Trying to Solve Fuel cut - at wits end - this one will stump you

[suprafanatic]

oh i remember somthing else i had to do. i have a 3in elbow. and for some reason some times the flap was hitting on somthing in the elbow and it wouldnt open right. i had to put 2 gaskets between the elbow and the turbo to give it alittle more space.

 

[suprafanatic]

theres one more thing i want you to try. see if it helps any... this is something else that allows my car to run higher boost with out cut. my air filter isn't completely sealed on. there is a gap for some free flowing air. this actualy adds alot of response to the car. it pulls alot harder to. but when i did have the filter sealed on i hit fuel cut alot sooner like around 10-11psi. so try running with out an air filter really quick and see if that doesnt do anything for you!

 

[Quin]

I definitely hooked you up that day. Come help me pull my motor! haha

Fail, ignore what he just said. That's a good way to suck up a baby or something, turbos don't like those

 

[Doward]

Here's one for you to check. FC is based on hz AND rpm.

Roll into the throttle a little slower, so that you are around 3/4 throttle @ 4500rpm, and don't go WOT until after that point. See if your FC clears up.

I'm wondering if you are simply coming on with too much airflow, too fast, and the TCCS is activating FC based on that. JetJock would know much more about the specific requirements to engage FC.

 

[suprafanatic]

you dont have to try it but i can about 98% assure you it would fix the problem! and if it does all you need to do is get a better flowing filter. running it once with a gap in the filter wont hurt anything.

 

[Doward]

If the filter did not flow enough, you would have fewer vortices in the KV sensor array of the AFM, and would therefore have a lower frequency coming from the AFM.

 

[suprafanatic]

it sure helped fix my fuel cut problem. if i went out and sealed up my airfilter i could only run about 10psi. with the small gap i gave it i can now run 15psi

 

[Doward]

I don't know what to say then. Your 7M defies physics and Toyota's engineering department.

 

[suprafanatic]

lol. i guess so. its been like that since i'v had it. it absolutly loves running with some kind of a gap between the filter and afm. but his car is running like mine was. .. very very rich. so maybe it needs the more air flow? maybe running way to rich. all i know is what i said helped my car. im just throwing out ideas, he said he was willing to try anything, and what it only takes maybe 30 seconds to loosen up the air filter some and try it.

 

[Nick M]

Fascinating...

remedies 1-6 and 8 deal directly with the amount of air being measured by the AFM either by way of bypass through boost leaks or intentional bypassing. this would most certainly affect the reading of the measured air by the AFM. Step 9 would directly affect the amount of air being sucked in the by the turbo...

Right. That is why I have no suggestion to retest those different. I am giving you the benifit of the doubt.

So it is time to stop thinking outside the box, and think inside it. Too high of boost pressure. Your turbo hits fuel cut on its own, or the wastegate isn't letting the excess go, as some pointed out. That is worth checking.

 

[Facime]

I know you are wanting to try to find an answer to the problem, but what if its not an actual problem and is more of a tuning issue? Since you are running rich you could run an A/F controller like the SAFCII or NEO and take air out of the system. This would simultaniously cure the FC and the "diesel" effect.

 

[suprafanatic]

how can you cure FC with a safcII?

 

[Doward]

Pulling fuel by lowering the frequency from the AFM. Scaling the airflow, I believe it is known as.

Also alters the timing map, fyi.

 

[Facime]

Basically like Doward said you trick the ECU by reducing the signal from the afm. The ECU of course adds less fuel in turn, but since he is already overly rich that isnt an issue. He should be able to easily "fix" the problem that way.
(note the "fix" in quotes, )

Of course you could do the same with a standalone or another piggyback, but I mentioned the SAFC because I was familiar with how it worked.

 

[pimptrizkit]

i thought fuel cut was determined by rpm, mass air flow, and open/closed loop. and the fail safe was fuel cut at 85% duty cycle on the injectors.

i know this is a long shot, but the ecu knows there is a switch to change the voltage the fuel pump sees.


the duty cycle would be different between 25psi 30psi, @ 7volts, were it would be 30-35psi at 12volts and climbing from the regulator.




honestly, i think you need to step up to a FPR, piggy back & Walbro.

