I've been at this now for months trying to find a boost leak from the secondary turbo. I've done so much reading, testing, and replacing that now I'm really stumped and don't know what else to check. So I'm hoping to get some pointers of anything else that I might be missing.

To start, engine compression is good, 105-110, and I have no smoking or oil leaks from the turbos themselves. Primary turbo works perfectly as it should in all gears up to 4500rpm. My problem is with the secondary turbo.

These are the symptoms:
On the transition it drops to 8psi as it should, but it doesn't rise back up to 10psi, it stays at 8psi until about 5500 rpm, then it slowly drops down to about 5-6psi till redline. If I try to release the throttle to full vacuum and then floor it again, it will only boost back up to the same 5-6psi that it was at, but no more. However, If I switch to the next gear and floor it again, it will pick up to about 7-8psi, and then slowly drop again to 5-6psi until redline. So basically, no matter what gear I'm on, it will boost max 8psi from 4500-5500, and then slowly drops to 5-6psi until redline.

For reference, my vacuum numbers I don't think are very good. It's a stock port engine and I get 15in. at warm idle, 17-18in. at cold idle, and about 21in. when releasing the accelerator while driving.

Here's everything that I've tested and replaced so far and is all working to spec.
All solenoids
All hoses
All check valves
Pressure and Vacuum Chambers
CR and TC Actuators
CRV and ABV Valves

I've checked and re-checked and re-tested everything I listed above several times, and everything is working how it should be.

The list of mods on my car is below in my sig. if you need to help with any suggestions. I'd really appreciate any ideas you may have on what else I can check because I'm just at a loss at this point. Thanks in advance!

 

Have you checked the turbo's? The secondary turbo may be bad. The rear turbo fails more often due to the heat.

 

What are you using to control boost?

 

I had the same issue a few FDs ago and it ended up being a clogged pre-cat. I see that you have a JDM dp. I'm not sure if the stock cat can get clogged up but nothing is impossible with this cars.

If the above issue doesn't apply then try this. Some people may disagree but to me it is easier to work backwards. I would change your car to non-sequential doing the poor's man method and see if you get full boost that way. If not that means the issue is the turbo. If you do get full boost then the issues is vacuum/solenoid related.

 

I haven't checked for shaft play on the rear turbo yet which I'm going to next, but there are no oil leaks, smoking, or abnormal noise coming from the turbos.

For now just the PowerFC with the stock pills. I haven't had any problems with over-boosting or spiking

Yeah I have a JDM DP so no pre-cat, I'm waiting to install a HF cat so I guess we'll see from there.

I was thinking of going non-sequential, I actually went to simple sequential because I was having the issues. When I did the conversion, I found a bunch of things that were bad, several solenoids, CR-actuator, check valves, cracked hoses. I replaced all of it and was sure I had fixed the problem. Everything was much more responsive and got better, but the leak was still there. I didn't want to go non-sequential because of all the work, and the wastegate issues. I forgot there's the quick non-sequential so I'm going to check it out and see if it's not too much work just for testing.

 

What are the boost settings you have selected in the Commander? do you have a Datalogit you can use for some testing?

 

Since you are able to achieve 10 psi on the primary, that would indicate that you do not have a boost leak. My suspicion would be a clogged cat. If your cat is clogged, it would work fine until a higher volume of exhaust tries to go thru (higher rpm), then it would restrict things. I see you have a bonez cat to install. I would install it and see if it solves your problem.

 

I have the boost set at .65-56% for both, I don't have a datalogit sorry

But you can have a boost leak in the secondary turbo while the primary works perfectly? The cat could definitely be clogged, I just didn't know that it could cause that. Unfortunately I still don't have the bonez cat with me, I just bought it but haven't received it yet. So I guess I'll put that on as soon as I receive it before trying anything more complicated.

 

Take the mid pipe off and go for a spin . Just add some fuel on your PFC and hope to stay at 10 PSI.

 

I tend to agree with the clogged cat theory. The reson is because, you said that if you up shift you have higher boost. This indicates to me that it is clogged due to the reduction of exhaust volume because of the lower rpms.



John

 

If the system holds 10 psi on the primary, it will hold 10 psi with the secondary. A boost leak from the secondary only is nearly impossible. You either have a problem with the function of the secondary, or a clog. I suspect a clog since your pressure drops at higher rpm.

 

Alright, I think I'm going to then just wait to replace the cat as soon as I receive it.

Idk if I want to remove the cat completely to test it, I'm afraid of getting major boost creep since I don't have any aftermarket boost control yet. Or do you guys think it'll be fine just to test it out?

 

IMO if the cat is in the mail you might as well wait for it. If you take the cat off and drive around when you do a pull you have to watch the gauge to make sure you dont have boost creep. Not worth the risk if you already ordered a cat.



John

 

The fact that you get 10 psi at all means that there cant be any leaks, and you obviously did everything right. I've never heard of a boost problem like this before but I agree it could be the converter, especially since its much easier to build boost in the earlier gears then in the later gears.

 

Well I hope the cat is already in the mail, lol. I bought it from someone on here a couple of weeks ago and haven't heard back from him about it yet.

 

^ That sucks, What you can do is take the cat out and break the catalyst out of the cat. If you do not care that you will ruin the cat if it is still good. Reinstall and test.

As you know just watch for boost creep. To alleviate that you can fabricate a restrictor in the exhaust. It is just a thin piece of steel put in between the exhaust flanges with a hole approxmately 2.5-2.75". From what I have read there is no set diameter hole to use as breathing mods vary from car to car. This way you can test without worrying about boost creep.



John

 

Update:

I finally got around to installing the H/F cat and unfortunately it didn't really solve my issue.

The secondary boost is still leaking to about 6psi. The cat did help out a little and now the symptoms are slightly different. Now in the transition the boost picks back up to 10psi and holds slightly longer. And also now when I change into any gear the boost immediately picks up to 10psi on the secondary.

So now this is what happens, 10-8-10, drops to 5-6psi by about 6k rpm, Then up-shift, boost picks back up to 10psi. Same behavior in all gears

With that info now do you guys have any further suggestions?

 

Wastegate issue perhaps?

 

This may or may not help but I had similar problems once. I had the connectors on the two solenoids just under the uim on the left as you look at the engine, backwards. You may have tried this already but given that it is a five second swap and nothing needs to be removed at least it's another potential cause eliminated.

 

A good point. The solenoid with the white dot connects to the connector with the white dot.

 

From what I've read, if the wastegate had a problem then I would be leaking boost in both the primary and secondary, but someone correct me if I'm wrong and I'll check it out.

Do you mean the 2 green solenoids right behind the pressure tank? Or the regular black ones under the UIM?

If you're talking about the black ones under the UIM, it's difficult for me to tell because I switched and swapped pretty much all the solenoids when I did the simple sequential. So none of them are color matched anymore. What I'll do is just look in there, and check which colored plug is attached to what lines and then re-check the diagrams.

 

Correct if it was wastegate you'd see it in both

 

The two green ones. There were no markings on mine so I swapped the connectors round and it was an instant fix. That was a good day that saw me smiling lots.

 

Alright I'll try swapping those connectors today and see what happens

 

Swapped the connectors, car behaved exactly the same, no differences. So what do you guys think I should check next now?