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By Benford's Law, October 23, 2006

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Did the mechanic shoot in some oil in the cylinder that was "dead" to see if it built up pressure or not? Didn't happen to pull the CEL by chance did you?

Hard to say at this point, could be anything from a holed piston, to blown headgasket, to dropped valve, cracked piston ring, etc. Almost have to open it up to assess the situation, not sure if a borescope or fibrescope will tell you that much in the meantime.

Double check the oil and coolant levels, see if any one of them looks "off" in color or odor. Look for the telltale signs of coolant in oil (looks like mayonnaise) - for oil in coolant, usually that forms a "slick" on the surface of the coolant reservoir, but that may not have made it to the top yet.

Interestingly is the pattern. Are those numbers form cylinder #1 - #4 or the other way around? If they were taken in order, since they are decreasing from one piston to the next piston (assuming he did a "dry" and "wet" compression test) - looks like it it could have been a blown headgasket or more likely the fuel pump died and leaned out, burning one or more of the valves, holed the piston top.

Benford's Law

Hi Fishexpo:

Thanks for lending me your expertise on this matter. The code was PO304 (cylinder #4 misfiring). Also, yes, those cylinder PSI's are in the proper order (1) 185, (2) 175, (3) 135, (4) 0.

I'm not sure if the mechanic shot any oil in cylinder #4 itself, though. I'm fairly certain coolant is not leaking into oil because I have to keep checking the dipstick/adding oil often and it looked normal the last time I checked. I will have to double-check and see if there is a slick on the coolant reservoir (radiator grille?), but I have my doubts it's an issue.

Your hypothesis on it (less likely) being a blown headgasket or (more likely) the fuel pump leaning and burning a valve and putting a hole in the piston top sound very plausible. The latter scenario is particularly intriguing because in the last several hundred miles before this happened I could detect a very faint "burning" smell through the vents on occasion. However, since it was not steady or strong I couldn't assume it was the car (could have been someone outside burning leaves in the fall, for all I knew). The only other possible warning was a very slight engine squealing noise at highway speeds, but I attributed this to simply the weather getting colder at the time.

However, I must add that if the fuel pump itself died, the car simply wouldn't run, would it? It still runs, just "roughly" due to cyl. #4.

Hope this clarifies things a bit. Your insights have been appreciated.

~Benford's Law

Correct, if the fuel pump died, the car would not run. The scenario that I'm worried about is the fuel pump limping along, just barely keeping up with the demand for fuel. Especially if the car has some mileage on it, as I'm assuming that the O2 sensor and ECT sensor are the original ones? This could lean out the air/fuel mix. The 1ZZ-FE already runs pretty lean at cruise, little bit leaner and you could burn up a valve pretty quickly. For shorter driving distances, this fuel issue might not even present itself. Another possibility is the injector for that cylinder is frozen or failed, that would also lead to poor air/fuel mix.

Correct, if the fuel pump died, the car would not run. The scenario that I'm worried about is the fuel pump limping along, just barely keeping up with the demand for fuel. Especially if the car has some mileage on it, as I'm assuming that the O2 sensor and ECT sensor are the original ones? This could lean out the air/fuel mix. The 1ZZ-FE already runs pretty lean at cruise, little bit leaner and you could burn up a valve pretty quickly. For shorter driving distances, this fuel issue might not even present itself. Another possibility is the injector for that cylinder is frozen or failed, that would also lead to poor air/fuel mix.

fish, when should the O2 and the ECT sensors be replaced ??

O2 sensor - replace when you notice a sharp decline in fuel economy, if the car has driveability issues related to a possible AFR issue, if you get a CEL indicating a faulty heater element in the O2 sensor.

ECT sensor - pretty much the same as the O2 sensor and if you see your temperature gauge read differently than normal.

There is no "set" lifetimes in years or mileage on these sensors - like they say, YMMV (Your Mileage May Vary). Rough estimates - O2 sensors generally hold up to last 60K miles, ECT should last the life of the engine, assuming no physical or electrical damage to the sensor body. If you run into a situation where these sensors are suspected of being faulty, I would first exhaust the easier issues for before I start swapping parts. Also note that these sensors can turn "lazy", ie. where they still barely operational, have not quite hit the failure threshold in the ECM programming - can cause all sorts of headaches when trying to diagnose engine/drivability issues.

Benford's Law

Correct, if the fuel pump died, the car would not run. The scenario that I'm worried about is the fuel pump limping along, just barely keeping up with the demand for fuel. Especially if the car has some mileage on it, as I'm assuming that the O2 sensor and ECT sensor are the original ones? This could lean out the air/fuel mix. The 1ZZ-FE already runs pretty lean at cruise, little bit leaner and you could burn up a valve pretty quickly. For shorter driving distances, this fuel issue might not even present itself. Another possibility is the injector for that cylinder is frozen or failed, that would also lead to poor air/fuel mix.

