Why No Fuel Cut?

[AlphaAssault]

I was driving my GSX after having to do some work on it, and punched it to see if it was boosting alright. The turbo kicked it, but I was not really accelerating much. A quick glance at the boost gauge reveals a boost pressure of ~22psi. Normal boost is ~14psi. Immediately I let off the gas. It still drives fine, so no damage was done I dont think. I adjusted the MBC down, but my question is why didnt the car hit fuel cut? Obviously timing was being pulled, but at 22psi from a s16g, thats more than enough airflow to trigger fuel cut.

 

[gsx4g64]

I would suggest that you post more info. what rpm did you get too? what size injectors you are using. Fuel cut can be cause by several reasons. Give us alittle more information.

 

[AlphaAssault]

It was at about 5.5k RPMs. information is in my profile, but the relevant stuff is: stock 450 injectors, 150lph pump, stock ecu, no tuning mods at all. ive never had it overboost this much, but I have driven it since and everything seems fine. I just thought the ECU should have killed the fuel long before 22psi.

EDIT: ive got a logger, and while I didnt log this particular run, I have logged WOT runs before with everything reading ok on the logger.

 

[TurboATM]

is it holding, or just spiking that high?

i know on my stock t25 right now (with my stock boost controller not working very well...) im seeing spikes of 20-22 psi for a good 2 or 3 sec, then drops to about 17-18 and holds, with no cut.

 

[AlphaAssault]

is it holding, or just spiking that high?

i know on my stock t25 right now (with my stock boost controller not working very well...) im seeing spikes of 20-22 psi for a good 2 or 3 sec, then drops to about 17-18 and holds, with no cut.

It held. Im not so worried about why its overboosting because im almost certain one of the guys messed with my MBC while my car was down, I would just like to know why fuel cut didnt step in.

 

[rEclipserGST]

It held. Im not so worried about why its overboosting because im almost certain one of the guys messed with my MBC while my car was down, I would just like to know why fuel cut didnt step in.

I've wondered the same thing a few times with my 14b when overboosting. Boost leaks play a factor. But, what kind of wastegate you running?

 

[AlphaAssault]

I've wondered the same thing a few times with my 14b when overboosting. Boost leaks play a factor. But, what kind of wastegate you running?

Thats a good question, I dont actually know what kind of wg it is. It was on the s16g when I bought the car. Im assuming its either stock or came with the 16g, either way it looks brand new still.

 

[GsXdSmKingGsX]

Check the spring in your MBC. and as for your boost spike. If it only happened once then it could be a simple mis reading or something. Because those injectors and that tiny fuel pump cant even come close to delivering that much fuel.

 

[AlphaAssault]

Check the spring in your MBC. and as for your boost spike. If it only happened once then it could be a simple mis reading or something. Because those injectors and that tiny fuel pump cant even come close to delivering that much fuel.

This echoes what I was thinking. For my setup, this was a massive overboost. Timing was OBVIOUSLY being pulled because it was hella slow at 22psi, but it seemed like fuel cut should have stepped in.

 

[pneumo]

How long was it hitting 22psi?
Fuel cut happens when airflow goes over a certain threshold for one full second.
Does your maf still have all honeycombs? Is it modded in any way?

 

[the_mork]

I wouldn't be honestly surprised if you could hold that much airflow with your stock injectors.

23psi on my e316g was around 90% idc on my 560s and this was at peak over full long runs.

Boost pressure is a poor measure of airflow so if you have restrictions to air movement such as stock exhaust, intercooler, intake box, etc then just because you have high boost doesn't mean you're really flowing a lot of air. Always remember that boost pressure is actually a measure of resistance not of airflow which is why large turbos, and freer systems produce more power at lower boost than small turbos and restrictive systems.

The reason that everyone is concerned with high boost and you're instructed to generally never pass about 15psi without fuel management is that airflow/fuel use is incredibly malleable depending on weather conditions, tVE, fuel maps, boost leaks, etc. 9/10 times a one time spike will happen during conditions where the actual airflow isn't incredibly high.