Question about 2005 Yamaha Road Star Silverado

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Rear cylinder misfires(vibration)Can feel it in exhaust.Coil primary-1.76ohms,Sec-13.5k ohms,Plug caps-9.7k-10.1k ohms,Pickup coil 296 ohms.can hear decompression solenoid operating. No engine noise top end(head)Could coil be breaking down? Ignitor Unit(not cheap and no way to test? Help, don't have much hair left!!!!!

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  • safisherman Nov 15, 2009

    Found a ignitor wire grounding out with the vibration. Thanks



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Hi and welcome to FixYa,

The coil resistance checks would seem to be normal. To confirm, compare with the readings of the front cylinder coil. If rear ignition coil is breaking down, then it would have excessive heat build-up or misfire would be after some time not right after starting.

An alternate method of testing the ignition coil would be to use extension wires and temporarily switch the trigger wires from the Ignitor to the front and rear coils. Determine if the missing spark would now be at the front. The sparkplugs would have to be tested just lying down on any metal part.

The only way to determine if it is an ignitor problem is to eliminate all the external factors. If all else checks good, then it would be an ignitor issue.

Would appreciate any updates.

Good luck and thank you for asking FixYa.

Posted on Nov 13, 2009


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Battery condition and connections may cause misfires. Inspect for corrosion at battery terminals, main circuit breakers, ignition fuse terminals (GY and R/BK), right handlebar connector [22] and coil connector.

Fuel system problems may cause misfires.

Spark Plugs OFTEN cause misfires, even plugs that look good. If carbon tracking is evident, replace them.

Spark Plug Wires may cause misfires - Front/rear 20 in. 5,000-11,666 ohms. Wires must be clean and tight. Excessive wire resistance or faulty connections can cause coil damage. If carbon tracking is evident, replace the ignition coil and inspect the spark plug wires. Spark plug wire connectors can corrode and should always be coated with dielectric grease to prevent this. If there is any corrosion replace the corroded parts.

Coils may break down and cause misfires but not usually at a given rpm range only. Coil testing can be performed by substituting a known good coil for one causing the no spark condition. The coil
does not require full installation to be functional. Verify a possibly
faulty coil by performing a resistance test. Test the primary coil resistance on your coil. Disconnect all the wires going to the small terminals (primary) on your coil. Using a good ohmmeter on Rx1 setting, test the resistance between the two small terminals. You should read somewhere between 2 and 3 ohms. If you read more, the coil is bad. Before you do this test short out both leads of the ohmmeter and if the reading is not zero you will need to write down or otherwise remember the number and subtract it from the reading you get from the primary circuit test or you will have an incorrect resistance reading for the primary wires because you will also be reading the ohmmeter internal resistance and/or the wire and lead resistance added to the primary wiring resistance.

You can also test the coil by leaving the "hot" wire on the coil and replacing the other side (ground side) with a short piece of wire. Turn the ignition on and temporarily ground the short piece of wire you put on the "out" (ground) side. When you take the wire away from the ground, (which will collapse the primary current into the secondary) you should see a spark at the plugs if it is a wasted spark system or at one of the plugs if it is not a wasted spark system. If you have current to both sides of the primary of a two part coil both plugs should get a spark whether wasted spark system or not as you are energizing both sides of the primary and collapsing both into both secondaries at the same time when you remove the ground wire from the cylinder head ground.

Take the plugs out of the cylinder heads and lay them back on it so that they have a good ground. Then watch the spark plugs closely when you turn the ignition switch off. You should see a single spark on each plug. This tell you that the coil is getting fire and that it is good and your problem lies elsewhere. You get a spark on both plugs because it is a wasted spark system that fires both plugs simultaneously, one on power stroke and the other on exhaust stroke. This will not work on 2006 and later EFI as there will be no spark with both plugs removed.

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My light says ignition coil b. also the primary and secondary.......what is the primary/sec / AT FIRST IT SAYED #6 misfire. also it still has a slight miss at idle and crussin in overdrive . Can you please...

