Corvette Z06 Forum banner

1 - 20 of 46 Posts

·
Registered
Joined
·
2,187 Posts
Discussion Starter · #1 ·
As many of us know, the "Pig Rich" question continues to rear it's ugly head with any of us sporting "Black Wings" on our '02's. I don't feel any loss on my car but it isn't broken in yet so who's to say? I thought I would pose the injector upsize fix with several "In The Know" types around and see what they had to say. I talked to TPIS, DRM and West Coast Corvettes and they all acted like I was nuts to suggest the injector swap.:roll: All three indicated that if the car is running rich, why would you need a larger injector? This response from guys who know far more about the subject than I do confused the heck out of me. I have read all of Jim Hall's posts on the injector swap. It seems to make sense to me. But as I said, they acted like I was nuts!! :-?

Hey 02Z06, have you been to the dyno yet?
 

·
Registered
Joined
·
2,187 Posts
Discussion Starter · #2 ·
Brian,
Your description of the mechanics of the problem is the same as all the others I've seen on the forum. I guess I just expected to get some confirmation from some of the shops around. I spoke with techs (makes you wonder) at all three places. This seems like the fix to me. :)
 

·
Registered
Joined
·
2,459 Posts
Well, if you're going to mod the car, you're going to need bigger injectors! So if you feel its a problem, put them in, and then make sure you mod the car to take advantage of it :)
 

·
Registered
Joined
·
327 Posts
Ok, what size injectors come on the '02 Z06's? Can I just put some 30# SVO injectors in and call it a day or will I need a re-program. I know going from the stock 24# injectors to 30# injectors on the LT1 F-bodies needed a re-program.

And I'm still not agreeing with the rich/lean deal.

So driving around the car is running lean from too much airflow. Then when it goes WOT, it runs rich to compensate. This makes sense, but why would the car not compensate for the leaness in the first place? If it can richen the car up enough at WOT (read more fuel needed at WOT) then it should be able to richen it up enough at idle and light load rpms...

I just got my '01 MAF to try on my '02 Z06 and see if it helps any. If not I'm still waiting for the MAFT with the correct plugs on it to come out :)
 

·
Registered
Joined
·
2,459 Posts
I don't think the engines are actually running lean when you're running around town. The trims are on the lean side however. So when you are closed loop around town, your mixture is actually correct (well, according to what the PCM is programmed to want), but the trims are telling the open-loop side of things that the closed-loop side is needing to add more fuel to get the mixture straight.

The open-loop then says, "hey, we need all this additional fuel for just toodling around town, we're going to need a SHITLOAD more for WOT," and richens the hell out of the mixture.

Ok, so thats just what I've understood about whats going on, maybe someone with actual tuning experience can verify this one way or another.
 

·
Z06 Maniac!!
Joined
·
1,541 Posts
Tom, TPiS and DRM are both premier C5 engine tuners. DRM does its own PCM tuning and is the one that first analyzed the pig rich condition. I would tend to believe their analysis. They programmed out the rich condition in the PCM. The MAF translator, as I understand it, can richen or lean the a/f ratios, but does so by what is in essence a "tricking" of the PCM. I don't know which is better or if bigger injectors help, but I do know that PCM tuning will work and will get additional hp over and above that which is lost by the pig rich issue.
 

·
Registered
Joined
·
1,590 Posts
I am now convinced that 30# injectors will likely be needed on my '02 and will probably take this step after I select/install headers in about three months. BTW, I did pop a MIL light in my Vortex equipped car about two weeks ago on a very chilly night (30s) and with aggressive driving. I figured that the lower temps, very low humidity, maybe higher O2 content of air, combined with the increased volume of cold intake air, caused the MIL to activate. I did the reprogram, and no probs since.

Now, as far as the injectors, it seems you can go with the Ford SVOs (choking here as I spell the F word) or with the RC injectors at a much higher price. I suspect there are differences between these two injectors other than just price. What are they and are they worth considering when replacing the injectors? It seems that the RC units are better quality and perhaps put out a superior spray pattern - at least that is what I glean from the RC web site. Sure some of their stuff is ad hype, but then again, I have never heard anyone say that RC was not on top of the injector game.

Thoughts - comments??

