moonbase1

I've got a 1991 runner with the 3.0 v6, CA emissions version.

Ok, so..... My runner has been running badly for a while: non-existant power at low rpm (i have to rev it to 3000 to get her to do anything!).... Less power throughout rmp range.... Bad gas milage (around 12 mpg) and a strange flappy sounding exaust that used to ping away nicely :-)

At first I thought it was a blown Head Gasket, and I didn't have the money to fix it...... so i just kept driving. After several months... There is no colant in the oil and no exuast in the radiator fluid so I don't think it's a HG issue.

I had a mech do a compression test.... And most cylinders were at 160 or so.... But 2 were around 40! My question is.... Are there any reasons (other than bad pistons, rings) that would cause such low compression in those 2 cylinders? I'm hoping so.... Cause i can't afford a re-build and would hate to scrap my yota!! :-/

Thanks all for any advice you can give.

MudHippy

Uh-oh!

You really should read my thread here on the subject.
https://www.yotatech.com/forums/f116...-w-pic-190796/

The compression on the bad cylinder was ~110 in my case. For comparison. And I didn't notice any loss of power like you...soo..umm.

My experience with such says to me it probably ain't your valves(wasn't mine!). Which is all it could be besides what's been mentioned.

moonbase1

hmmmmm i sure hope thats not whats wrong with mine!!! It does go through oil..... and my oil pressure is quite low at the low rpm's..... are there any other tests i can do without pulling the heads to look at the pistons ???? I'm still hoping the symptoms are a result of me installing the timing belt incorrectly.... but i'm starting to lose hope :-/

MudHippy

Add a tablespoon of motor oil to the suspect cylinder. Recheck compression. If pressure isn't any higher, then it could be a messed up valve(s) or a cracked/damaged piston. If it is higher then it's probably the rings/scored cylinder.

Goes through how much oil?

I wouldn't think low compression could possibly lower oil pressure. But maybe I'm confused...Someone would have to explain to me how.

Did it ever run right after the timing belt install? Because I wouldn't rule that out if it didn't.

moonbase1

mud.... it seemed to run GREAT after the timing belt install.... but there was some confusings aspects of the job.... such as the TDC on the cams was one belt notch (for lack of a better word) away from where it was before i took the belt off. I know thats not a very good explaination!!! There was lots of slack on the non tensioner side.... and when i took the slack out on the install there was one less belt tooth between the cams.

MudHippy

Hmmm...the cam timing marks are known to be tricky to get line up right. Some people end up with what looks like one or both sides being off by a 1/2 tooth or better. Even mine looks a tad off(not a full tooth) like that on both sides with it correctly installed. The slack in the belt is all wrong though. I've had a loose belt skip a tooth and end up exactly like your saying. I didn't leave like that though. I got it realigned before I went any further. So maybe it could run like that?

BUT...

If it was running well after that was done. You're running out of possiblilties quickly...IMO.

Sorry to have to tell you that.

It's not the end of the world, I managed to fix mine for pretty cheap, so could just about anybody with a good pair of hands and 1/2 a good back.

Good luck with 'er what ever ends up being the case.

Give us another shout if you think you need any more advise.

awsumfn

I would check the valve clearence. A valve adjustment shouild be done by a shop that works on alot of Toyota. If the valve clearence is to tight it will hold the valve slightly open causing low compression. To ajust the valves on your V-6 they need to install the correct size valve shim to get the proper clearence. At my old shop we recemmended our customer to have the valve clearance check every 60,000 miles.

MudHippy

Checking/adjusting the valve lash on this particular motor is quite a hassle. But the skill required is minimal. I'm pretty sure if this guy can install the timing belt on it, he can certainly handle removing the upper intake to get to the valve covers. Feeler gauges are available at any auto parts store, along with the tool you need to get the shims in/out.

It's possible they could need adjusting, though it's not really possible to adjust them incorrectly(unless your purposely trying to). And the ammount of wear required to cause them to become that excessively tight, even over several 100k miles, seems a bit improbable to me. Lifters can also become stuck, or sticky. Causing the valves to close out of time(or not close at all). Which I find more likely if the valves really are the issue here.

All the valves and seats on mine had considerable wear after 220,000. The exhaust valves were shot to the point of not being regrindable, but...they still had plenty of clearence. Severely worn seats and/or valves don't seal to well.

However...

I'll still place my bet on cylinder/piston/ring damage(wear).