INFINITY

with a stethoscope on the injectors i can hear them firing at a nice even pace at idle and with slight increasing throttle they increase the ticking accordingly. just as it begins to stumble the ticking slows WAY down and becomes slower than when the motor is at idle when the stumble starts and continues.
if i rev it above the stumble they are ticking super fast (as they should be at high rpm)
so i am going to look back into reasons why the ecu reduces injector duration....like the main sending units-- afm/air temp, knocks, ect, cps,_____????
i think now i should be looking more at reasons for the ecu to cut injector duration vs the ign timing

ilovemyz

Pics finally

ilovemyz

Have you verified intake cam timing? Also check fuel pressure and verify it's around 50psi. Low rail pressure will make it fall on it's face under load. And fuel pumps will run low pressure towards the end of their life

INFINITY

yea the intake and exhaust cams are perfect intime with the crank. the fsm calls for 32-40 psi rail pressure. i have ran a new higher flow pump and it was around 45psi and it did the same thing. this thing falls on its face just reving at idle.
i can put a mechanics stethiscope on the injectors and hook up a timing light and slowly rev the engine and the timing advances as expected as does the injectors BUT just as the stumble starts the injectors drop way off and tick slower than when it is at idle. so the ecu is cutting the injector pulse. wtf. i rewired a new weatherpack plug on the cps plug and the harness side of the cps plug has corrosion in the wires up inside of the isolation.
so i think i am going to make a full new harness. nothing is showing improvement.
also how did you re-clock your turbo compressor housing? is it an aftermarket turbo?
also how does yours preform with the stock afm and the bov venting to the atmosphere?
what year is your motor out of?
thx

ilovemyz

That's interesting. I haven't come across that before but I'd be willing to bet it's not a wiring issue since the engine does run. At this point I'd assume there was a faulty component the injector pulse should speed up rather than slow down with engine rpm. Generally your pulse width varies with engine load and that generally is calculated by intake air volume at the maf and rpm signal. That's what I would be looking at next. And double check that fuel pressure spec. I thought 45psi was at the low end of the spec. Regardless 45psi wouldn't cause that. If it's low it's not low enough to make it fall on it's face. Also try to get avac gauge on the intake manifold and see what your primary manifold intake vacuum does when it's stumbling. At first I was using a stock ct26 turbo. Loosened the compressor housing. Un bolted the waste gate and welded a bracket to the engine mount to mount it. Clocked the housing and snugged it down. Now I'm running an aftermarket t3 turbo on an eBay exhaust header with an external waste gate w divorced down pipe. The bov doesn't seem to make much difference. I'm running a 4.0 maf. And my motor is from an 89

INFINITY

yea afm, ect, tps, knock, rpm have the main role in how it controls duration. but if my cps is not able to send correct pulses to the ecu when it is fast due to corroded wires it would cut the injectors due to it sees air coming in and not the rpm to confirm it, so it would get wrong signals.
when it is stumbling it is at 0 vac/psi. in one of the videos you can see the boost gauge with corresponding vac in it when it is stumbling.
http://www.turboninjas.com/mk3supra/...-EFISystem.pdf
page 76
what do you mean you are running a 4.0 maf? in your pict it looks like a factory afm??

ilovemyz

what do you mean you are running a 4.0 maf? in your pict it looks like a factory afm??[/QUOTE]
Bear in mind the cps sends a digital signal rather than an analog signal So if you were to use an oscilloscope you would see either on or off signals (square sine) rather than an analog wave form sine wave. The only electrical components that will be heavily affected by resistance in wires will items with potentiometers in them such add the maf and temp sensors I'm not saying corrosion and resistance are ok. That's never the case but what your looking at doesn't seen to be the byproduct of resistance in wires. I say this only because the stumbling is not happening all the time at all rpms. It's isolated. If you're having issues only at full throttle, 0 inhg id be looking at fuel pressure again it's possible even with decent pressure the rail is running out of fuel. My maf is from a sc400 it's larger and there is a bypass screw on the body of it that opens and closes a small port for un metered air to pass through. It helps with mixture control under load

INFINITY

yea i am still banging my head over this. i put in a new big fuel pump, new 3/8" line and it acted the same.
do u think there might be a possibility with the turbo...... i am just sick of going over the same thing again and again and not finding any difference in any of the systems when i test them or replace them.
thx for the help it keeps me motivated.

egesledder

The turbo wouldn't cause this.

Have you put a new wiring harness on yet? New (brand new) AFM? From what I remember, it definitely looked like you've got fueling issues based on the videos of the AFR.

ilovemyz

Agreed your turbo system seems fine. Looks like starvation. I suppose you could try crimping your fuel return line and taking it for a quick soon and see if you see a difference that's red neck diagnosis. It may our may not make a difference. If you're fuel pressure regulator on the fuel rail is toast that might possibly shed some light on it. What did you install for a fuel pump?

INFINITY

i will do some more work on it soon. i had a oe tacoma pump and then i tried a inline walbro, then i could even turn them on inline together, then i tried a new pump AIRTEX #: E8119
i have tried another fpr as well. i also ran new 3/8" hard line from the tank to the engine bay with 3/8" fuel line to the rail.
i am gonna build my own harness. they want $600 for a new one. autozone does not have an afm for the supra but can get one for a 1uz (same electronics but different housing right?)
thanks again guys.

egesledder

If you have a pressure gauge on the rail and its saying it has good pressure, you are getting enough fuel. From the AFR video, it goes waaaaaay rich before it goes lean and stumbles. Something is feeding the computer bad data. The only way your fuel system could be related is if there was a restriction in the line on the way back to the tank, but I'd guess you're fuel pressure would have to get super high to cause anything like this, which it sounds like its not.

Lexus AFM electronics will work on the stock 7m afm housing.

There are used harnesses that pop up on the various supra forums quite often.

superextracab

It's definitely going into fuel cut. This is designed to happen when the computer sees RPM above 2000 and throttle closed. I think it would be in your best interest to find someone with a lab scope and check all sensors( especially TPS) to make sure there isn't a glitch. A DVOM will not catch this.

wagigknp

BUMP? I'm having issues on my 7mgte as well, but i am in the early stages and have a lot of things to check. Wondering if there was resolution here cause the symptoms are very similar to mine...

INFINITY

nope. no progress. now it wont even rev over the stumble. FML. i am going to rewire the entire harness with new wire and see if that helps. but i need to find time.
a friend in WA is having this same problem. he just swapped out his other 7mgte for a "good running" one in another truck. he swapped it (but kept his old afm from his previous engine) and it ran great for a month or so and is now doing this ˟˟˟˟ mine is doing. i think the wires in the 25 year old harness are having too much resistance and messing with signals.
i have swapped out every part of the engine and checked everything else but a new harness.
wagigknp did yours run good? mine falls on its face around 2k rpms and is cutting fuel according to my wideband.

wagigknp

Well, I have a massive exhaust leak that I am fixing. (blow by through the gasket). I was able to somewhat fix mine by making an tester to pressurized the intercooler piping. I found that I was getting boost leaking when psi started getting around 5. It really fixed it pretty much. Check your idle air control that the one way valve isn't blown.

What I found was that the engine will run without signal from the maf sensor but will cut out at 2k rpm. I wad having so much boost leak that the engine would disregard the maf and cut fuel.

INFINITY

i wish it was that simple for me. tried boost leaks and other afms but no luck. i think it is getting mixed signals from the afm and tps
or some ˟˟˟˟

New Red Truck

Was this issue ever resolved?