prjctRx7

i was driving home today after work and on the freeway when i was going like 80 i decided to give it full throttle and it read 10-11psi on the boost gauge then when around 100mph the boost slowly dropped to 5psi, is this normal??

also when at a full stop i punch it in first gear and it doesnt boost up to 10psi, is there a limiter in first gear or something wrong???

the car is all stock except for a hks downpipe, idle is at 700-750 rpms and vac on the gauge reads 16-18, car has about 88,xxx mi's on original motor

birdy01

wat gear were u in wen u went full throttle @ 80mph? i heard it was a no no to go full throttle in 4th or 5th depending on your speed

prjctRx7

5th gear, why is it a nono to go full throttle in 4th or 5th??

jeremyb

i full throttle all the time in 4th and 5th on the freeway... sometimes WOT i 4th on the street if its longs enough and no lights... maybe you broke a solenoid? Hose to one of the soleniods or chambers popped off?

Jeremy

prjctRx7

what solenoids should i check?? when you full throttle it on the freeway does it read a consistant 10psi until your foot lets off??

scratchjunkie

for me when i wot in 5th @80mph, i hit 13psi then it will drop to 12 by 4k rpm.

ijneb

You've probabily got a stock cat on there somewhere.
At high RPMS the exhaust systems starts to restrict air so much that the backpressure at the turbines cases the turbo's to stop spinning as fast causing you to loose boost.

1st gear happens so fast, but I think it does have a limiter of some sort.


birdy01- who told you it was a nono to go WOT in 4th or 5th? the highway patrol?

WOT

prjctRx7

any suggestions what can be going on mith my car??

ijneb

Your stock main cat is causing a restriction in your exhaust flow which is causing a "back up" of exhaust gas at the turbos, causing them to slow down.

Open the intake up, open the exhaust up and you wont have that problem anymore, but you'll have to worry about getting boost spikes/creep.

prjctRx7

thanks ijneb for the help...i do have a stock cat, still need to take care of my smog. it does feel like it has a restriction. if i add a mid-pipe and a intake what is the best way to approach the boost spikes and creeps

FDeez

I don't think the stock cat does that kind of restriction. I have a stock cat and that doesn't happen. Scratchjunkie has a stock cat and that doesn't happen. I don't know what's wrong with your car.

prjctRx7

does the stock turbos stop pulling after a certain rpm's??

ijneb

His cat is probabily collapsed, causing it to flow horribly.
My car had the same problem- boost would drop off in high RPM's- took the stock cat off and it was a mess.

prjctRx7

the other day i found a crack in the airpump hose. i probably drove on that for a few days. dont know if that can be a cause??

how do you diagnose a collasped cat??

dgeesaman

iTrader: (7)

Remove the cat, hold it verticall and shake. If it's collapsed, pieces will fall out. A midpipe has no catalytic element - you won't ever pass smog with that. I suggest you replace with a Bonez high flow cat.

WaLieN

No, that isn't a pressurized hose -- it won't cause it to leak boost.

http://www.autosportracetech.com/RX-7/rx7stuff.htm

That's a good start to diagnose your turbo troubles. At what RPM does your boost drop off at? A 10-8-10psi boost (10psi at 3000RPM all the way to ~4,500 where it'll drop down to ~8psi, then it recovers to 10psi shortly after) is normal. It sounds to me that you might have a clogged main-cat (which is what some of the other guys suggest as well), or you might have a small leak somewhere on your intake. Check all of the 1" hoses, the y-pipe coupler, and the intake hoses to make sure that your intake hoses are okay. Good luck with your search.

maxcooper

There is no artificial boost limit in first gear. But there sometimes isn't enough load to produce as much boost as you will get in higher gears. And if you have a problem that limits boost at high RPM, that will reduce your boost at the top of any gear.

It is somewhat normal for boost to drop a little (like 10psi down to 8psi) as you rev toward redline, but dropping to 5psi is excessive. There is no limiter or anything that artificially limits the boost, but it just drops off for "natural" reasons. I think you have a restriction and as others have pointed out, it is probably your main cat. I don't think the failure is related to your problems with the cat's air pipe -- it is just old and probably failing.

Another thought -- do you know about the turbo transition around 4500 RPM? Many cars drop boost before the transition and then spike a bit after. If you happened to glance at your boost gauge at the start of the transition, that may explain why you only saw 5 psi.

-Max

prjctRx7

how do you check the intake hoses?? the ribbed ones. do i just remove them and start bending them to see if they go cracks in them?? could it be as simple as a bad check valves?? is the check valves suppose to hold pressure for only a limited amount of time??

WaLieN

Get a bright light of some sort and flex the hoses a little to look for cracks. Hard/brittle hoses could also cause a leak, as they will not be soft enough to conform to nipple. Check valves are designed to "check" air one way, which basically means that it will allow air to pass through one way, but not the other. Bad check valves *could* be the problem (the pressure tank/vaccum tank are supposed to hold air/vaccum), but it's really hard to tell since you haven't told us what boost you get at what specific RPM's.

wrankin

<sigh>

before you go jumping in and pulling stuff out of your engine bay, go do a real boost test.

actually, before you go do this, read the newbie FAQ for the FD and understand *what* you are looking for and how the turbo system operates.

in 3rd gear from a rolling start, floor it and hold it until redline. you should see ~10psi with a little dip around 4500 rpm. if you are a pound or so off, don't sweat it.

make sure your car is properly warmed up and that you have a big open empty straight road.

-bill