Strange boost issues....FD boost doctors?
 

I just bought a 1993 FD with 117K on the clock. The engine has been rebuilt, but I don't know about the turbos.

Here is my problem...

The car builds full boost on the first turbo, but drops to about 6 psi and doesn't climb. It either holds 6, or drops.

Another issue I have is when shifting into second, from full boost in first, the boost drops to nothing...and the car feels like a dog. If I let off the gas, and get back into it, sometimes the boost will shoot up to 9-10....

Here is what I am going to try...

-Replacing stock downpipe with HKS...
-Replacing the midas muffler on the car with an appropriate muffler....it has a single in, single out muffler on the car, and doesn't seem to be moving enough air. It even melted the little plastic trim piece around the tip!
-Replacing all the vacuum hoses..

Can you guys think of anything else to try?

Thanks...

Patrick

I would go for the vacuum hoses first, then go from there.

Do you know what your vacuum pressure is at idle?

My idle is fluctuating a bit right now...Sometimes it idles at 1200 rpm...(maybe that is just till it is warm)

But is usually around 16-18 in hg..

I think that is normal, isn't it?


Thanks,
Patrick

Yes, from what I've read, 15+ inHg should be about normal.

You should be able to hit full boost without modifying the car, but check this thread and see if it has any ideas for ya:

https://www.rx7club.com/vforums/show...threadid=14563

bump...

Anyone have any ideas...or do you just think it is a vacuum hose.

I am going to be doing the vacuum hose replacement within the next month...

Could an incorrect muffler cause this. The muffler on the car is a single-in, single-out muffler. As opposed to the single-in, dual-out that came on the car...

Later,
Patrick

By the symptons that you describe about letting off and getting back on the gas and the boost jumps up to 9-19 psi check your check valves it might be leaking and losing vacuum. Next time drive it until the secondary comes online, then when the boost drops let off of the gas until vacuums hits about 20 hg then get on the gas again, if the boost comes back on, it could be a bad check valve.

Hmmm...

Now, how many check valves are there? 4 or 5 I think.

I guess I could pull them off, and blow through them to see if they work...

Thanks.

Any more ideas?

Later,
Patrick

Sounds like the vaccuum hoses, but it could be a check valve. I have heard of problems like this bfore, and it turned out to be a bad vaccuum line.

Just thought I mention this. When you take off in 1st gear, if you are revving between 4500-6000 rpm and shifting into 2nd and the rpm did not drop below 3100-3200 rpm then the first turbo will not kick in. Try this, if you rev to redline in 1st and shift to 2nd, the engine should drop to around 4500 and you'll feel both turbos kick in in 2nd.
The moral of the story is this: From 1st to 2nd gear shift at 3000 (conservative driving) or 3800 to 4000 (1st turbo kicks in) or above 7000 - redline (when you are trying to whip a corvette):dragster:

been there..... still there, kinda
 

pweizman, maybe it's the Ohio weather ??? :-} I've got a '93 with 70K miles and I was getting similar boost patterns lately.... used to get 10-8-10 and now I'm 10-6-9.5, but I have days where the 2nd turbo doesn't kick in and I'm 10-6-6..... sound similar ? Just started doing it two weeks ago and it's my daily driver, therefore, I haven't dug into the vacuum lines, yet.... let me know if you would like any help. I may be doing the same...THANKS.

Welcome to Mazda's sequential twin turbo hell....

With 100k+ on the car, definitely replace the hoses soon. My car had 49k when I replaced em, and there were so many cracked and broken hoses, I was surprised the car ran at all.

Also, check the intercooler hoses. The short rubber piece that connect the y-pipe to the upper IC pipe can tear fairly easily. You have to take it off and tug on it to see the rips though. Also, the hose coming off the back part of the Y-pipe that connects to the CRV (charge relief vavle - looks like the BOV) has a tendancy to crack and leak some boost, especially from that 2nd turbo.

Re: been there..... still there, kinda
 

Matt -

I usually get 10-6-6. I think it is a check valve or vacuum line somewhere....or a clogged pre-cat. I already bought a down pipe, I just have to install it. I guess I will just take it one step at a time.

Then, I have to find my oil leak(s)....:p

Do any FD guys meet up in Columbus? I would like to hang out with some other FD owners and talk about cars...

Email me if you want... pweizman@cinci.rr.com

Later,
Patrick

Check the hose to the vacuum chamber BEHIND the power steering pump.

Almost EVERYONE forgets about that there. Check ALL hoses first, and then call us in the morning :D