:D
 

·
Registered
Joined
·
467 Posts
How about just running the '01 Z06 injectors... GM part, dealer would never know the difference, probably wont need a reprogram... But it would be a lot of work only to go from 24lbs to 26lbs injectors :(
 

·
Registered
Joined
·
1,321 Posts
Or, if you wanted to do that you could go with the 99 injectors which were 28.5 lbs. Or you could get the GM/Delphi injector for the buick GN which is a 30# injector.
 

·
Registered
Joined
·
26 Posts
Here’s my theory of the observed rich condition.

An inertia wheel dyno provides a single load which does not simulate real world conditions for a computer controlled engine which makes dynamic load corrections to timing and A/F ratio.

The drums on a 248 are sized for up to 1200hp, a condition the PCM simply considers an extreme high load situation which it guards against detonation my going rich.

Consider what the PCM is dealing with on the dyno. The vehicle is running at a constant 2000rpm, with the drums storing the energy so the PCM thinks it is at a no load condition, delivering near 0 rwhp, it’s running in a stable lean condition. Upon going to WOT in 4th gear the load is extreme, it’s similar to dropping the rear wheels off a jack at 2000rpm in 4th on a steep hill. It’s a situation that the PCM is not tuned for, the assumption is that the driver will downshift to a reasonable gear.

This might explain why the numbers on a Mustang dyno are higher, the load is set correctly, and the over-rich condition probably does not occur.

It would be interesting to check the A/F ratio on a Mustang or other load controlled dyno, or simply run on a 248 in 2nd gear or on a 224 which is sized for 500hp.

Tuning the PCM with a 248 likely will not give ideal result on the actual road for any reasonable load situation.

Changing to the 30lb injectors is a good plan if it’s near 100% duty cycle.

I was considering buying a 224 or 248, so I’ve done a little research. Instead, I’ve decided to use a datalogger (not a g meter) on the road which plots the hp/tq curves under real load conditions with instruments to measure weather and inlet air temp.

Again, this is just my theory, no practical data to back it up.

-Len

:)
 

·
Registered
Joined
·
2,388 Posts
ZO SIC said:
Ok, what size injectors come on the '02 Z06's? Can I just put some 30# SVO injectors in and call it a day or will I need a re-program. I know going from the stock 24# injectors to 30# injectors on the LT1 F-bodies needed a re-program.
Of course your going to have to reprogram. The fuel maps at WOT are based on the engine's intake, exhaust configuration AND what injectors are in it.

If larger injectors are installed and the same pulse duration is sent to it by the PCM, then its going to flow alot more fuel. Trying to perfectly match the required WOT A/F ratio by just changing injectors with no remap would be impossible.

Obvioulsly, if the thing is running rich already, its not the size of the injectors thats causing the problem ... its the control of the injectors by the PCM. If the C5's PCM is able to 'learn', them maybe after driving for awhile with alot of WOT action will correct the trim tables to the correct settings.
 

·
Registered
Joined
·
1,590 Posts
EB0206 - neat and provocative post, but with absolutely no data for my position either, I must disagree.
(1) I continue to believe that the dynojet is the most accurate chassis dyno because the numbers it produces are pretty close to the manufacturers ratings for the many different cars I have seen tested. My own '02 (see dyno section) tested on a 248c at 357.5 rear wheel h/p or using the commonly agreed upon .85 ratio - 420.5 crank h/p running on Sunoco 93, and using a Vortex Rammer and Bridge. That number appears reasonable considering the mods and rated h/p on an extremely low mileage engine. Of course, as has been stated repeatedly elsewhere, all dyno results need to be looked at in a relative fashion. My modified '93 ZR-1 put out notably different numbers between 2 Dynojets under nearly identical atmospheric conditions. However, having tested on several different dynojets, I believe that is the exception, not the rule. That said, the average Mustang dyno results appear consistently higher to the point (for me at least) of exaggerating power. of course, there is nothing wrong with measuring relative gains on the Mustang.

(2) I suspect that the dynojet drums are very carefully balanced and their test procedures designed to ensure that such an obvious flaw that you are speculating about would have been accomodated long ago. After all, PCM equipped cars have been out there and tested for at least 15 years now.

As for my earlier question - anyone care to comment on the RC injectors - and why they are so much more expensive - what if anything is gained by using them?