It sounds like you need a coil for # 6 cylinder .LS's have a issue with the valve cover seals leaking oil into the spark plug holes and causing a misfire if this is the case you have to replace all the gaskets for the valve covers clean out the oil and might as well do sparkplugs then too. Its more of a dealer repair then. If no oil in that cylinder try replacing coil and spark plug.

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How to tell which of the 8 coils on a 1998 Pontiac trans-am ws-6 is bad?

This may help in some cases... At night turn all the lights off, wait a bit for your eyes to ajust to darkness, start the engine and look at your coils. Bad one will have a blue sparking inside. This solution does not work in all the cases though. But it is fast and easy. If you can't find a bad one like this then try to measure resistance of the primary for each coil because it could be a burned primary.

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1 Answer

1998 chevy venture has electricity arcing across the harmonic balancer

The coil pack on these engines runs hot, so it's important to make sure there is heat sink grease under the coil to transfer heat. If the coil module gets too hot, it will fail.
If an engine is hard to start or has a misfire at higher speeds, the problem may be a weak coil, a bad plug wire, or a fouled or worn spark plug. On 1996 and newer vehicles, you should get a cylinder misfire code. A code for one cylinder would likely indicate a fouled plug, bad plug wire, or possibly a clogged or dead fuel injector, or a compression leak (burned exhaust valve). Misfire codes for two cylinders that share a coil would likely point to a bad coil.
Another way to figure out if a misfire is a bad coil is to swap two of the coils on the coil pack. If the misfire moves to the new cylinders, the problem is the coil. If the misfire remains in the same cylinders, the coil is OK and the problem is the wires, plugs, injectors or compression.
If you test a coil with an ohmmeter, the test specs are 0.5 to 0.9 ohms for the primary terminals under the coil, and secondary resistance of 5,000 to 8,000 ohms at the high-voltage terminal.

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code 300 random cylinder misfire, code 303 cylinder 3 misfire detected code 304 cylinder 4 misfire detected. check the spark plug wires 3 and 4 inline tester for constant fire. also check the spark plugs , clean and reset the gap if necessary. if all is good check the coil terminals for corrosion. if this is all correct then check the coil with a ohm meter for primary resistance by attaching the leads to the positive and negative terminals. then check the secondary resistance by hooking one of the ohmmeter leads to the center terminal and the other lead to one of the outer terminals the resistance for primary test should be 0.95 to 1.20 ohms and the resistance on the secondary side should be 11,300 to13,300 ohms. hope this will help!!!

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All my cylinders are misfiring.

Hi. This vehicle is equipped with a Electronic distributor ignition assembly. There is no ICM(ignition control module) on your model. This will narrow the problem areas down a bit. The most common area of concern will be the distributor cap.This Component may be worn, cracked, or loose. Inspect the cap for faults, and replace if necessary. The next area of concern will be a set of faulty, or worn spark plug wires. Inspect the wire sets for damage. If you have not replaced the sets for quite some time, simply replace them asap.

Another area of concern will be the coils. The ignition coil is designed to operate without an external ballast resistor. Inspect the coil for arcing. Test the coil primary and secondary resistance. When using an ohmmeter, the primary readings should be 0.97-1.18 ohms and the secondary resistance should be 11,300-15,300 ohms. replace the coil(s), that do not rate correctly.

The above areas are the most common. Here is a list of some other problem areas, that will cause multiple misfiring.

1. Crankshaft/Camshaft sensor- Check the wiring at the Crankshaft sensor housing. Make sure the sensor is not loose, or damaged. The cam sensor is mounted in the distributor rotor area, under the cap. It is an integrated part of the distributor.

2. Spark plug(s)- replace if necessary.

3. PCV Valve - Check the valve, and hose for damage.

4. Fuel Pump - A weak fuel pump will produce less than normal pressure. this will cause the engine g to misfire. Check the ground at the pump for corrosion. Clean, ro replace, if necessary.

5. Timing settings - A slipped timing chain, or belt will cause a misfire, also. check the timing ratings for slipped intervals. replace the belt, or chain, if needed.

6. Injectors - A faulty set of injectors will cause a misfire. make sure that the injectors are functioning properly.

7. MAP- A failed MAP sensor will induce misfiring. This will, usually, will trigger the engine light.

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