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vvti GTE swap hesitates under 10psi or more (with code 25)

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vvti GTE swap hesitates under 10psi or more (with code 25)

 
Old 05-13-19, 08:03 PM
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BruceGSgte
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Default vvti GTE swap hesitates under 10psi or more (with code 25)

Hello!

I've been a car enthusiast for about 15 years now but new to the 2jzgte.

Car: 2003 gs300 with vvti gte swap, using Aristo automatic, in TTC (sequential turbo system is permanently disabled).

Mods: BPU, twin GT28 upgrade with billet compressor from Driftmotion, front mount intercooler, stock Aristo ECU. car only runs 11psi with or without a boost controller.

Problem: car hesitates (feels as if the ecu is pulling timing at WOT under full load) and is very laggy, does not hit full boost till almost 4800 rpm.

Tried so far: I have spent hours on boost leaks (still has them in the turbo outlets) and vacuum leaks for plumbing before the turbo. The FPR is leaking boost as well. All boost leaks should be fixed by the end of the week. when checking the ECU for codes it gives me 25 every time (air fuel ratio lean malfunction) and I have replaced the 02 sensor, spark plugs (bkr7e gapped at .28) and coil packs/wires with a good used OEM Denso parts.

The GT28s spool like a T76 then hit hard, soon after hitting hard the ECU pulls timing causing a hesitation and loss of power.

Please help, I have spent a great deal of time and nothing, outside of replacing the ignition components has helped whatsoever. The turbo's are brand new, just put them in. After fixing all the boost/vacume leaks (which are that severe) I am planning on testing the fuel pressure under WOT to see if my pump or FPR is bad.
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Old 05-14-19, 06:56 AM
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Originally Posted by BruceGSgte View Post
Please help, I have spent a great deal of time and nothing, outside of replacing the ignition components has helped whatsoever. The turbo's are brand new, just put them in. After fixing all the boost/vacume leaks (which are that severe) I am planning on testing the fuel pressure under WOT to see if my pump or FPR is bad.
Wouldn't even entertain discussion until you deal with vacuum and pressure leaks, especially if you're throwing a lean code.

We've had our fair share of 3S-GTE and 4A-GZE MR2s, and the slightest vacuum/pressure leak would throw havoc at the factory config. Fix the vacuum/pressure leaks, then we can go from there.
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Old 05-15-19, 09:57 AM
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Thank you for the clarity on the vacuum/pressure leaks. Being new to this power-plant I did not understand how sensitive the stock Aristo engine management is to small air leaks of this nature. I hope to have all the leaks fixed this afternoon when I get back to work on it and perform the follow up boost leak test. I'll post again thereafter.
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Old 05-15-19, 08:44 PM
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Ok, I finished sealing the boost/vacuum leaks (even those before the turbo) and the problem still exists. The car runs just fine until about 10-11 psi under WOT, that's when it starts pulling timing (least that's exactly what it feels like, its not breaking up or backfiring). Remember, code 25 for "AFR lean malfunction" is consistently returning every time I delete it then go WOT. Help me out here, but it seems as if I have a fuel pressure problem.

Today I checked out what type of fuel pump is in the car (the swap was done three owners ago, lol) and it appears to be a walbro 255 stuffed in the stock fuel pump housing/assembly. I've heard that walbro's can give out, or weaken over time (not sure if this is common or not). Also, the fuel pump intake screen seemed pretty dirty but not to the point of restricting all flow.

Pending anyone else's recommendations, tomorrow I will perform the 12v fuel pump mod to rule out there being a malfunction with that control module. Then, if that has no effect I'm going to go to my friend's shop and borrow is long hose fuel pressure gauge and check fuel pressure under all driving conditions. That's the final straw folks! new fuel pump if this joker is weak. I'm praying this is the problem. Fun fact, I have never gotten the car to boost over 11psi, doesn't matter if I pull the hoses off the wastegate, it goes to 11 then hesitates.

Also, during boost leak test a steady stream of air from the PCV come out. From what I remember this is normal, correct?
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Old 05-16-19, 02:49 AM
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Originally Posted by BruceGSgte View Post
Ok, I finished sealing the boost/vacuum leaks (even those before the turbo) and the problem still exists. The car runs just fine until about 10-11 psi under WOT, that's when it starts pulling timing (least that's exactly what it feels like, its not breaking up or backfiring). Remember, code 25 for "AFR lean malfunction" is consistently returning every time I delete it then go WOT. Help me out here, but it seems as if I have a fuel pressure problem.

