For Months I have been using the Greddy Profec B Spec II boost controller (Installed version 2), to control my boost, set to stock 10psi. Ever since installation, my boost has been dead on 10psi, perfect. No spikes, no creep at all.

Mods are: intake, full exhaust (midpipe), Power fc base map, SMIC, no emissions, Walbro Fuel pump, SARD Fuel pressure regulator @40psi base pressure

This past weekend I took the car out for a cruise, did a small pull and noticed my boost crept up almost instantly to almost 15psi. I immediately let off in fear of hurting the motor. I turned the boost controller off completely (what should have been 7psi) and got on it again, almost 15psi yet again.

Today I got the chance to re-check all of my vacuum plumbing and make sure something didn't come loose.

And this is what I found, both caps on the other side of the actuators cracked all the way around, not possibly able to hold any kind of pressure.





Taken from another Thread -

I've read horror stories about people blowing their motors from sudden increased boost like this happening, I'm lucky I caught it before it happened to me, which is why I believe there must be an alternative way to "cap off" the other side of the wastegate/precontrol actuators. Which how I came up with "Version 3" simply take a vacuum line, and connect the two nipples together, resulting in a sealed system that can build up pressure just like capping it off would do.

I haven't had a chance yet to test if this works or not, any input on if this would work or wouldn't work would be greatly appreciated.

 

crazy... coglad you cought your overboost when you did. When I blew my wastegate line off I blew my motor right along with it

 

Plug it with JB weld. Put some JB in there, let it cure overnight, then do another round of JB and let it cure. I've plugged coolant nipples that way. You just have to be thorough with it as I just described. Otherwise you'd have to physically weld it ****.

Also, you turned off your overboost fuel cut. I'm having trouble getting through to people on this... fuel cut saves motors. There's a reason why almost every turbo engine has programmed in from the factory. Set your boost levels (Pri and Sc values) to about .50 kg/cm^2 and you should hit fuel cut around 11-12psi

 

or get some silicone caps from mcmastercarr
http://www.mcmaster.com/#silicone-caps/=9rj4su

 

Thanks for your input Arghx, I'll try some JB weld tomorrow. I'm not sure how I would have turned off my overboost fuel cut, I would love for that to be set around 11-12psi.

I also failed to mention that the car is running non-sequential right now

As for setting fuel cut, would that be going from this:



To this?:

 

You didn't turn it off. Some people do--they set all the values to 2.00 . In some cases there are good reasons to intentionally turn it off but IMO most guys would be better suited setting it up properly. The default values (displayed in the first picture) were just too high for your setup.

The settings displayed in your second picture should be ok. When the fuel cut hits the engine feels like it's hit a brick wall (you'll probably hear it too). Then you

1) adjust/turn off your boost controller
2) check for mechanical problems as you just encountered
3) raise the fuel cut setting a little bit if you are willing to let it spike a bit due to changes in the weather or for some other reason.

for reference here is one method for setting up fuel cut on engines with external boost controllers: https://www.rx7club.com/showpost.php...9&postcount=46

for engines with stock turbos and stock MAP sensor with default calibration here are some guideline values

If your target boost level is

10psi: set boost to .50 kg/cm^2
12psi: set boost to .65 kg/cm^2
14psi: set boost to .80 kg/cm^2

these are guideline values for setting up a fuel cut that is 1-2psi higher than your intended boost level. you can raise or lower these boost values in increments of .05 kg/cm^2 to make the fuel cut a little more or less sensitive. Each vehicle might need some slight tweaking because of differences in altitude etc.

 

Several sources for caps and methods of blocking off vacuum lines.
https://www.rx7club.com/3rd-generation-specific-1993-2002-16/silicone-vacuum-caps-928572/

 

Wow a lot of info in that post. I've read your thread "How to make untuned PFC basemap safer" a few times before, and ramped up the enrichment for higher rpm, but I never saw the "overboost fuel cut" post. I now have a much better understanding of how the overboost fuel cut feature works on the PFC. I think that it deserves to be in a sticky.

I went ahead and JB welded the wastegate/precontrol nipples today, gonna do a second coat in the morning after it cures.

Thanks again for such great info arghx

Good info there too, I have quite a few of those crappy rubber caps blocking a few other vacuum hardlines that I'll be replacing soon with those McMaster-Carr caps.

 

Just make sure you get JB weld inside the hose barb so it will hold.

man I just found a mistake in that post about how to set your fuel cut. I said that .80 - .25 = .65 ... wrong . I'm trying to get stuff worked out with the moderators so I can make corrections to that thread. You can't ever catch all your mistakes right after you write something. There are so many little things that I want to fix.

 

I definitely did, and I'll be doing a second coat sometime tomorrow, and probably put some kind of silicone cap over them as well just to feel better about it

Yeah I didn't even catch that until you mentioned it now. But I think I get the idea of how fuel cut works, and the equation of how to acquire desired fuel cut.

So the equations would instead come out to:

10psi: set boost to .40kg/cm^2 or .45kg/cm*2
12psi: set boost to .55 kg/cm^2
14psi: set boost to .70 kg/cm^2

I think that whole thread deserves to be a sticky in the PFC Forum, a lot of great info in there, and would probably save a lot of guys motors if they understood how to use their PFC

 

Ahh nevermind, you had that right. Missed the part where you said guideline values for setting up a fuel cut that is 1-2psi higher than intended boost level . It's late.

 

just to make it clear: the way I wrote it, and I think it may have been confusing, is that I calculated the target fuel cut psi and associated setting. You wouldn't have a 10psi fuel cut unless you intend to run less than stock boost.

So if you intend to run 10psi, you would want a boost setting of around .55 which would be a fuel cut of around 12psi

if you intend to run 12psi, you would want a boost setting of around .70 which would be a fuel cut of around 14psi

if you intend to run 14psi, you would want a boost setting of around .85 which would be a fuel cut of around 16psi

boost is always going to fluctuate a bit with the weather and the altitude affects the settings a bit as well. So you can raise or lower those values a bit, in increments of .05, depending on your setup and your preference.

One of the moderators is going to revise my big PFC thread so that the overboost settings are in the first post. As for making it a sticky, that's up to the moderators. If there are too many stickies they tend to get ignored.