red_dragon

iTrader: (10)

I just bought an FD and I'm getting a little confused with the boost. Here's the mods list:

motor is street ported/built by pettit
"high flow" turbos built by pettit
M2 Carbon fiber intake
M2 dual tip exhaust
Pettit downpipe
stock cat
stock ECU (ya i know getting to it soon)
stock intercooler (ya, i know, also getting to it soon)

So when I bought it in southern california (warm day) it was boosting 11.5 pretty consistently, then later on it somehow started boosting 12.5 ,13.5 ish. Obviously I was like holy WTF and quit boosting. I've been paranoid about it ever since. First thing, isn't stock fuel cut at 12PSI? Second, he's been driving the car in this configuration since early 2000 if it's actually boosting that high, why isn't the motor pwned yet? (compression was tested 10k or so ago and came out 8.5-8.6 on all faces on both rotors) Tonight I took it for a spin, it's about 45 degrees F outside. I stepped on it, and it instantly jumped to 12-13ish PSI. So yea, I'm really confused. Do you think I'm actually overboosting? Maybe the gauge is just wrong? ECU looks like a stock one and it says it's remanufactured for Mazda by Denso? It's a 10 year old pettit boost gauge if that makes any difference.

WaachBack

iTrader: (21)

Yes, I think you are overboosting. With your mods, that is very common if you have not ported your wastegate.

red_dragon

iTrader: (10)

Hm, so for some reason I'm not hitting fuel cut. Does that not come in til later? I don't think the previous owner ever hit it either in his many many years of ownership... And that also means he's been overboosting for yeeeears. Is that even possible?

RotorRyan

iTrader: (3)

Rpm abs. Cut off(psi) sea level cut off(psi)

1000 26.5 11.8
1500 26.5 11.8
2000 26.5 11.8
2500 26.5 11.8
3000 26.9 12.2
3500 27.1 12.4
4000 27.5 12.8
4500 28.0 13.3
5000 26.9 12.2
5500 26.0 11.3
6000 25.8 11.1
6500 25.4 10.7
7000 25.4 10.7

i believe this is the stock ecu fuel cut

impactwrench

Your AFR must be on the rich side to allow the constant overboost without detonating. Consider yourself fortunate and get the problem fixed. Port the wastegate or install restrictor plates in the exhaust. Also. I would recomend a wideband A/F guage in every FD.

revsteve

iTrader: (6)

let me ask a question also instead of adding my own thread.

My car is creeping to 13-16 in 4th gear around 3500 rpms at WOT.

Mods: 99 turbos, efini Y, Catback, DP.

I have never seen anything like this before. Could a loose connection/leak at the Y pipe or in the exhaust cause this kind of creep? I'd like to avoid teh whole boost controller thing if possible.

Thoughts?

impactwrench

At RPM's that low, I would suspect the wastegate is not opening properly.

DaveW

1. Yes you are probably over-boosting,, your boost gauge is probably fine, and should add a boost controller to be safe.
2. You are probably not creeping, since you still have the stock cat, and creep usually occurs over 4500 RPM when both turbos are on line.
3. There is a delay built into the stock ECU, so it is rare to hit fuel cut in 1st or 2nd gear. Fuel cut will usually only have time to be triggered in 3rd, 4th, or 5th.
4. Cold weather will increase boost, so what you are seeing is not unusual for 45-degree weather.
5. The stock ECU will do fine with your mods once you add boost control and keep the boost at stock (10-8-10) level.

I am running similar mods to yours (see my sig), and dual ball-spring boost controllers, along with the stock ECU, and have great performance, and no problems.

djseven

iTrader: (56)

Remove your boost "pills" going to the wastegate and precontrol actuators. Just remove the two vacuum lines coming off the primary turbo compressor housings and replace them with new empty vacuum lines. Then remove the two lines coming off the side of the actuators at the 3 o-clock position and cap them. This should help keep things safe for the time being. If this doesnt help with the problem then it is likely time for a vacuum hose job to try to eliminate your boosting issues.

red_dragon

iTrader: (10)

Thanks for the info. Will I be fine with the boost control that the Power FC provides (since I'll be getting one no matter what), or do I need a dedicated boost controller as well?

DaveW

You're welcome. On the PFC boost control, IIRC, dedicated boost controllers work better, but some people use the PFC anyway with reasonable results.

Someone with direct experience (I still use the stock ECU) in that will hopefully chime in here.

Dave

theorie

iTrader: (31)

i would also confirm with a second boost gauge.

i have a pettit (mechanical) boost gauge in my car that has become uncalibrated. for now i just read my boost controller or the power fc reading - theyre slightly different, so i usually estimate the average. having a "peak" read-function on the controller helps a lot also.

WaachBack

iTrader: (21)

I blew a motor 2 years ago. One of the reasons was because the power FC could not control my boost. Port your wastegate, buy a $30 mechanical boost controller, and get a PFC asap and you'll be good.

red_dragon

iTrader: (10)

Where would I find this "$30 mechanical boost controller." Also, as I was looking around, I found some dual and single MBC's. Which one am I actually looking for?

WaachBack

iTrader: (21)

Search Ebay.

DaveW

For reference: https://www.rx7club.com/showpost.php...6&postcount=10

Dave

red_dragon

iTrader: (10)

Has anyone tried these ebay controllers?
http://cgi.ebay.com/High-Quality-Man...3A1%7C294%3A50

red_dragon

iTrader: (10)

Actually I forgot to mention, I looked under the hood yesterday and found one of the vacuum hoses had popped off. It's the one that's close to the strut bar on a black lookin thing. I've attached a picture. What would happen if that hose is not connected?

DaveW

That's the pressure chamber. Having that pop off will delay or prevent the secondary boost from coming in. I had mine pop off once also, due to more boost than usual on a cold day. You will need to tyrap it to prevent its happening again.

Dave

red_dragon

iTrader: (10)

Alright I've decided to just replicate Damian's setup. For now, I'm driving the thing without boost =). I'm just wondering if it's going to be difficult to get to those vacuum lines...

red_dragon

iTrader: (10)

Just wanted to post an update to make this thread useful for other people with this problem. I installed a set of Hallman Pro RX just like Damian did (man the hoses were a pain in the *** to install!). My boost pattern and levels are now perfect. The transition is so fast that I can't even tell if the boost drops from 10 or not. My friend said it was like 10-9.5-10 or something. In any case, this method is awesome. Thanks for everyone's help!

Pic of mounted controllers:

DaveW

Dave