QuestionQUESTION: when i bought the car it had a very light misfire,then the coil went bad so i change it.the spark plugs were changed with the wires.i changed the distributor magnetic pickup,the gm amplifier,cleaned the coolant temp sensor and the misfire is getting a little bit worse.there sounds like a puffing sound through the exhaust which is a straight through no cat.i have the distributor a little advanced right now it has power when i drive, but still missing.i even changed the fuel filter and the pump runs good ,i have no more money and need the car in a few days to get to work which is far.please help.thanks.
ANSWER: Hi Andre,
It is cool to put a lot of new stuff on a car you just bought so as to make it more reliable but you will run short of funds if you do it to diagnose a problem.
When we receive a car in the dealership with a miss, we have to run tests before replacing anything. I was lucky to have a scope and CO equipment to test with. But most people don't have that test equipment so you have to run tests another way.
First run a compression test (throttle open) to confirm that the engine is ok. If the compression is ok and only if it is ok can you proceed.
Set the timing to factory specs and do not alter that to get it to run better. This is important.
You need to do a "Cylinder Kill" test to determine if the miss is in only one cylinder. (DO NOT remove one plug wire at a time to run the cylinder kill test because of the danger of a spark tracking down on the coil to the primary of the coil and destroying the new GM amp.)
Without a scope you can just probe each plug cover with a grounded pointed probe to kill each cylinder and watch for how much RPM drop you get.
If you find no RPM drop in a cylinder and you have a good compression test and you have replaced all of the ignition secondary (cap wires and plugs) then you need to look at injectors. They are too expensive to just replace to diagnose, so if you have isolated one cylinder just switch the injector of that cylinder with another cylinder and redo the cylinder kill test to see if the problem has moved too.
If you can not isolate the miss to a cylinder then you may need to find a shop with a scope and CO test equipment to test it.
Howard
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QUESTION: hey howard i have to tell you i did the spark plug cylinder test and all cylinders respond with a heavy miss when the spark is interrupted so i guess all cylinders are firing.there seems to be a very small amount of white smoke coming from the exhaustmaybe 40 seconds after startup.did i mention that the cars does not misfire when it is first started,only after it starts to warm a little and the rpm drop to 800 idle then it begins to misfire.do you think there is a chance the head gasket is slowly starting to leak.it started when i went to buy the car and in about two weeks it started to get worse.i dont have much diagnostic tools to do the proper check.p.s i did not notice any bubbles in the coolant while the cars was running to see if the head gasket was leaking.thanks howard.........andre.
ANSWER: White smoke is either coolant or brake fluid. If it is not overheating look at the brake booster to see if it has brake fluid in it and check for a coolant leak at the intake manifold.
Howard
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QUESTION: is there a condenser in the distributor that could be going bad.would this cause a misfire after a couple miles down the road or when operating temp has been reached.
AnswerAndre, at this point you need to locate a shop that has a scope and CO equipment. They can run all the necessary tests in a matter of minutes and it usually cost much less then the cost of all the parts you have already tossed at it.
It is 100% waste of time trying to guess what might be wrong of the thousands of possible causes. Testing is the ONLY method to find a problem. You can easily run out of money tossing parts at the problem hoping to hit the fault.
Howard
