newTOyotas

Looking for a "how to" on doing a vacuum test on a 3vze (1995 ext cab 4x4 5 spd, 145,000 miles). I have tried multiple searches here and even using google but can't find anything that gives someone who doesn't know what to do and what to look for/expect. I have no idea what readings I should be getting and what certain readings can indicate. Right now, my truck has a miss at all rpms and I can't seem to figure it out. I have verified that the TPS is set correctly, the VAF is right within specs going by the service manual, the EGR is functioning as it should, the timing is correct, I already changed the plugs/wires/cap/rotor with no change, and whatever is causing this miss does not throw a CEL.
I am thinking it is either a valve issue or a fuel delivery issue (clogged injector?). All plugs seem to be showing normal signs of proper cumbustion.

I purchased a vacuum gauge, but to be honest I have never tried to diagnose anything using this method and was hoping the FSM would show a step-by-step method but I can't seem to find anything that refers to doing a vacuum test.
I plan on doing a compression test but I am rigging my own tool up to do this since I didn't want to spend $50 on one right now.
I have everything I need to make my own, just need to get it done.

I have searched and read the multiple threads associated with a 3vze and an engine miss, but 99% of them never reach a resolution so they don't really help much.
The head gaskets HAVE been changed at some point by a previous owner(doesn't show any signs of coolant consumption/leaks/etc) and the truck DID run as good as a 3vze should up until about 10 days ago when a miss just appeared out of nowhere and is present at all engine temps/rpms.

Hoping a vacuum test can point me in the right direction if only I had enough information to accurately diagnose a problem from the results I get and actually knew what normal readings would be.

Any and all help is very much appreciated. TIA

scope103

You know, I've never heard of anyone doing a "vacuum test" since the days of carburetors. (And even then, such a test wasn't worth much.) There are so many different levels (and uses) of vacuum on a modern engine I'm not sure what I would look for.

If you have a bad injector it should show up on a plug (but you've checked that). Why don't you try pulling the plug wire one at a time to see if you can narrow it down to a cylinder?

I, too, am a big fan of build-it-yourself tools, but for $20 http://www.harborfreight.com/quick-c...ter-95187.html it's hard to justify.

newTOyotas

That looks like a good deal. I will grab one the next time I'm at HF but the way the truck is running right now, I don't want to risk getting stuck 25 miles from home and in the middle of city traffic. Thanks for the link. It appears that it already has the correct spark plug threaded fittings(?)
Sure beats modding 1/2 of a spark plug

newTOyotas

I pulled each wire individually and all cyl had an effect on running condition EXCEPT for cyl 1 and cyl 3. Even cyl 5 had an effect on idle, but not quite as definite as cyls 2, 4, & 6.
I put 2 new plugs in cyl 1 & cyl 3 and replaced each plug wire with 2 almost brand new ones which ohmed out good and no change. Engine still has a miss which is mostly noticable under load.

I'm not sure what to make of that(?)

I'm going to check compression next and hopefully it checks out good even though I'm not sure what else to try.
Sucks that I just got a new inspection sticker on it and wanted to run it for another winter. I know I'm not going to toss a bunch of money in it. I'll just scrap the POS.

These trucks leave alot to be desired anyways.

oldblue

when i have a vehicle that is running rough or missing, and the cause isn't fuel or ignition related, a vacuum test is a quick and easy test to check the mechanical condition of the engine. i usually hook into the vacuum line off the brake booster because its usually easy to access, and it connects directly to the intake manifold. if you're suspecting fualty valves, the vacuum gauge will bounce erradically. typical vacuum should be around 18-20 in. if a valve or valvetrain component is faulty, you'll still be in the 18-20 range, but the needle will be dancing. from there a more comprehensive compression and leakdown test can be performed. for me, a vacuum test is a quick way to tell a customer they better pull out their wallet.

newTOyotas

At idle, the engine is making ~around~ 16 in Hg vacuum. I see the needle bouncing, but it is only bouncing between 15 Hg and 17 Hg. I read the general instructions that came with the vacuum gauge, and it said "A pointer which sweeps or wanders erratically through several inches indicates a malfuntion........"(etc). It also says that on BOTH 6 cyl and 4 cyl engines "A certain amount of pulsing is normal and does not necessarily indicate a leaky condition."
I seem to have a 'slight' flucuation of 2 inches while at idle, so I am confused as to whether or not this is normal(?) or indicates an issue(?). Of course *IF I had an issue, it would more than likely be on the passenger side of the engine since that is the side that 2 out of the 3 cylinders showed no change to idle quality when the plug wires were removed.

I have never used a vacuum gauge before, but to be honest it DOES seem like a vaulable general engine condition gauge to me. I just don't fully know what is "normal" for a 3VZE engine to show.
-should the needle be 100% steady/no 'bounce' at all?
-what should the needle read at idle?

I am open to anyone who has any input. It sure would be nice to have a thread on here with an actual conclusion to the problem IMO.

j2the-e

It should have steady vacuum. But any misfire will cause the needle to bounce. You NEED to do a compression test. No way around it. ANY drivability issues on a 3vz, first thing I do is a compression test.

oldblue

the needle should be pretty steady.if the needle looks "blurry" because it's bouncing so rapidly between its low mark and high mark, you probably have an issue. a compression test would be a good idea, and you'll likely find a lower compression reading on those suspect cylinders. from there, a leakdown test would show/tell you where you're losing compression. but you're also talking a couple hundread dollars in tools as well for this. tools can be a good investment though if you plan on tinkering on other cars in the future.

newTOyotas

I am going to do a compression test today. I suspect cyl #3 as the culprit. I will also research a leakdown test to determine whether or not I can fab something up to perform this without spending hundreds of dollars. I realize I may be out of my mind for thinking this may be possible, but I guess I will find out after a little research.

