Valve Burning - any way to know before disaster strikes?

As anyone who has read my threads knows -

Back a year and a half ago, at 157,000 miles (?) on my used '93 Geo Metro with
a 3 cylinder engine, the engine died.

I did a compression check & found numbers 1 and 3 cylinders did not hold much pressure.

Because many folks on this Forum talked me into it, I pulled the Head and found
valve number one was burned thru on two sides.

http://img301.imageshack.us/img301/9430/cyl1valvests2.jpg

I had the Head rebuilt for $225.

http://i70.photobucket.com/albums/i86/DoctorBill_SCC/Metro%20Head%20Rebuild/Rebuilthead-Bottomxxx.jpg

I was also convinced by these good folk to replace the Rings and Connecting Rod
Bearings.

http://img132.imageshack.us/img132/3990/piston12ze7.jpg

http://img475.imageshack.us/img475/1492/pistonrodbearingplate2qp5.jpg

All that, step by step, was posted here with numerous photographs.

I have now been driving the rebuilt engine in what I call "The Phoenix" since
it arose from the ashes, as it were...

But as I drive merrily around the countryside oblivious to all the gasoline stations,
getting 49 miles per gallon and grinning at the "Hybrid Cars" that cost more than
$20,000, I wonder whether or not I am burning up my "new valves" as I drive
along....

http://img65.imageshack.us/img65/8687/alfredeneumans8bg.jpg

Long story short - is there some way that I can check my valves for burning, now,
short of pulling the Head off again?

DoctorBill

Doctor Bill,

Exhaust valves burn as a direct result of combustion that does not finish in the combustion chamber when both valves are closed. They overheat (melt, break, deform) when the ignited fuel charge continues after the exhaust valve opens, burning the face and causing said deformations.

High combustion temperatures can aggrivate this (lean fuel mixture). Retarded ignition timing (a spark which occurs too late in the combustion cycle) can directly result in burned exhaust valves. An inoperative EGR system can directly result in burned valves (and in these cars is often THE reason why the valves burned) as well as burned pistons/rings/head damage etc.

If you keep your car well maintained you will avoid burning the valves. When you change a timing belt, make sure it is properly installed and the sprockets are properly aligned. When you set your ignition timing, make sure it is at least 5°BTDC. Keep your plugs wires cap and rotor in good repair. Keep the O2 sensor before the cat in good repair. And by all means, be sure that your EGR system is functioning properly. Also, keep your exhaust system in good condition. Exhaust restrictions that have not advanced far enough to contaminate the A/F charge in such a way as to seriously impede performance, will still raise temperatures at the exhaust valves, and may compound other contributing factors.

In other words, with all the systems working properly in a well maintained vehicle, exhaust valves willn't burn.

-MechanicMatt

Matt has hit on most of it, I'd add make sure you use 5W-30 oil and don't run it at high speeds for long periods. No more than 70 mph for a manual and certainly no more than 65 for an auto. High rpms are particularly hard on the valves. Advancing the ignition timing will reduce it and give you better mileage, and stainless steel valves are much tougher than regular steel. Basically though, if you're driving it, you're burning the valves.

1. I hope the EGR System is not all "Carboned Up" now like it was when I replaced the head and rings....

2. I want to check the plugs (has about 15,000 on them now) soon.

3. I'll check the timing when I check the plugs.

4. $250 to have the Head Rebuilt is not bad at all if I get 100,000 miles out of
these valves before they get burned up...

5. I hope the Rings don't go T.U. during that 100,000 miles !

I see so many Geo Metros around now - one this morning was BEAUTIFUL !

There are quite a few guys I meet at the COSTCO gas pumps with Geo Metros
who say hello and we get to talking and they LOVE their Metros!

I often offer to buy their Metro, but they yell, "Hell no! I love this car!"

50 mpg is sooooo nice!

DoctorBill

Doc,
Some time ago (years?) you posted a tidbit about cleaning the EGR passageway with a brush. It involved removing the header every so often and then snaking the tunnel going to the throttle body. I tucked this away as being a great idea and have planned on using it perhaps once a year as a routine. This should alleviate any valve burning problems. If you could re-post it, it might save some folks a lot of headaches, Thanks for your insight.

