lex afm, rc550's, 15-16 psi fuel cut.

[dav_dman]

just installed the goodies; screw only a few threads in so plenty of unmetered air under the honeycomb..which is supposed to raise fuel cut (actually it's spark cut, isn't it?).

Throws a code 34, turbo pressure excessive, at 15-16psi. I won't be running that high with this ct26, but i wanted some play room and i thought this mod was good for 18-20 psi FC. I'll be running 12-14 which it does fine, but i'm still puzzled and pissed after spending the time and money.

I have the vdo gauge and mbc in the line from the turbo to the actuator..wanted true turbo outlet pressure, not at the intake mani. No leaks.

There is no turbo pressure sensor, right? it's all what the afm see's as excessive air flow or something?

Aggravating.

 

[aye mate]

Are you sure there are no boost leaks? Also if the weather is fairly cold that might be it too. The air is more dense.

 

[97TSiAWD]

Questions:
1. Do you have a wideband O2 sensor?
2. Do you have an SAFC (or something equivalent to tune with)?

Also, first check that you don't have boost leaks like aye mate suggested. If you don't have boost leaks, you can continue reading.

Here is what I posted in the VPC fuel cut thread:

Fuel cut is caused by a number of factors, but the main one is the ECU "seeing" too much airflow. With piggyback tuning devices (such as the SAFC), the way to work around fuel cut is to simply reduce the airflow signal the ECU sees by reducing the %-adjustment settings across the RPM range. Obviously, reducing the airflow signal will reduce the amount of fuel delivered, so it will lean things out.

Basically, having the Lexus AFM alone doesn't necessarily eliminate fuel cut. Each car is different so the amount of airflow the ECU needs to see to cause fuel cut (along with the other factors) will vary. So if you are still hitting fuel cut, it just means you need to reduce the airflow signal further to avoid it. Don't go any further if you don't have a wideband O2, however, since you won't know when you have left safe air/fuel levels.

 

[Doward]

1) Check for boost leaks. (check the BOV, mainly ) And by check, I mean pressurize the intake tract, and VERIFY no leakage.

2) It *IS* fuel cut - not spark cut. No fuel in combustion chamber = nothing happening in the chamber.

3) There is no 'pressure' sensor - the AFM measures the actual airflow directly, coming into the motor. Code 34 is set when the ECM gets a higher-than-allowed signal from the AFM. That air has to be going somewhere - so see number 1 again

*edit*

The Lexus AFM + 550s does not eliminate FC - it only moves the ceiling upward, by scaling the airflow signal approx 25% lower than it truly is. The larger injectors make up for the difference in fueling - but your timing will be increased over what Toyota set it at (the ECM is reading a lower airflow signal = less load = more timing)

 

[dav_dman]

Good info, thanks guys.
Agreed, i can't tune leaner without getting a wideband on it. No safc..wanted to stop at the lex mod and run a little rich..not concerned with eeking out the last bit of hp, with the stock ct26. Was going to upgrade turbo next stage (next yr) and wideband and safc at that point.
It's the porsche bypass valve.

I will have to pressurize the intake before going further. Time to use the search function again..

thanks,
D.

 

[starscream5000]

Keep the boost around 13 psi for now until you get a wideband man. Anything over 13 on the stock CT is just hot air anyways....

 

[dav_dman]

Keep the boost around 13 psi for now until you get a wideband man. Anything over 13 on the stock CT is just hot air anyways....

That's my target, but i need to find the root of this problem and fix it before i drive it again.

 

[jdub]

Might want to reconsider the location of your boost gauge input. Placing it on the intake manifold shows how much psi is actually flowing into the cylinders. Plus you can read vacuum at that location as well...useful for figuring out other issues.

 

[dav_dman]

Might want to reconsider the location of your boost gauge input. Placing it on the intake manifold shows how much psi is actually flowing into the cylinders. Plus you can read vacuum at that location as well...useful for figuring out other issues.

I will , after i get the psi out at the turbo, set. I'll want to monitor at the manifold, as you suggest. I might even run two gauges for a couple runs, and see what kinda loss i'm getting. Gotta test my hoses first..

 

[dav_dman]

HEY:

how much psi will the upgraded bypass support..will the porsche/bosch handle more than 15psi before it starts leaking?!? that would be too easy..

anyone running higher boost on that valve?

 

[foreverpsycotic]

the 105 is supposed to hold 15, the 110 is supposed to hold 20ish IIRC

 

[jamesdem1123]

ive had problems trying to source the porsche bypass around here, anyone know where to find one online? i think mine is leaking, i hit fuel cut at like 11 on an upgraded ct26

 

[dav_dman]

mine is a 110, but I just gave to a buddy today.. getting a billet one with adjustment springs. I still need to pressure chk my system .

 

[SupraDupra500]

referring to the boost gauge hooked up directly after the turbo.. i was having trouble similar to this wasnt building much boost so i put the boost gauge down there to see what the turbo was putting out.. wellll i built some 10-12 or so psi then when i let off the throttle it had that split second surge of pressure before the bov could open and it broke my gauge.. so be careful.. of course it could have been the fact that it was a cheap ass boost gauge at the time..
i have lex and 550's on my car.. with holset hx35w turbo.. i ran 26psi on 110 octane leaded fuel.. no fuel cut.. a/f ratios were still safe.. slightly lean.. but still safe.. sounds like a boost leak to me!!! best of luck!

 

[dav_dman]

yes, gauge will not work well without the restrictor.. bought a box of six welding tips with a .032 hole in em and cut a 1/4" section of one and deburred and slid it into the boost hose and it works like a charm.

thanks for the info on your setup... you guys are the experts and i am now convinced i must have a leak. Gotta eat some soup today so i can do the test with the empty soup can ;-)... am NOT looking forward to removing the lex ..that thing barely fits into the accordian pipe, after much effort.

 

[antman]

yes, gauge will not work well without the restrictor.. bought a box of six welding tips with a .032 hole in em and cut a 1/4" section of one and deburred and slid it into the boost hose and it works like a charm.

thanks for the info on your setup... you guys are the experts and i am now convinced i must have a leak. Gotta eat some soup today so i can do the test with the empty soup can ;-)... am NOT looking forward to removing the lex ..that thing barely fits into the accordian pipe, after much effort.

you don't need to take the lex out of the accordian hose. you want to hook up your pressure tester on the turbo not the accordian hose.
this is the tester i built for mine. works very well.
http://www.supramania.com/forums/showthread.php?t=19718&highlight=pressure+tester

 

[dav_dman]

you don't need to take the lex out of the accordian hose. you want to hook up your pressure tester on the turbo not the accordian hose.
this is the tester i built for mine. works very well.
http://www.supramania.com/forums/showthread.php?t=19718&highlight=pressure+tester

cool! heading over to home depot...