My car is misfiring and I have fixed everything

Tiny
SORA01225
  • MEMBER
  • 1997 PONTIAC GRAND AM
  • 158,000 MILES
I had monro replace parts but its still doing it and they have no idea why
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Monday, November 21st, 2011 AT 11:32 PM

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Tiny
DRCRANKNWRENCH
  • EXPERT
There are a few reasons that cars mis-fire. Since you said you replaced most everything, I will give you the reasons that take a little more than plugs or plug wires, etc. to cure a misfire.

The head gasket could be bad. This allows either oil or anti-freeze into a cylinder(s) and keeps it from firing.

The crankshaft/camshaft position snesor could have failed. This essentially will throw the timing off really bad and keep the spark signal from firing at the right time causing a mis-fire.

The timing belt/chain could have skipped a tooth due to where on it or the cam and crankshaft gears. This also throws the timing off bad enough to cause a mis-fire.

The link below is a diagnostic walk-through of the genral causes of a mis-fire in an engine. Since I am not sure what you replace, I thought it may help to solve the problem.

Here is the link;
http://www.2carpros.com/articles/engine-misfires-or-runs-rough
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Monday, November 21st, 2011 AT 11:56 PM
Tiny
MFOLEYINFO
  • MEMBER
It could be bad lifter, take your valve cover off and make sure all your rockers are moving, if not, replace your lifters
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Thursday, November 24th, 2011 AT 4:49 AM
Tiny
DRCRANKNWRENCH
  • EXPERT
A bad lifter will still move the valve, just not as much as it should. It is the equivalant of the clearnce being off. A valve not miving would lead to other problems such as flooding if it si intake valve or hydrolock or detonation if it is exhasut valve, but I have never come across a situation that bad. The Car would not run at all in that condition.
What happens to a bad or, "crushed" lifter is that the hole which allows oil into it, as lifters are either solid or hydraulic and solid lifters are a race car item generally, and the proper pressure cannot be built up in the lifter to give it the proper clearnce and it starts making a tapping noise which can get bad enough the where the valve will not open or close quite fast enoguh, and we are talking a millimeter in extreme cases at the most and that would cause other issues, that the valve get forced closed by the piston in its compression stroke. That is as extreme as it can get and I honestly don't think it is happening as you would hear a tapping noise from the top end and the engine would probably not start or have the power, if it did, to move the car. The most that happens with a bad lifter is the play between the rocker or cam bucket shim gets to where the spring closing the valve and the cam opening the valve casues a tapping noise.

One thing I would suggest that I di not is to have the trouble codes pulled. The check engine light does not have to be on for a trouble code to be shown by ECU and it displays trouble codes in ECU memory since it was last cleared. Advance Auto and Auto Zone parts stores will do this for free.

The other thing is that if the timing Chain/Belt has not been replaced in the last, 60,000 for belts and timing chains can often last over the mileage you have. However in either case a tensioner, which keeps tension in propwer spec, can fail and cause slop in the chain/belt and can lead to wear and possibly damage the chain enough that it too migth need replacing as either a belt or a chain when worn can skip a tooth and throw the timing off severly enough to stall the car. It can casue detonation as well which will put a hole in the pistons.
I metioned this before in a short sentance and I think the walk trough talsk a little bit about it, but it can cause damage that is severe so I wanted to make sure I relayed that information to you as well as explaining what can happen when a hydraulic lifter fails. I cited extreme cases which I have never seen, but I wanted to lest you know that it would make a severe taping noise and probably not start. A bad lifter genrally just makes a tapping noise and most people just live with the noise and drive the car as it won't cause any damage. Some people change the valve clearnce to attempt to eliminate the tap, but don't do that as you never know when the spec of dirt or carbon may let the lifter gain pressure and then the tight clearance will cause issue. It also seldom alleviates that tapping as the lifer is kind of soft in a sense and has to be completly crushed in order to make the tapping go away and to do that would require a valve clearnce far too tight to be within spec.
You are on the right road so far. Let me know if you need anything or have any questions.
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Thursday, November 24th, 2011 AT 5:45 AM

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