:)
 

·
Registered
Joined
·
2,388 Posts
If you think that the unrealistic load of the dyno is effecting WOT A/F (which is hard for me to believe, because I'm not sure if the C5's PCM can detect load as such), then rig-up an onboard O2 sendor on the car and go do some tuning on the road :D.
 

·
Registered
Joined
·
2,388 Posts
EB0206 said:
I was considering buying a 224 or 248, so I’ve done a little research. Instead, I’ve decided to use a datalogger (not a g meter) on the road which plots the hp/tq curves under real load conditions with instruments to measure weather and inlet air temp.

Again, this is just my theory, no practical data to back it up.

-Len

:)
So, just how do you measure RW torque on the road. Did you install an accurate torque sensor in each of your axles? This one is new to me :)
 

·
Registered
Joined
·
2,388 Posts
EB0206 said:
Consider what the PCM is dealing with on the dyno. The vehicle is running at a constant 2000rpm, with the drums storing the energy so the PCM thinks it is at a no load condition, delivering near 0 rwhp, it’s running in a stable lean condition. Upon going to WOT in 4th gear the load is extreme, it’s similar to dropping the rear wheels off a jack at 2000rpm in 4th on a steep hill. It’s a situation that the PCM is not tuned for, the assumption is that the driver will downshift to a reasonable gear.

Again, this is just my theory, no practical data to back it up.

-Len

:)
Do you think the PCM really has the ability to determine how much torque is on the rear wheels? Humm. I know of no such system.

For one thing, in order to keep the dyno drum rolling at a constant speed once its inertia has been spun up, the throttle would have to be feathered way back ... just like on the road if you where cruising at 2000 RPMs. Then all of a sudden, the throttle is hammered WOT ... this also happens on the road. The only difference past this point maybe the rate at with the engine revs to redline. If the dyno has more inertia than the car would accelerating downt the raod, then it will take longer for redline to be reached. Its hard for me to believe that the FI system is capable of telling if the car is on a dyno or on the road.

If this was the case, then theoretically it would also run too rich on a brake dyno since that type of dyno is capable of applying a load to the rear wheels to hold the engine RPMs to what ever you want at WOT. It would be like going up a super steep hill on the road, or pulling some huge trailer behind you at WOT.

If someone can come up with how the car could sense road load and if it adjustes the WOT A/F because of it, I'd sure like to know :D.

:cheers:
 

·
Registered
Joined
·
26 Posts
Hi BLEUBYU ,

I agree, the Dynojets are extremely accurate for fixed weather
conditions (the drum weight is controlled), but they only work for WOT testing.

The Mustang dyno's have many more sources of error, but
can adjust the load, they may very well be optimistic.

The mfg's need a wide range of load conditions and use
dyno's that cost 10x a 248c. Only they know the true driveline
losses.

Empircially, you've proven the info on your ZR-1 which is great.
I believe the ZR-1 ECM is not as sensitve as the Z06 PCM (low emission tuning and more sensitive KR) and doesn't exhibit the over rich condition.

I still think a Z06 shouldn't be tuned for WOT on a 248c.
The experiment would be fairly easy, just do a run in 2nd gear
and log the A/F ratio or as ZeeOhSix points out drive it with
an in-car A/F ratio meter ( I don't know of an accurate portable one, the sensors alone are $1k, but I'll check into this). Using a scan tool on the O2 sensor while driving won't help either, at WOT it will either just read rich or lean.

ZeeOhSix,
The PCM probably knows it in an unrealistic load condition.
WOT, no vacuum, low air flow for throttle angle, rpm slowly increasing. (Once LS1edit is completed we'll know for sure).

To measure torque and the rate it's delivered, a datalogger
time stamps the rpm by connecting to the coil or plug wire.
Knowing all the vehicle parameters, Cd, frontal area, weight,
tire diameter, overall drive ratio and weather conditions, HP and
torque are computed, producing the same type graphs as
other dyno's. Absolute accuracy is based on the parameters
and not having tire slip. Again, driveline loss must be estimated.
If it doesn't rain all weekend, I'll collect data and post an example.
There are a lot of these systems on the market, and I really
wouldn't endorse the one I have without more data. There's one
advertised on the "other" forum with a lot more capabilites (and cost) than the one I've got.


