Hi all,

Well my '94 finally ran into it's first problem, seemed to come on all of the sudden -- It loses boost and won't accelerate after shifting. For instance, if I launch, it pulls strong and true thru 1st making full boost the entire way but when I hit the shift to 2nd, power and boost completely dies off... if I hit the clutch and let the revs drop to idle, then try slowly getting on it again, boost and power will come back up.

It also does this when I shift from 3rd to 4th on a freeway pull. Just sudden complete boost and power loss... the gauge still shows 3 or 4 psi but there's nothing there and the needle bleeds off if I keep the gas pushed down.

The engine runs strong, still pulling 17" of vacuum at idle (over 475 on the PFC commander). 65,400 miles on the car and original engine. Stock sequential twins, Downpipe, catback, PFC, and cheap bastard airbox mod. Boost is normally 11-12 psi. I tried searching a bit but can't seem to find anything as of yet so I wanted to get some input on where to start with this specific problem.

Anyone seen anything like this before? Very very depressing...

Thanks in advance.

 

Vacuum line check valve not holding!

 

You might want to go through and replace all your vacuum lines with silicone. Thats what ended up fixing my issues for a while til the solenoids started taking a ****.

 

I had a similar problem when I had twins. It ended up being a solenoid. There are a number of posts on it, and some very good directions on how to check the solenoids.

 

Sounds like check valves to me

-Geoff

 

Thanks guys.

So should I reference the diagram of the vacuum system and replace every check valve? Or is there a way to pinpoint a specific one?

Is it a very difficult task to do? I'm assuming you can remove the hoses going to the airbox to get access and work from above...

In the meantime I'll look for the posts about solenoids in case it's that.

 

Good info on replacing the vacuum hoses can be found here: Vacuum Hose Replacement

 

Good stuff, thank you sir.

How can I get ahold of new vacuum line check valves? Is there a kit, are they all the same, do I need to buy a bunch of different ones? Where do I get them from?

 

DALECLARK search he sells the aftermarket viton ones!

 

Thanks, I'll look him up.

Can you guys give me an idea of how much work is involved with just replacing the check valves? Can I do it pretty easily by just removing the intake elbow and airbox hoses? Or does the whole TB assembly and everything else have to come off to do it?

I don't have access to a garage any longer, my baby has to stay under thick cover and tarp in the back yard of the house I'm renting, so I'm hoping I can fix this problem easily. One day when I have a garage to put her in again I'll pull the whole shabang off and do all the upgrades the vacuum hose writeup recommends... but for now I'd really just like to fix the boost problem. I really don't want to have to rip everything apart in a yard or driveway.

Thanks so much guys!

 

You can replace all the ones in front of the intake manifold fairly easily, will need to remove the little pressure tank to access its related check valve. The one at the back of the upper intake manifold is the only one you cannot access with out removal of intake, but i don't believe it is the problem one for your case. Try to change the ones to the pressure tank and the vaccuum tank first and then test it out. You can also test your check valve with a hand vaccumm, pressure pump to see if they are bad!

 

If all of your hoses/solenoids are stock then this can be a frustrating job. I suggest buying enough hoses to replace all of them. I would advise you do replace them all while you're in there, but if you refuse to, hoses may break unintentionally.

A Mityvac is a great tool to test out hoses and actuators. A little pricey, but I considered it to be worthwhile.

You'll need to remove the intake box/hoses, throttle body, and the intake manifold. There might be more, but those will get you to a lot of hoses.

When removing hoses from plastic nipples like on the solenoids, be EXTREMELY CAREFUL not to break them. The solenoids are not cheap. My method was to try and twist the hose on the nipple first to make sure it wasn't stuck on. Then, I'd slowly wiggle it off. I also took a 9v battery, cut the typical 9v connector in an alarm clock, and used that to test the solenoids. Its not optimal, but it does work!

 

Guys!! I think I might have found the problem!

