ON3 turbo boost help!?

turbomustang363 · May 28, 2019

Hello all, I have been trying to figure this boost problem out for a year now... I have the on 3 performance 76m turbo kit and I am only making 8 lbs of boost with springs set for 18+... I have removed and blocked the wastegate and still no extra boost. I did a boost leak test and only found minor vacuum leaks and fixed them. Also performed a cylinder leak down test and all numbers came back great. Fixed the minor exhaust leak I had and still no more boost. The turbo seems to only be making 8 lbs no matter what. There is no boost spiking or lag with the turbo, no shaft play or any problems with the turbo to make me think it would be the turbo itself.... I even pulled the turbo off and inspected inside the turbine housing to make sure nothing was jammed in there, like i've seen from some other posts on here. Any ideas on what could be the problem!?
My setup includes:
363 sbf built by TREperformance
ebay aluminum heads
comp cam -NX274HR
76mm on 3 turbo kit
ran through a C4 with transbrake and custom torque converter built for ~1000hp.

CarMichael Angelo · May 29, 2019

After thinking about it, you have to have a bad turbocharger. They're pretty simple in how they function. Exhaust temps may be causing something to expand, and bind in the turbo housing, or you have exhaust getting by the turbine wheel. If you blocked the Wastegate hole, and nothing changed, then it's time to spend the money on a new Chinee turbo.

I had a similar problem with the junk Chinee waste gates I had on my car two years ago,..( now have TurboSmart) there was so much air leaking past the Wastegate valve, the car wasn't making any boost at all. Upon removing the gates and bench testing them, it was taking 15 psi to lift a 5 pound spring. Put the TS gates on, with 7 pound springs, and the car instantly ran right.

turbomustang363 · May 29, 2019

I mean after testing everything that's what my thought is too.. Bad Chinese turbo loll I just would hate to spend $1000 on a precision 7675 and than same problem... lol I appreciate the input, I do think exhaust could be passing by the turbine wheel since there is no real backpressure through my exhaust. its literally a 16 inch pipe off the turbo out the hood...

turbomustang363 · May 29, 2019

I am also running the Fitech EFI power adder system, although I don't think this system has any kind of way to limit boost... Atleast that I can find throughout the controller and forums.

jozsefsz · May 29, 2019

PCV and EGR are great places to lose some boost. So is the wastegate valve seat (if you hadn't put it in or put it in backwards). BOV could also be suspect if it's hanging open (or perhaps if you have it connected wrong).

You can also do your best to bypass the whole intercooler setup and run a pipe from the turbo outlet to the intake to see if the situation improves (eliminate pinhole leaks in piping, connectors, and the intercooler). Honestly if the turbo's spooling up at all, and to as much as 8psi, I'd suspect it last in the array of issues you might have.

I don't know much about your cam, but turbos don't like a lot of overlap. The stock cam is perfectly suitable for a turbo application. A street / strip performance cam with a nice lumpy sound is very counter-productive with a turbo.

Edit: after brief googling, that cam is a 'nitrous' grind. those tend to feature a wider lob-separation angle but a longer exhaust duration which results in higher-than-stock overlap. Which is not what you want.

turbomustang363 · May 30, 2019

Well I have no egr on my car and would a cam really make me lose 10+ lbs of boost just from overlap? the car had no problem making 7-8 and when I changed the wastegate springs it still only made 7-8 lbs... Very strange to me how I can only make 7-8 lbs with this turbo with no leaks and good cylinder leak down %'s.

turbomustang363 · May 30, 2019

Where's all the pro turbo guys at!?

Noobz347 · May 30, 2019

Performing annual inspections on their jack-stands?

General karthief · May 30, 2019

You may need to ask a cam grinder that question to confirm the answer you got from a turbo guy.

turbomustang363 · May 31, 2019

@Noobz347 haha yeah there prolly too busy figuring out their own problems...

jozsefsz · May 31, 2019

Well @turbomustang363 I'm not sure I'd call myself a 'pro' but I've been running a Boost Brothers turbo kit on my '95 since 2009 at 11psi and running strong. Self-tuned as well with QuarterHorse and no engine parts on the ground yet. I also custom fabricated a turbo installation onto a 78 Mustang 2.8 v6. So for the advice you're getting for the price you're paying me (I'm also a mechanical engineer), I'd say it's pretty reasonable.

In that time I've learned that if you think you don't have any leaks, you probably have a leak. Hot-side or cold-side. I gave you a suggestion on how to troubleshoot the cold side (straight tube from turbo outlet to intake). You could also remove the BOV to eliminate that as a leak possibility. The hot-side you can troubleshoot with your ear and / or a 'mechanic's stethoscope' (i.e. hold some heater hose up to your ear and check at the header, couplings, mounting flange, etc.) It doesn't take much (a blown header gasket) to cause you to fail to spool as high as you'd think.