DL

It's easy to test to see if the EGR system is clogged. Start the engine and let it idle. Apply vacuum to the EGR valve and see if the idle drops. If it doesn't, it's clogged.

Q

DavidLang - Have a look at the recent "Help high idle after I rebuilt engine??" thread.

Hugemoth - How would I go about applying vacuum to the EGR valve? Where?

Haven't worked on The Phoenix for quite a while now.

I need to pull out my Speedometer Cable - never did get it back in correctly so
now the Speedometer jumps and falls.

I hope the end of it in the Transmission isn't screwed up or worn to a nub.

That was hard to get connected up correctly and the clip didn't want to set in the slot correctly.
I guess I never did it right.

DoctorBill

Easiest way if you don't have a vacuum pump ($20 at Harbor Freight) would be to pull the vacuum hose off your cruise control and plug it on to the EGR valve. Plug it on to the small connector. You'll be able to see the diaphragm move and at the point the engine idle should slow significantly.

Q

a vacuum leak will cook valves quicker than anything else

Yeah vacuum leaks can't be good for valves - good insight. Also, you sould be able to kill the engine entirely in short order by manually opening the EGR valve at idle - if the engine doesn't stumble out and die immediately (10 seconds MAX) there is definitely a restriction in the system. I just use two fingers on the diaphram, on opposing sides to open the valve. Becareful though, it does get hot.

-MechanicMatt

Why would a vacuum leak cause burned valves? Shouldn't the computer add enough fuel to keep the mixture correct? The result should be just a fast idle.

Q

a vacuum leak will cook valves quicker than anything else

Why would a vacuum leak cause burned valves? Shouldn't the computer add enough fuel to keep the mixture correct? The result should be just a fast idle.

Q

Okay clarification is needed here. You are correct when refering to a "speed density" fuel system, or one which does NOT use a MAF sensor.

However, in systems which incorporate a MAF sensor, a vacuum leak introduces "unmetered" air into the engine which causes a lean condition, which raises combustion temperatures, which is not good for the exhaust valves. I think thats where mx was coming from.

As far as any metro I've come across (including those late 4-cyl with waste spark ignition and MPFI) we are all driving speed density systems. So a vacuum leak in our cars wont nessecarily result in a lean condition.

Speed density uses (primarily) the MAP sensor, engine RPM and O2 readings (and secondarily, ECT, IAT etc..) to calculate engine load. Hence the name speed (engine) density (manifold absolute pressure). If the computer sees a massive vacuum leak (high pressure - open throttle) and low engine speed along with a lot of excess oxygen in the exhaust stream, it seems natural that it will add fuel (artificially climbing a hill) which as you stated would cause a mere high idle.

-MechanicMatt

Let's see if I understand this then...with a Geo metro (mine is a '93 3 cyl) the
ECM will sense a vacuum leak and compensate by adding more fuel to the air
mixture.

Won't that start to Carbon Up the Engine?

Won't your miles/gallon fall drastically and you'll lose POWER....?

Did I get that right?

In any case a Vacuum leak is a baaaad thing! YES?

If I remember correctly from rebuilding my engine (Head and Rings), when I
reassembled all the hoses, there are essentially two (2) vacuum lines.

One comes from the front of the TB and one comes from the back end of the TB.

If one has a vacuum leak somewhere - would a Vacuum Gauge on the dashboard
be a good thing to monitor for a leak?

If so, would it be bad to tie the gauge to both vacuum hoses via a "T" connector?

Or should one have separate gauges for the front and back TB hose barbs?

What I am thinking is that by having a Vacuum Gauge as an after market
dashboard gauge, one could see when a leak develops instead of finding
out later by having one's valves burn up.

If the Vacuum Gauge reads low of a sudden - immediately check for leaks with
a Butane hose device and FIX IT !

Does this make any sense?!

