5VZ-FE Running Bad

Looking for some sound mechanical advise. I own a 2004 Tacoma with a 3.4L 5VZ-FE engine. It's running bad. This is my 3rd Toyota pickup. Purchased it new in July of 04. Just shy of 250k mostly highway mileage. Been using Mobil Syn 5W30 since new. After sitting for sometimes up to a week without starting there is no puff of smoke. There is no coolant loss or tell tale foam on the oil fill cap. I noticed about a year ago it started getting a vibration aroud 50-55 mph. When I would back off or speed up it would go away. When I press the O/D button on the auto shifter the RPM's will increase, the speed stays the same but the vibration goes away. At first I thought it was the u-joints but that was not the culprit. I took it to a local shop & they narrowed it down to the engine after a road test & compression test. At the time I decided to hold off on anything as the truck was not getting much use. The truck was well maintained & is in fairly decent condition. I did a compression test both dry & wet. Cylinders 1,2,3 &6 all ranged from 170-175 dry then 175-180 wet. #4 is 60-65 dry & 65-70 wet / #5 is 45-50 dry & 50-55 wet. This is telling me the rings are still in good functioning order. I would like to just replace the heads with a remanufactured set. I've been reading about the 5VZ-FE engine & I'm understanding that the bottom end is a good solid pretty much bulletproof system. My concern is will new heads effect the bottom end. Years ago you would never just replace heads without doing the bottom end but we are talking old muscle car days. I've found a company online that has heads at $400 each complete. I've gotten pricing for rebuilding my heads the local shops and it's allmost the same price. After talking to a few different shops about the heads it scares me to take them to the shops in my area. They just didn't seem to knowledgable about my heads. The company is cylinderheads.com out of Rockwood, PA it looks like they specialize in only cylinder heads. Any questions or advice would be greatly appreciated.

 

If #4 and #5 are bad, aren't they on opposite banks? I really find it highly unlikely that both banks have head gasket/ warped heads issues unless it had some serious overheating issues. Whats the timing belt like, has it been repaired lately? Maybe the belt has stretched and thats throwing off the timing or not allowing the valvetrain to work correctly?



Either way, a used engine sounds alot cheaper if you have compression that is that low in 2 Cyl.

 

replacing the heads wont cause and increase in oil comsumption... I assume that is what you are refering to with your muscle car days comment. The motor oil manufactured today is so far superior to what was avalible back in the 60's and 70's... you would regularly have to re-ring and valve job a cast iron V8 about every 100,000k. The metalurgy is far superior today too. I have seen Audi 5 cyls with over 400k on the odometer and the hone pattern is still visible in the bore.

as for an additional diagnosis, a leak down test can be preformed to see if it is indeed the valves or the rings.

have the valves ever been adjusted?

 

Yeah, kind of sounds like maybe the exhaust valves on #4 & 5 are not closing all the way and maybe the vibration is unrelated to the lowered compression.

 

Fella Tacomers & members it's been almost 2 years since I requested your input on my engine running bad situation. I've been busy completing a rehab on my home.

Anyway, my first step in the investigation process was to pull the heads. After getting them off I found that I had 2 burnt intake valves. I also noticed that the cylinder walls still had very noticeable cross-hatching in them & there was no ridge in the cylinders. It was at this point I decided to do a valve job only. (My truck only gets used about 32 miles a day on average mostly towing my boat & driving on the beach to surf fish.) I had the head work completed at a machine shop that I used to do my work back in my muscle car days. After receiving all of the appropriate (OEM) parts & gaskets sets (I also rebuilt the fuel injectors & used new head bolts) I reassembled the engine. Hit the key & it started just like it does every day.

That was almost 20,000 miles ago and it's still running great.
I just wanted to thank everybody for their input.
I’ve included a few pictures for prosperity.

 

Outstanding!
Today is the first I ever saw of your post.
Thank you.

 

those are exhaust valves... a couple of thoughts, check the clearances and examine the adjustment shim that is associated with the burnt valve. The theory of operation is as follows. The cam lobe contacts the adjustment shim and it pushes AND rotates the shim/bucket/valve assembly. If the assembly does not rotate then the valve will sit in one place and burn. An examination of the shim should tell you if the taper across the face of the cam lobe is still present. You can do the same with a micrometer. I have only seen this on Chrysler products or cams that went broken in properly and usually the cam goes flat in 50 miles.

 

Thanks for coming back and finishing up the thread and I’m surprised you had ANY compression in those 2 cylinders, them are big holes.

 

I don't think the valve is going to rotate, the keepers at the top of the stem hold onto the valve too tight. The bucket will rotate though

Valves usually burn because of an adjustment issue, like being held slightly open all the time. if they aren't allowed to fully seat there won't be enough heat transfer through the face of the valve to the cyl head.. where the coolant passages can carry the heat away

 

That would be "posterity" not prosperity. LOL. But seriously, did the machine shop have any idea what caused the valves to burn? Seems an odd thing to just happen on an otherwise well-running and non modified engine. Were you running hotter/colder plugs or anything like that? Or different coil packs? And this really happened to two different cyinders 'at the same time'? Another thanks for the follow-up. I would not have guessed this was the prob.

 

Maybe prosperity was a pun? He’s more prosperous since he only fixed his heads, no bottom end work, and he did the fix himself?

It does seem strange that 2 valves would burn like that.