edward frank

My 1991 Toyota 4Runner's has a V6 engine that recently began making a thumping sound when it is in gear -- drive or reverse (its an automatic).

When it's idling in park, its smooth and quiet. When you put it in gear and put a little bit of a load on it, the thumping begins. However, once you get going at a normal driving speed, its runs smooth and quiet.

(A little history: About 4 months ago, the car was tuned and timed, and valves adjusted by a good, certified mechanic... alls good there. The vehicle only has 99,000 miles on it. Maintained well.)

OK...Back to the problem. If I put on the brakes, put it in gear and give it a little gas, it makes the thumping sound without the car moving.

Last week, I took it to a transmission shop, they said it was definitely not the transmission.

Someone has suggested the main bearing or replacing the engine... but given the symptoms, it doesn't seem to make sense.

Any experiences in this regard?

Thank you in advance for your time and insights.

TNRabbit

Could it be a u-joint?

edward frank

Thanks for the suggestion. I'll try checking for the u-join this a.m. I'm not a mechanic... just do everying thing I can that doesn't require all the computers and fancy equipment.

It's my wife's car, ... except when it needs repairs.

I drove it again early this a.m. and noticed the sound was virtually gone at startup and in the first several blocks. But after several blocks the sound became noticeable again. Even in park, I can hear it ever so slightly for a second when the idle speed is just right.

I'm not sure if the fact I can hear it just a split second when idling in park cancels out the u-joint factor or not. (My lack of knowledge is showing.)

Anyway, thanks, I'll check it out. It would be a great blessing if I didn't have to replace the engine. OUCH!

edward frank

Not the u-joint. And several mechanics seem to think it's the main bearing on the No. 1 cylinder.

When they pull the spark plug wire to that cylinder it stops.
We've scoped the top end with a camera.

So looking at replacing the engine ... long block / complete -- or short block. There are three options here. A remanufactured long block complete. A remanufactured short block... both have a 7 year guarantee. OR a complete long block from a Japanese aftermarket importer... has about 35,000 miles on the engine.

I'm not a "mechanic"... but have done most common mechanical work on our cars for years.. Tough stuff I've left to the pros.

Due to cost, I'm thinking about tackling this one myself when I have a full week to do it... with the help of a friend who has worked on cars as a hobby for 30 years.

Advice from any mechanics would be welcome. ... like your nuts. OR a good place to get a repair manual is _____ where? Tips, things to avoicd, etc.

Thanks in advance for your insights.

Silas

wow, 99,000 and cooked already.

read over that 7 year guarantee. A longblock will yeild less room for error, and make the job shorter.

Where the motor is only starting to "thump" now and hasnt spun a rod out the side of the block it still stands a chance to be rebuilt... that'll take a touch more mechanical knowledge though!

TNRabbit

There are a TON off good threads on this subject; here are a few:

https://www.yotatech.com/forums/f116...-ghost-108156/

https://www.yotatech.com/forums/f116...perate-123651/

https://www.yotatech.com/forums/f116...et-job-104934/

https://www.yotatech.com/forums/f116...w-going-88538/

https://www.yotatech.com/forums/f116...thread-120824/

RobD

If you can swing it and are willing to learn a lot in the process, try to find a 3.4 and do the swap. Mechanically it's an easy swap since most of it bolts right up. The electrics are the hardest part, but doesn't take too much to sort out. The biggest hurdle would be your automatic, but it's been done before on here and there would be plenty of help.

I did mine (with 5-speed, mind you) and haven't one single regret about it. It beat rebuilding the 3.0 doorstop.

Up until the swap, the hardest thing I'd done is change a timing chain and head gasket on a Sunflowe...er, Sunfire.

abecedarian

Thumping under load (powerbraking the engine- which rules out u-joints as a problem since they're not moving) sounds to me like a rod bearing... assuming it is a 'thump' and not a double-knock (which would suggest wrist pin / small end rod bearing).
If that's the only problem, pull the oil pan, plastigauge the bearings and mic the crank throw (rod big end) journals and replace the bearings if the crank throw journals aren't worn. If the they are, you're going to be pulling the engine and THAT'S when to decide how much more you want to spend on a rebuild or an engine swap.

edward frank

Wow. Thanks for the various insights!

I'm picking up the trend that getting a 3.4L V6 rather than a 3.0L 3VZE might be a good idea.

How big of an improvement would you say the 3.4L is over the 3.0L in engine quality?

And how big of a jump in difficulty trying to make it fit?

I guess what I'm getting at is, if I'm buying a "remanufactured" long block engine, is it worth the additional money and the additional challenge in difficulty?

And, here's another big one, how do you know which remanufacturer is the best? There's one major remanufacturer here, and the BBB shows him having 9 complaints over 36 months.

OTHER ALTERNATIVE: if I can find a "used" one at a local wrecking yard with low miles, is it worth going that way?.... Difference in cost appears to be about $1400 vs. $2500-$2900.

I realize these are loaded questions with lots of unknowns. But, it's worth asking, it seems.

Thanks again for the insights on 3.4 vs. 3.0. That's going to be the big question.

edward frank

I'm not seeing any responses. Have I lost everyone?

I"ve read a lot of threads referred to in the posts above -- thanks TNRabbit. As a relative 4Runner rookie, I'm pretty overwhelmed with some of the potential snarls ... but it's also kind of an exciting challenge. An opportunity to learn a lot. And I like the 4Runner... which helps a lot too.

Any insights to the questions in the previous posting would be greatly appreciated.

Thanks

Ed

T-1000

It would definitely be cool to put in a 3.4, and I don't want to discourage you, but just be prepared to be up at 3 in the morning (maybe more than once) saying to yourself, "WTF was I thinking?"

Again, that's no reason not to do it. I say go for it. Just be ready for the challenge, and some testing of your patience.