travisnd

Took the car over to All Aspects for a fresh NASA verification dyno. I last dyno'd summer 2010. This winter I swapped the OEM intake for a Halltech filter and deleted the cats. I also converted to a single Spal fan.

The car's air/fuel was very erratic on the dyno. The first pull it was lean at 13.6:1... figured that might be the case with the intake/cat delete w/o any tuning.

Tuner is Ed Hutchings who is the best in the area and has tuned 4 C5s for me... we figure it'll be an easy fix to fatten it up to account for the mods. As Ed starts making changes the car isn't reacting to them properly. He's making small changes and the AFRs are going way rich in the 10s or way lean into the 14s.

First we suspect bad wideband. We have the wideband in the driver's side rear O2 bung (I have both rears gone). We put a 2nd in the tail pipe and it matched the one in the car so not the wide band.

Then Ed put it in speed density to take the MAF out of the picture. Car is still acting up. I decided to put fresh gas in it as the car had 3/8ths of a tank and it was gas I had put in at Road Atlanta in December. I put 10 gallons in and it was like magic. The AFRs became consistent and the car was reacting to the tune changes properly. Ed dialed it in in SD then turned the MAF back on and dialed that in.

We had the car making 368-371 rwhp with a 12.6:12.8 AFRs consistently. Then we let the car cool off some to make the 3 back to back to back pulls required for the new NASA dyno procedure.

The first two pulls the car was a 1/2 point richer running 12.0 to 12.3 AFR and made 365 each pull. On the 3rd pull the car went way rich into the high 10s and made 356 rwhp and 352 torque.

I'm stumped... we had been on the dyno all day fighting a basically stock 2001 Z06. I'm taking it back over there on Friday and Ed is going to wipe the car clean with his Tech 2 and upload a fresh tune and start from scratch.

My main questions are what causes the car to go into "piston protection mode" or whatever it's called? The coolant was a max of 221 at the end of the 3rd back to back to back pull. When we started the pulls the oil was 180. I'm not sure what it was the last few pulls before the back to back ones when it seemed to be acting fine.

We checked fuel pressure as well and that was fine. Ed was shocked the gas made any difference because "bad" gas usually makes the car go lean and only lean... not be erratic.

Any ideas? Any suggestions?

Cliffs:

1. Car has very erratic AFR on the dyno
2. Fresh gas fixed it
3. Car is dialed in making 370 rwhp with 12.6 to 12.8 AFR
4. Let the car sit for a few minutes to do the 3 back to back pulls for NASA's new procedure
5. Car goes richer first two pulls (12.0 to 12.3) then way rich on the 3rd(low 11s high 10s)

WTF?

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UPDATE - 2/13/2012

Car doing the same thing, but only on the 3rd pull of the back to back to back dynos. It's fine if you let it sit and fine on the first two pulls. 3rd pull goes over a full point richer around 11:1 and maked 10-15 less horse. Here's the odd thing... the commanded AFR isn't changing. The PCM isn't asking for the car to go rich on that 3rd pull, but it is

If the car was getting hot or doing anything to fatten up it should show up via a change in the commanded AFR, but it's not. The injector pulse width isn't changing, the MAF voltages aren't changing and the fuel pressure holds steady at 55 psi.

Ed is usually the diagnostician people turn to for odd issues, but this has him stumped. He said at first he figured the car must be getting more fuel somehow. Says the next step would be to hook up an actual fuel flow gauge, but he doesn't have one. Also, my EVAP is unhooked and deleted so it couldn't somehow be pulling fuel via that.

I'm going to run the car this weekend and compare segment and MPH times to see if the car is noticably down on power. It could be the car has been doing this all along, or it could be a dyno-only issue.

I'll try to get a wideband in the car before the March VIR event to see if it's doign this on track.

Anyone with experience with this stuff have any ideas?
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UPDATE - 2/19/2012 CAR IS FIXED
Most likely a bad filter/pressure regulator.

Car is fixed... set the TTA track record at VIR this weekend with a 2:03.65

In the colder AM sessions the car was 12:0 - 12.3 the whole time. In the later sessions when it was hotter out I was 12.3 - 12.5. No going rich.

I think this has been a problem ever since I built the car and put in a "newsed" fuel filter/regulator off my old Z06. There were times the car just felt sluggish on track.

This weekend my TM data showed a top seed in the back straight of 149 vs. 145 from my 2:04.6 lap from last March.

drivinhard

are you logging the pulls on the dyno? what do the logs say? that is the best way to look at "everything" at once and figure out what is amiss.

redtopz

It's not clear to me if you have a halltech filter with the oem intake or a full halltech intake. I think the older halltech intakes had the maf too close to the air filter causing some issues. Like drivinhard said, get the full logs and see what's going on. But things to check would be:

1. clean the maf
2. check fuel pressures (replace fuel filter if necessary)
3. make sure you have no vacuum leaks (all ports are plugged or have hoses connected)
4. when in doubt install new oem plug wires. These cars seem to hate aftermarket plug wires.

Your listed temps should not be pulling timing or fattening the afr. Good luck.

travisnd

Yes... Ed sits in the car logging everything. He was a bit put off. Nothing was showing amiss. I wouldn't know what I'm looking at. He probably made 20 pulls on the car tweaking it.

