Am I running out of gas?

[turbojimmy]

I was looking at my DirectScan files this morning from Friday's runs. I was goofing around with the timeslip function which I had never done before. Pretty neat. Anyhow, I noticed on all the runs that my O2s began to drop toward the end of the run. They were high-700s until about 90 MPH where they steadily dropped to low-700s even dipping into 700-teens by the end.

Would a chip have it go that lean or am I running out of fuel? I have 60# injectors but a single 307 pump. If I am running out of fuel, can I put my 307 and 340 (new in the box but not installed yet) together in a dual pump bracket?

Thanks,
Jim

 

[murphster]

I think most chips put max fuel at WOT, so I would doubt its the chip. I am not 100% sure on this though.

Anyway, I know I am leaning out due to fuel (too small injectors) on the T and I see exactly the same thing. Nice O2 readings until the end of the run where they drop to low 700's.

From what I've read, all you probably need is the 340. But I'd double check on that.

With too small a fuel pump, I'd think you could use a hood mounted fuel gauge and see the pressure not increase with boost linearly (1psi per lb of boost) ?

 

[turbojimmy]

Originally posted by murphster
I think most chips put max fuel at WOT, so I would doubt its the chip. I am not 100% sure on this though.

Anyway, I know I am leaning out due to fuel (too small injectors) on the T and I see exactly the same thing. Nice O2 readings until the end of the run where they drop to low 700's.

From what I've read, all you probably need is the 340. But I'd double check on that.

With too small a fuel pump, I'd think you could use a hood mounted fuel gauge and see the pressure not increase with boost linearly (1psi per lb of boost) ?

Thanks for the reply. I have a fuel gauge in the car but the sender has gone wacky on me. Showed well over 100 PSI FP at idle. I have an underhood gauge that is correct but obviously I can't see it from inside the car.

I figured if I do need to replace the pump I may as well hang the 307 along with the 340 since it still works.

Thanks again,
Jim

 

[Eric Stage I]

Jim,
Send me some of those DS files if you can.

Is it knocking when it happens?

Regards,
Eric

 

[turbojimmy]

Originally posted by Eric Stage I
Jim,
Send me some of those DS files if you can.

Is it knocking when it happens?

Regards,
Eric

No - not knocking. I had 116 octane and relatively conservative boost, though.

When I get home tonight I'll shoot them over. I have 3 of them - you can see it in all of them.

Thanks.

Jim

 

[turbojimmy]

DS Files (right click, save as):

Run 1
Run 2
Run 3

For some reason they save as .htm files but I uploaded them without extensions.

Thanks!

Jim

 

[bruce]

A 307?

I'm running a double pumper for my 60s, but I at times run some serious boost.

IMO, you never want to even approach not having enough fuel, or good enough ignition. Maybe a bit of over kill but I've had rather good luck for the amount of boost I've run, ie often 26 PSI on pump gas.
When I was running a single 340, I always replaced it every 2 years, and ran a hot wire kit, with volt booster.

The only accurate AFR sampling you can do is with a WB.

 

[turbojimmy]

Originally posted by bruce
A 307?

I'm running a double pumper for my 60s, but I at times run some serious boost.

IMO, you never want to even approach not having enough fuel, or good enough ignition. Maybe a bit of over kill but I've had rather good luck for the amount of boost I've run, ie often 26 PSI on pump gas.
When I was running a single 340, I always replaced it every 2 years, and ran a hot wire kit, with volt booster.

The only accurate AFR sampling you can do is with a WB.

Yeah, I should probably move to a double pumper. And WB. Where can I get just a DP hanger? I have 2 pumps.

Thanks,
Jim

 

[azgn]

nobody that I know of will sell just the hanger....Racetronox made some noise about making one, but isn't avilable yet

you may as well buy the complete kit with new pumps and sell what you have

(BTW, the "hanger" also includes the fuel tank sending unit so not all that simple to duplicate)

 

[Eric Stage I]

I think the runs look good Jim. I don't think the O2 numbers you're seeing are bad enough to say its going lean. Many cars O2 readings drop into the low 700's are even high 600's by the end of the track (on race fuel).

I don't think I would run any more boost with the 100 octane chip though (at least the way its set up now). The fueling is set up for around 23-24psi boost. If you want to run more boost, then wot fuel needs to be added in the chip. Also, the timing can be increased if you are running higher octane.

I think you've got it tuned in pretty good!

Regards,
Eric

 

[mgmshar]

My car runs 57 pounders and about 23psi of boost. The DC on the injectors never goes above 80%. Yet, I still see the same thing. At the beginning of 3rd gear, my O2's will be 790's. By the time I cross the finish line, they can be as low as 740's. When I first noticed this, I of course freaked out, and I taped the fuel pressure gage to the windshield. To my surprise, it didn't move AT ALL in third gear.

Then I remembered reading something: The O2 sensor gets hotter and hotter during the run. As the O2 sensor gets hotter, it reads a little lower. So, I've chalked this up to "normal" O2 sensor behavior. I've confirmed this by looking at my O2 sensor readings in 1st and 2nd gear. Generally, the readings decrease slightly through my entire 1/4-mile run. If I were running out of fuel, I would see the O2 readings go down to 740 at the top of 1st and 2nd gear as well.

Some day, I will put a WBO2 in the car and prove this. Maybe somebody else already has.

If your car isn't knocking as the O2 reading goes down, I wouldn't worry about it. I really believe this is normal O2 behavior.

Hope this Helps,

 

[turbojimmy]

Thanks everyone for the replies. I think at the very least I'll pop in the 340 pump. The 307 is nearly 5 years old and I have a 340 new in the box among the other pile of parts I bought but haven't gotten around to installing yet.

Eric: I won't push that chip too much more. I'll probably want a 110 chip or something like that in the future but I'll shoot you an e-mail on that.

Thanks,
Jim