should O2 drop with RPM?

[Pace 1989]

Trying to tune my TTA and did some WOT runs. My O2's were steadly going down with RPM to the point that I didn't like it (765mV@4300rpm). This is on Amoco 93. I then turned up my fuel pressure to 44psi (was at 43psi) and made a couple more WOT runs and the O2's still got down to the 770's. This is doing a couple of 30mph and 60mph punches and going to about 100mph. When first punched the car is in the 820's+ but rapidly falls to 790, 780, 770 etc. My combo is below. Any help is appreciated.

.030 over
TA49
ported heads
009 injectors
Joe Lubrant chip
K&N
RJC Power Plate
THDP

 

[WSLN 6]

Have you checked your fuel pump? Does pressure drop at WOT?
Might be somewhere to start...........

 

[azgn]

you didn't mention what boost you are running, but I suspect you are just running out of octane......pump gas won't support much over 15-17 lbs boost

 

[Quick6'n'-K.C.]

pace 89-
change the fuel filter again
are you getting any knock when your 02's are steadily dropping?
im wondering if the 02 is really reading correctly cause i can never get any 02 below 800 without any type of knock-
especially on pump gas- what is you boost level and what kind of timing is in the chip are you running in the car?

are you considerring buying a SMC EGT PROBE in the future??
now i only tune on knock and egt temp-- i think the 02 value is no where near as close as tuning on the EGT-- but thats just me and my cars-

 

[Pace 1989]

I'm running 15-16lbs of boost. How do I check my fuel pump? What pressure should I be looking for? I've heard people tape a gage to the windshield, but what number should I see for about 15-16lbs of boost. This is right at stock, stock TTA's had 16.5lbs of boost. I get no knock, very rarely do I get any. Thanks for your input guys.

Ken

 

[TurboDave]

Originally posted by Pace 1989
Trying to tune my TTA and did some WOT runs. My O2's were steadly going down with RPM to the point that I didn't like it (765mV@4300rpm). This is on Amoco 93. I then turned up my fuel pressure to 44psi (was at 43psi) and made a couple more WOT runs and the O2's still got down to the 770's. This is doing a couple of 30mph and 60mph punches and going to about 100mph. When first punched the car is in the 820's+ but rapidly falls to 790, 780, 770 etc. My combo is below. Any help is appreciated.

.030 over
TA49
ported heads
009 injectors
Joe Lubrant chip
K&N
RJC Power Plate
THDP

It's a somewhat common problem (all this assumes you're comfortable with your fuel pump's performance), and usually has a couple of causes, not the least of which is due to the O2 sensor because as the sensors get hotterand hotter, thier output generally starts dropping off.
Another possible cause could be as simple as the programming in the chip's Power Enrichment (PE) tables.

 

[Pace 1989]

I'm not sure I'm happy with my fuel pump's performance. How do I check it?

Thanks,

Ken

 

[Quick6'n'-K.C.]

FUEL FILTER!!
do that first and see what happens-
the best way to check your f.p. is to put gauge on car, start it, and carefully pull hose off the f.p. regulator- that will give you the BASE fuel pressure-- prob with age and your clogged fuel filter around 39-41
so you put the hose back on and now it will drop back down like normal-
all you do is add your base fuel pressure 41 + boost level (15) = your what your gauge should read at WOT @56

my 12k TTA's fuel pump was in bad shape- so i installed a walboro 340 fuel pump and did the fuel filter( man was the filter horrible) i can t believe the car actually ran!!!

so that is why i said to just change the fuel filter--- its less than 10.00 and takes about 10 minutes to do-- need some good size wrenches
what scantool? scanmaster2 or directscan?
heck-- my tta is real stock too, but im runnin 24 psi of boost with the smc alky kit and egt-
that is about 130 more horses than 15 psi of boost-
and that is on the ole 91 octane we have here

 

[Carolinaturbot6]

With the fuel pressure set at 43lbs (line off), running 16lbs of boost, you should see 59lbs of fuel pressure at wide open throttle. 43 (PRESSURE)
+16 (BOOST)
59 (WOT fuel pressure).

 

[Pace 1989]

Thanks everyone!!! The fuel filter is less than 10 months old I usually do one every year. I currenly have my static fuel pressure at 44psi, but I will check my fuel pump. THANKS AGAIN!!!

Ken TTA#1426

 

[dconnor]

What fuel pump are you running? If stock, it's probably nice & tired by now being ~12 years old. Plus keep in mind the TTA pump while better than the GN's stock pump, is only safe (as in supplies enough fuel) for mid 12's or so.

May want to have the chip programming check out as well, looks like it's kinda fat down low & could use some extra fueling in the upper rpms.

Doug C.

 

[azgn]

keep in mind the fuels available in 1989 were much better than the garbage we have today and 16 lbs boost may be a little much........