If you have no EGR, and you blocked it off appropriately on the upper intake, and if you have the PCV system removed, then you've eliminated those causes. With the wastegate blocked off you eliminated that cause.

Other than a bad gauge, you're then left with a faulty turbo (suggested), an improperly sized turbo (not likely from a kit), or a cam grind that's not giving you enough pressure due to its overlap. You're welcomed to wait for a pro to chime in, but there's not much more to a turbo system than that I'm afraid. Best of luck.

turbomustang363 · Jun 4, 2019

Yeah I was not trying to sound like I wasn't taking your advice. Of course any advice is always great and i appreciate your help in my situation. Just trying to hear as many possible situations that some people may have encountered as I can . I might try to get my hands on a stethoscope to ensure that i have no leaks on the hotside. @jozsefsz

jozsefsz · Jun 4, 2019

It's cool @turbomustang363 you know it is just internet advice, you should always take it with a grain of salt.

To be a bit more helpful to you, you'd of course be welcomed to post your question to the parent forum. There are many more Fox guys than 94-95-ers around here, and the On3 turbo kit is largely the same between the years since we have the 5.0's. You might have some more opinions there than here. This is a great group of guys, but somewhat small due to the limited model years.

On the stethoscope, seriously heater hose works great. You do look stupid while holding it up to your ear, but it works and it's cheap.

For gaskets, many people run the copper RTV with no gasket at all if the flanges are nice and smooth. I have some Remflex graphite gaskets and those have worked great for several years, my flanges aren't so smooth. Either one of those is a bear to clean up when you need to change them, but they do a better job under pressure than the paper-and-foil stockers. Keep in mind little pinhole leaks won't keep you from building decent boost (our engines move a lot of air) - I had quite a leak at one time and while it robbed me of a psi or two, it didn't shut things down altogether. It'd have to be pretty noticeable to limit you to 8psi.

General karthief · Jun 4, 2019

Before we start another thread (and I catch flack from 'the bear' that I poke far too often) lets invite some fox turbo guys in on this.
@FastDriver
@TOOLOW91

FastDriver · Jun 5, 2019

I agree with Mike and Jose.

Only things that haven't been brought up: a bad reading, which would come as a result of a bad gauge/sensor or a bad line to the gauge/sensor. This has happened to me when the boost signal line laid over onto a header, though I'm fortunate that I have 2 boost sensors on my car and could spot the discrepancy right away. Also, an obstruction in the intake tract somewhere before the sensor or in the exhaust before the turbine could dampen boost. Has it ever run right, or is it a new system? The mesh flex pipe on the exhaust side of the On3 was known for fraying. I believe it was on the crossover tube. This was years ago, but check if your kit has one. It's a known weak point. An exhaust shop should be able to weld a fixed pipe in its place.

"On3" is your biggest problem... ty parts across the board, but you get what you pay for. If you're using the BS On3 wastegate, get rid of it. If it's not your problem now, it will be, eventually. Then you'll have a shortblock problem, too. I admit my bias towards the company. They put other good companies with quality products out of business, had extremely shoddy customer support refusing to stand behind products with obvious and common defects, & of course they source to the cheapest bidder, which ended up being the Chinese. They are a volume company, and it's hard to look past a turbo kit for less than half the price of a quality one, but I will personally never do business with them, despite the temptation. If any of these comments are no longer true, then at least that's where they came from.

TOOLOW91 · Jun 5, 2019

Even though I have one of them belt things that turn my power adder . I’ll chime in and say that your Ching Chong choo choo boi is prob no good .

So long as you smoke tested everything and your certain no leaks . Your waste gate test alone should’ve sent that turbo to the moon

turbomustang363 · Jun 5, 2019

@FastDriver Yeah the car runs fine, has been for about 2 years now. I just wanted to turn it up and get the most out it... than i find out i cant turn it up LOL I'm looking to purchase a precision 7675 and go from there. I'll keep you guys posted about what happens... Thanks for all the feedback guys ! @TOOLOW91 @FastDriver @jozsefsz @CarMichael Angelo

General karthief · Jun 5, 2019

What about me?
after all I called in the rest of the 'power adder playas'!
i just don't get no repect! I am a mod you know, jeez!

turbomustang363 · Jun 9, 2019

haha yea sorry thanks for your help as well @General karthief

68stangturbo · Aug 23, 2022

@turbomustang363 did you ever replace the turbo and find the culprit? I’m have the exact same issue with my on3 88mm and been chasing it all summer.

ON3 turbo boost help!?

turbomustang363

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CarMichael Angelo

my rearend will smell so minty fresh,

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General karthief

wonder how much it would cost to ship you a pair

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wonder how much it would cost to ship you a pair

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I was uncomfortably high & wearing a helmet

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If you're the village idiot what's that make me?

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wonder how much it would cost to ship you a pair

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