Another Fuel Cut question

[supradjza80]

Guys,

Here is my car's only engine modifications.

Apexi intake
Shimmed wastegate to 8-9 psi
3" BIC DDP to 2.5" straight pipe

I was under the impression from things I had read that I would not hit fuel cut with these mods, however I am hitting fuel cut in every gear but 1st. Is this normal? I was also under the impression I could have run even more than 10psi and have an upgraded Intercooler/piping without hitting fuel cut, is this just plain wrong? Is it just due to the 30-50 degree weather right now in wisconsin (dont worry no snow yet )

I have searched around and haven't found much to confirm or disprove what is going on with my car for sure.

Any help is appreciated.

 

[jdub]

Boost cut is based on the volume of air the AFM "sees"...colder OAT will affect it (occur at a lower psi).

You might want to check for boost leaks.

 

[supradjza80]

I was thinking it was pretty unlikely that the temp really effected it enough to make it hit fuel cut, but maybe.

I will check for boost leaks, I will check but the car runs completely normal so I fear I may unfortunately find nothing...

Thanks for the help Jdub, Im hoping its a boost leak bc I would hate to have to go back to stock boost

 

[jdub]

Drops my FC (on a Lex/550 combo) ~2 psi when it gets colder...and, that's in AZ

Sometimes a leak doesn't show until you are well into boost...about where you are.

 

[jdemara]

I believe i have the same problem. However, it is only when my engine is cold and I boost in say 1st or 2nd gear. It momentarily hits fuel cut, engine light comes on, and within a second its back to normal! Now when I say boost when the engine is cold, I do NOT mean just after being first started. But under 140 degrees farenheit.

Weird..? does not do it what so ever when engine is warmed up fully.

edit: just thought of something.. could it possibly be bad injectors or some problem with the Fuel injection, causing the engine to run really lean, sending a signal to the ECU to disable fuel?

 

[jdub]

Under 176 deg F coolant temps, the ECU is in warm-up enrichment...it should not be lean. In any case, the ECU does not cut fuel for a lean condition.

 

[supradjza80]

I have one other quick question

Where should a properly functioning, stock injector, stock MAF car hit fuel cut with an intake and turbo back exhaust? I have tried to find a thread with some basic guidelines but haven't found much. Is it 10psi, 15psi etc. with a stock CT26?

Thanks

 

[Poodles]

Depends entirely on the atmospheric conditions...

 

[bdjames02]

without getting all Bill Nye the Science Guy on you....roughly 13psi on your setup. Sometimes its easier to just answer a question. Speaking from experience, when my car only had a full exhaust, k&n air filter at 13psi BANG full cut.

 

[jdub]

without getting all Bill Nye the Science Guy on you....

And not knowing how/what/why the ECU controls this motor will turn around on you and bite...really, really hard.

 

[bdjames02]

And not knowing how/what/why the ECU controls this motor will turn around on you and bite...really, really hard.

thats for sure...real hard. First time I felt fuel cut it scared the crap out of me. By the way, were you agreeing with me or not?

 

[Poodles]

No, he was mocking you a bit...

During the summer, fuel cut is close to 15PSI around here... Winter, it can be as low as 10PSI.

Like I said, depends ENTIRELY on the weather, PSI is a shitty measure of flow.

 

[jdub]

Wasn't exactly "mocking"...but, the point is the correct answer usually sounds like "Bill Nye the Science Guy". I've tried to dumb answers down in the past and it doesn't work very well...or, I get someone roll in on me nit picking what I said.

 

[supradjza80]

No, he was mocking you a bit...

During the summer, fuel cut is close to 15PSI around here... Winter, it can be as low as 10PSI.

Like I said, depends ENTIRELY on the weather, PSI is a shitty measure of flow.

Ok cool, I wanted to know the range, I must have a boost leak then if those numbers are on stock turbo, stock MAF, and injectors. Currently I don't have access to an air compressor (college...) so I wanted some verification that I do or do not have a leak.

PSI really ins't a shitty measurement system in this example as long as the motor peripherals are the same (turbo, intake, exhaust) obviously RPM matters since 10 psi at 2k is not the same flow as 5k etc. For what I'm looking for I just needed the psi range (approx) for my mods. I understand the MAF doesn't care if its 2 psi or 30 psi it is just measuring the volume of air the motor is ingesting.

either way, thanks for the help. I will try to leak test the car asap.

edit - Poodles are you running the Lex MAF+550cc's or stock?

 

[Poodles]

Stock

Keep in mind I'm in Texas and it gets hot as hell here during the summer (100+ easily), and can get pretty cold in the winter (20's)

 

[bdjames02]

Ok cool, I wanted to know the range, I must have a boost leak then if those numbers are on stock turbo, stock MAF, and injectors. Currently I don't have access to an air compressor (college...) so I wanted some verification that I do or do not have a leak.

PSI really ins't a shitty measurement system in this example as long as the motor peripherals are the same (turbo, intake, exhaust) obviously RPM matters since 10 psi at 2k is not the same flow as 5k etc. For what I'm looking for I just needed the psi range (approx) for my mods. I understand the MAF doesn't care if its 2 psi or 30 psi it is just measuring the volume of air the motor is ingesting.

either way, thanks for the help. I will try to leak test the car asap.

edit - Poodles are you running the Lex MAF+550cc's or stock?

He was asking for the range. Not for the exact number at 70 degrees with an elevation of 1500 ft above sea level and whatever else you can come up with. Its always different with each car and where you live. give him some help.

 

[jdub]

He was asking for the range. Not for the exact number at 70 degrees with an elevation of 1500 ft above sea level and whatever else you can come up with. Its always different with each car and where you live. give him some help.

During the summer, fuel cut is close to 15PSI around here... Winter, it can be as low as 10PSI.

He did give him a range...looks like Poodles is trying to help to me. A "guess" at an answer does not help...in fact, if you guess in the Tech Section, you will take a hit. I'll be one of the 1st to slap you.

Boost psi is a crappy measure for air flow on the Karman Vortex AFM the 7M uses...it's output is in a frequency, not voltage like you see on EFI systems using a manifold pressure and OAT system. That is going to result is variations based on outside conditions, regardless if 2 motors are identical mod wise. This is exactly what Poodles was trying to get the guy to understand.

If you don't want to know how it works, you are in for a lot of problems. I suggest you buy an old Chevy with a carburetor.

Poodles are you running the Lex MAF+550cc's or stock?

I have the Lex/550 combo...I live in AZ, it pretty much does not get cold here very often. In the summer (105 deg OAT) I'll hit FC at 17-18 psi...in the winter (50-60 OAT) that drops to 15-16 psi. Where you live (colder climate), you will hit FC earlier.

 

[supradjza80]

He was asking for the range. Not for the exact number at 70 degrees with an elevation of 1500 ft above sea level and whatever else you can come up with. Its always different with each car and where you live. give him some help.

For the record, I am him/the OP so I guess I could help myself

EDIT - looks like I may have misread what you said. Either way no worries I have the informaton I was looking for...