Thank you guys for your feedback. It is very much appreciated.

newTOyotas

Well, compression test showed pressures to be good on all cylinders except #1 and #3 which both show about 30lbs Put a little oil in the cyl and didn't change the readings so I'm assuming it is a valve issue or head gasket(?). AFAIK the head gaskets have already been changed once.

Looks like I will have to remove upper intake and pull the passenger side valve cover and hopefully see something that is an ~easy~ fix although I'm pretty sure that won't be the case. If it needs a new head or head gasket, I will just run it until it dies completely and scrap it.

If anyone reading this has any suggestions on what to try or what ~could~ cause this to happen please share. TIA

oldblue

unless you have a rotten yankee rust bucket, i wouldn't scrap it. thats just a waste of a good truck

newTOyotas

I live in NW Pa just south of Erie(it is a rotten Yankee rust bucket

newTOyotas

I will check this thread after work to see if anyone has any suggestions. Not quite sure how the valvetrain geometry works on an overhead cam engine (I've never had to mess with one before) but I'm not sure if wear could cause low compression anyhow (as far as valve adjustment that is, I understand how ring/cylinder wear can effect compression).

newTOyotas

Hmmmmm. I hope that now it's known that I am a "Yankee" people will still contribute to my thread. I wasn't alive 150 years ago so I assure you that I didn't fight for either side in the civil war

Anyways, I couldn't find anything in the FSM about low compression so I will just have to use general knowledge and a bunch of Google searches to figure this out. Seems to me that if the intake valve isn't opening when the piston is drawing down or if it is open too late in the up stroke that that could cause a low compression reading.
Just like 90% of the 'common' parts I seek to pick up at the local parts stores, they don't have a plenum gasket in stock and will have to order one. That is another thing I don't really care for about this truck: everything HAS to be ordered and is never in stock

oldblue

this is where the leak down test comes in, it will help you find where air is leaking causing low compression.

j2the-e

Yes the valves can wear and cause low compression. As the face and seat wear, the valve clearance shrinks to the point that the valve can no longer close all the way.

newTOyotas

Would improper valve adjustment(loose adjustment due to wear on shims/etc) cause an issue like this(?) since I have never adjusted the valves in the ~24,000~ miles I've put on this truck since ownership. I am only familiar with simple gen. 1 small block chevy engines (which are still BY FAR my favorite engine of all time for many reasons). I'm assuming the valve is pushed open by the cam lobe on the 3vze and closes automatically on the base of the cam lobe(?) due to a valve spring(?). Like I said, this entire engine design with cam over the head design is completely new to me.
Am I totally wrong in thinking that ~possibly~ the cam slipped a few teeth on the timing belt which has the valves opening/closing at entirely the wrong time not allowing air to be drawn in/compressed at the right time while the piston is moving up/down? Or would that be quite obvious because the piston would be slamming into an open valve(?)

I'll have to do some more research to figure out how exactly the valve geometry works on this particular engine since I admit this is all totally over my head/unfamiliar to me.

Thanks guys for the replies. It sucks that this is my daily and I can't tear it too far apart in the driveway after work for fear of not being able to get it back together to get to work in the mornings.
Hopefully it still keeps chugging along until this coming weekend and I will try to get under the passenger side valve cover and also pull the belt cover off to confirm the timing marks all line up on the timing belt/etc.

newTOyotas

Well, after a little research I guess adjusting the valves on this engine is par for everything else I've learned since owning it.
The quicker I seperate myself from a 1995 Toyota pickup with a 3.0 3VZE, the better off I will be.
Really wanted to get one last winter out of it. It ~only~ has 145,000 miles although the body is rough.

How do people get 300,000 out of these engines anyways? Do they change the head gaskets every other weekend and adjust the valves once a month?
145,000 isn't that impressive to me considering it's already ate at least one set of head gaskets and apparently now the valves are so far out of whack that 2 cylinders are basically dead

Just curious if the toyotas newer than this generation are any better? Or all they all misleading to their true reliability?

oldblue

adjusting the valves isn't gonna help, not if its showing only 30spi. if it were out of time, all of the cylinders on the bank(s) out of time would be low on compression. no doubt this sucks, but don't knock yotas, or even the 3.0 for that matter. this can happen to any engine by any make of vehicle.

RSR

Look into a 3.4 swap. toyonlyswaps.com can execute for $3500. Depending on the shape of your rigs body, drivetrain, etc, it might make $ sense to go that route...

3.4 parts are a lot more common. The 3vze (V6) was largely made as a marketing ploy to/for the American market. For the weight of 4runners and 4x4 trucks, I think it's the way to go, but since it's arguably harder to work on (in part, Toyota crammed a V6 into an engine bay created for 4 cylinder engines) and has a smaller market presence, there's definitely less aftermarket support/familiarity... 3.4s are much more common and a much better engineered engine -- just look at the air intake components alone...