90hp not starting

[bobec]

I have a 1990 90hp merc will not start. So I took one of the plugs out to see if I was getting spark and with it grounded to the block it fires. Then I put the plug back in and it will not start. So I took the plug out and it did the same thing.The motor is getting fuel and spark. This happened when I removed the center plug as well as the bottom plug. I only assume it would do it with the other one as well.When I say it fires I mean it will start and run with the plug out of the cylinder 3 inches from the plug hole. But put it back in and it will not hit a lick! Anyone.

[Faztbullet]

You need to test the spark on a air gap tester as against the block is not a good test. It could be a weak stator as with a plug out there is less drag on engine and it spins faster. It should jump a 3/8 gap easily. You could take a spare plug and ground it against block with others installed to see if you still have spark...

[Texasmark]

Not a sparkplug engineer, but I have determined over the years that a plug that can fire at one atmosphere (rested against the side of the block) can fail to fire under combustion pressures! Replacing the plugs cures the problem (has for me anyway). I have an '02 90. You don't have any other mechanism on that engine that I know of to cause what happens with the givens you mentioned.

Mark

[stackz]

have you checked compression? how did you test for fuel? it may be getting to the carbs but they could be clogged internally.

[bobec]

I will try to do some of your ideas this weekend thanks for the input!

[bobec]

I have tried a few things no spark with plugs in. The comp. is good 145 on all cyl. But it will spark a little with the plug out of the cyl. but with all plug in no spark.Whats next!

[bobec]

How do you check the stator on the motor? 1990 90hp merc. 3 cyl.

[Texasmark]

How do you check the stator on the motor? 1990 90hp merc. 3 cyl.

Get a manual and they have a resistance test to answer your question. I just got a Solec online 3 year subscription and having an original Merc manual and now this one I am thrilled with illustrations and detail. $38 if you have no patience (like I didn't), or they sell the manual on here for $20 something; don't remember what if any shipping is required. Well worth the moolah.

Mark

[Faztbullet]

Go to CDI electronics website and download the ignition troubleshooting manual and test it per their instructions(below)...

No fire at all:
1. Check resistance from blue and blue/white stator wires. OEM reads approximately 3500 ohms (CDI stators will read from 500-700 ohms. Check resistance from red to red/white. It should be approximately 80 on OEM stators, and 30 on CDI's. There should be no reading to engine ground with the wires disconnected. DVA (peak voltage) test stator output. It should be 180v or more on the low speed coil and 25v or more on the high-speed coils.
2. Inspect the flywheel outer and trigger magnets to see if they are loose or broken.
3. Disconnect the rectifier/regulator and retest. If the fire returns, replace the rectifier/regulator.
4. Disconnect red and red/white wires and retest. If DVA test above was OK, the pack is usually bad.

[CharlieB]

The ignition has a minimum cranking speed of 300 RPM.

Leaving even one plug out may allow the weak starter/battery to turn at, or near this minimum, but with all plugs in, fail to turn fast enough for the stator to generate sufficient voltage for the ignition to operate.

Clean all battery and starter cable connections, BOTH ENDS< clean, bright, and tight.

Make sure the battery is fully charged. Grab your trusty battery jumper cables and jump directly from the battery to the starter while cranking, any increase in cranking speed indicates a poor connection within the starter relay.

As a last resort, disassemble and clean the starter, lightly sand the commutator, and lightly lube the bushings.

Retest spark with all spark plugs installed. If any one fails to spark follow the previous instructions posted to download the CDIElectronics Troubleshooting Guide.

[bobec]

Sorry for the delay it ended up being the stator. The ohm test gave it away. Thankyou to everyone that helped me.GREAT SITE!