Yes, another one.
It's a long story- I'll spare all of you.....

Almost a year ago, I changed plug wires, and adjusted the throttle to ensure full throttle operation. Buttoned it back up, and it ran fine, except I had no boost whatsoever. I decided it might be a vac hose, so I changed all the silicone over to viton (great stuff!), and while I was at, simplified the rat's nest by removing, things like the EGR valve, double throttle butterflies, tb coolant line, putting a greddy elbow and eliminating the air bypass, etc.

All back together, and the car ran insanely rich, and I spent months trying to diagnose it. Don't even ask about all that I did, but in the end, I returned all the removed equipement (had to get another UIM with butterflies still in..) and with crossed fingers fired it up. Wouldn't you know that the car ran perfectly- great idle, no rich condition, drove wonderfully......except NO BOOST! I'm back where I started a year ago. Arrrgghhhh!

The car fine, plenty of vacuum at idle; runs clean through the rev range; no strange sounds. I don't suspect a boost leak-I have an j-spec y-pipe, the couplers to the PFS stock mount IC are new with t-bolt clamps, I'm back to the stock intake elbow with air bypass. The turbos are fine (they're Wael's TEC-Turbo modified twins). Check valves are new, and the vac lines are plumbed correctly (I checked them a bunch of times before putting the UIM back on.

But there's not even a glimmer of a boost signal, and after this past year's ordeal, I''m sorry, but I could use a few extra heads on this. I'm sure it's something painfully obvious.

Thanks everyone, and sorry about another boost question...

 

If there is NO boost signal, IMO, 1 of 2 things must be wrong:
1. Sensing boost where there is none or boost sensor disconnected or faulty
2. Massive boost leak (but you said you checked all that)

Dave

 

- Checked the boost sensor a few months ago in the midst of my 'too rich' plight, and it was fine.

- there doesn't appear (you'd hear, wouldn't you?) to be a boost leak in the intake tract

Also, just for the record, there is not even 1lb of boost registering on the gauge.

 

is your boost gauge connected? lol.

 

Yes, it is. It only shows vacuum, though. Do you think it's in backwards?......lol

 

Does it feel like the car is boosting at all? If not take your intake off and spin the turbos by hand. They might be seized (highly unlikely). Do you still have the factory downpipe and cat? Those might be plugged but even still you should still get some boost. Where are you getting your boost signal from? There are nipples on the uim that you can put a boost guage on. Also your boost guage might be screwed. IF still there is nothing then make sure all of your connections on the intercooler piping is tight including your Y pipe. BTW what is your vacuum reading on your guage?

R.K.

 

No boost whatsoever. Boost gauge is fine, and I get 16-18inches of vacuum at idle. The boost guage is plumbed to the nipple on the UIM.

I'm running a 3" mandrel-bent downpipe and a high-flow cat that I checked for flow. No problems there.

The turbos are excellent. No problems there, either.

Actually, the car runs great....except for the no boost.

Thanks for the input.

 

I assume you've already done this, but just for s**ts & giggles, apply a small amount of pressure (5-8 psi) to the boost gauge and make absolutely sure it responds to positive pressure. just because it responds to vacuum doesn't mean it is good.

Another thing, from personal experience, DON'T ASSUME ANYTHING, unless you actually checked it.

Dave

 

Whew, that's a tricky one!

Few things that come to mind -

- What type of boost gauge do you have? Reason I ask is the plumbing that Autometer gauges come with (nylon hose and brass ferrules) are notorious for leaking. I have seen some that would read vacuum but not boost. Might be worth going over the plumbing to the gauge, maybe testing the gauge with a pressure source to make sure it's telling you the truth.

- At the end of the day, turbos WANT to make boost. They're totally mechanical. Even if your turbo control system is TOTALLY hosed up, you'll still get SOME boost. So, if your boost gauge is giving you a good reading, time to look at the very basics. Any severe intake or exhaust restriction will cause problems - I would also double-check the primary turbo's inlet duct to make sure it's not collapsing. Rare, but can happen. Also, make sure the wastegate actuators are on there well - if the arm popped off the flapper door, the wastegate will stay open and you'll have little to no boost.

- Do you have a boost controller or anything? Make sure the basic turbo control plumbing is fine - if you're using the factory boost control to some extent, you will need the pills in the line, or you will get very little boost.

- I'm also assuming the engine in general is in healthy running shape save for the boost - starts easily, idles smooth, no smoke, plugs and filters are new and healthy, etc.

- I'd also do a worst-case check and make sure the turbos spin freely. Could have been a bolt dropped into the intake that took one out or something.

Keep at it!

Dale

 

Thanks, Dale!

- boost gauge is a Greddy, and it's fine- checked it with a mighty-vac. Of course, I didn't need to, as there's just normal aspiration performance from the car. It runs perfectly, but when you dip into it for some boost, there's nobody home...

