rich condition with raw gas hitting the sensor? If so, it kind of fits the scenario in the post about shooting flames on the dyno with a SC/VEC2 setup with a stuck injector or lost spark.

http://vca2.viperclub.org/forums/showflat.php?Cat=&Board=UBB14&Number=436263&page=0&view=collapsed&sb=5&o=&fpart=1

 

[Miles B]

If I were you, I would try to get an oscilloscope with data capture, and capture the voltage across each injector during a run. This will rule out, or reveal, if injectors are staying shut or open.

 

[Tom F&L GoR]

If the 100 hp quantity is valid, it must be more than one cylinder.

I don't know the VEC 2 well enough to know the answer to this: is the fuel injection timing such that it can spray through an open valve? (Fuel triggering off by 360 degrees?) I believe most OEM systems are against closed valves to avoid wetting the plug tips.

 

[Jack B]

Tom:

explain what you mean by "against a closed valve". How what that stop wetting the plug.

This is definitely not a bad injector. All four cars wouldn't just have a bad injector, plus, my car did it with stock injectors and did it with new 50 lb injectors and new clips. A PCM or VEC induced injector error is another issue.

The 100 hp event was by far the worse case, most events were 20-40 hp. You can feel it and hear it when it happens. As far as the temporary lean condition, it could be raw fuel hitting the O2 sensor or just a plain misfire which adds the air from the misfire, therefore, showing temporarily lean. The three Gen 2 cars had the O2 sensor in the OEM forward well. The Gen 1 had the tail pipe sniffer.

 

[Tom F&L GoR]

Jack, again, I am not familiar with OEM settings and certainly not VEC 2 characteristics, so I could be all wet.

OEM sequential fuel injector timing is such that the fuel is "injected" while the intake valve is closed (not open.) It forms a puddle in a doughnut shape while sitting just above the valve seat. Fundamentally, there are two reasons; the fuel is somewhat heated and vaporized while sitting on the warm valve (better emissions and fuel economy) and often the fuel spray direction, although in a fine mist, can wet the spark plug gap or the far side of the cylinder wall if shot through while open. The latter phenomena can cause interesting lubricant problems because the fuel hitting the wall constantly enters the oil.

Where I was going was if the fuel injector timing with the VEC 2 was such that the trigger was one crank revolution off. If it's not specified as to what is the appropriate trigger signal, then the problem could randomly show up depending on which signal is chosen. The fuel would be sprayed through an open valve (possible?) and at WOT and high RPM, the large volume would have a large liquid content and find it's way to the plug gap, quenching the spark... All of this does assume injectors and plugs are working well.

It would kind of fit the situation because you see the result of a no-burn, where raw fuel in the exhaust shows lean.

 

[Sean Roe]

We're doing everything we can to capture this phenomena and determine the cause.
We've been running the Gen3 on the dyno recently and it's not doing this.
So, I'm kniocking the boost down to 5PSI on the GTS so we can just beat the heck out of it on the dyno until it will produce the V. If we can get it to do it, we can capture it with the oscilloscope with logic probe and VEC2 logging.
It will be solved.

 

[Joel]

This is a very interesting post, as an uninvolved observer, I'll be keen to see the outcome.
And good info from Tom.....thankyou

 

[Custom Builder]

Very interesting indeed, as I am about to purchase a 5lb Roe and a VEC2.

 

[Miles B]

With speedy and willing support like that, I wouldn't hesitate to buy

Rare these days.. just ask ab

 

[txlen]

sean...did you look at the tune i sent you for the N/A car??..that one has never missed a beat since i did it after we talked...Len

 

[Jack B]

Tom:

Interesting - please expand your last explanation, how could there be a random error if sync'ed to the cam or crank rotation and why would it only exhibit itself when timing was added over oem timing.

 

[Jack B]

Bump - Tom waiting for a reply

 

[Tom F&L GoR]

Sorry I missed your question. And I think this might not be it, since you can make it come and go with just timing.

Originally I was looking at the V notch as not random and thinking from there. I was also assuming that the VEC2 could be wired so that the injection timing was 360 degrees from OEM. I don't know if this is possible.

At small fuel volumes, spraying through an open valve creates a short "snake" of fuel through the opening. At larger volumes, the "snake" becomes longer and the tuning dynamics of the intake system may steer it differently. Based on volumetic efficiency, the snake could be moved to and then away from the plug.

Years ago Texaco worked on a multi-fuel capable engine (what would now be looked at as a crude version of a GDI system.) One component was a snail-shaped intake port that brought fresh air in a rotating manner (swirl rather than tumble) to the plug area (and a fuel injector in the cylinder aimed at the plug delivered the fuel.) Unfortunately, the intake port could only be designed to operate well over a small RPM range, about 2/3 that of the equivalent gasoline engine. The takeaway was that you can get extremely stratified intake charge conditions, certainly if you want them, sometimes even if you didn't.

The Texaco work and the OEM developments to create the most homogeneous charge possible were what led to to ask about fuel "conditioning" and how it was entering the cylinder. With the large power loss, you would think it's easy to find, but I know it's not always.

 

[Jack B]

Thanks Tom - Lets go guys, lets get to the bottom of this

 

[Sean Roe]

Re: VEC2 V notch

Hi Everyone,

Thanks to a little testing assistance from Ken and Jack, I think we're close to wrapping up the cause and correction for the V notch. Until we try the change on another couple cars, I reluctant to say that it's 100% fixed, but we're getting there.

If it works out that we've solved it with this change, I'll go into some detail about what we did. If this "is' the fix, everyone will be sent a VEC2 update along with the software and connector for logging from the VEC2 at the same time.

Ken, I'll be sending you a package Friday so you can test what Jack did.

Jack, let me know when you need the files for the other VEC2's in your group.

Thanks guys.

Regards,
Sean