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Dead Cylinder?


peabees's Avatar
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05-10-05, 10:53 AM   #1  
Dead Cylinder?

93 mazda protege, 1.8l SOHC, 5 spd w/ 92K+

Yesterday while returning from work, the car started running like crap. It had a rough idle and less power. It seems to have a miss at all speeds and the exhaust smells like gas. I did not get a CEL.

My initial guess was a loose wire or vacuum leak. After finding none of these, I pulled the plug wires one at a time. While nos. 1, 3 and 4 were disconnected, the car almost died. Number 2 seems to be dead, since being disconnected made no difference. It is getting spark and the injector seems to be ticking like the others. The plug looked fine, but I only drove a mile with the problem.

I plan to do a compression test next.

Any other suggestions or known problems with this engine?

 
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bejay's Avatar
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05-10-05, 11:58 AM   #2  
check the plug wire closely for any holes in the boot that could cause the spark to arc to the cylinder head instead of firing the cylinder, it will need atleast 100 psi compression to hit should be 125 plus you might also check for vacum leaks along intake gasket.

 
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05-10-05, 03:21 PM   #3  
DNT1
Take your car to a real dark location, take along a spray container of water now open the hood and spray a mist of water over all the engine area and watch closely for sparking, it should show up well, most likely you have a bad plug wire, this simple test should verify that. I have seen some vehicles that look like a lightning storm is going off under the hood when doing this test LOL.

 
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05-11-05, 09:25 AM   #4  
Compression test results

'93 mazda protege 1.8l sohc 16 V w/ 92k

The car suddenly started running bad like a wire was loose. There was no gradual demise. It even passed the emissions test 1k back, and all plugs looked good when checked before the test.

The no. 2 plug was soaked with gas and pulling the plug wire or injector wire made no difference to the rough idle.

I drove home approx. 1 mile on 3 cyl. Will it hurt the car if I unplug the injector and drive on 3 cyl?

I did a compression test on a warmed engine last night with a 25+-year-old sears compression test, and I live at about 4000 ft above sea level. Results are given as psi.

Dry:

1: 145, 2: 25, 3: 148, 4: 155

W/ a few squirts of oil in each cyl:

1: 170, 2: 35, 3: 169, 4: 170

The radiator hose does not pressurize quickly. I see no evidence of oil in the water or the reverse, but remember I only drove I mile.

Can I prove/diprove a bad head gasket by removing the plug and letting the car run until hot? If I get water out of the plug hole, is it a bad gasket?

If I take the valve cover off and see no obvious problem with lifter, spring or rocker arm should I assume a bad valve? If I take the head off, will I recognize the bad valve?

What is the next step w/ diagnosis? Remember the onset of the problem was sudden. The car ran as smooth as glass and suddenly started idling poorly at a stop.

 
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05-11-05, 10:00 AM   #5  
If that cylinder is really gone, you will probably have abominable gas mileage and have to start buying a quart of oil every 100 miles or so. I ahd an 84 Mazda B2000 that lost a cylinder and as a result got 8 mpg and wouldn't run with my foot off the gas as well as having to put in a quart of oil every 80 miles or so.

 
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05-11-05, 11:50 AM   #6  
Squirting oil in shows whether the rings are sealing. The valves or head gasket is leaking (my guess),could also be a hole in the piston. Water out the tail pipe is a bad head gasket sign, as is bubbles coming up in radiator, but no you can have a bad head gasket and not get water out the cylinder hole. If its a bad head gasket one way to cheat is to use water glass (sodium silicate) 1/4 cup, no antifreeze or now they are putting it in block sealants (look at ingredients). It won't help with bad valves however. Did you overheat it (precursor to headgasket prob.s)?

 
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05-11-05, 12:38 PM   #7  
it is likely a burnt valve head gaskets can go bad a couple of ways and effect compression one which is blown between cylinders which would affect the compression of 2 cylinders next to each other and by your readings this is not the case the other way is a gasket blown to coolant passage this allows coolant into the cylinder, often this doesnt affect compression much if at all and in bad cases where it does affect compression alot then coolant is usually obvious in the cylinder and will be blown out of the plug hole when engine is cranked over.
you should pull the valve cover and look at the valvetrain for anything broken or worn out and if nothing found pull the head and a burnt valve should be easy to see if its effecting compression that much.