Pending anyone else's recommendations, tomorrow I will perform the 12v fuel pump mod to rule out there being a malfunction with that control module. Then, if that has no effect I'm going to go to my friend's shop and borrow is long hose fuel pressure gauge and check fuel pressure under all driving conditions. That's the final straw folks! new fuel pump if this joker is weak. I'm praying this is the problem. Fun fact, I have never gotten the car to boost over 11psi, doesn't matter if I pull the hoses off the wastegate, it goes to 11 then hesitates.
If you are lean, you have too much air, or too little fuel. The question is... which?

My suggestion is to not make changes until you measure your current-state... measure, change, measure. Seems to add some complexity to start changing the fuel system ("12v fuel pump mod"), without knowing what your current fuel pressure is (across rpm range).

What is sounds like you're hitting is fuel-cut. On the gen-2 3S-GTE, there was a boost-pressure sensor that would trip fuel-cut after 5sec continuous 11.5psi... and the car would stumble, until you shut it off and re-started the car, and would throw an over-boost engine code. It sounds that when you hit 11psi, the fuel-cut kicks in, you loose fuel, go lean, lose performance, and throw an AFR-lean code. Never was able to trip the fuel-cut in 1st at full-throtle... it was a time-based over-boost sensor, and you weren't in 1st long enough at wot to trip it. Yet it would trip in 2nd at around 4k-5k rpm, it took longer to get to best-shift-rpm. Each higher-gear had a lower-rpm trigger point. Most EBC's would leave the boost controller valve open in 1st, then start to modulate electronically in 2nd-5th. Stock, the 3S-GTE was good for about 160rwhp, add an FIPK and manual boost controller at 11psi and you're at 200rwhp, then adding an FCD with manual boost set at 15psi will get 240-250rwhp. Next step was usually exhaust and a bigger turbo, plus larger intercooler, yet you'd then have to manage AFR with extra fuel (fuel pressure, different injectors, etrc), yet there were some almost 400rwhp cars, back in the day.

Hook up a fuel-pressure gauge, and see if you have a non-linear introduced fuel-pressure drop, at 11psi. If so, sounds like you need a Fuel Cut Defencer, there's plenty out there... just set it to reasonable psi level. Sooner or later, you will reach the limit of the fuel pump, then you really will go lean, and that's bad. Here's an example of an HKS one:

https://www.driftmotion.com/HKS-4501-RA002-p/dm126.htm
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Old 05-16-19, 06:22 PM
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Thank you for the suggestions. I took it to a local performance shop and he recommended replacing the fuel pressure regulator first (since it was leaking boost from around its diaphram) then checking fuel pressure while driving. I'll hopefully take care of these test next week.

I hear what your saying with the fuel cut, I used to be an MR-2 guy (had 4 of them), however the Aristo ECU has a fuel cut at 14,7 psi, and I'm nowhere close to that. I also remember what it was like to hit fuel cut in my MR-2 Turbo (gen3 swap). What I'm experiencing in this GS300 is nothing like that, it does not feel like fuel cut. It feels like the ECU is pulling timing from the engine knocking (my assumption is its lean due to code 25). I've already replaced all the ignition components with the exception of the igniter.

I suppose I could disable fuel cut just to make sure. I have spark, air, and compression, now I'll figure out how good my fuel delivery is.
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Old 05-20-19, 11:47 AM
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Another update, I have some time before my new fuel pressure regulator comes in, however I made an important discovery. The previous owner who did the gte swap did not eliminate the GS300 in-tank Fuel Pressure Regulator! This means my car is running two FPR's with the one on the fuel pump hanger being the "master" since its right next to the fuel pump. This FPR is of course not designed to run on boost, therefore it would make sense that my car is having trouble (we think not getting adequate pressure) under boost! I've ordered a new in-tank filter, and filter sock for the walbro fuel pump, and am going to JB weld/bypass the stock FPR in the tank and run the return line to the siphon venturi valve (so it pulls fuel from the other side of the tank as designed to). Once I take care of this stuff I'll post an update.

Last edited by BruceGSgte; 05-20-19 at 12:33 PM. Reason: spelling & grammar
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Old 05-20-19, 04:14 PM
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So you measured fuel-pressure, under active load, to identify you reached max/static fuel pressure lbs/in? Or did the pressure fall?
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Old 05-20-19, 04:43 PM
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Originally Posted by sbagdon View Post
So you measured fuel-pressure, under active load, to identify you reached max/static fuel pressure lbs/in? Or did the pressure fall?
No, I have not yet tested pressure at the rail, thank you for asking, I'm going to first fix the fuel pump hanger problem, then do a pressure test. I could do a check first, however, I don't own the tools and the person who does has instructed me to fix all known problems first to avoid "chasing my tail" as he calls it.
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