Misfire has me stumped - help needed! (1 Viewer)

[LostInMyLX]

Hey y’all, hope everyone is good on this fine Oct day. So I have a misfire that has me stumped, I’ve chewed through every misfire post mostly on here and even some others with vehicles that share my engine (2uz in a 2000 lx470).

I’ve got a rough idle, regular throwing of a p0304.
Weirdly it goes away above 1800ish rpm, at times won’t throw code but will flash CEL. Sometimes there’s nothing but you can feel a little stumbling. Also it’s hard to start like a hiccup or hesitation. Sometimes! Not always.

Sometimes i get a solid CEL with the trac lights as well.

Here’s the stumper: I’ve replaced all coils, swamped them around to diag and replaced fuel injectors, swapping them to diag. The CEL code always comes back p0304. I recently did timing belt and have put 2000 miles on it since tbelt, zero issues. (Did it myself, forgot to mention I’m an ambitious DIY mechanic).

Car info is well cared for and looked after 2000 lx470 w 353k miles (I want a million out of it!!)

Chasing gremlins with the coolant temp sensor and the pcv valve and grommet today. Also oddly on this mornings 40 min drive to job site it stumbled a little bit but then threw a 0300 and 0303, 0301,0304 but it’s only done that this once this am. Cleared codes while driving and alas that stupid 0304 came back. I’m praying someone can help bc this is my everything truck and also I love it. Thank you for any help in advance! Cruise on!

 

[white_lx]

Since you rotated spark plugs, coils and injectors, my next step would be to look at the signals of the ignition coil and injector. Start with a DVM to check the power and grounds on those connectors. Next would be a scope during the missfire. If that does not show anything wrong, my next step would be a compression test to make sure nothing strange is going on with cylinder #4.

Bw Toyota's missfire information is not very accurate, except for at idle conditions. So it is not garantueed that there are no missfires at higher rpm if the counter is not counting. There is another way to look at missfires more accurately. Here is the process of how to do it in Techstream.

 

[woodwateradv]

Vacuum leak? Mine had misfire at idle too, turned out to be cracked intake manifold gasket. PO used cheap aftermarket gasket. Also, good thing to check all vacuum lines.

 

[LostInMyLX]

WhiteLX, thanks for the info. Installed new Coolant temp sensor and pcv valve and grommet with no difference. I’m not having any signs of blown HG and the truck has given me many miles with no temp flux ever. Always had oil changes early. Misfire started after 1 hr cruise on highway at 85 turning 2650ish rpm’s (I’m on 35s). Not sure if that did the truck in or what. Can hear new injector clicking away, also tested voltage on good cylinder and number 4, all voltages were pretty much identical. No change in running condition when #4 is disconnected, going to pressure test tomorrow. Praying it’s not bad compression but based on all other factors along with hard starting compared to before I think I may have low compression. Any suggestions?

 

[white_lx]

WhiteLX, thanks for the info. Installed new Coolant temp sensor and pcv valve and grommet with no difference. I’m not having any signs of blown HG and the truck has given me many miles with no temp flux ever. Always had oil changes early. Misfire started after 1 hr cruise on highway at 85 turning 2650ish rpm’s (I’m on 35s). Not sure if that did the truck in or what. Can hear new injector clicking away, also tested voltage on good cylinder and number 4, all voltages were pretty much identical. No change in running condition when #4 is disconnected, going to pressure test tomorrow. Praying it’s not bad compression but based on all other factors along with hard starting compared to before I think I may have low compression. Any suggestions?

How are the fuel trims for that bank? Are they any different from the other bank?

You can use the "control injection volume" active test in Techstream to increase/decrease the injection volume and see if the missfire improves with more/less fuel. That may send you in the right direction.

 

[Bsas2]

I have just done a heap of work on an 05 UZJ100 4.7lt. Water pump , Timing Belt Kit, Crank Angle Sensor, Heads machined & valve seats recut. Motor purrs like a kitten until you drive it. Just touching the throttle it is fine, but as soon as you add any acceleration, the thing bogs down & won't rev at all. If you persist, the revs start to increase & the motor rattles like it's about to jump out. It appeared to me to be a built up of exhaust gas causing back pressure. So I pulled the Catalytic Converters off. Without them, the motor revved freely in the driveway, but a little too noisy to drive around. With the aid of an endoscope I could see that the first Cat was definitely very dirty & needed cleaning, however the second one had the initial screen missing completely & the system completely blocked off. Interestingly that side was showing cylinder misfires for that whole bank 1, 3, 5, 7. Waiting for new Headers & Cats & hope that fixes the problem.
If noting else shows up, this could be worth your checking as well

 

[LostInMyLX]

Well boys, bad news. Compression in @ 30psi in cylinder 4. Leak down test is next. If I can find someone to lend me a scope I’ll do that as well. I can’t imagine it being a cylinder or ring letting go. I’ve heard of the heads at times failing but this truck has never over heated or been ran over 3k rpm really. Also the non vvt 2uz are notoriously tough and reliable. Any guesses? How hard is it to swap the heads? Id imagine i gotta undo the timing belt stuff i just did right?

 

[white_lx]

30psi is really low. That is almost no compression at all. I think you would get higher compression numbers without rings or with a worn cylinder wall. The compression number is probably also too low for a head gasket failure, unless it has been progressing for a long time. My first guess would be that this is valve sealing or valve timing related.

Is there any chance the timing is off since you mentioned a recent T-belt job? Did you happen to check a few other cylinders on that same bank for compression?

How hard is it to swap the heads? Id imagine i gotta undo the timing belt stuff i just did right?

The timing belt parts would need to be removed, but you also have to unbolt the manifold from the cat on that side and remove the intake manifold. Let's just hope for the best, and see what the leak down results are first.