Sequential setup - no boost until 4500
 

I just bought my first RX-7 about 2 months ago and the turbos were blown and in the back of the car. I thought it would be a good learning experience to put some new ones on and learn about the car. Turns out it was a great experience. However I've got a problem... I think.

First of all, I'll give you a little back ground. I'm not sure whether or not the boost guage is working properly. It's showing a vacuum of -15 psi at idle. It then only goes to 0 after moderately hard acceleration. At 4500 rpm I get a kick from 1 of the turbos ( I'm assuming ) but I never get another hit from the second. I was under the assumption that I should be feeling the boost at about 2800 - 3000 rpm from the primary turbo and the second should come online at 4500 rpm. As it is now, I'm only getting boost at 4500 rpm and it's not showing more than 4.5 - 5 psi on the guage.

Also, the turbos are brand new Efini twins.

Here are my questions:

1) Is it possible that the boost guage needs to be recalibrated or is that normal operation (for the guage).

2) Has anyone else had this problem and how should I go about resolving the issue?

I would really appreciate any help you could give me.

Thanks,
Jeremy

your primary turbo is not working. secondary kicks in at 4500. yes you should feel boost way under 4500

So is it that I've connected some vacuum line or a solenoid incorrectly? From what I've read, the actuator feeds off the primary turbo's boost to open the secondary turbo up. By that assumption, wouldn't it be the primary turbo that is spooling late and never opening the secondary up?

Check your Charge Control (and solenoid):

http://www.autosportracetech.com/RX-...erOverview.htm

If its not separating the primary and secondary boost, then you'll vent all your primary boost until the CRV closes which is around 4500 rpms at which point you should have both turbos online.

Yeah, that's what I was thinking as well. However, why would the boost guage never show a reading above 5 psi? Could there also be something else in addition to that?

Many times, a bad (or improperly installed) check valve will cause your symptoms. Best to replace them if you have not already done so.

Which Check valve(s)?

Your best bet is to look at the vacuum diagram and verify "everything". Start with trying to get your primary boost working. Use the link I provided as there is a troubleshooting guide there as well which you can work through.

How can I find out if my boost guage is working properly?

Use a MityVac or air compressor (something that you can measure/meter the incoming air) to test it. With these cars, more often than not your boost gauge is just fine; its most likely a vacuum line mis-routing problem.

^Agreed. I'd assume for now that your boost guage is working. I think 15 at idle is average. And if your primary isn't working, I wouldn't expect to see any boost until ~4.5 k.

I appreciate all your comments. My next question is that if in fact it is the problem described above, why would it never show more than 5 psi of boost on the guage after 4500 rpm if the valve is fully open?

I'm thinking that the boost guage may not have a tight enough fit on the nipple. Any suggestions on snugging that up?

Jeremy,

There are many parts to the turbo control as outlined in the link I provided. You most likely have more than one problem. However, you can't necessarily fix everything at once.

Concentrate first on the primary boost problem (i.e. no boost before 4500 rpms). After that, you can concentrate on the low secondary boost.

is your boost guage mechanical or electrical? if its mechanical then it should be ok. the vacuum hose doesnt have to be that tight. just ziptie it on. itll hold. if its electrical check the selonoid and wiring. on the twins check for any boost leaks in the IC and piping. and like everyone else said, check the 'check valves' and all the solenoids. i had this problem with my primary and it ended up being one of the solenoids in the rats nest, so i went non-sequential.

Thanks guys, I'll let you know how it shakes out. I just got a Mity Vac today and tested the boost guage. Turns out that the guage works fine but the rubber piece that connects to the nipple was leaking a little, I put a zip-tie on it and it's fine now. I'll start with the rubber hoses and connectors, it seems that the clamp on the y-pipe was a little loose because I could jiggle the plastic piece a little. Then I'll try the air bypass and the charge control actuactor. If that doesn't work, I'll be asking some more questions.

Once again, thanks for all the comments and I'll keep you posted.

Jeremy