RB26 boost leak? limp mode?

[Max32]

Hi there,

so i recently took off the intake manifold on my R32 GTR to fix a coolant leak. replaced all the coolant hoses with silicone ones, all new HKS metal gaskets + some extra hylomar sealant around the throttlebody ones, new oem vacuum hoses and clamps as well. Everything went pretty okay until going on test drive. Somehow car hardly makes positive boost now. Obvious thing to think -> i f**ked something up on reinstallation, so i pressure tested the manifold this weekend, see attached video... never done this before but to me that pressure loss seems pretty much normal over the TB's, valves, and so on isnt it? Engines overall in unknown condition, unopened in my ownership. No other obvious hissing noises, only thing i found is a slightly leaking PCV valve, that must have leaked before i worked on the manifold tho and it did make boost before. new one is on order anyways.

turbo spool up is not delayed or anything... got the car with some probably old af HKS turbos that always kicked in between 4.5-5k, thats still the case it just doesnt go over like 0,2mmhg on the stock boost gauge anymore. idle is smoother than ever. also tried spraying break cleaner around the mating surfaces of the intake with the car running, no reaction.

I dont have a boost solenoid anymore, dump pipe goes straight back into the intake with no restriction. no external boost controler or anything, stock ECU afaik, wastegates work like theyre supposed to according to the manual when pressurizing directly onto them... should make ~1bar.

Any ideas? The car has to be f**king with me if the problems not actually on or around the manifold/ air chamber area as i didnt do work on anything else and it ran just fine before... i just cant seem to find it. i was thinking maybe some electrical error but the stock ECU has no more ways to mess with boost control in my setup has it? only thing it could do is pull timing which generally shouldnt affect boost, right?

opinions and input on what to do or check next are appreciated, thanks in advance

Max

[joshuaho96]

First, if you deleted your boost solenoid what is your vacuum line routing for the wastegate? I have personally seen people do the exact opposite of what they need to do to run wastegate boost when deleting their boost solenoid so this is an important question. Also I recommend checking for boost leaks starting after the MAFs.

Second, what do your fuel trims look like? Long term and short term. If it's off by more than a few percent you still have problems.

Third, have you inspected the turbos? Turbo failure can start with not making boost.

[Max32]

For the solenoid: All i did was remove that cause it wasnt opening anymore, just connected the two lines directly so it should run at "no-restrictor" boost all the time.

What do you mean by fuel trim? afr? cant tell that, stock ecu, no external gauge. Judging by the plugs car does run a bit rich, didnt mess with that tho and as stated it did make boost before. forgot to properly tighten a clamp at the fuel tube under the plenum, fixed that and still same issue.

Didnt check the turbos yet, if one was broken it wouldnt make boost at all as it would leak through the broken one, wouldnt it? Or at least should have a noteable delay in spool up...

[joshuaho96]

1 hour ago, Max32 said:

For the solenoid: All i did was remove that cause it wasnt opening anymore, just connected the two lines directly so it should run at "no-restrictor" boost all the time.

What do you mean by fuel trim? afr? cant tell that, stock ecu, no external gauge. Judging by the plugs car does run a bit rich, didnt mess with that tho and as stated it did make boost before. forgot to properly tighten a clamp at the fuel tube under the plenum, fixed that and still same issue.

Didnt check the turbos yet, if one was broken it wouldnt make boost at all as it would leak through the broken one, wouldnt it? Or at least should have a noteable delay in spool up...

I haven't measured the wastegate solenoid duty cycle but a local near me had something similar going on with his RB26 where the previous owner looped the wastegate line to atmosphere. It pegged the stock boost gauge. Once he capped the wastegate line so it no longer vented to atmosphere he ran wastegate boost. If you have any doubt that your ECU is not tuned for the turbos your engine is running you should run wastegate boost.

The factory ECU has narrowband O2 sensors. It doesn't know anything other than roughly stoichiometric but it will adjust how much fuel it injects based on that information. If the short term fuel trims to hold it around stoichiometric are reliably offset in one direction that feeds into the long term fuel trim. If the long term fuel trims out are of spec that will tell you that you have some kind of running issue like unmetered air leaks.