-Len
 

·
Registered
Joined
·
803 Posts
EB0206 said:
Consider what the PCM is dealing with on the dyno. The vehicle is running at a constant 2000rpm, with the drums storing the energy so the PCM thinks it is at a no load condition, delivering near 0 rwhp, it’s running in a stable lean condition. Upon going to WOT in 4th gear the load is extreme, it’s similar to dropping the rear wheels off a jack at 2000rpm in 4th on a steep hill. It’s a situation that the PCM is not tuned for, the assumption is that the driver will downshift to a reasonable gear.

I was considering buying a 224 or 248, so I’ve done a little research. Instead, I’ve decided to use a datalogger (not a g meter) on the road which plots the hp/tq curves under real load conditions with instruments to measure weather and inlet air temp.
:)
An easy way to check your DynoJet theory might be to run a little brake during the 2000 rpm steady state condition to simulate load then swap feet to make the pull. You could also do this in 2nd gear to reduce the load.

Also, what data logger are you considering and with what sensors?
 

·
Registered
Joined
·
803 Posts
ZeeOhSix said:


If someone can come up with how the car could sense road load and if it adjustes the WOT A/F because of it, I'd sure like to know :D.

:cheers:
I think the usual way for a PCM to sense load is MAP, TPS, and rpm.
 

·
Registered
Joined
·
568 Posts
The ECU definitely has the ability to determine how much load is on the engine. It has quite a bit of sensor data available to track this (beyond the old standby's that Roger mentioned).

Check out the parameters available for monitoring here:

http://obd2.com/scantool/cardata/obdiigeneric.txt
http://obd2.com/scantool/cardata/gm2powertrain.txt

There is an extremely sensitive system to measure crankshaft acceleration in response to the firing of each cylinder. It is part of the misfire detection system. I think this is the "18X crank sensor".

Unfortunately, Dynojet doesn't disclose the 'equivalent mass' of their dynos. That seems like a silly thing to keep 'proprietary'.

I think you will see a wide range of loads in 4th and 5th gear. Consider the 140+ mph case. *Lots* of aero drag load.

I've played around with using mph vs. time to calculate torque. One challenge is an accurate input source. I haven't found RPM to be as interesting due to traction issues (6-10% slip) and noise. I've also had trouble finding enough *flat* road, steady or no wind, etc. I look forward to seeing your results, Len.

I bought EASE PC for scanning my Z06 a couple weeks back. I've played with it a bit and it is very nice. But I've been too busy enjoying the car to scan it much :D
 

·
Registered
Joined
·
26 Posts
ZeeOhSix,


--------------------------------------------------------------------------------

Do you think the PCM really has the ability to determine how much torque is on the rear wheels? Humm. I know of no such system.

--------------------------------------------------------------------------------

Yes, as Roger Ramjet said, MAP, TPS, and rpm.


--------------------------------------------------------------------------------

For one thing, in order to keep the dyno drum rolling at a constant speed once its inertia has been spun up, the throttle would have to be feathered way back ... just like on the road if you where cruising at 2000 RPMs. Then all of a sudden, the throttle is hammered WOT ... this also happens on the road. The only difference past this point maybe the rate at with the engine revs to redline. If the dyno has more inertia than the car would accelerating downt the raod, then it will take longer for redline to be reached. Its hard for me to believe that the FI system is capable of telling if the car is on a dyno or on the road.
--------------------------------------------------------------------------------


Cruising on the road at 2000 rpm will be somewhat different.
It takes considerable fuel and throttle opening to maintain 2000
rpm in 4th (aero-drag and driveline loss).
The last stored PCM fuel table value will be for part throttle vs.
no throttle. This is probably enough to prevent the over-rich
condition from being dialed and locked in. From there, the
WOT time to redline is completely different on the 248, and
it might be inducing more KR than would occur on the road.

Only if the clutch is broken, would someone creep up
a steep hill in 4th gear at WOT.

For a brake dyno, the load is set, and hopefully not for 1200hp.

Roger Ramjet has a great idea, load the engine with the brakes
before going WOT. Maybe someone can try this.

The datalogger I have is Road Dyno, with inductive pickup.
Believed repeatability is +/- 3hp and I think there was a
factor to use to make it match up to a Dynojet.

-Len
 
1 - 20 of 46 Posts
Top