I ordered Dale's check valves today and in anticipation of doing the replacement job next week, I unbolted the Pressure Chamber and slid it aside to have a look at the hoses underneath... well apparently the vacuum line from the turbos to the Pressure Chamber check valve had completely come off! Tried sliding it back on and there is almost no resistance, no grip holding it on the check valve nipple so I think that must be what happened!

All I have to do now is get a zip tie or tiny clamp to secure the vacuum hose to the check valve so I can take my baby out and test it out to see if that was the culprit.

What do you guys think, am I on to something here? Any other good ways of securing the vacuum line to the check valve nipple?

 

That was it!!! I got some small zip ties and reattached the hose, used 2 zip ties to lock it into place. Took the FD out for a spin, put her through her paces in a big way, and everything is 100% now!! I'm so excited.

I could also tell that spool and boost in all gears and all speeds had picked back up considerably... obviously the pressure tank vacuum line is very essential to all turbo functions, not just regulating pressure after a shift. I can't remember the last time she felt so damn FAST lol...

Thank you very much for your input everyone!! When those check valves arrive I'll just hold on to 'em and once I have access to a garage again I'll do a proper vacuum system update with the valves and silicon hoses. I'll take this as the first sign that the original components are getting ready to retire.

 

Bumping this back up for an identical problem, with a different cause.

I have the same problem. After a hard shift from one gear to the next, I cant make any boost.

Initially, my search revealed that the intake hoses may have been collapsing. I had a blitz intake, and stock intake hoses. I decided to switch out the blitz intake for an HKS RS intake.

This didnt correct the problem. I then found this thread, and decided to try the check valves. I had done a simplified sequential conversion (which may have been when the issue started, too vague to remember :-\ ). I replaced the check valves on the vacuum and pressure chamber. Each chamber popped off their respective pressure or vacuum when valves were pulled. This didnt correct the issue.

My next step is to look into the solenoids. Which ones do i start with? Would it make sense to start with the two easy to reach solenoids (turbo precontrol and wastegate control)? or is there another likely culprit?

 

Trying changing the vacuum lines on the actuators that you can see from the bottom. Theyre at the front of the turbos. I replaced those and it fixed my issue.

 

those are the ones with the restrictor pills right?

 

Yes

 

As I mentioned, i had done a vac hose job when i did the simplified sequential. so all the lines (except the two with restrictor pills) are new.

 

Yeah i'd check there and i'd also check the bottom of the wastegate where the actuator connects to the door and see if the little clip hold the actuator to the door is wore out not allowing the wastegate to open correctly.

 

problem solved. kind of ashamed to post the mistake i made, but in hindsight, it all makes sense, and, before knowing what i know now, i can see how someone else might make the same mistake.

-a few notes, i was following the simplified sequential instructions on robinettes rx7 page, and the following diagram: http://www.turborx7.com/images/turbo...simplified.jpg
-i had no idea the 4 vacuum posts on the LIM werent common to the runners of the LIM.

Anywho, when the EdwardNorth posted that he found his identical problem to be related to the pressure chamber, i started researching how i had done the simplified conversion, and referencing the OEM vac chart, and the simplified vac chart.

In the directions, it states "And the hose that goes to nowhere, it obviously goes to the intake manifold" or something similar. Well, I put it on one of the vac ports on the front of the UIM near the throttle body. I thought it was silly at the time, thinking it was just a way of reducing the use of caps. Anywho, now i realize i was just retarded.

In hindsight, its even the same color as the one adjacent to where its supposed to go, to the pressure chamber.

anyway, my pressure chamber, similar to the OP's, was not getting a pressure source. this was causing my issue. hope this helps anyone else in the future. I think i may even drop a line to the owner of Rob's site to put a note or clarification, as there is room for misinterpretation.

also, i have never felt the car feel so alive.

 

We all make mistakes. Glad to hear you fixed it! I hope when I get mine running I experience the thrill of full boost