Fishexpo:

I wish I could answer your question properly as to whether the O2 and ECT sensors are originals. I cannot know for sure until I talk to my dad in a couple days, but even then I seriously doubt he will remember since we've had the car for 11 years. I wanted to point out that the temperature gauge had been remarkably steady to the end, so I cannot say for sure if the O2 and/or ECT may have leaned the air/fuel mix enough to burn a valve (but it seems very possible right now).

I have to put this issue on ice for a few days (I have other transportation available), but I will look into this further late in the week. It is beyond my capabilities to open up the engine proper, but I would like to ask you this: If you couldn't tear down the engine itself would you simply ask the mechanic to shoot some oil in cylinder #4 (to see if pressure returns) and explain the possibilities you mentioned above? Would there be anything else you would ask him to check knowing what you know now?

I'm still in the process of deciding whether to continue my Corolla project and your insights have been invaluable given that you cannot see the car itself. I'm trying to exhaust any lower-cost options before doing something more drastic (ie. simply give up and buy another car). Thanks again!

~Benford's Law

Tough to know for sure without opening it up - but there are some quick tests (old school) that can be easily done.

It is standard operating procedure to shoot some oil into a "dead" cylinder to see if it improves or not - as it will point at possible ring or valve damage. That oil will temporarily improve the "sealing" characteristics of the piston rings. If compression jumps up - you have damaged rings or badly scuffed cylinder walls. If compression doesn't change - you have a problem with the valves or possible blown headgasket. Not a headgasket in your case, as it would immediately spike the temperature (assuming the ECT sensor is working).

Quick test for a blown headgasket - is to pressurize each cylinder (both intake and exhaust valves should be closed, turn crank to make sure that cylinder is lined up with the compression or power stroke) while having the radiator cap pulled off. If coolant bubbles out of the radiator neck - that cylinder is involved with a blown headgasket.

Assuming that nothing else seems out of the ordinary - plenty of oil in the crankcase, oil doesn't look discolored. Coolant levels have not dropped. No heavy smoke on startup. Etc.

fish, the O2 sensor, where abouts is it located ??

Just a socket wrench to get it out ??

thanks again

fish, the O2 sensor, where abouts is it located ??

 

Just a socket wrench to get it out ??

thanks again

It's attached to the downpipe just below the exhaust manifold. It's held on to to 2 studs by 2 12mm nuts. It helps to take the exhaust manifold heat shield off before you attack the sensor.

Bad_dude

I got a 99 VE. It has about 180k miles on it. It does consumes oil but very little. I put in about half a quart in between oil change. The problem that I have is the mileage. It only gives about 24mpg. It's is uncharacteristic of the car. Plugs and cables are pretty new. I did seafoam it and we use only Chevron 87 gas. What I do to improve the mileage as it should be better? My wife drives it mostly on the freeway thus the mpg should be better.

Thanks.

I got a 99 VE. It has about 180k miles on it. It does consumes oil but very little. I put in about half a quart in between oil change. The problem that I have is the mileage. It only gives about 24mpg. It's is uncharacteristic of the car. Plugs and cables are pretty new. I did seafoam it and we use only Chevron 87 gas. What I do to improve the mileage as it should be better? My wife drives it mostly on the freeway thus the mpg should be better.

 

Thanks.

Given the mileage - have you verified O2 sensor is still functional? This a 3-speed or 4-speed automatic transaxle or 5-speed manual?

Bad_dude

I got a 99 VE. It has about 180k miles on it. It does consumes oil but very little. I put in about half a quart in between oil change. The problem that I have is the mileage. It only gives about 24mpg. It's is uncharacteristic of the car. Plugs and cables are pretty new. I did seafoam it and we use only Chevron 87 gas. What I do to improve the mileage as it should be better? My wife drives it mostly on the freeway thus the mpg should be better.

Thanks.

Given the mileage - have you verified O2 sensor is still functional? This a 3-speed or 4-speed automatic transaxle or 5-speed manual?

Some corrections on my last post. It has 151k on it as I changed the oil yesterday. I calculate her MPG on the last fill up was almost 32MPG, so the O2 sensor is ok. No code at all. Now I just need ways to help the suspension handle better. Any ideas?

Thanks.

Typical bolt on suspension mods and better tires are the ticket to improving the handling. The car started out pretty softly sprung, so any swap here will make a noticeable difference.

Tires, struts, springs - first, see how that works. Then to swaybars and braces. Besides that and their variations (i.e., coil-overs) - you'll be looking more extreme ways to stiffen the car, to continuously weld up body seams and add interior bracing / roll cage.

For mine - tires, TRD springs and KYB GR2 struts were the perfect mix of good control + decent ride. Now looking to drop in some Tokicos with the TRD springs, if they haven't sagged too much. Otherwise, I'll be replacing those with some H&R springs - more drop, little more aggressive.



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