rysbrnr

My 98 GS400 started running poorly the other day and a CEL came on.
I read the spark plugs and #8 was black and carboned up. It must be misfiring #8 so I throw on a new spark plug and fire it up. Still no improvement.... next guess is the #8 coil pack is bad so I remove it and measure coil resistance at the pins and compare it to another "known-good" coil. Measurements are the same. Next I swapped #8's ignition coil with cylinder (#3). I start the car and it's still missing... while running, I disconnected the harness from cyl #3 which is using #8's coil..... the car stumbles!!! Oh no!
Looks like my suspected coil is actually still good!
Now I disconnect the ignition harness from cyl #8 which is using #3's coil and cyl #8 is STILL misfiring!

Next thing I did, while the engine is running was unplugged injector #8... NO CHANGE in rough idle. I measure #8 injector and it's reading 16 ohms. I measured a couple other injectors and they're reading the same value.


To sum it up, cyl #8 is misfiring badly. #8's ignition coil works fine in another cylinder. #8 injector measures out to be the same as other injectors. There's a brand new NGK iridium plug in there.

Why is it misfiring???

Anyone have any insight or experience with this?

GS_OREO

Try running a compression test.

sockfocks

iTrader: (1)

Sounds like you did all the troubleshooting necessary. Try putting another injector onto cylinder 8, it might be leaking fuel.

rysbrnr

I just a compression test. Now I don't know what is the "norm" but the test showed ~160psi on a cold engine. That's enough compression to ignite a mixture.

Now the other thing I haven't tested for is the #8 injector. I did test the resistance and seems okay....but is it safe to assume it's in proper working condition? If it's clogged or stuck can it still read correct impedance? It measured 16 ohms with my test leads in either position. I used my Fluke 77 DMM for testing. I wish I had an oscilloscope so I can read the injector duty cycle, IF it's even there to begin with.

Sockfocks, I'll put the #8 injector somewhere else and see the misfire follows the injector.

I don't really want to pull all that stuff off just to get the fuel rail off!

sockfocks

iTrader: (1)

Well...you could tap the injector lightly something and maybe that will help. Here's what can happen. The injector may have something stuck between the pintle and the opening causing the injector to stay open. Injectors are spring loaded to stay closed and fuel pressure helps them to seal even tighter. So, the only thing left is FOD or foreign objects. I hope this is the cause. There are fuel injector testers that blink when the injector cycles, I think you can get them at the auto parts store.

BTW never assume anything...lol.

FrankT

160 is good...
Your on the right track.

Did you happen to get the code pulled if you did what is it?

You can test the #8 injector connector and see if the injector harness has voltage pulse.
Just unplug the connector, insert your voltmeter to it and run the motor to verify injector pulse.
You can also listen for the injector pulse with a piece of hose or a screwdriver up against the injector.

Good luck and keep us posted

dung0981

iTrader: (1)

the scanner read the code.
look to me the injector #8 got problem, also check the harness plug into the coil ...
160 psi should be fine

rysbrnr

Yeah I went to Autozone after the spark plug change and with their generic scanner, it pulled a "cylinder 8 random misfire" code. No Lexus dealer around me within 120 miles...but I don't like getting raped anyway!

I did hook up the volt meter to the injector harness while running and tried to look for a pulse. I set it to AC volts but I don't think the pulse is fast enough, however it did read about 1.5 vAC but steadily dropped to ~.350 vAC as I held the connection for a few seconds. I did the same test with another injector harness and same results. I don't think there is a DC component in the injector pulse but should I have looked for a DC voltage there instead?

The best thing is to remove the injector and stick it somewhere else IMO.

19psi

the injectors are dc, but there's no way your dvom will read the ipw fast enough to do any good. a noid light is what you need.
i'm betting ont he injector though, as you've pretty much isolated the elctrical portion of the system as being good.
i've seen injectors fail mechanically while the solenoid is still good, meaning your resistance measurement will show good even while the injector doesnt' work...

PetesLS400

I've been following the same gremlin with my moms '99 GS400.

I have a cylinder 5 misfire, same symptoms as yours. First swapped out the plug, next the coil and now I'm going after the injector.

Let me know how it ends up with yours.

rysbrnr

Any of you guys happen to know the stock flow rate of a GS400 injector is?

Since there are only 2 Lexus dealers in all of Iowa and they're both 120 miles away from me I was going to try and substitute one of my NT DSM injectors in there to see if the misfiring goes away. A non-turbo 4g63 injector is 240cc/min and if the plug matches it'll be a great troubleshooting tool.

PetesLS400

Lexus has 2 part #'s for our Denso injectors it seems like. The front 4 injectors (cylinders 1-4) have a different part number from the rear 4 (cylinders 5-8).

I verified this with an auto parts store and my local Lexus dealer.

Now sure what the flow rate is.

rysbrnr

front and rear injectors? The engine is longitudinal mounted so how is there a front and rear set? That's confusing! What's the difference between front and rears? So when I call local scrap yards or the dealer I need to tell them that it's a "rear" injector (#8, passenger side closest to the firewall)?

I hope I have the numbering correct. If I'm wrong, please correct me.

Cyl #1 driver's side closest to radiator, Cyl #4 driver's side next to firewall

Cyl #5 passenger side closest to radiator, Cyl #8 passenger's side next to firewall

PetesLS400

Nope, I'm 99% sure its.


Firewall
8 7
6 5
4 3
2 1
Radiator

http://catalog.autopartsgiant.com/Re...autopartsgiant

http://www.partsamerica.com/ProductL...=Fuel+Injector

Notice how they have one injector for cylinders 1,2,3,4 and another injector for cylinders 5,6,7,8.

Lexus also has two different part numbers when you call them up, the first guy I spoke with didnt know about it and was confused why two different part numbers were listed, so he asked another guy working there and the other guy told him the same thing about the front 4 and rear 4.

Go figure

sockfocks

iTrader: (1)

front and rear?...how strange...I think they all flow the same. When my friend put a RMM supercharger on his GS400 the RC injectors that came with the kit were all the same p/n.