My 5VZ-FE 3.4L has a strange problem.

The engine starts up, runs/drives fine. When I give it gass its fine till about 1/3rd throttle then as I contiue to press the gas further the engine power falls off noticeably. The engine tone doesnt really change and I have no CEL. WTF

What could be going on? Clogged fuel filter? Dirty MAF?

I have new plugs, new factory air filter allong with several other new components. This is off boost BTW with the wastegates wired open so its not modification related. All the other components are bassically stock.

Please help with any input

 

my wife's 99 SR5 did something similar when it had a bad TPS.

 

That thought had come to mind. Ill look up the test procedures on the TPS. What else causes that problem. Could the plugs be bad already they were just cheap autozone brand plugs.

 

I'd guess TPS or fuel filter.... Something's starving the engine for fuel. The more "exotic" things could be a pinched fuel line, clogged injectors, clogged tank pickup.


Is this the 3.4 that's in your swap? bummer.

 

Yea its the swapped motor, Its still quick but there is obviously an issue with the fueling or perhaps ignition. The tank picup is probably fine and the fuel feed is definatly ok too since thats all off my 4cyl motor and were working fine. I took care when reinstalling that stuff.

Ill change out the fuel filter and check the TPS tomorrow
thanks guys

Ill check back in and let you know the outcome.

Jim

 

You might try to hook up a guage to the fuel rail and see if you are getting proper pressure at the injectors (that should eliminate everything else downstream except injectors). I would also highly suggest changing out those plugs you have in there for some OEM (Denso or NGKs....definately NO Bosch!).....the Japanese import motors prefer these plugs for whatever reason.

Do you have at OBD II port hooked up on the motor?
....if so I would plug into that because you should be able to see all the engine vitals through a decent scanner (timing, O2 readings, MAF, TPS, etc). That way you can see in realtime what is causing the engine to underperform.

 

I think Jamie may have hit it...

Given that:
Then, what kind of flow is the original fuel pump? You need to be pushing about 60psi at the rails for the 3.4.

 

60 psi huh? I thought it was 47ish at idle? My pump may not be up to that. Im useing a 3sgte turbo pump that was supporting roughly 270+ on the 4 cyl that was in there. It should more than fuel the engine for NA opperation. I should technically have enough fuel for about 8psi of boost before the pump cant flow enough.

Yea I have the OBDII port that I wired in the engine bay. The diagnostic connector is still present too.

Ill take all your ideas under advisement and start with the easiest/cheapest to check first.

Thanks for all the help

Jim

 

Yeah, it's up there... I'm ballparking a number from memory, but this is where my memory's coming from:

http://www.gadgetonline.com/fuel.htm...ssure%20Gauge:

Past that... I was running the stock fuel pump when I first put on my S/C. But after a while, I started realizing that the surging that was going on under acceleration wasn't supposed to be there. I never dropped a gauge on it to be sure, but I can tell you that the surging went away when I replaced the fuel pump with a Walbro 190lph.

In hindsight, the "surge" of the surging was the good stuff, the lag of the cyclic surging was the bad. The engine would come up hard using fuel that was in the rails, but then the pump couldn't keep the pressure up, so it would lag.


Gadget's selling the Walbro's for $86:
http://www.urdusa.com/Merchant2/merc...gory_Code=fuel

 

You are right.....at stock it will be just below or right at 50psi at idle, but in order to run those twin turbos on the 3.4L you will definately need to have rail pressure above 60 psi as Mark mentioned (a walbro is the fastest way to solve that issue). Now I am not sure this is the root of your underperformance problem, but it certainly needs to be addressed anyway.

My hunch in more of an ignition retarding problem, but it is tough to diagnose without any CEL or seeing the OBD data.

 

Problem solved!!!

Cleaned MAF and Changed fuel filter. MMM lots O torque and smooth power now.

Thanks for the help guys.

 

Nice! Glad you got that one solved and that it was simple and cheap to fix.