DK Audio

This started because I was throwing catalyst below threshold codes PO420 PO430. I posted on here and people said to check for pinhole exhaust leaks. I crawled under the car with it running and couldn't find anything. I searched online and found many people using a vacuum cleaner hooked up to the tailpipe so you can hear sucking air to find the holes. I thought this was a great idea, I found a couple small holes and sealed them with exhaust pipe sealing compound from Autozone. However, now my car in park or at a stop pulsates, the entire car pulsates. At one point even my RPM needle would pulsate up and down. It doesn't seem like the car is going to die or anything, this is just very annoying. As soon as I increase the RPM's slightly by pushing on the accelerator everything is as smooth as can be. What did the vacuum do? Worst part is my codes are still there!

DK Audio

So today the car was really bad at stops, my body was shaking sitting in the car! Then I saw my check engine light flash, never seen that before. As soon as I got home and opened my door I could hear a weird sound, it was an exhaust leak, much bigger than I've ever heard. Could this be the cause of the car shaking, confusing sensors and throwing codes? I guess when I used the sealer before I didn't do the right spot. I put more of it on today, I know the leak is right around the brackets that hold on the rubber disc. Hopefully I will find out tomorrow.

Lexusfixer

Take it out for about a 2O minute ride in the dark, Pull off the road somewhere that there is little light. keep car running, turn off the head lights, pop open the hood or crawl underneath and see if you have a glowing red catalytic converter. It would not surprise me if you had a converter that was failing. Since most Lexus exhaust was double wall I doubt the sealing any leaks has anything to do with the problem that you are having but it is a sign that you might want to think about replacing whatever exhaust parts are bad.


Before you do anything else though, make sure the plug in connector on the MAF is connected, or isn't loose dirty or corroded.

RA40

iTrader: (6)

Exhaust leaks become more of an issue if they are before the cats. After them this is a minimal issue other than an odd exhaust sound. Has the ECT sensor been changed out? What kind of MPG is the car getting?

DK Audio

Thanks for the replies. I did not take the car to work today just incase.

I will check the MAF connector.

No, no sensors have been changed out since I have owned the car (4 years or so).

Maybe I'll do the drive thing tonight, hopefully I'll have free time to do that.

As far as MPG, usually get 18-20, drops in winter obviously. I live fairly close to work and drive in decently heavy traffic so that seems right to me.

DK Audio

Definitely need help on this one guys...

You're right, sealing the exhaust did not change things so it must be something else. I was going to drive it yesterday to check for a red hot cat but a few blocks in my CEL started flashing again and then Check VSC came on the display and then the VSC Off light came on as well. I brought the car back home then. My MAF connector looked fine but I have never cleaned the MAF. I think on my 98 it is safe to spray with cleaner, is that advisable to do? Also, as I stated no sensors have been changed since I've been the owner, is the ECT suspicious for these symptoms too?

I had to get a ride to work this morning which was a huge PITA! I need to figure this out quickly.

Yamae

When the MAF connector is not connected, the circuit opening relay stops the fuel supply, and you can't keep running the engine. Lexusfixer seems don't know the fact which is indicated in the FAQ.

DK Audio

So is it advisable to replace the ETC and spray clean the MAF sensor as a starting point? Clean the throttle body maybe too?

djamps

@yamae -- I was able to drive my 98 with the MAF disconnected (was by accident, oversight when working on engine). It ran terribly rich, idled poorly, CEL and VSC Off were indicated. But it still drove.

Yamae

How long were you able to run the engine?
The ECU is designed to stop the fuel supply opening the circuit opening relay when no signal from the MAF for more than 3 seconds is detected.
The engine can start but it is supposed to stop after the fuel pressure becomes to low to inject.

Other than the MAF, the ECU forces to stop the voltage supply to the fuel pump at one of following conditions is detected.
No signal from the crank position sensor for more than 5 seconds.
No signal from the cam position sensor for more than 5 seconds.
No IGF signal from the igniter for more than 3 seconds although the IGT signal is sent.

DK Audio

Ok guys, tonight I cleaned my MAF sensor, put in a new ETC and removed and cleaned my throttle body. Everything went great with no hiccups. When I started the car it idled odd, white smoke out of the exhaust and odd pop sounds out of the exhaust too. I drove it about 4 miles, when going on city streets at 35mph it drives like a dream but at a stop it still shook/pulsates. By the end of the drive my CEL came back on. I did not have glowing red cats though. I had the negative disconnected as I worked so I assume some of the above was the ECM learning everything again.

Now here's the weird part, I scanned my codes when I got home...

PO300
PO301
PO303
PO305
PO300 P
PO301 P
PO302 P
PO307 P
PO171 P

Most of these are cylinder misfires, is this why the car shakes at a stop? Why does it not happen when driving? Any ideas, I'm super worried now!

RA40

iTrader: (6)

I suspect the OCV and I would change to O2 sensors since they are probably fouled and possibly showing age related issues brought on by this.

This thread may be of help:
https://www.clublexus.com/forums/ls-...miss-fire.html

Gdwrench35

I'm guessing from the PO307 that we are working on the V8. I'm new here and I'm not sure how to tell what ride your referencing.

The pulsation you describe is indeed the cylinders misfiring. You should stop driving the car as continuing to do so could damage your cat's. Got some questions

1. What did you clean your MAF with?
2. How and with what did you use to clean your throttle body?
3. What kind of scanner are you using? I'm not familiar with the p at the end of the code number.

Bank 1 of your engine is running lean so you can rule out the throttle body, MAF, ECT, etc. because all that would affect both banks equally, not just bank 1. Also notice that all but 1 of your codes are odd numbers? They are all happening on the same bank. I'd look for a vacuum leak around the intake area. Also look at data stream and watch for good upstream air fuel ratio signals. An upstream AFR sensor is a common failure.

And from what I've seen, most cars will run with the MAF unplugged.

DK Audio

I watched a video of the OCV replacement, doesn't look too bad. I assume this is an OEM only part? Ouch, just looked it up, $100 each and probably should do both.

We're in the LS400 forum so yes, 4.0 V8

I cleaned the MAF with CRC MAF spray.

I cleaned the throttle body with CRC throttle body spray and just used a towel, all the carbon came off nicely.

I'm using Autel MaxiScan MS300. The P at the end means pending, it sensed something is wrong but it didn't happen enough to be a full code yet.

Could this cause it? See the top tube, some fibers are coming out of it, I don't think the break is all the way through though.

Gdwrench35

That doesn't appear to be a leak but its hard to tell from the picture. Start the engine and run your hands along the hose. Listen for a suction type noise as your looking for a vacuum leak.

Without the right equipment, a vacuum leak can be tricky to find. I typically use propane or a smoke machine if I can't find it easily.

You can spray propane around the intake manifold area while the engine is running and watch for a response in the RPM. There should be no response if there is no leak present. If there is, the engine will either rev or sputter. The same can be done with any flammable spray such as carb cleaner, throttle body cleaner. Just be careful and use it sparingly. Don't spray it on the exhaust manifold.

A smoke machine can be used to inject smoke in the intake area so that you can just watch for smoke escaping from the source of the leak but those things are expensive. I've heard of people hooking up a vacuum cleaner to the to an intake port and listening for a suction but I've never personally tried it. Like I said before, I like the spraying it down.

Has the starter ever been replaced?

What I commonly see is a leak around the base of the intake where it attaches to the head. Is your OSV on the 4.0 on the driver side? Its also possible that the valve is sticking open causing an internal vacuum leak that you won't hear. To test this, simple pinch off the hose going to the valve while the engine is running and see if the misfire goes away. It should respond pretty quickly.