binary89

Wow,

Ok well I've been driving the Rx-7 a couple of weeks now, sporadically of course. Any ways there has been a couple of problems that I have been having with it, engine hick-ups when at like 3000rpm for some reason and I sometime hear a weird moo/brrr for a brief instant when I'm at 2000-3500 rpms and applying 3% throttle. So I decided to finally try out the search feature on this forum and looks like I may have diagnosed the problem.

I have a PFS tuned car with sequentials and being an idiot I assumed that primary turbo is supposed to kick in at 4000rpm and the second kicks in some time during the tunnel vision experience so its hard to notice. Then I find out that it really is supposed to kick in at around 3000rpm and make 10 psi of boost then when you reach 4000 it drops to 8 psi and then climbs up to 10 again. So my primary turbo is waste gating unappropriately which could mean that the noise is simply some type of check valve, pressure tank, vacuum line failure. To solve the hickup mystery I thought about the time when I was in 5th and I was getting 10 psi of boost at 3000rpm, possibly when I'm make no boost at 3000-3999 rpm the waste closes real quick a couple of times.

Any ways it 4:00 am and I can't work on my car right now.

My analysis of the boost is done by a hks boost pressure gauge.

I may be wrong but I think I may right.

I'll post back in the morning if this topic was a waste of time or if I am kid on Christmas having just experienced the full potential of his car.

binary89

hmm well I've been starring at some vacum diagrams and am confused. Does the pressure tank manipulate the the first or second or both turbos

binary89

Hmm If the problem has something to do with the vacum system then it is narrowed away from the pressure thank and aimed towards the pressure sensor

SayNoToPistons

hmm... edit button...

binary89

If my hunch is correct, then problem is resulting in the waste gate control valve remaining open. So now basically I need to fallow the vacuum line on the diagram and see what I run into.

Because the second turbo is operating fine I can rule the Solenoid Valve (Turbo Precontroller) and the Actuator (Turbo Precontroller) out. Prime candidates could be Solenoid (Wastegate control) and the Actuator (Wastegate control). My hypothesis is that the Solenoid (Wastegate control) is not working properly thus not creating enough vacuum pressure to operate the Actuator (Wastegate control). I'm still stumped on why I got 10 psi of boost pressure in 5th gear at 3000rpms

CantGoStraight

Your best bet for turbo diagnosis is to use the 3rd gear test run for a better picture of what you actually have 1st gear happens way too fast and second isn't a whole lot better.

revsteve

iTrader: (6)

i get close to full boost at 3k in 5th gear.... but like all other FD's i just get no power there

binary89

am I sapposed to get close to full boost in other gears at 3k rpms

revsteve

iTrader: (6)

If I am not mistaken the primary turbo is fully spooled at about 3000 RPM's. If you have any vacuum mods (for instance I have a boost controller running in between my Wastegate and Pre-Control actuators so my boost spools a little faster) then that would affect it.

In first gear you wont hit full boost, you should get close in second, you should hit full boost in 3rd 4th and close again in 5th.

At least thats how my car works.

dgeesaman

iTrader: (7)

Yes, my car makes about 10psi by 3k in all gears. It may take a moment to build it if I'm in 5th, but it will get there. The 8psi dip should occur at 4500 not 4000. At 3% throttle you're probably hearing the air pump 'moo'ing, which is a subject you can search for. It's unrelated to boost issues.

The pressure tank only works for the 2nd turbo. At 4500 rpm, the pressure helps (along with vacuum) open the turbo control door, which is what opens exhaust to flow over the 2nd turbocharger. The solenoids that control that actuator can go bad and cause the door to open too slowly or not close fast enough. Not opening fast enough at 4500 will cause low boost above 4500, and not closing fast enough can cause low boost below 4500.

I suggest you run the boost pattern test in 3rd gear as well.

twisted7

iTrader: (3)

you said that your car stutters in or around 3000rpms if so, that would just be what everyone else usually gets. Sometimes goes away with cleaning the injectors, adding a PFC, or changing the spark plugs. different people experience different things. do the boost test as suggested and let us know what the boost pattern really is

binary89

hmm well I was looking at all the vaccum line and noticed one that was slightly lose so tightened it and added a quick tie, took it out for a spin and I got 10psi at 3k so thats all good. but the hessitation still occurs im not sure what it is I think it might be running to rich because I have feather the trottle and upshift to prevent a huge bogging down when it happens. I also am still hearing the weird buzz/moo/brrrr randomly. Im thinking a good oil change will probably take care of that weird bogging but im woried about the noise.

CantGoStraight

If your car is fully warmed up (as it should be before getting heavey into boost) the 3k hesitation your referring to should be next to non-existant when doing WOT boost runs in third gear. Typically the 3k bogg or hesitation occurrs whe ntrying to drive moderately with some boosting.

binary89

yeah I guess thats what it must be because normally the bog occurs when im just cruising and I need to move a little in second.

scotty305

iTrader: (2)

Your buzz/moo/brr is probably due to the air pump. Do you have an aftermarket intake?


https://www.rx7club.com/3rd-generation-specific-1993-2002-16/eliminate-air-pump-moo-%241-1-minute-486061/

-s-

White94RX

The 3k stutter is pretty common. Some people say it's a fuel issue, some say grounding issue with the electrical, some say ignition, etc. I haven't heard of a 100% for sure fix.