Noobie with an odd issue on a 2UZ-FE (4 Viewers)

[Freddy1333]

Hi folks and greetings from Western Australia and thanks for the sign-up approval.

Background: my son bought a 2005 4.7L V8 6-8 months ago with unknown service history. It had about 350,000km (210k miles) on the clock and it's done another 8,000km since. A few months ago the CEL came on, showing code P0156 - O2 sensor bank 2 (right). He fitted a new sensor, cleared the code and all was good for a few weeks. It then developed a misfire under load - no CEL. A new fuel filter didn't fix it but new spark plugs did. Another month goes by and the misfire returns - still no CEL. As the service history was unknown, we decided to replace the timing belt, pulleys and fan belt & pulleys anyway and do a compression test and valve clearance check, both of which showed that all cyls were within spec on cyl pressure and valve clearance. and thought: no root cause here, so what is it? However , we noticed that 2 plugs from the right bank had moderate carbon deposits attached to the sides of the inner metal body and the ceramic tip around the electrode was quite brown though they had no carbon there. All other 6 plugs had no carbon and the ceramic tips around the centre electrode was still clean and mostly white. The 2 dirty plugs were cleaned of carbon and all 8 plugs were refitted to the same bank from which they came. When started, the engine seemed to idle fine but when driven the misfire was obvious. Those 2 'cleaned' plugs were replaced with 2 new plugs and the vehicle drove perfectly for several day when the CEL lit up showing P0156 again, but no misfire. My son then swapped the O2 sensors from left to right, drove it and the same fault code has returned.

Question for those with more experience on these vehicles than me: can the injectors deteriorate over time to such an extent they will 'flood' a cylinder when under load that it will foul plugs and not show a CEL other than P0156 eventually?

TIA

Freddy

 

[awesomeissquid]

Wouldn't clean spark plugs light that indicate a lean running condition as opposed to a rich running condition?

 

[Freddy1333]

Thanks. They've done only about 1000km (600m) at most. The 2 on the left are fine (same as the 4 in the left bank), the other 2 are faulty and were replaced - misfire fixed for now.

The question remains: can the injectors deteriorate over time to such an extent they will 'flood' a cylinder when under load that it will foul plugs and not show a CEL other than P0156 eventually?

 

[Toyo8696]

I have never heard or seen an injector "flooding" under a load but they can start to drip beyond the specified limit.

 

[Freddy1333]

'Flooding' is a wild exaggeration - 'drip beyond the specified limit' is closer to what I really meant. I've not seen s/plugs get fouled to the point that they fail in such a short distance on any vehicles with even higher mileage and original injectors. Have you Toyo, or anyone else? If so, what caused it?

 

[J1000]

Yes I would service the injectors or at least run some injector cleaner product in the fuel. Other things to do on a high mileage 2UZ that isn't running right is cleaning the throttle body and the MAF sensor. If those are dirty it can throw off the air-fuel ratio but it won't throw a CEL.

Does your exhaust header tick/leak? If so that can cause a rich condition on that bank because the O2 sensor reads lean from fresh air getting into the exhaust so it will inject more fuel. Can destroy the cats too.

 

[Freddy1333]

Thanks J1. Yes the MAF sensor was a little dirty - cleaned up with the specific MAF sensor spray cleaner. The right bank O2 sensor CEL showed up for the 2nd time a few days after doing so. It's already had a bottle of injector cleaner thru the system when this trouble first showed up. I just got a set of aftermarket injectors which I will fit on the weekend. As for the exhaust, I can't hear any ticking or leaking from the manifold area - but I'm half deaf. My son hasn't mentioned any such thing.

Question: will the O2 sensor throw a CEL for a rich condition (which seemed to be what caused those 2 plugs on the right to fail)?

 

[vipergrhd]

Did someone suggest new coil packs? My coil packs were showing signs of arching and got rid of stumble at idle almost feels like a misfire also check for crack manifold. @Freddy1333

 

[Freddy1333]

Good point Viper - thanks for asking. I forgot to state in the first post that 8 NEW coils were fitted when those 2 failed plugs from the right bank were replaced a week ago. A couple of days later the right bank O2 threw a CEL for the 2nd time. The vehicle is running fine since it was cleared but expect it to return, hence new injectors to be fitted.

 

[Toyo8696]

Just in case you don't have this info I have attached the Toyota diagnostic info. Please let me know if you need anymore info.

 

[Freddy1333]

Appreciated muchly Toyo. Related components - MAF meter & VSS. No VSS probs show.

I assume it means MAF sensor - correct? I just got a new MAF sensor as it happens. Tho it's easy to replace, I will do the injectors first (as t's the right bank with the issue) and see what happens after running it for a week.

Just thinking out loud - if it was a faulty MAF sensor, you'd think it would throw a CEL for both P1056 & P0136 wouldn't ya?

 

[excessive]

swap your coilpacks around to see if the misfire follows the coilpacks. they are known to go bad over a long period of time.

 

[Freddy1333]

Thanks ex. See reply 9.

 

[Freddy1333]

UPDATE: Bugger - it's blowing lotsa bubbles into the coolant and out the rad cap. Cyl leakage test coming up tomorrow to pin point the leak, then it'll be off with the new timing belt, cams and leaky head(s).

Stick around for more fun updates.

 

[Freddy1333]

Cyle leakage test showed bubbles from cyls 6&8, so off with the head - both actually, to get em planed to ensure we don't hafta go back in there ever again. Bit of a mongrel job getting the RH exh flange support bracket and LH rear heat shield attached to back of heads free - obviously fitted before body was lowered onto to chassis. Gasket set is VERY pricey! I'd say the vehicle was traded when PO was told the cost of the fix. O well, It'll be as good as new by the time it's done. and a good learning experience for my son doing the job with me.

 

[awesomeissquid]

Cyle leakage test showed bubbles from cyls 6&8, so off with the head - both actually, to get em planed to ensure we don't hafta go back in there ever again. Bit of a mongrel job getting the RH exh flange support bracket and LH rear heat shield attached to back of heads free - obviously fitted before body was lowered onto to chassis. Gasket set is VERY pricey! I'd say the vehicle was traded when PO was told the cost of the fix. O well, It'll be as good as new by the time it's done. and a good learning experience for my son doing the job with me.

View attachment 3111631

Nice work! My dad and I did something similar earlier this year and I will cherish the memory. Not doing the water pump at the same time?

 

[Toyo8696]

UPDATE: Bugger - it's blowing lotsa bubbles into the coolant and out the rad cap. Cyl leakage test coming up tomorrow to pin point the leak, then it'll be off with the new timing belt, cams and leaky head(s).

Stick around for more fun updates.

Doesn’t that look like fun. OEM parts?

 

[Freddy1333]

Not doing the water pump at the same time? New one's already on there.

I can think of better things to do on a weekend but it'd a good learning experience for my son. The retail price of the aftermarket gasket set is $1580. Another son works at Repco (a car parts retailer) - he got it for $1000 off regular price. I'll strip the heads today, clean em and drop em off to get planed. I used to do this sort of thing fer a living way back in the last century, on Cummins diesels.

 

[Freddy1333]

You can see where combustion gas was blowing into the coolant passage.

 

[Freddy1333]

Both heads planed, all back together again and running sweet.