A Butane Torch Set-Up for detecting Vacuum Leaks....makes engine rev up when the
Butane gets near the leak point !
http://img529.imageshack.us/img529/3869/finleakdetector3py6.jpg

DoctorBill

PS - What Vacuum values should a well running engine be exhibiting on a gauge?

Won't that start to Carbon Up the Engine?

A vacuum leak will and will not cause excess carbon build-up (see below). Infrequent oil changes, ignition components in poor repair and spark plugs that are not "hot" enough are the things to concern yourself with in terms of carbon build up. Making lots of short trips is also a good way to pack on the carbon.


Won't your miles/gallon fall drastically and you'll lose POWER....?

A little vacuum leak can actually serve to pep up our cars a bit. I know from experience. Not that it is adviseable to have one - but you are essentially adding throttle. You will see a fall in fuel economy. Please take note that in carbureted engines, and MAF fuel systems a vacuum leak is very detrimental to the vehicle performance.


In any case a Vacuum leak is a baaaad thing! YES?

Suppose you have a vacuum leak at the throttle body gasket, or the brake booster hose for example. All three cylinders are going to lean out, and the computer will will add fuel via a wider injector pulse width which will be equally distributed among the three cylinders, effectively canceling out the vacuum leak and making it as though the throttle body were opened up just a tiny bit - high idle etc. This condition will not cause excess carbon build up.

Now suppose you have a vacuum leak at the intake manifold gasket at the #2 cylinder. The o2 sensors will pick up the high oxygen content, broaden out the pulse width and adding more fuel until it finds the oxygen content acceptable. But remember, the ECM cannot give more fuel to one cylinder than the others, so the added fuel is divded by the 3 cylinders. 2 cylinders will run richer than the leaky one, and sense the added fuel is in proportion to the leak, it will only compensate for the lean cylinder by 1/3. So that #2 cylinder will still be lean. So it really depends WHERE the vacuum leak is occuring. This condition if left uncheck has the potential to cause excess carbon build up in the cylinders that are not experiencing an isolated vacuum leak.



If one has a vacuum leak somewhere - would a Vacuum Gauge on the dashboard
be a good thing to monitor for a leak?

If so, would it be bad to tie the gauge to both vacuum hoses via a "T" connector?

Or should one have separate gauges for the front and back TB hose barbs?

Many guys actually do this - and it's cool to watch the gauge react to throttle position. This is a good way to monitor for a leak. You only need one direct, unimpeded source of "manifold" vacuum - its the same no matter where you get it from.



PS - What Vacuum values should a well running engine be exhibiting on a gauge?
18-22in.hg. at idle is the widely accepted figure. And 0 at wide open throttle =)


-MechanicMatt


PS sorry for the long responses - but you're diggin it out of me ;) Too much time on my hands? Noooo...

"Many guys actually do this - and it's cool to watch the gauge react to throttle position.
This is a good way to monitor for a leak.
You only need one direct, unimpeded source of "manifold" vacuum - its the same
no matter where you get it from.

Are you positive about that?
I thought I saw a difference when I was farting around obtaining a vacuum
source for my Cruise Control....front versus back barbs of the TB.
Front barbs gave higher vacuum and at different positions of the throttle than the
back barb gave.
FRONT Barbs - Zero full throttle - 26 PSI during deceleration - connected to EGR Valve
BACK Barb - 8 PSI during acceleration - 18 during deceleration - connected to MAP
(If I remember correctly...)

18-22in. hg. at idle is the widely accepted figure. And 0 at wide open throttle"

That's what I wanted to know!

So a Dashboard Vacuum Gauge is useful along with monitoring the miles per gallon to
keep an eye out for vacuum leaks - which burn up the valves.

ALSO - my "green arrow" - the CHANGE GEARS light is caused by vacuum - is it not (or is it run by the ECM?).

My "green arrow" lights up a lot when I stay in 4th going up hills. That is showing
that I am pulling a strong vacuum - isn't it?

"sorry for the long responses - but you're diggin it out of me" - That's my job!
It is why I annoy people so often.....

