azndriver

Oh and another sensor to check..

maybe I missed it

But have you checked the Pedal Position Sensor as well?

Refer to this thread:
https://www.clublexus.com/forums/gs-...ing-out-4.html

PTYGS400

Thank you azndriver. I have two spare throttle assemblies. I will install one of them if everything else fails.... TPS seems to be working fine though, I can see it operating on the scanner.
As a matter of fact, since it was late at night and very quiet in the garage, I heard a little noise with the engine off and the ignition on. Like a little motor running. The noise seemed to come from the throttle motor. To confirm, I disconnected one of its plugs and the noise quit. Back on the scanner I got P0120 "TPS Circuit A Malfunction"

Today I´ll focus on fuel pressure and smoking the intake to make sure I have absolutely no vaccum leaks.

PTYGS400

Hello fellows.
I thought I would not work on the lexus tonight since I had to replace the radiator on the wife`s Murano and it took me way longer than anticipated...

Nevertheless, I gathered some strenght to work a little while on the GS. Earlier today I borrowed a fuel pressure gauge and bought a fitting to install it on the end of one of the fuel rails.

But first I tested the throttle motor and TPS:
In my opinion its perfect.

Then the much-anticipated fuel press test!
26 psi, with 28 psi spikes.... Seems weak to me. Factory spec anyone?

Is it just me or the engine sounds a little better? I left a 1.5 amp battery tender connected since last night. The engine almost idled without steping on the gas. Well, enough for today, tomorrow´s episode with bring the.... INTAKE MANIFOLD SMOKE TEST. I´ll plug the intake tube and blow smoke from a cigar into the intake manifold.

Regards,

-Angelo
99 GS400

DMPesso

It's the gs400. There is no APPS (accelerator pedal position sensor) that's only in the 430. But the TPS I have heard of them causing some weird issues like this so it might be worth giving that a try if nothing else works because when my APPS went out it was supposed to throw a CEL but it never did. So based on the symptoms I went on a limb and replaced it anyway and it fixed the problem!

PTYGS400

Thank you DMPesso, I´ll keep that in mind. Now I need to know if 26 psi is normal pressure. Somewhere on the web I found a spec of 44-50 psi.
Using the lower number (44 psi) against my actual pressure (26 psi). That results in about 23% less fuel flow. (255 cc/min injectors act as 196 cc/injectors)
http://www.witchhunter.com/injectorcalc1.php

DMPesso

Tire pressure? For our cArs the best psi is 32. But you can play with it a little it drives differnt when you have higher psi. But it should never be less then 32 for sure and that's on a cold start

PTYGS400

Ran a quick test to diagnose a lean mixture. Started the engine, held it at about 2000 (missfiring and running rough), and while the throttle was held in that exact position, I sprayed carb cleaner into the intake. RPMs would climb to about 4000 as long a as the additional fuel was sprayed.

A lean a/f ratio seems to be one of the problems here, maybe not the only one, but a definetly a piece of this puzzle... I could hook up a timing lamp to cyl #1 and verify it the readings match what the ECU is commanding.

I will retest fuel pressure with 12v on the fuel pump and also measure pump motor resistance and the voltage from the pump ECU.


- Angelo
99 GS400

PTYGS400

Hello again, New findings:

1- I tested fuel pump resistance. (1.5 ohm). PASS
2- Tested fuel pressure with direct 12 volts on the pump. Same 28 psi. FAIL
3- Tested 5 volts on misc sensors. PASS
4- Measured current draw from the battery with everything off. 1 amp. FAIL???
5- Tested the fuel pressure gauge against my bike pump gauge (known fairly accurate)... off by about 25 psi!
This means I have about 50 psi fuel pressure. PASS!

Other things I noticed:
1- When the ignition switch is turned to the ON position, the fuel pump does not do the normal 2-3 second prime. I remember spilling gas from the pressure line one time that I turned the key without the engine in the car. What has changed?
2.The gauges still don´tt work (speedo, tach, fuel and temp). I have some pages from the Service Manual that covers this section. I´ll chase this ghost to see where it leads me.

