Random Ignition Misfires: Grassroots Motorsports forum: Grassroots Motorsports Magazine

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Sept. 28, 2009 7:02 p.m. iolite New Reader

My engine has an issue with random ignition coil misfires at WOT or close to WOT, above 4500-5000rpms. When I check the OBDII with a code scanner, it shows a different coil or pair of coils at fault whenever it misfires, even the two coils that I have just recently installed, not being an exception. There seems to be subtle lifter noise on acceleration, but I wouldn't say enough to suggest sticky lifters. The code scanner isn't showing any other fault codes being tripped. Has anyone ever run into a similar problem?

I don't think I'm going to be able to re-register for the 2010 auto-x season if I can't get this sorted out.
Sept. 28, 2009 7:52 p.m. aussiesmg SuperDork

A little info on the car and engine might help us out
Sept. 28, 2009 8:14 p.m. Jensenman SuperDork

Partially plugged exhaust will do this, as will lifters 'pumping up' and poor electrical connections. Yeah, we need more car/engine info.
Sept. 28, 2009 10:09 p.m. iolite New Reader

1998 M3 Sedan, S52 3.2L I6. 156,000miles. Using NGK Iridiums. I did two cylinder leak down tests and the numbers for all the cylinders were within spec., 177-180psi. Just changed the oil, looked free of coolant. I haven't replaced the rubber boots between the coils and the plugs yet, they look a little tired, though.

I had been using that Turbo 108 Octane booster for about 6-8 months pretty religiously. I'm wondering if my cats may be clogged.
Sept. 29, 2009 8:25 a.m. njansenv Reader

Double check the harness (at the firewall) that plugs into all the coils. I bought a cheeeep M3 that way.... (Although, to be fair, I bought new coils trying to solve the problem...and was pretty frustrated when it didn't)
Sept. 29, 2009 8:25 a.m. Strike_Zero New Reader

Change the coil boots . . .that solved my misfire problem on my former S52. Also check all the connections and make sure the wiring is in good condition.

Lifters noise is sometimes confused for VANOS noise as well. Does it make the same noise on free rev or only under load? They also tend to be a bit noisy on startup as well.

I do know the M5x/S5x engine family is infamous for lifter noise if drive it aggressively. It's usually solve by running the oil at a slightly higher level.
Sept. 29, 2009 7:24 p.m. stan_d Dork

If it's gm change crank position sensor I have seen them go bad without sending a code.