One broken turbo can lead to the engine make some boost. It will be noticeably less but still some boost. Also, if the turbo bearings let go from a boost leak you need to stop driving it sooner than later. Turbo failures often cascade into whole engine failures.

[Max32]

Thanks for your input mate. the solenoid is only a "safety feature" that doesnt do much after all. it wouldnt open on my car which led to boost staying at 02-0,3bar, just bypassing it leads to "stock" boost 0,7bar with restrictor, about 1 bar without restricting the airflow back into the intake pre turbo (blue tube in diagram) or am i dead wrong somewhere here? 

i wouldnt focus too much on WG or fueling anyways tbh, as mentioned didnt do anything to those systems and it ran for the last ~4 years like that without noticeable issues. oil always looked fine, no smoking, overheating or popping... i feel like it has been running healthy enough with the setup the japanese dudes before me installed.

Whats your opinion on the pressure drop off on the manifold test?

guess ill check turbos next, then pressure test the system from MAF till plenum, maybe the rubber hose from IC to that metal piece under the battery tray got loose from massaging the hose between that and plenum out.

[joshuaho96]

11 hours ago, Max32 said:

Thanks for your input mate. the solenoid is only a "safety feature" that doesnt do much after all. it wouldnt open on my car which led to boost staying at 02-0,3bar, just bypassing it leads to "stock" boost 0,7bar with restrictor, about 1 bar without restricting the airflow back into the intake pre turbo (blue tube in diagram) or am i dead wrong somewhere here? 

i wouldnt focus too much on WG or fueling anyways tbh, as mentioned didnt do anything to those systems and it ran for the last ~4 years like that without noticeable issues. oil always looked fine, no smoking, overheating or popping... i feel like it has been running healthy enough with the setup the japanese dudes before me installed.

Whats your opinion on the pressure drop off on the manifold test?

guess ill check turbos next, then pressure test the system from MAF till plenum, maybe the rubber hose from IC to that metal piece under the battery tray got loose from massaging the hose between that and plenum out.

The R33 GTR manual specifies 8.56 psi minimum to crack open the wastegate, purely spring pressure. It's not significantly different from the R32 GTR. Something was already wrong, it's just more wrong now. A 0.3 bar spring would only allow for a theoretical max of something like 0.6 bar boost. 

[Max32]

My mate has an R33 with the exact same boost levels when he forgot to hook up the solenoid. The spring opens at the pressure the manual states, you have tot take into consideration its not just boost thats working the gates but exhaust backpressure too.

[joshuaho96]

11 hours ago, Max32 said:

My mate has an R33 with the exact same boost levels when he forgot to hook up the solenoid. The spring opens at the pressure the manual states, you have tot take into consideration its not just boost thats working the gates but exhaust backpressure too.

Exhaust backpressure alone is not going to make you lose half of that spring rating. Anyways, if you really do have some HKS turbos in there you don't want to be running a lot of boost regardless. It's not that hard to max out the factory MAFs.

Edit: We've had this discussion before two years ago, my answer still remains that you have some kind of mechanical issue. If you had a boost leak before papering over it by running max bleed on the wastegate vacuum line isn't a good idea.

[Max32]

Update: Took things apart again, checked all the air chamber hoses, pressure tested the WG control line, tested the manifold with smoke+2bar, soapy water, pressure alone - nothing. No hissing, no bubbles, no smoke visible, WG line holds pressure forever, gates open as they should at ~0,6-0,7bar when putting pressure directly onto them. Also checked the BOV line, properly hooked up, gets full manifold pressure + and -. A bit of blowby thru crankcase, thats all.

What i found out is that the stock gauge is lying, cars actually running at 0,6-0,7bar with unrestricted WG bleed tho, yet the actuators are operating, see attached video of a short pull.

I dont get it. Any more ideas?

On 18/07/2023 at 3:56 PM, joshuaho96 said:

Edit: We've had this discussion before two years ago, my answer still remains that you have some kind of mechanical issue. If you had a boost leak before papering over it by running max bleed on the wastegate vacuum line isn't a good idea.