 
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05-11-05, 03:15 PM   #8  
Pull valve cover and put it on TDC with both valves closed. Put air into the cylinder with an adapter and see where it leaks.

Air intake=intake valve
tail pipe=exhaust valve
crankcase=ring/piston problem
rad=headgasket/cracked head/block cracked

I merged your two threads for the same problem, please use the reply button

 
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05-20-05, 07:35 AM   #9  
toytaman

I finally returned to this car.

I hooked up a compression tester hose to the thing with a trigger and gauge I use to fill tires. I set the regulator to 100 psi and gave no 1 at tdc a 3 second shot of air. The gauge went to about 60 psi and dropped to 0 in about 2 seconds. I moved no.2, the problem cylinder, to tdc and got the same results. I moved off tdc and clearly got air out the tailpipe and no reading on the gauge. I moved it back to tdc at no.2 and held the trigger. I was getting air out of the pvc valve hole.

I think this is inconclussive. If the valves are good the air has to go by the rings and once I blow the oil off it will leak out faster. I will do it again with all cylinders and crank it between tests to coat the cylinder walls with oil with fuel pump fuse out.

Am I doing your suggested test correctly?

when I run the car i get white or light grey smoke out the tailpipe but only after it heats-up. does this suggest anything?

My goal is to prove it is not a cracked block. I can handle anything but that. The car has not overheated and did not freeze.

Thanks

 
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05-20-05, 04:29 PM   #10  
You need to supply a constant flow of air at TDC, sounds like a ring/piston problem by leaking into the crankcase.

 
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05-21-05, 02:08 AM   #11  
I had a similar problem with a motor that used push rods.
Yours has a SOHC so it may not apply.
I had a seized intake valve closed, compression test was about 25 psi.

Turn the motor by hand, Take a good look at the cam and valve stems maybe one valve is not closing or something like.
In my car I was able to see the top of the pistons for damage thru the spark plug hole.

When pumping air into the cyl, look in the radiator for bubbles or the oil dip stick hole for air pressure.

 
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05-22-05, 10:06 PM   #12  
you will likely get a small amount of air coming from the crankcase in every cylinder as most piston rings have about a 10 percent compression loss if there is a valve problem such as burnt valve or valve not seating you will hear air coming either from the tail pipe or the intake you may have to remove the air intake hose for it to be noticable.
a ring problem should of showed up on the compression test the wet test should have been alot higher, a hole in the piston would probably not show any different readings between wet and dry test and would leak air through the crankcase.

 
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05-23-05, 05:44 AM   #13  
keep in mind...

Pull valve cover and put it on TDC with both valves closed.

what TM has said here. when doing a leakage test, the piston MUST be a TDC on the compression stroke...that's why he specified removing the valve cover so you can see that the valves are closed. TDC also occurs on the exhaust stroke but because of valve overlap, you'll get leakage every time.

when you apply the air, watch the crankshaft (belts or pulleys), if the engine turns, it wasn't exactly on TDC. (the piston and connecting rod must be perfectly verticle)

 
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05-23-05, 08:07 AM   #14  
thanks all

I did the test with a different helper, and I was less rushed this time. Clearly, I did not get a puff of air out the tailpipe with no 1 at tdc, but I did with no 2 after rotating the crankshaft counterclockwise 180 degrees and confirming the rotor pointed to the no 2 wire.

I was so convinced that I stared tearing it down. I only got the exhaust manifold off before I quit.

I will take the valve cover off and test again. I lined up no.1 with the timing mark and eye-balled the 180 backwards. I did see engine rotation with compressed air, so I put the car in gear. I do not remember which cylinder I was on, but after that I did the test in gear. Maybe I was not at tdc.
What do I look for? Should the rocker arms be at the top of their cycle? The lifters are hydraulic, so there will not be any clearance.
With the exhaust manifold off, I will not need a helper to listen at the tail pipe, since the exhaust, port is inches from the plug hole.

I am willing to do a valve job on the car. If it needs anything else, I will sell it as is.

 
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05-23-05, 08:55 AM   #15  
If it rotates your not on TDC, don't put it in gear, you want to know if it moves. If it does your not on absolute TDC.

Rotate the engine so the intake opens and closes, then bring it to tdc. Maybe you could put something in the sparkplug hole to feel when it reaches TDC?

 
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