DFI Question

[Butch]

Guys, I have transplanted an LT1 from a corvette into my Full Size Blazer and I have a few issues that I could use some help with.
I also have a WE4 and have learned almost everything I know from this board!

The Engine is stock with a ZZ9 cam (not sure of specs, I will find them and post) and nice PnP LT1 heads with big valves and roller rockers, electric Water pump, long tube headers with duals, no cats right now.

The DFI and FastTrack harness was installed by very reputable shop and tuned with me riding in the truck, but...

It is being run closed loop with a heated NON Wideband O2 sensor. Unless I am missing something the system is constantly correcting to 14.7/1 AFR. I dont think you can set a target AFR with this system. It is a BtB system. Well it pretty much runs like crap, just doesnt have much power until like 3000 RPM's. It doesn't backfire or anything like that and it idles fine at 750 RPM's with about 18" of vaccum.

My thinking is that maybe I should be running it open loop, I mean what good are non Wideband O2 sensors right?

The other problem is that I think this cam might be ok for a car but this is a very heavy 4 wheel drive vehicle, heavier than a Caprice even. What is the cam theory for building power at lower RPM's? I mean this thing go's 70 MPH at like 17-1800 RPM's, If I try to accelerate it's a dog unless it downshifts. About the only time it seems to pull hard is above 2000 RPM's.

Sorry so long but I want to try to fully describe my problem.

Thanks in advance for any suggestions.

Butch

PS. Can I upgrade this sytem to Wideband? Would it be worth it?

 

[Butch]

Here is some info on the zz9 cam...

TPIS ZZ9
282/287 adv. duration
212/226 dur. @.050
.483/.520 lift
112LSA

The ZZ9 has 60.5 degrees of overlap.
((282+287)/2)-(112x2)=60.5

I was just reading something that says I should stay below 195 duration to move the power into the lower rpm's

 

[Butch]

Please help!

Thanks,

butch

 

[JDEstill]

I'm not familiar with the O2 sensor capabilities of the DFI, but here's some free advice

I presume there are settings that tell it under what conditions it is closed loop (rpm and MAP I would guess) and under what conditions it is open loop.

I would let it stay closed loop at idle and cruise, but under acceleration and WOT it should be open loop.

You are right in thinking that using a narrow band O2 sensor to control the fuel in a situation where you don't want it to be at stoich is not a Good Thing.

The TEC-3 has a setup where you essentially tell it you want xxx mV at some point in the map. You could command it to have 780 mV all through a pass for example. Which sounds good on the surface, but I don't think it really offers the positive control over the a/f ratio that you really want it to have. Not sure if the DFI setup you have is set up to do anything similar.

You didn't say what version you are running?

John

 

[Butch]

John,

It is a version 6 Accell Bank to Bank DFI and I am using the latest Calmap software (6.32, I think).

It's been a while since I played with it but if I remember correctly the system go's into closed loop when the water temp gets to a prescribed level. I think mine is set to like 130 degrees. I think the system go's into open loop at a certain TPS value. I will have to look into that when I get back home and have the appropriate tools.

I noticed this weekend that it seems to idle and run pretty good until about 130 degrees which is about when it go's into closed loop! Could be my imagination!

I sure could use some help on the cam thing too!

Thanks again,

Butch

 

[vtec4gs]

If its the Calmap 6.0 DFI then it inherently adjusts a/f to 14.7:1 ... even says so somewhere in the manual if I remember correctly.

You really should not run DFI 6.0 in closed loop, except to tune fuel maps at non WOT positions such as just street driving to get nice clean maps as 14.7:1 is perfect for street driving but too lean for WOT runs - I'm sure for the V8s naturally aspirated. Run it open loop and at full throttle to set to your target a/f ratio.

If its DFI 7 then thats a different story and they all come with the 5 wire wideband, you said you had heated o2 no wideband, thats the 3 wire one ...

Greg

 

[TwinTurboIroc]

Originally posted by vtec4gs


If its DFI 7 then thats a different story and they all come with the 5 wire wideband, you said you had heated o2 no wideband, thats the 3 wire one ...

Greg

the wideband is an option for the gen 7, not standard. They also make 4 wire heated 02 sensors also

lastly, your DFI is batch fire not bank to bank

 

[Butch]

Guys, I would like a few more opinions.

Thanks!

 

[PaulRV6]

Butch, I use to run a DFI 6.0 and there are values in the main setup screen to change at what point you want to go open loop, I believe it is TPS and one other input (its been awhile).

paul

 

[Butch]

Paul, Yes I found those settings, one is like a low rpm setting and the other is high. My question is really more about whether I should be running open loop or closed loop. Also the question about the cam...

Thanks,

Butch

 

[PaulRV6]

The way I had my GN setup (and I was still tweaking) was I had it closed loop until 30-40% TPS and at that point let it go open loop and work off the fuel map. But in my case with the turbo I did not want to be building much boost running in closed loop.

paul

 

[Craig Smith]

Closed loop at WOT with a non-wideband system is not recomended by anyone, even DFI. 14.7 is a dangerous a/f ratio at WOT.

May I suggest advancing your camshaft to increase low-end grunt? You'll need to recheck piston to valve clearance but it would certainly help to advance it.

 

[DFIfixah]

Is your Gen VI ECU setup to even run the LT-1? This whole deal transplanted from a car into your truck, the DFI & all? If not, it is possible the board may need to be modified to run with the LT-1.

 

[Butch]

I have a FastTrack harness and the engineer that designed the FastTrack harness installed it for me.

Thanks for the suggestions guys!

Butch