DoctorBill

The upshift light is controlled by the PCM and includes a few different calculations. It's along the same lines as a vacuum gauge, but it figures throttle opening, rpm, vehicle speed, and load percentage, then goes to a lookup table to determine if you should be in a higher gear. If you can keep it from ever coming on, you'll get better mileage. Hint: lots of right pedal with low rpm, when in doubt, upshift.

"Many guys actually do this - and it's cool to watch the gauge react to throttle position.
This is a good way to monitor for a leak.
You only need one direct, unimpeded source of "manifold" vacuum - its the same
no matter where you get it from.

Are you positive about that?
I thought I saw a difference...

I am ABSOLUTELY positive about that. The key words here Doc are DIRECT and UNIMPEDED. I do not know which barbs have what opstacles but a very good place to get an accurate manifold vacuum reading (and where I always get mine) is from the brake booster hose. Be sure to avoid any check valves inline to the booster that are sometimes used for backfire protection.


My "green arrow" lights up a lot when I stay in 4th going up hills. That is showing
that I am pulling a strong vacuum - isn't it?

Wood gave a very good explaination of the shift light.

Going up hills you actually have very little vacuum. Way back in the day, when accessories such as wind shield wiper motors were run with vacuum - they'd crap out going up hills, and break speed records descending the other side. Vacuum is created by the closed throttle resisting the intake stroke's breath for air - so it is highest when decelerating with the throttle closed, and loweset with the throttle open. BTW when looking for a source for accurate vacuum - if your reading drops to 0 when the throttle is wide open, you've probably got a good source.


-MechanicMatt

The Phoenix is a '93 three cylinder one liter 5 speed manual transmission.

I don't believe that I have any vacuum assisted brake boost...

If I do, where do I look for this?

Been all thru that engine compartment doing the rebuild, cruise control, wiring, etc.
and I don't remember any hoses going to anything on the brakes.

If I am wrong, please educate me.

I have a disassembled TB and Intake Manifold in front of me now and I do see
that the front two barbs on the TB connect with the main large chamber in the Intake manifold
as does the rear barb that goes to the MAP Sensor.

I hate to go back and reconnect hoses to front then the back and drive with each
to see if they read the same, but I was sure I got different vacuum characteristics
from each.

That is why I connected BOTH hoses to my Cruise Control Vacuum Canister via two barbs,
each with a one way vacuum valve to keep the different vacuum levels separated.
Didn't want to confuse the MAP Sensor data to the ECM.

The front gave 26 PSI at deceleration while the back barb gave less and at different times.... (????)

Otherwise one could connect all three barbs together with vacuum hoses via
"T" connectors. They are hosed separately on my system - front versus back.

Front goes to the EGR system and Idle controller while the back goes to the MAP and that strange air bleeder valve.
The back side has an air bleed controlled by the engine temp also - wouldn't
that affect the vacuum at the back?

I'm not trying to be provocative - just need clarification.

This is a rather complex multi-valve interacting "system" controlled by temp, the EGR, the throttle, engine vacuum, etc....
and I am trying to visualize how it interacts at different times.

Is there a simple diagram such as a view of the TB - Intake Manifold cutaway
side view available somewhere? Like slicing the two down thru the middle lengthwise showing it from the side...?

DoctorBill

The Phoenix is a '93 three cylinder one liter 5 speed manual transmission.

I don't believe that I have any vacuum assisted brake boost...

If I do, where do I look for this?

You do have vacuum assisted power brakes. The black drum that the master cylinder is bolted to is the "brake booster." It will have a relatively large vacuum hose attached to it. If you follow this hose, through some hard pipe (across the firewall) and to another hose, it will lead you to the intake manifold. T-off your gauge from this hose, as close to the manifold as possible and this will give you the most accurate vacuum reading you can get.



Otherwise one could connect all three barbs together with vacuum hoses via
"T" connectors. They are hosed separately on my system - front versus back.

Front goes to the EGR system and Idle controller while the back goes to the MAP and that strange air bleeder valve.
The back side has an air bleed controlled by the engine temp also - wouldn't
that affect the vacuum at the back?

I'm not trying to be provocative - just need clarification.


