Hi guys new to the forumn and like most I'm joining because I've got an issue I haven't been Able to diagnose so hoping someone can just pinpoint it with a crystall ball based off of my vauge description

I haven't figured out how to upload the video of the issue yet but soon as I do I will

So essentially I have an 05 STR Powerhouse rebuilt unit Ported both sides smaller pulley and a map ran great boosted hard no issues for a long time til recentely, the Only way i can describe it is at WOT asking for full boost itll pull up to a certain RPM and then bounce/stutter at that Rev and lose all boost almost as if fuel can't keep up (1st guess) til the gear shifts up revs drop back and then the SC will give a little more but then same story (I only did this a couple of times to try diagnose)

I did also smoke test for boost leak and only found a puff from the crusty o ring on the brake boost hose TB side

If driven smoothly the V8 will drive fine but it lacks any real grunt, i continued to daily it for maybe 2 weeks before parking it up

Going by online threads and the common issues I decided it was the coupler finally giving up, so SC off and disassembled and lo and behold no issues its all mint inside, even the oil is nice clean and smelly so this bring me back to a fuelling issue

As I'm Mapped to near enough the limit have the fuel pumps maybe given in a little and can't pump up enough at the high end when the issues hit? Or is there another suspect area i should be looking at?

Any and all advice really appreciated

TIA
Kiefer

 

Welcome to the forum.

Do you have a scanner to read live data on a test drive? I'd think if the pumps can't keep up, you'd see a drop in pressure.

 

Could be a pump, could be a cat conv.

 

Maybe plugs breaking down ?

 

Pulled the supercharger, no issues with any of that short of finding a damaged brake vacuum pipe, the map sensor annoyingly snapped as the elbow lifted so that's on order. Once back together will go into live data and check the fuel pressure, I have Read 55psi at idle and 70psI at WOT is this correct?

I had good air flow from both pipes when engine running and digitally checked temps on cats after a drive so I don't think they have blocked up, I've checked all plugs also so hopefully its just one of the pumps 🤞 will update

Also any idea what photo uploader to use so I can upload the video of the issue on here?

 

You could always post a video to YouTube and put the link down we could watch it that way

 

Supercharger back together diag measured in KPA so have 390 at idle and 483 at WOT which is 56psi and 70psi but this is smaller pulley, Mapped etc so should that be even higher? There is a horrible clanging noise from the supercharger still. Will create a YouTube link

 

https://youtube.com/shorts/tw0AISeI4IQ?feature=share

 

https://youtube.com/shorts/5c1DXjcSvjM?feature=share

 

Updated with two short videos on your tube

To note I have now swapped over the supercharger for a stock low mileage unit in known good working order to have the exact same fault

Unsure if it can be made out in the video but when pushing it there is a horrible loud clanging that I previously assumed was the Original SC

Running out of ideas now 🤦

 

I think your fuel pressure at 70 psi is your problem. It’s way too high and it’s probably dumping fuel into your cylinders causing it to bog out

 

There’s another problem if your scanner is reading 56 psi boost pressure your sensor that measures the pressure is not working correctly because there’s no way you can get that high even with a small pulley

 

70 psi fuel rail pressure at WOT is good.

 

This is fuel pressure not boost pressure

But I have found that I have no boost pressure according to diag, moving onto bypass valve and some other bits next to see what's up

 

is this a real 2005 with the old ecm and brembo brakes or is it a 2006

2006 without a tune will hit the torque limiter with just a decat

 

OK sorry I guess I got confused when you were talking about the pressure in the supercharger in. My mistake but I still believe that 70 psi for a fuel pressure is much too high and they should maintain somewhere in the 55 range at high rpm or else you gonna be pushing fuel through the injector. There’s no reason to have a 70 psi fuel pressure at high Rpm because all you’re looking to do is maintain sufficient fuel volume for the RPM and you’ll get that at 55 psi I believe.

good declining noise you hear be the engine pinging? You should. Log the fuel trims over the RPM range as well as look at the ign timing, misfires knock sensors using your scanner. And also log the fuel pressure.

 

This is the 05 with brembos and old ecm

I'm convinced now its a fuelling issue however, plugs show it's lean its a 3k onwards sort of issue ive noticed and from what I gather one feeds into the other over 3k revs?

 

what do you mean by that? Are you going to post a log of the fuel pressure as you drive from idle to 5000 RPM? I’m telling you 70 psi fuel pressure is way too high! You can try whatever you want but I would focus on that 70 PSI.

By the way earlier in your post after mentioning 70 psi you said “but it has a small pulley. What does the small pulley”. what does the small pulley have to do with the fuel pressure?

What are your fuel trims at idle and at 2500 RPM?

please post a datalog showing the fuel pressure and boost pressure as you drive thru the rpm range. until I see your fuel pressure log from idle to 5000 RPM I’ve got nothing more to add.

 

The fuel pressure on the STR is boost referenced. What this means is that 70 psi is at full boost say 13 psi. So really the injectors are only seeing 57 psi. On my old 2005 STR (Same car) I had a fuel regulator failure and ran a manual fuel pressure gauge taped to the windshield for several weeks while troubleshooting and it read from around 45-70 psi depending on operating conditions. Just a note? If the car can't see the regulator the fuel pressure defaults to 70 psi (at least it did on my car). Ran fine but had a constant check engine light on with a fuel pressure regulator error code (P0193).

So just from those numbers it seems the fuel pressure is in the correct range and is changing based on boost. Now this all falls apart because you now say the car has zero boost? It should have almost no power if true? When I broke the SC belt on mine it ran fine and had no errors but man what a dog!

Can you do what Aarcuda suggested? We need to see boost and fuel pressure if possible.
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Clubairth1 is on to something there , the raise in fuel pressure at the injector tip from 55-70 is cancelled out by boost .
hence the need for a fuel pressure increase in the first place .
but the fuel rail pressure sensor will show both target pressure points if all is well with the reg.
i believe the primary pump is (PWM) the secondary pump only turns on at WOT above a certain rpm . and just assists not PWM.

i had a fuel pressure reg go bad a couple of years back . it was lying to the ecm .
so the obd2 was reading a perfect 55-72psi but when i put a mechanical gauge on the schrader valve . it was actually reaching 110psi.
and cooked a pair of cats very quickly . so don't ,mess around getting this issue sorted .
you can do an up-stream back pressure test on the cats also if suspect .
edit i just watched the vids , i swear that sounds like when my cats melted and broke up . give the cats a liberal whack with a rubber mellet and see if there are loose bits in there .