Backfiring through intake
 

Hi folks. I need some help from someone who's a lot more experienced than I am.

I was de-winterizing the engines (2000 Mercruiser 8.2L (502CI)) MPI and the starboard engine is giving me a fit. It ran perfect until when I just tried to start it this week. When turning over, it will idle but the idle is erratic and it will backfire through the intake. I did a compression test (all were within spec), checked the spark plug wires a half dozen times, made sure the wires are routed right, installed new distributor cap, installed new ignition coil.... .but still backfiring through the intake. Plugs looked fine as well.

What should I do next? Could it be a bad / clogged up fuel injector?

Any help or suggestions would be greatly appreciated.

I'M NOT A MECHANIC

Could it be the timing? Bump the distributor and knock it out? Lord knows I did that by accident in a car I once owned - drove me crazy.

Just a thought

3pointstar

Haven't bumped the distributor. It's in the same place bolted in just the way it was when I put the boat away for the winter. I have to loosen up bolts to move it.

intake valve may have some rust build up,,it's not seating properly,just back firing thru to the intake.

Wouldn't the compression be low if it was a valve issue?

a bad injector would be a dead miss. no fuel to backfire with. yes, a bad intake valve, bad enough to blow back like that would show almost no compression. do both these engines turn the same way? or is this a shaft boat, not I/O? check plug wires again. it is always plug wires or some other spark going to wrong plug thing.

Did you pull distributor to ck gear and shine down in and take a look at the cam gear. Also double ck ignition grounds. All grounds for that matter. Your symptoms sound almost like your dist is 180 off which I know isn't the case but. Ignition module?

It sounds like an ignition problem. Check all plug connections to ignition system for corrosion. Pick up module in distributor could be a possible cause as well.

You said you changed dist cap--what about the rotor???

Checked plugs and firing order several times. Did not replace the rotor because I really don't want to just throw parts at this.

Ya be careful those rotors are pricey. Lol. Should replace at time of cap as a rule of thumb. Kinda doubt it's the problem though. Isn't this fun.