Riddle me this batman

[V6 Beast]

Ok here is the riddle...


What would cause you to have a WOT o2 reading of .630-.691 no matter what boost or fuel pressure you set? Simple enough?


It reads the same on WOT blasts @ 14 PSI boost and 50 PSI fuel pressure as it does @ 17PSI boost and 45 PSI fuel pressure. always in the .630-.690 range. At idle the o2 readings seem normal as do the crosscounts. I can send anyone some DS files if they would like to see them.

To get you started, here is a list of what it isn't:

- O2 sensor - Currently has a brand new bosch heated but have tried 5-6 both heated and non-heated.
- O2 sensor wire - I have run a seperate lead from the sensor to the ecm and it read the same with my wire or the harness wire. Same goes for o2 ground circuit to ecm.
- Fuel Pump - Double pumper and WOT fuel pressure verified to be in the 70's via mechanical pressure guage. Jumping across hobbs switch makes pressure jump up immediately as well.
- ECM tried another one(maybe 2)
- Injector size - I have 72's
- Injector flow- I put my 55's back in and it was the same. Also removed injector wires 1 by 1 and noticed engine idle change on each one.
- Injector harness. I got a new one at Nats and put it on.
- Grounds - I have verified all the grounds at back of head and I am using casper relocation kit. Also verified good ground on wire going to ecm.
- Chip - I have tried several versions and Red re-burned me some at the NATS.
- Low Voltage - Added a Volt Booster and had no effect(other than raising voltage).


Combo is a 109 block .030 over with TRW's and Billet Mains, TE-45A, 72 # Siemans, Champion Iron Heads, ATR 208/201 CAM, THDP, RJR Power Plate, AC 19930 9", various other mods.

 

[KEVINS]

bad regulator... I didn't see that on your list.. If it's not sensitive enough then it's not going to increase the psi accordingly..

ks

 

[John Larkin]

Header or crossover leak. Not affected at idle due to low exhaust gas velocity.

 

[gofstbuick]

With the engine in closd loop, plow some propane into the snorkel and see if your sensor will flat line above 850mv, then when you turn the propane off, does the reading drop below 150mv for a moment. If so, I would discaount a sensor problem and look elsewhere.

 

[Reggie West]

I will take a stab at this.

First, your second fuel pump is kicking in too soon. You have these massive injectors on the motor and once the second pump kicks in you double the volume hitting the injectors.

With that combo I would set the Hobbs switch at 14 psi or so. It is much easier to lean out the fuel curve with a DFI but you can do it by changing where the Hobbs switch kicks in.

Reset the fuel pressure at idle where it should be. Dont try and change anything there. It wont help as you have noticed by now.

That should get you going in the right direction. Start out slow with the changes to the Hobbs switch so you dont blow up the motor.

I have used the ATR set up with a DFI and had the same problem. Runs great out of the hole and then for some strange reason it is very rich. You just have to find the spot where the 2nd pump is really needed and then the car will be smooth.

Let me know how it turns out.