Still pending the intake manifold vacc leak with a cigar (no cigars around here, non-smoker). However I feel I need to focus on the electrical part now, too many gremlins, they could be related.

- Angelo
99 GS400

PTYGS400

Thought it`d be nice to share....

PTYGS400

It`s gotten awfully quiet around here....

Today´s news....
I removed the combination meter, did the whole electrical inspection and test by the Lexus Service Manual (I have this part of the manual in PDF format). All voltages, grounds, resistances, etc are ok.

The abnormal 1 amp draw from the battery was not a continuos condition. I measured for a Little longer and it dropped to 0.09 amps after about 30 seconds.

SMOKE TEST.
Got a cigarette, plugged the intake hose with a nitrile glove and blew smoke into the intake manifold through one of the ports by the throttle body (see attached image). Smoke started coming out from the passanger side cyl bank. Something is really wrong in that area. Maybe injector seals, maybe something loose. Tomorrow I will try to get to the bottom of this.

angus

iTrader: (4)

A test that I like to use is a propane torch with a rubber hose attached.

If there car will idle, take the torch (not lit - lol) and run it around various parts of the intake manifold etc. - you'll know when you find a leak as it'll speed up.

angus

iTrader: (4)

I'm guessing here, but you put your factory intake manifold back on the JDM engine?

I am doing the EXACT same swap right now -

You might have something stuck in one of the intake gaskets.

JeffTsai

iTrader: (1)

Fuel pressure should be around 40-50psi or so. You might have a clogged fuel filter. I have had that happen on a few peoples cars I have worked on in the past. Do you have a OBD2 scanner that can read live data? Take a look at the short term and long term fuel trims. If they are in the double digit values, so around +15-20% then you are having some sort of fuel issue. The ECU is trying to compensate by opening the injectors up more, but the maximum trim or add is +/-20%. If it is not able to reach stoich AFR even with +20% then the engine will still run lean and want to stumble.

Look around on the intake, and more specifically the resonator on the intake. The big box thing that runs off the intake tube, before the air filter box. It's called a Helmholtz resonator, and is supposed to reduce the induction noise of the engine(Lexus trying to keep the car quiet lol). On the GS400, that thing is notorious for developing cracks. If you have a crack there, then it will give your car a false MAF reading and the car will run lean.

Also, the fuel pump does not prime until the ECU detects movement on the crank position sensor. The system is a dead head/returnless system. The fuel pump assembly retains fuel pressure for a very long time even after the car is shut off. If theres no movement of crank sensor, then pump stays off even when you key the car on. The reason that it spilled gas last time is because the ECU was unplugged. Not sure why, but it triggers the fuel pump if you unplug the ECU and key on the car.

Do another test to see if there is a vacuum leak by spraying brake cleaner all over the manifold and injectors. If there is a leak then the engine will start to idle differently once hit with brake cleaner. Similar to angus' idea of using propane, but I usually hit it with brake cleaner since it's a more direct shot. It will be easier to see and pinpoint the leak.

PTYGS400

Hello Angus, thanks for your input.
I am using the JDM intake manifold, but I had a mechanic replace the starter wiring. That`s why I am going to inspect the whole intake system myself.

Parts I had to use from the old motor:
1- Exhaust manifolds
2- Lower oil pan
3- Large idler pulley (replacing hydraulic drive pump)
4- Engine electrical harness
5- Transmission disptick / tube. (I am using the JDM tranny)
6- Starter / knock sensors wiring

PTYGS400

Ok, I will hunt down this vaccum leak and report back.
As posted above, I tested the dash gauges by the Service Manual. Every resistance, ground and 12v is ok. Do you know what could cause all my needles to be dead?

Thanks once again, you guys have been very helpful.

- Angelo
99 GS400