- turbos are fine. And I agree, they want to make boost, and probably are...but it's not directed into the intact tract. As for restrictions, that's what started all this a year ago (!). It's a fresh street-ported motor with DP, hi-flow cat, RB catback, PFS intercooler and intake, TEC-modified turbos, Y-pipe, PFC, hi-flow pump and 1300cc secondaries. Steve Kan tuned it, and it made 300 rwhp and despite increasing boost, there was a marginal hp lift on the dyno. Steve thought it was a restriction, and I went through everything: new dp, flow checked cat, IC, catback, even replaced the turbos!.... and it turned out it was the throttle wasn't open all the way!!! Duhhh. Some restriction. So, I adjusted the throttle and replaced the plug wires while I was in there....and.....no boost! Changed all the vac hoses to viton, and simplified the rats nest, and then the car ran full rich!!! Countless efforts to diagnose, and finally I returned everything back to where it was, and it now runs fine....but no boost!

- Using the PFC for boost control, and the pills are in the lines.

- New plugs, oil filter, etc. a

- I'll check the intake duct (again) but I believe it's ok. And I'll check the wastegate actuators.....

Thanks,
Bob

-

 

Wow, I thought you fixed your boost problem a long time ago.

Here're some suggestion if you're still in the simplified seq diagram. There were two solenoids that are pointed in the opposite direction as the stock OEM diagram. So basically, the solenoids are pointing towards the coils instead of the LIM. Make sure those two solenoids are in the right direction so that it would work correctly.

What you mentioned sounds like the flap door on your Y-pipe is fully open bypassing all boost into the rear turbo causing the rear turbo to spin backwards. You should see some boost when both turbos are operating though.

just my .02

Steve

 

Good point, Steve. Also, if the double throttle is acting up (as in staying closed) you'll have VERY low power. Simply removing the vacuum line from it is enough to test it - with the line off, it will stay open. Dunno if you still have that system.

Dale

 

Hey Steve:
No, I'm back to the full sequential diagram. But, I'm curious about the solenoids that you referenced. Any idea what system they control.

I'm suspecting it's the flap on the y-pipe, too. It must be making boost, but it's not directed into the intake tract. Interesting point on the reverse spin on the secondary turbo.....

I appreciate you help.

Bob

 

Dale:
Double throttle is back on the car. I had to buy another UIM to restore this function, though, as once you've drilled them out there's no going back (anyone want a UIM without double throttle plates??). I know that the valves operated freely when I installed the UIM, but to be honest, I did not check for operation with and without vacuum. Just to make sure, though, the butterflies are 'open' normally, and closed when vacuum is applied- correct?

Just for discussion, were the double throttle valves to be closed, we're suspecting it would inhibit boost. And with the gauge downstream of the throttle valves, it wouldn't see a signal. Good so far, but, the motor runs fine all the way throught the rev range (as if it were normal aspirated motor). And wouldn't we see a little bit of boost? The gauge (and seat of pants) feel no boost whatsoever....

Thanks!
Bob

 

Long time ago I worked on a buddy's FC that had the double throttle stuck closed. Car was TOTALLY gutless. You wouldn't get much of anything power-wise with the DT closed.

You're right - when vacuum is applied, the throttle plates are closed, then the solenoid switches to atmospheric pressure to open them. If the vacuum line is removed from the diaphragm, the DT will be open.

Dale

 

God, I hope that's it.....

Probably make sense to check the vacuum line circuit that operates the DT, too....

 

Here's the diagrams.

https://www.rx7club.com/attachment.p...hmentid=164934

Notice F and H are facing backwards.

 

Checked double throttle operation last night, and they are fine: open normnally- closed with vacuum.

It has to be the air control valve in the y-pipe. It should close under 4500 rpm (vacuum applied to actuator) and direct primary boost into intake tract. If it stays open, boost goes into secondary turbo or out charge relief valve. Or it could be the operating vacuum circuit for the actuator which includes vacuum tank, solenoid, and check valve. Right?

 

So, here's the latest:
Still no boost at all.
- I did check the boost gauge (just for the hell of it), and it's functioning.
- I did pull back the intake elbow on the primary turbo and wiggle my finger in- the turbine does spin- so there's no impediment.
- I checked the air valve in the y-pipe, and it wasn't functioning. Turns out that the new UIM I bought (with the double throttle blades intact) was carboned-up and the vacuum ports were blocked. No vacuum- no air valve operation. Cleaned it out, checked the vacuum chamber (holds vacuum perfectlly), fired it up and the valve now works. Problem solved, right? Of course not......
- checked the MAP sensor and it works fine.
- checked the primary blow-off valve again, and it works fine. Even disconnected it, and still no boost.

Can it be the turbos? There's no smoke, the car runs just fine (as if it were a normally aspirated motor). Could the exhaust and intake impellers have separated? Wouldn't you hear something? I forget, can you access the exhaust impeller without removing the turbo?....maybe just the downpipe?

Woe is me.....

 

Bob,
I will call you this afternoon.
John

 

Is vacuum being stored in the vacuum tank after running the car? Pressure in the pressure tank? (It's not hard to get a check valve switched when changing the UIM).

Also, did you inspect for boost leaks or loose clamps? Can you hear anything when you paste the throttle in neutral (normally the turbos can generate a few psi of boost in neutral, so you should be able to hear a boost leak).

Your turbos are probably fine. It's probably just a hose or check valve or loose connection somewhere. That doesn't relieve your frustration, but it should relieve your wallet a little.

Dave