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Contact Us. Find My Part. Select Language. Message Regarding Your Privacy. I accept Submit Submit. Sluggish or rough acceleration When the engine misfires, you may have trouble getting your vehicle up to speed. Rough idle A rough or uneven idle can be an indicator of an engine that is misfiring. Back Back to Diagnose Car Symptoms. Plugs good, plug wires not? Those on this truck were as old as the truck itself and probably original, so even though they ohmed out fine and looked good — if dusty — at , miles, it was not hard to justify a new set.
There are a few easy ways to test plug wires. Examine them in the dark, engine running, and watch for sparks jumping. Next, mist the wires with water and see if this causes any sparks in the same dark environs.
You can remove a wire and gently bend it to see if the rubber sheathing cracks. The bend test: Even with , miles on them, the OEM plug wires take a curve without cracking. Quality OEM product right there. With the spark throwers and spark carriers cleared of responsibility for code P, we moved along to the spark makers.
On this Toyota, three coil packs live on the 1, 3 and 5 cylinders, and each power a plug there and on the opposite side of the engine, at 2, 4 and 6. The system is called waste-spark: The coil shoots two sparks at once, and the plug fires twice in the combustion cycle —once to fire the cylinder and once more to clean up the leftovers in the exhaust stroke.
Find the problem, and solve it. Using a multimeter, you can test the ohm ratings of both primary and secondary outlets on the waste-spark coil, and all of those on this truck tested well between 0. Consult your repair manual or factory service manual FSM for all the test ratings. With no indication of a bad coil, a return to the swap methodology sensible method had us switch the 1 and 3 coils, but the miss at 4 remained. One of three waste-spark coils on the Toyota V6. With P continuing despite plug, wire and coil checks, we were done with easy fixes.
On to the next suspect, indicated by the plugs lean read on 4 , misfire behaviors intermittent, heat-related and occurring at consistent rpm and the elimination of other suspects: fuel.
Though an injector problem had been suggested earlier, it was best to rule out the ignition parts before moving on to a set of injectors that required some real wrenching to access. Have a few spare O-rings around. Expect to replace gaskets most of the time. The fuel injector is nestled beneath the rail in this shot, with the rail holding it gently in the injector port.
The good news is that most of these parts are easily accessible and can be self-serviced with a little know-how. The longer you leave it, the more fuel you will waste, the more toxic emissions you will release into the atmosphere and the more likely it is that the damage will spread to core engine components. You can use a scan tool or code reader to diagnose engine misfiring. These tools retrieve data from your vehicle to identify the cause of the misfires.
Scan tools and code readers identify:. Answering the following questions will also help you to identify the cause of the engine misfiring:. Engine misfiring is typically the result of one of three issues: loss of spark, an improperly balanced air-fuel ratio or loss of compression.
In each of these instances, one or more of the cylinders fails to fire, stunting the combustion process. Misfires due to lack of spark are especially problematic as unburned fuel can enter the exhaust system and destroy the catalytic converter. Look out for the engine light or malfunction indicator light on your dashboard — at least one of these will flash if your catalytic converter is at risk of damage.
A diagnosis can often be made quickly if the cause of the misfiring is the spark plugs. Worn spark plugs can be replaced easily at a low cost. Check that you have the right spark plugs for your car, that the plug gaps line up with the recommended gaps in your vehicle handbook and that the spark plugs are in good condition.
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