Billiumss

iTrader: (11)

I know this is a mainly an LS1 board but by posting this in this active section, I am hoping someone has seen some of the problems that I have been having with this car that I am trying to tune.

I had a guy contact me a few weeks ago about tuning his 1997 T/A M6 Vortech Supercharged car. He had someone else try to tune it and couldn't even get the part throttle tune down, basically the car would barely run. Since he already had LT1 Edit, I said I would give it a try since I do has experience in tuning Supercharged LS1 cars, I figured, it shouldn't be too different....

Once I got the car, I basically started from the stock file and did the normal things I would do to get the car running. Before I go any further, here is his mod list:

- Forged LT1 Shortblock, 8.5:1 CR
- Ported LT1 Heads
- Comp Cam 218 230 114lsa
- 50lb injectors
- New 255L intank fuel pump
- New Optispark
- New Stock MAF
- Vortech intercooled Supercharger running about 10lbs boost
- LT Headers
- Catback
- New FPR
- 4.10 gears
- NO FMU

Once I did a base tune, I got the car running pretty good. A few tweaks here and there the car started up fine everytime (hot or cold) and drove very nice on light throttle loads. After I thought I got the part throttle tuning pretty close, I did make 2 seperate WOT bursts to 6,200 RPMs in second gear and it pulled pretty good. I didn't want to do any more since I had no clue where the A/F was at. So off to the dyno shop we go for WOT tuning.

I got the car up on the dyno and did my first pull up to about 4,500 RPMs to see where my A/F was at. Did the pull and I was about 10.5 A/F across the
board. Since this was my first LT1 car that I have ever tuned I started to take away fuel in the WOT PE table by 5% increments, I figure that should be safe.

Uploaded new program and did another pull this time to about 5,000RPMs. Kinda same thing with the A/F. So I took out another 5% fuel from the PE and
this time I told the dyno operator to take it to 6,000 RPMs. Now the fun begins.....

We did the pull and before we got the car to 6k, you could tell that the power dropped off alot by the sound of the engine during the pull. After the pull, we checked the dyno computer for the results and the A/F was about 11-1 but at about 5,400RPMs the A/F went straight up to 13.5 and stayed there! The power and torque was also climbing rather well until 5,400 and then dropped off about 50 HP.After a little bit of talking about what we saw, we did another pull to watch the fuel pressure gauge to see if the pressure dropped. Did the pull and had someone else watch the fuel pressure gauge and sure enough, the fuel pressure dropped about 10PSI and then jumped back up.

Ok, so we are thinking fuel pump. After some more talking, I asked if they upgraded the power wire to the 255L intank fuel pump and they said no. Ok, that must be the problem then. But a few other things were also going on too. As the boost came in the fuel pressure went up to almost 60PSI, stock fuel pressure for LT1s are about 43lbs. We were only seeing about 5-6lbs of boost, so if it is a 1-1 riser for the fuel pressure regulator it should have only went up 5-6 PSI in fuel pressure, correct? Follow the boost....

I'm not sure what the MAFs max out at on the LT1, but I was reading about 56lbs/min on my scanner right when this problem happened. I tried to add fuel
via the VE table and WOT PE table and didn't help at all. We got the car off the dyno and the owner of the car ran a wire from the battery to the relay to the new intake pump to eliminate the voltage/current problem. We got the car back on the dyno and did another pull. This time, the fuel pressure was rock solid and didn't drop at all but we still had the same problem around 5,400 RPMs, the car dies and A/F goes straight to 13.5 and levels off. I can post the dyno graph if that would help some. At the time the A/F went lean, it was only making about 390HP & 405 TQ with it still climbing pretty good.

So this is where we are at now. Has anyone ever seen this before? Why would the A/F go way lean at the same RPM if we have fuel pressure and have 50lb
injectors? Optispark, Fuel Pressure Regulator?

Any thoughts, tips, advice are greatly appreacaited.

Bill

RealQuick

iTrader: (14)

Spark blowout perhaps? What are the gaps at?

BLWNZ

iTrader: (2)

Did you check for underpants gnomes in the ECM!

Got Me SOM

iTrader: (2)

what' s the duty cycle on the injectors?

10.5 Dave

iTrader: (5)

Bill you might want to check with Ed Wright or Joe Overton.The seem to do a good job tuning LT1'S.

2001WS6Vert

Is there a parameter for "commanded air/fuel ratio" with the data logger? At least you would know if the computer is whats leaning it out or not.

Pro Stock John

iTrader: (34)

Intmd8 (Jim M) at www.ls1speed.com can tune an lt1 blower car in his sleep. Might want to take the car to him, or see if he can give you a bit of help.

99.9percenter

iTrader: (2)

LT1's need aftermarket ignitions really bad... MSD,Accell,etc....

qqwqeqwrqwqtq

When an obd2 LT1 maxes out the maf, the injector pulsewidth gets cut down by roughly 1/2, which obviously equals really lean.

Ed wright has the fix for this, or you can switch to an obd1 pcm.

As far as the ignition, most obd2 LT1's can get up around 600rwhp on the stock parts. (with the exception of plugs/wires)

JZ 97 SS 1500

iTrader: (2)

I definitely agree with Jim. If your ignition is not up to par, you may want to swap to the LTCC.

Jose

Billiumss

iTrader: (11)

Thanks for all the tips guys!

With my HP Tuner scanner, I can't read the injector pulse width or the knock sensor for the LT1.

Jim, I'll be calling you within 2-4 hours today.

Billiumss

iTrader: (11)

Jim,

I tried to call, but they wouldn't let me talk to you.

All I need is a 2 minute phone call.

I sent you an email, I can send you the file if you would like.

Bill