5.3 LS fueling help

NYSpeed Automotive
1

Preface:
1972 c10 daily driver
L33 5.3 swap
4L60e
shorty headers
dry filter CAI
no cats
stock otherwise

http://img.photobucket.com/albums/v201/XwalkerX1/03C772CC-DDAB-49F3-9246-71418C5D921F_zpsrcjjvvap.jpeg
03C772CC-DDAB-49F3-9246-71418C5D921F_zpsrcjjvvap.jpeg1024×768

Issue:
as of late whenever I make my weekly drive from LA to San Diego I usually get a pair of soft or confirmed codes.
doesn’t only happen on long drives though. codes will pop up randomly (5 min drive around the block or 2 hour drive)

p0172 - system too rich (bank 1)
p0175 - system too rich (bank 2)

these codes started coming up about a month or two ago but I would also get the occasional MAF code so I tried to clean it (which basically is just a band aid fix IMO) but it started to stumble again
so I put a new MAF on it figuring the codes would clear up but nope.
the engine runs completely smooth since I changed the MAF though.
I can watch my live data via a wifi obd reader and I can see the pcm pull fuel then back to 0 then pull fuel then back to zero and so on and so forth. never just a steady reading.
also my though is that since I get both codes simultaneously I highly doubt its 2 leaky injectors (one on each bank)

so last night I checked the MAP sensor.
(engine off / key on) im getting a reading of 14.7 (1ATM) which is perfect.
(engine on) im getting a reading of about .2 ATM at idle and it rises as it should based on throttle input
so to me I feel like the MAP is working as it should be.

next I decided to check the fuel pressure at the rail…
so my truck has a corvette style external filter/regulator back by the tank (returnless system)
currently running a fairly new (based on the time of the swap) wix 33737

fuel pressure
(engine off/key on) 55psi
(engine on)[ open loop ] I would see 62 psi
(engine on)[ closed loop ] it started to rise to 63/64 psi and it would bounce around between those numbers pretty steadily and when you blip the throttle it goes to approx 61 psi.

from all my searching I cant find the pressure that the Wix filter is supposed to regulate to but I see that the range for the 5.3 is between 55-60 psi
so if I am getting 3-4 more psi at the rail do you think that is enough to cause the rich issue?
I ordered a new wix 33737 just in case.

lastly.
the truck has upstream o2 sensors after the shorty headers but no cats (or downstream sensors obv) both of those items are coded out on the pcm so no codes pertaining to those.
is there a possibility that the o2 sensors are failing and causing the issue based on not having cats? perhaps the lack of converters changes the heat range and thus the voltage reading and that could trigger the pcm to add or subtract fuel.
just to be clear I have not ever pulled a code (either soft or confirmed) for an o2 sensor problem.

thoughts?

EDIT: forgot to mention that the coolant temp sensor reads accurately and steady. I typically see 185 degrees on highway and a bit higher up to around 200 in idle/stop and go traffic

2

Maybe it needs a tune?

3

clean the MAF … its getting contaminated from the air filter

4

its literally a brand new MAF and the filter is clean with no oil on it.

5

what year is the motor and PCM

6

L33 engine from 05/06

wiring harness/PCM/throttle body from 99-02

harness was purchased new from Prevatt harness

7

OEM maf or aftermarket? My old GTP and my Trailblazer SS were very sensitive and only liked OEM.

Edit: Also the position of the maf was important. It had to be rotated correctly.

8

You put the MAF back in the right direction? :slight_smile:

9

MAF was installed in the exact same position and the correct flow direction lol.

I put in an aftermarket MAF…BUT the codes popped up before the original MAF threw a code and they are the same codes after so I don’t suspect the MAF sensitivity.

are we ruling out that the extra fuel pressure is causing the rich condition?

10

No idea I haven’t had this issue my primary concern with fuel psi has always been falling off up to not driving mrs daisy cruises :slight_smile:

Fuel filter swap is easy I would just do it as maintenance anyways and see if anything changes.

11

yeah I don’t flog the shit out of my stuff.

at most ill take it up to like 5k rpm lol.

12

coolant temp sensor

13

the CTS gets up to temp and doesn’t deviate unless im in traffic and even then I can see it get up to like 199/200 then drop down to 192/194 with the fans on.

14

there are only like 4 causes for those codes … dirty MAF,CTS,flex fuel sensor(which your pcm doesnt have)leaking fuel pressure regulator

15

so you don’t think o2 sensors would cause this issue?

I also dont think it is related to a TPS because its not just one rpm range that will trigger the pcm to cut fuel since it happens at idle too

16

The lack of cats wouldn’t affect the performance of the upstream O2 sensors.

How big are the injectors? From what I can tell for each bar of pressure you will get ROUGHLY 10% more fuel. So if you had a 1-3 PSI deviation (assuming its not your gauge thats off) You would be seeing a ~1% change in fuel flow. I dont think a factory PCM would ever see that, even a wideband ECU probably wouldn’t see it.

Do you have an aux wideband gauge?

17

stock injectors and no on the wideband

18

How do the plugs look, see if they look rich?

19

That idle fp seems high to me. I wanna say the most it should ever read is 58 and should idle and cruise around 43. That’s what my 09 does.

20

so i just swapped out the regulator/filter and the pressure is down to 57/58 and under throttle blips up to like 3500 rpm it drops to like 55/56

i suspect this was the issue but i wont know till i put some miles on it this weekend.

thanks everyone for the help