Snap a picture of your air bleeder valve if you can - I can't visualise what you are talking about off the top of my head. I'll study some throttle bodies and intake manifolds at work tomorrow and take some vacuum readings from various points to see if I get the same results and see if I can't offer some explaination for your difference in vacuum readings. No provocation taken =)


Is there a simple diagram such as a view of the TB - Intake Manifold cutaway
side view available somewhere? Like slicing the two down thru the middle lengthwise showing it from the side...?


Not that I am aware of. Although, I haven't looked.

-MechanicMatt

Trust me, you don't want a car with disk brakes without power assist. You can get away with it on drums, but it takes a ton of pressure to make disks work. Incidently, that hose going to the vacuum assist servo is prone to carbon fouling just like the EGR system. That's what did in my first Metro. The brakes work fine until you get in a stop and go situation where you hit the brakes multiple times in quick succession. Third or fourth time, you've got a brick beneath the pedal, the car just doesn't stop.

Doctorbill,

Maybe the 3 cyl throttle body is different but the 4 cyl throttle body has a 1/4" vacuum port near the idle speed screw. It was just capped off with a rubber cap. That's the one I used to power the cruise control.

Q

I will take some photos of my brake system and the hoses as they are in The Phoenix now.

BUT - am up to my neck in 56 students right now teaching two Chemistry courses with three labs sections,
so the pics etc will be a couple of days from now....

Thanks for the help folks!

I'll be baaaaack.....and get this sorted out.

DoctorBill

will a exhaust leak at the head burn exhaust valves?

Hi my name is sondra. I currently was given a 94 geo metro 3 cyclnder. It was given to me because the lady that owened it blew it up over a divorce. I put a new engine it from a junk yard that sworn that it ran fine. It was put in three weeks ago and a week and a half ago i had a compression test done by muffler man and they said first cyclnder has 40 pds compression in and said i had a bad ring. But I don't have any blue smoke coming out of the tail pip and it was burning any oil. till today when it started to knock and i stopped at auto zone and found that there was no oil in it at all. what causes that can anyone help me. I was told these engines can't be rebuilt. CAn you or not?

I'm not used to these engines. All I'm asking is for a little help please.

First - the Metro's 3 cylinder engine is EASY to rebuild !

Whoever told that they are not rebuildable is a moron!

Second - if you had that low a cylinder pressure, the valve is burned.
Head job $250 and you can take it off and put it back on yourself.

Third - if you ran it w/o oil - ugh! Bad leak? Got to attend to THAT
immediately! Where is it going. Check it every day until you are
confident it doesn't leak out anymore!!!!!!

Fourth - being a woman...be very careful of what mechanics tell you!
Find one you can trust (hard to do - ask around) - a lot of buttholes out there
who try to con women. I know - they do it to my wife all the time!

Not nice to say, but unfortunately - it is true!


Do you know anything about auto's? Mechanical stuff? Sorry - not trying to be sexist....

If you have the patience to read thru all the stuff I wrote and see all the
photo's - have a look at how I rebuilt my '93 3 cyl Geo Metro...

I did a lot of stuff you may not have to do....but look at what I put in here.

Anyone out there reading this - give the lady some help!

First Page of ..................."That's the end of my '93 Metro....."
http://www.automotiveforums.com/vbulletin/showthread.php?t=611713

First Page of..................."NOT the end of my '93 metro...Life after death! RINGS"
http://www.automotiveforums.com/vbulletin/t613410.html

First Page of ..............."The Flight of the PHOENIX !"
http://www.automotiveforums.com/vbulletin/showthread.php?t=645309

First Page of ..............”A way to Clean the Carbon out of the IM Passageways !”
http://www.automotiveforums.com/vbulletin/t622536.html

You may very well have totally different problems than I had with my '93 Metro
3 cylinder - but then again maybe the same!

This little car is a breeze to fix.

And mine gets 49 mpg in the summer!

If I did it, a monkey with five fingers could do it!

DoctorBill

Twinkie - start a new thread with the issues your car has, include year, mileage, engine, trans and anything else pertaining to its current condition. I think you'll be pleasantly surprised with the helpful responses you'll get.