 

[jdub]

^^^ You thought wrong. How many times in this thread does it need to be said that FC is determined by the volume of air flowing past the AFM. The fuel pump has absolutely nothing to do with it.

 

[ArmandoP]

Fascinating...



Right. That is why I have no suggestion to retest those different. I am giving you the benifit of the doubt.

So it is time to stop thinking outside the box, and think inside it. Too high of boost pressure. Your turbo hits fuel cut on its own, or the wastegate isn't letting the excess go, as some pointed out. That is worth checking.

Nick, I apologize if I came off dickish, that wasnt my intent at all. I think you (and some others) may be right. so I will check with the wastegate flapper open today and see what I get, this should be pretty interesting. It may be time to upgrade to a standalone, but again I want to know thats the actual problem and that Im not just throwing a few thousand dollars at a $12 problem. I appreciate your help. Some background on me, I have built several very fast MKI MR2's over the last 12 years, Im no newbie, but this karman vortex AFM and fuelcut thing has me nailed like a cheap hooker. I had to swallow a bit of pride to post here, so I want to get the most out of it.

Suprafanatic... that filter thing makes no sense. besides, I have run the car for very short runs with no filter in between tests and it still hit fuelcut. LEt me edit my previous statement... I am willing to try anything based on a sound theory. I have also inspected the downpipe and flapper door and there are no signs of interference in there.

Doward, Im more than happy to try this 4500rpm trick to see if I can get around fuelcut, but Im confused as to what this will tell us about the condition. If it doesnt hit fuelcut what is the solution? standalone? safc? disconnect the fuel line and throw matches at the car? Im not sure how to read the results of this test, still Ill try it and post back this afternoon with results.

 

[Nick M]

Remember volume is measured, and mass is calculated with other variables. Fuel cut isn't that complicated. But the Karman Vortex is.

A nice Hitachi mass air flow sensor like Ford has been using since the mid 80's would have been good. They even use one on the GT, and it can push 1000 hp on the stock meter without extensive tuning. Mass air=good.

I know Doward won't agree with me on that last one.

And the JJ style mocking wasn't at you, the monkey who said removing his airfilter cured fuel cut.

 

[ArmandoP]

Basically like Doward said you trick the ECU by reducing the signal from the afm. The ECU of course adds less fuel in turn, but since he is already overly rich that isnt an issue. He should be able to easily "fix" the problem that way.
(note the "fix" in quotes, )

Of course you could do the same with a standalone or another piggyback, but I mentioned the SAFC because I was familiar with how it worked.

Im willing to go this route if I can determine that the car is acting as it should and theres nothing "wrong." The flapping wastegate test today should tell me this I hope. Obviously Id rather get a standalone, but if the SAFC will work and prove to me that this theory is right then it will be an acceptable stepping stone until I find out what kind of ecu I really want. This of course would require atleast a wideband and some dyno time.

pimptrizkit, I agree, I need a weldon pump and an AFR but Im pretty positive that wont solve this current problem.

 

[Doward]

Nick you're right, I'll disagree

Armando, if you do not hit fuel cut doing as I mentioned, that means you are getting too high of a signal from the AFM, at too low of an RPM.

Fuel cut isn't a simple value that once exceeded, triggers it. When playing with my 57 trim on the MAFT-Pro, I found I would hit FC @ 16psi @ ~4200rpm when I was running a dog rich 10:1 AFR. I was only reading about 1275-1300hz from the AFM, so I was confused at first.

Once I leaned back the AFR to around 11.8:1. suddenly I'm at around 1200 hz at that same 16psi @ ~4200rpm, and no more fuel cut at that point.

It's my understanding that FC is based on X airflow @ Y rpm. That means you can hit FC at a lower rpm, if your signal goes too high - and that 'too high' does not necessarily need to be 1400-1450hz.

It's also my understanding that the 'ceiling' for the AFM signal increases as rpms go up - so if you suddenly are finding you can run from 4500-6000 rpm with no fuel cut, then your problem is as I described.

If you still hit FC doing as I mentioned, then I believe you are triggering the maximum ceiling for the frequency of the AFM.

In all honesty, if you had a MAFT-Pro, this would be a lot easier to figure out (since you can read the frequency from the MAFT-Pro)