iamdk72986

Hey Baetke, sorry for constantly disturbing you with this but last night, I tried to run the fuel pump itself while the car was off but was not able to do that. So I opened up the fuel pump access cover under the rear seats and noticed that I was hearing two different sounds while the car was running. The first sound was the sound a typical fuel pump would make. The second sound was the sound that I've been bothered by, which is the sound of a vacuum leak. It doesn't seem to be as loud compared to when I was hearing it from say either under the car or outside the car.
My friend suggested that it may be not the fuel pump itself but the assembly that it sits in. That big plastic thing that holds the fuel pump in place. He told me he had a customer that came in with a Sienna that was throwing a System too Lean code and discovered a crack in the plastic assembly after he checked out everything else (vacuum leaks, fuel filter, etc...). Any insight on that?

Daniel

Baetke

No worries. I'll help as much as I can but you are getting into an area I haven't had any experience in. If you really think it is a vacuum leak, here is a link to a video for a technique I've allways wanted to try for finding vacuum leaks. Kinda hillbilly but it looks like it would work pretty well.
Check it out...
https://www.youtube.com/watch?v=zMok2y05jNE

Baetke

Daniel,
Sounds like we're still not sure if its a fuel delivery problem or a vacuum leak but here's a couple of ideas to test for vaccuum leaks. Refer to the picture below.

The vacuum line on the left supplies vacuum to the VSV for EVAP purge valve and thence to the charcoal canister. Try disconnecting this hose and see if your vacuum leak sound goes away. You should also plug the brass line you removed the hose from because this will create a vacuum leak directly into the induction system. See if the idle gets any smoother or rougher with this line plugged and unplugged.
Try the same thing with the hose on the right. It supplies the vacuum reservoir located under the battery. The vacuum reservoir supplies vacuum to the induction air valves and the fwd engine mount.
Were you not able to locate the source of the vacuum leak sound by ear?

Baetke

iamdk72986

Sorry Baetke, for some reason I didn't get a notification email stating a post on this thread. I just came back from vacation (snowboarding at Whiteface and Jay Peak) and am now reconnected with the world. Happy New Year!!

I have just noticed another symptom. I was parked outside this girls house and we were chatting it up in my car. The car was idle for easily over half an hour to keep the heat going. As I left, the car knocked like crazy in every gear, even with a very light load. It went away eventually as I continued driving and the ECU compensated. Could the symptoms be related?

I'll be sure to check out those 2 vacuum hoses after work but I don't recall hearing any vacuum leaking sounds from the engine bay. I suppose a second look wouldn't hurt lol. I'm really starting to get fed up with this car. I'm pretty sure I need to do the valve stem seals also. I did them on my 3000GT VR4 and it was not fun at all. I'll be sure to chime in soon.

Daniel

Baetke

Hi Daniel,
Did you get a chance to check out the video link I posted on locating vacuum leaks? I think we still need to figure out if its a vacuum leak or a fuel delivery problem. From what you described, it sounds like the knock sensors are doing their job. Vacuum leaks can be hard to locate by inspection, thats why I suggested the smoke test in the video. Where exactly does the hissing sound seem to be the loudest, in the engine compartment, under the body, in the rear? Seems like if its pretty loud, you should be able to isolate it by ear.
Baetke

iamdk72986

I have checked out the video. I actually have seen many of scotty kilmer's videos lol. Personally, I like ericthecarguy better as he's more detailed in his videos but to each their own. The vacuum sound is by the gas tank. I haven't taken off the cover for the EVAP as the sound didn't come from there and the bolts/nuts (I don't remember what they are) looked quite rusted. I haven't heard any vacuum sounds from the engine bay but I'll check again.

Daniel

Baetke

Ok. The only thing I can think of that would cause a vacuum leak sound under the middle of the car would be the EVAP lines. Thats why I suggested disconnecting and pluging the hoses in the picture in post #18. That is where the EVAP vapors return to the throttle body; the vacuum being supplied through those hoses by the throttle body. If plugging them eliminates the sound then you've narrowed down your search to that system. If not, it must be something else.

I've watched Ericthecarguy too but he's a little too wordy for me. I also like Real Fixes Real Fast and my very favorite is ScannerDanner. He's done several RX300 specific videos.

iamdk72986

Sorry for the long delay. It's been ridiculously cold here and I didn't have the shelter of my friend's shop since he is in the middle of a move. I unplugged the vacuum line on the left and i was getting vacuum on both the hose and the nipple. I still heard the sound. I found that unusual but I was on a huge time crunch so I just put the hose back on. I did the same with the one on the right for the vacuum reservoir but the sound remained. As I was about to close the hood, I saw the vacuum diagram under the hood. I noticed there are 2 lines for the VSV and they get bridged. That would explain why I was getting vacuum on the hose. I will try again tonight after work and see what happens.

