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Discussion Starter #1
Car was running great after changing water pump, thanks to everyones help.
Drive home mis firing. Trys to keep running but engine shakes hard. All air hoses connected, fuel pump and filter changed two months ago. How do I check if valve is burnt or stuck. Other do I need to look some place else for faults
 

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a simple test for stuck valves is to remove your sparkplugs and look in the hole while someone cranks the engine. they should take turns opening and closing. also, while you cannot see all the valve surface, you should be able to get an idea of their condition through the plug hole.
cliff
 

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HOW OLD ARE YOUR PLUG WIRES?

Is it possible that doing the water pump that you bumped the distributor cap and perhaps knocked it out of position, or cracked it or broke a spark plug wire? Pull the cap, look it over along with the rotor.

Try to figure out which cylinder is not firing. Pull a plug wire and using insullated plyers crank the engine and put the wire back on and see if you get a smoother runing. OR pull all the plugs and see which one looks black and wet compared to the others.
Also burned valves lose compression. A compression testor will tell you if you have a burned valve. REad the instructions. Basically pull one plug disconnect coil wire, fuel pump. Put compression testor in Spark plug hole
Push Acc. pedal fully to the floor and crank away until you get no more gain on the gauge. A burned valve will be pretty much ZERO compression.

good luck
Stan
 

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joe said:
How do I check if valve is burnt or stuck.
A leak down tester is a good tool to have. Put the piston at TDC with valves closed, apply air pressure **careful - the motor can suddenly turn** then listen for escaping air. The leak down tester will give you a measurement (in percentage) of how well the cylinder will hold pressure.

do I need to look some place else for faults
Always look for the common and easy things first. Air leaks via a loose or cracked hose, loose or defective spark plug wires, loose/cracked cap or rotor, fouled plugs, etc. Also clean & tighten the ground wires attached near the rear of the intake side of the cylinder head.

I had a problem with ignition cross-fire in our '84 Spider. (Wires running parallel can induce spark in adjacent wire and loose current in the correct circuit.) I feared it was something internal gone majorly wrong. Then I re-arranged the wires and it immediately began running fine!
 

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With the engine running in the dark, look under hood for stray sparks flying around. Many times plug wires that are failing will allow the spark to go to the block or a manifold instead of firing the plug. With the engine running in daylight, or in your garage with the door open and lights on, use a pair of insulated pliers to remove the plug wires one at a time. If the cylinder is firing, the engine will slow down or stall when you remove a plug wire. When you remove the one to the cylinder that is misfiring, the engine won't change. Shut down the engine and use a phillips screwdriver in the end of the wire to the engine block or a manifold, have someone else crank the engine over for you while you check for spark. If you get a spak at the plug wire, pull the spark plug, check the gap, hook up the plug wire and lay the plug against metal on the engine. Have someone crank the engine over and check for spark at the plug. If you don't get a spark in the first test, pull your distributor cap and check for condition and especially check the condition of the contacts and rotor. Also, use a volt-ohm meter to check resistance through the plug wires. You want as low a resistance reading as you can get. If one wire shows a much higher resistance than the others or if one is showing infinity on the meter, you need new wires. Make sure all of the easy normal maintanence stuff is good first before jumping to conclusions about internal engine problems. If ignition checks out, pull your valve cover and check your valve clearance. If one is tight, adjust the valves and see if the problem goes away. If the car has been running fine, and then just started missing, a valve might have tightened up and you can adjust it back to spec before damage is done. Once you are sure of ignition and valve clearances, start the engine and see if the miss has gone away. If the miss is still there, then do a compression test. All 4 cylinders should be within 20# or better of each other. If one is low, squirt oil in the cylinder and see if the compression comes up on that cylinder. If the compression does not come up, you have a hole somewhere, either a burned valve or a hole in a piston. If the compression comes up, you have worn rings. Note a tight valve that is not closing will not seal and will act like a burned valve, that is why you check valve adjustment before doing a compression test. If you have an internal compression problem, you will have to pull the head and see if a valve job will fix it or if you will need an overhaul. What you don't want to do is pull the head off and find out there are no internal problems with the engine.
 

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Discussion Starter #7
1989 spider FIRING PROBLEM

tHANKS FOR THE HELP EVERYONE . I HAVE TO GO OUT OF TOWN THIS WEEKEND BUT START ON EACH STEP ONE AT A TIME . START TO SOLVE EACH PROBLEM THANKS AGAIN AND WILL UP DATE NEXT WEEK
 
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