I didnt paper over anything. i got the car running without restrictor, +-1bar, same turbos, same ECU, same fueling system, same everything and it ran fine like that for the last couple years. I LOST a bit of pressure somewhere while taking off and reinstalling the plenum and cant seem to find out where, thats all.

[joshuaho96]

17 hours ago, Max32 said:

Update: Took things apart again, checked all the air chamber hoses, pressure tested the WG control line, tested the manifold with smoke+2bar, soapy water, pressure alone - nothing. No hissing, no bubbles, no smoke visible, WG line holds pressure forever, gates open as they should at ~0,6-0,7bar when putting pressure directly onto them. Also checked the BOV line, properly hooked up, gets full manifold pressure + and -. A bit of blowby thru crankcase, thats all.

What i found out is that the stock gauge is lying, cars actually running at 0,6-0,7bar with unrestricted WG bleed tho, yet the actuators are operating, see attached video of a short pull.

I dont get it. Any more ideas?

I didnt paper over anything. i got the car running without restrictor, +-1bar, same turbos, same ECU, same fueling system, same everything and it ran fine like that for the last couple years. I LOST a bit of pressure somewhere while taking off and reinstalling the plenum and cant seem to find out where, thats all.

0.6 to 0.7 bar is still low if you've bypassed the solenoid and you're venting the wastegate vacuum line to atmosphere. Have you checked how much exhaust backpressure you have?

[Max32]

Nope, think i got it tho.

Running the wastegate bleed line all open or completely closed (where the solenoid wouldve been) only does like 0,1bar difference in boost. also checked the bleed pressure in the line itself -> equally like +-0,1 bar.

My best guess at this point is that the hardline part under plenum smh mustve got mangled and is blocked. Ironically enough these lines are the only ones i didnt touch or renew while working under the plenum.

Guess ill bypass the hardline part now and go plenum -> T-Connector -> (1) hardline to WG behind engine and (2) vent line back into intake.

[Max32]

Update 2: That wasnt the problem either, hardlines completely bypassed and boost still wont rise over 0,6ish bar.

Any more ideas somebody...?

[joshuaho96]

On 9/16/2023 at 7:28 AM, Max32 said:

Update 2: That wasnt the problem either, hardlines completely bypassed and boost still wont rise over 0,6ish bar.

Any more ideas somebody...?

Have you inspected the turbos at all? I had a friend with the same issue on a different car. In the end it was turbo failure. Check the compressor and turbine blades carefully for damage, they have to be extremely close to the housing in order to actually generate boost/spin a compressor and any little thing can damage that "seal" and cause your symptoms. If you have one turbo functioning properly and the other isn't it can cause similar behavior as one turbo effectively turns into a boost leak because they're joined together at the twin turbo pipe.

[GTSBoy]

It won't be fun if one of the turbines has come off. But it could be the cause.

[Max32]

Jup, i did... pics taken with an endoscope so not the best but id say the compressors look alright. They do both spin at idle w/o weird noises or smth. could only reach the front turbine with my hand, feels fine/ has hardly any play in it.

[GTSBoy]

3 hours ago, Max32 said:

They do both spin at idle w/o weird noises or smth.

Not conclusive proof that the turbine is still there, but would seem less likely to have lost one.

[Max32]

Sure, i just cant believe thats the issue tho. as i said it started right after i messed with the plenum and what not, hot-side failure somewhere inbetween that would be the weirdest coincidence.

i did some research on the turbos and judging by the compressor housing they look like old HKS GT2530s... dont know if they even still have the ceramic exhaust turbines

[joshuaho96]

10 hours ago, Max32 said:

Sure, i just cant believe thats the issue tho. as i said it started right after i messed with the plenum and what not, hot-side failure somewhere inbetween that would be the weirdest coincidence.

i did some research on the turbos and judging by the compressor housing they look like old HKS GT2530s... dont know if they even still have the ceramic exhaust turbines

Also, checking the front turbo is not that useful. Usually the rear turbo is first to blow up.