Daniel

Baetke

Understood.

The vacuum line to the vacuum reservoir shouldn't make any difference since all of those lines go forward in the engine compartment. The vacuum reservoir just provides vacuum for the front engine mount and the acoustic controlled induction system. All of that stuff is in the engine compartment so it should have no effect if the noise you hear is back toward the gas tank.

The other line, or more correctly pair of lines (one for each throttle throat) connect together and go to the VSV for EVAP system. If this is the source of your hissing sound, it should go away when you disconnect both of them.

Baetke

moonphase

Hi iamdk72986;
Just joined CL yesterday and read your thread. According to the Haynes obd ll manual; If the long term trim is high above 10%, and the short term trim is low in the negative numbers then the MAF/VAF sensor is usually at fault. You might try cleaning the mass air flow sensor with MAF cleaner. Good Luck!

iamdk72986

Hey moonphase, welcome to CL. I have cleaned the MAF recently as a precautionary measure. I am now starting to think it has something to do with my idle control valve. My idle seems to be a bit on the low side whenever the car is in drive or reverse. I have cleaned the IACV recently as well.

Baetke, i disconnected the hose under the engine cover as it was much easier to reach compared to the two hoses under the factory strut bar. The hissing sound remained under the fuel tank. I went under the car and it sounds to be coming from inside the gas tank on the driver's side. I'll check the fuel pump assembly once the weather cooperates and let you know my discovery.

Daniel

Baetke

Daniel,
Thanks for the update. I think we can now rule out a vacuum leak in the EVAP system. Looking fwd to your next update on the fuel pump.

Baetke

moonphase

iamdk72986;
You can hook up your scanner and with only key on position (not running), push the gas pedal in and out while watching the throttle position sensor numbers in live data for smooth operation. I had to change our ES300 tps at 115,000 miles due to poor fuel mileage. The only way the on-board computer knows the throttle position is through the tps, and if it is sketchy you might be seeing the flat spots while accelerating. The sensor should be getting 5 volts from the computer. No guesses about the hissing though, unless it is coming from the fuel filler tube or gas cap o-ring.

iamdk72986

moonphase, that is an interesting idea. I would've never guessed to check the TPS sensor. So is the sensor constantly getting 5V from the ECU regardless of position? And does the sensor send back variable voltage, relative to the throttle position, back to the ECU? All this time, I've completely overlooked the fact that the TPS could possibly be at fault. I guess assuming that it is fine is foolish of me lol. I'll take a look tomorrow when I plug in my scanner.
On a side note, I've noticed that my IGN ADV was at roughly 20 degrees. I can't seem to find the specs on it. Does that number seem out of spec? I've been under the assumption that it should be as close to zero as possible and if anything, given the fuel trims showing a lean conditions, it should be a negative number as to retard timing. Unless if I have the whole concept wrong. I'm just thinking out loud I guess lol.
As far as the hissing goes, it really seems to be coming from inside the fuel tank on the driver's side. My gas cap o-ring seems to be doing its job as whenever I open it to fill up, I hear some releasing of pressure, although nowhere near as pronounced as my 3000GT. It didn't sound as if it was from the exterior of the fuel tank but I'll take a look at the filler tube when I get a chance to get under the car. I didn't see any signs of fuel leaks anywhere under the car if I remember correctly.
It sucks how the OBD2 system was supposed to make diagnostics easier (which is does for the most part) but when things like this happens when the ECU can't detect anything, it sure is frustrating lol.

Daniel

PS - Thank you all for your thoughts and replies. It's nice being able to talk to someone about this. Dealers don't know jack and most mechanics don't know jack either. They know how to fix things. They don't know how to diagnose. At least from my personal experiences. Which is why all my cars have only been handled by me. =)

Baetke

Daniel,

With the engine fully warmed up, all accessories off and the transmission in Park, the idle rpm should be 700 +/- 50 rpm and the timing advance should be 10 +/- 2 degrees BTDC. At 55mph cruise I typically see about 37-39 degrees of advance.

If you have 20 degrees of advance at idle then that would explain your engine knocking problem, especially at low rpms. Could be a slipped timing belt.

Baetke