I put the Haltech filter on the OEM air bridge, but I have the full thing, just left the stock air bridge because the Haltech coupler kept coming loose. When I go back to the dyno I'll take the OEM air-box and the Haltech bridge. Your are correct that Haltech re-designed the intake to put the MAF just ahead of the TB like the C6s; they called it the Venom. My MAF is still in the stock location.

1. The MAF is clean... cleaned it before putting the intake on and re-cleaned it today as a check.

2. We had the fuel pressure gauge on the car. Was at 55, went to 57 then leveled out at 55... so that's fine. Fuel filter was changed in 2010 when I build the car.

3. Zero vacuum leaks... no issues there.

4. OEM plug wires. Replaced them with low mileage ones when I built the car.

There were no issues with spark, fuel or any kind of KR or misfires. The car was just very inconsistent with the AFR at wot. Then I put fresh fuel in it and thought it was good to go.... it was good for four pulls in a row. Then we let it sit for 10 minutes to do the NASA official pulls and it was fatter again going really fat on the 3rd pull.

redtopz

You got me then. Maybe try a different maf sensor?

Bink

closed loop - replace your O2 sensors??
open loop- map sensor??
Any codes?

Black89Z51

Temperature sender for the PCM?

I know it's nothing of Ed's fault. He's a damn good tuner.

Rob's 73

Make sure the CAT over temp protection is turned off.

travisnd

We'll probably do that. We had a spare from another car ready to try but we thought everything was fine so I put it back on the other guy's car. When the car acted up at the end again everyone was ready to call it a day.

Open loop is where the issue is. No codes.

You mean the IAT sensor? It's integrated in the MAF for the later model cars like mine. When Ed tunes it again he mentioned starting from scratch then scanning more areas while tuning to see if things like the MAF or IAT are sending the wrong signals.

I would assume Ed would turn that off, but you never know... will make sure that is off.

RX-Ben

I have heard of Ed so I assume he has covered all the basics like making sure knock was proper (ie not switching to low octane, which would likely be disabled when doing an SD tune) and also making sure that timing wasn't pulled for any other reason (eg ECT temp - I thought the magic number was 220 but it has been a while).
As mentioned, cat over temp can screw things up but that was likely accounted for.
Any other changes (only change was cat delete?)? If the car sat, might be worth draining the tank and refilling with known good fuel.
No leaks, all connections are tight (air, electrical, etc)?

The only protections modes that I am familiar with are pulling timing w/high ECT or adding fuel for cat over temp; my car barely runs in limp mode so I think your numbers would fall off the bottom of the chart if that was enabled.

travisnd

SD was only used to see if the MAF was the source of the issue. MAF was turned back on. Does anyone know which coolant temp the car starts to pull timing? If it's indeed 220 and that wasn't changed then maybe that's what was going on. I know the car runs in the low 210s on track. On the dyno the blower fan really can't replicate actually moving.

Not much I can do now other than wait until Friday and hope for better results with a re-do.

redtopz

I looked at that one time in my tune and it was in the 230's that it started pulling timing.

travisnd

Thanks

96CollectorSport

According to my EFI Live a stock 01Z has a value of 132 C or 270 F for ECT overtemp and it turns off at 126 C or 259 F.

travisnd

Dang.... that's a bit warm.

2002rich

IIRC - if the temp stays at that temp for 5 minutes, then the engine will shut down. I have set this to a lower temp. Seems to me that the engine would be toast but I won't second guess GM engineers.

With regards to the Hi/Low Octane tables, tuners will copy the hi octane table to the low octane table.

Erractic A/F is usually related to a leak. Doesn't take much of a leak to cause havoc. Someone mentioned changing out your O2 sensors, that's not a bad idea. You already ruled out the WB by comparing it to the sniffer out the tailpipe. That was my problem (bad WB) which behaved very erratic. Wild swings

g/l
Rich

CHJ In Virginia

My car goes into reduced power mode when the coolant temp hits 228, it then pulls timing. Last dyno session first run at 230 and subsequent runs at 210. Picked up 16 hp don't remember torque increase solely by getting temp down. Keep it on the cool side for consistency.

96CollectorSport

Only a inexperianced tuner would copy the high spark table and paste it in place of the low spark table. If the engine started to knock what's the engine going to do then? The low spark table is a good thing, it's there to save your motor. I check the tunes on all of our cars with aftermarket tunes and it the tuner did that I would have it retuned.

I did a little more looking around on the EFI Live and there is a modifier in PE mod (Power Enrichment - WOT). There is no modifier from 140 - 212 then there is a .5 adjusment at 230 and a .9 point adjustment at 248 and above. That may be what you're running into you may just need a bigger fan in front of the car.

RX-Ben

Nice legwork.

So - two protections might be kicking in - spark retard and some fuel dumping.
But his temp was only at 221.

Are you sure your injectors are good? Do you have a set to swap in?
Do you have datalogs showing the spark timing and injector duty cycle during the pulls?

travisnd

Thanks for the info. So what's it do between 212 and 230?