Do you have an engine MISFIRING problem? Here are a few tips for you!

Misfire means one or two of your engine cylinders are not firing. This will cause your engine to miss resulting in a rough running engine.

These are the symptoms:
Engine shakes when idling
Hesitation when accelerating
Loss of power

You cannot let an engine miss (misfire) for a long time. Sometimes, it will take your ignition module, which will cause a NO START later.

What are the types of MISFIRES?

Mechanical misfire happens when the cylinder fail to fire because of mechanical failure.


Valve train failure if the cylinder valves are worn, the cylinder looses compression. The same applies if the piston rings get too small clearance causing it also to loose compression. This kind of failure is easy to check, using a compression tester. Measure the cylinder compression of ALL the cylinders. Anything below 100 PSI or below the norm or average reading is an indication of a failing cylinder. The only repairs you can do here is either pull out the cylinder head or replace the engine.

Vacuum misfires happens when your engine has a vacuum leak.

When this happens, your engine will have a rolling miss. It is called rolling because unlike the first one on top, your engine miss could travel to any cylinder, whereas the first one is confined to one or two cylinders. This is hard to diagnose because the compression testing won’t help you. The trick here is to find the vacuum leak usually by spraying carb cleaner to suspected vacuum hoses and gaskets. When done on idle, the RPM usually change when the carb cleaner hits the vacuum leak.

Ignition misfires is almost similar to the second one above except this one could be caused by ignition failure.

Again, this engine miss will happen like a rolling misfire because the weak spark could happen in any cylinder. The most common fix on this is to check ignition parts for proper readings.

Coolant misfires happens after your engine overheats (this is also a mechanical failure).

When this occurs, your cylinder head gaskets has a crack. This will cause your cylinder to lose compression just like the first case above. The same thing happens when the cylinder head itself gets warped because of the heat. A compression tester can test both of these problems.

Engine problem MISFIRE TIPS:

One of the leading causes of rolling misfires is cause by EGR failure. As you remember, EGR is a devise that introduces exhaust gases to your intake to make your engine run cooler and reduce emission. The EGR valve, which opens and acts like a door for the exhaust gases does this. However, the EGR is stuck open all the time, your engine will miss. It must be done on acceleration only but not on idle.

Here are some misfire fixes shown on ATS database:

GM engine EGR tips:

To check the egr:

First, make sure it will open and hold vacuum with the eng. off. Next start the engine, it should slam closed. If it does not, then it is bad. Also, it is a negative feed back EGR valve and requires eng vacuum to regulate how much it opens. To know if was not regulating, the egr would close, but VERY slowly.

GM digital (electric) EGR fixes:

“The fix, was electric solenoid for EGR valve, it has a dump in the top of it (has a filter over it)and it was holding the vac on so when the engine was started cold it already had EGR valve open enough to cause minor over fueling (vac leak through egr valve)that the long decel period customer went through to second stop sign must be enough to flood engine just enough to kill it and not enough to make it start like it was rich”

Dodge Caravan fix:

“The fix turned out to be the EGR valve - it was open enough to completely mess up the engine when cold but the engine ran okay when warm.”

Ford F150 EGR testing:

“To check this, take your vacuum pump and open the EGR valve, The engine should stumble like it is going dead and then recover and run fairly well. If this does not happen, the EGR passages are stucked up. However don't jump the gun too quick, remember the DPFE (EVR) solenoid still gives it a share of problems too”.

Demo pictures:

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Happy troubleshooting!


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