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I'm in the inconvenient process of replacing the plugs on the td manifolded turbo car this afternoon. Its recently begun misfiring under boost, which is at times like hitting a fuel cut rev limiter, while other times its only single, very loud pops. The tach has also begun to jump around near 6k and up, which to me was a sign of the electronics picking up an unusual amount of noise. Leaning out the mixture and reducing the ignition timing has helped tremendousy. Apparently it was running super rich and with overly advanced timing to offset the mixture. Its running stronger with the right mix, but it still kicks the tach needle around and occasionally misfires, either coming up into the boost in first gear or accelerating through the triple digits in 4th and 5th.

The first plug I got out measured 3.3k ohms resistance between the terminal and the electrode. A brand new BPR8ES measures 4.7k ohms through the plug. That is a significant difference to me, and I'm hoping thats the problem. The gap on the plug came out at .030, which is a good 5 thousandths larger than it was when it went in there. I guess I'll see how it runs when I get everything replaced...

The plugs helped, bit the tach still jumps and it still misfires slightly. I guess the ignition rotor is next.

So, ya got that WBO2 controller installed yet?

Yeah, about that. Bought it new from TCD. Wired it in with the reset button and status LED. It worked great for a week or so, but it took me a few days to get Megasquirt to recognize the 0-5 volt signal. I got maybe an hour of tuning in once I got everything configured correctly. Then it shut off and didn't come back on. I figure its probably the LC-1 controller, but I dont know. It has 12 volts and a good ground at the block, it just doesnt work. I got an RMA# from Innovative, and it went in the mail last week. I hope they can turn it around reasonably quickly, because I clearly have some more work to do.

I'm thinking I killed some ignition components while it was running super rich, perhaps the ignition cap and/or rotor. I'm doing the rotor next. I'm thinking thats it.

Replace all of your plugs, cap, rotor and wires. I would also seriously look at the coil.

You are pushing the engine quite nicely now and the electrical components have to be in perfect working order. If I had any indication of spark blow-out, I immediately replaced the plugs and checked the gap, I ran .028.

Get the WB02 back on-line or have it serviced under warranty. That is your critical tool for tuning.

Believe this or not - I would run some water through your engine to clean out all of the carbon or fuel fouling residue. Here is how you do it. Get a water hose and nozzle that can spray a very fine mist that you can control. Star the engine and put he hose nozzle in the AFM while modulating the water flow vs the RPM manually (REV it). You will find that too much water bogs the engine. Go ahead and bog the engine and then reduce the water flow. so you can inject the water while the engine is still turning around 3000 rpm. I usually do this until I get white smoke out the tail pipe.

Ever seen a cylinder and piston that has received the water from a blown head gasket? Is clean as new usually.

I learn this trick when I had a 1967 Dodge Dart which had a slant-six 225. I dumped water through it until it smoked like Spikcolies (sp?) van and after that, it ran like a sewing machine.

BTW - My exM535ti has water injection that does just what I am describing (too a much lesser degree) anytime it is over 7 psi of boost.

Cap and rotor won't suffer from running rich, but the plugs will. Your ignition system really does need to be in very good shape to fire the turbo motor properly though. New cap/rotor/coil certainly can't hurt if they're of unknown condition or haven't been replaced in a while.

My Wrangler developed a mysterious misfire on the way to Lime Rock last weekend, turned out to be a bad cap. Turns out they only last about 30k miles on that old AMC motor instead of the ridiculous mileage you tend to get from BMW components. Who knew?

Point is, get that ignition in shape. If you're replacing the rotor, get the cap as well. They're not that expensive IIRC.

Jeremy

It got a new cap, rotor and set of plug wires when I put the engine together last November. The components might have 20k on them. I dont mind going in twice, so I think I'll try the rotor first. One variable at a time. I can see burning one up with too much plug gap (a tight .030) and a super duper rich mixture under boost. I dont know if thats actually realistic though. I can say its not the plugs. Those are new. It doesnt misfire like it used to, with the loud pops and occasional rev limiting blowouts. But it still kicks the tach around near 6k, so its either picking up noise from the ignition or experiencing some sort of electrical shit going on with the MS ecu.

I didnt replace the coil, but I've got other spares laying around. Considering the things like dwell and spark duration that you have to set in Megatune, I wouldn't be suprised if I killed a coil or two. These aren't things I really know how to configure.

I still havent heard back from Innovative about the status of my LC-1. Hopefully they'll let me know whats going on this afternoon.

They just told me it takes about TWO WEEKS to turn an LC-1 around. I'm pretty bummed out. I fixed the tach problem with 1 millisecond less ignition dwell. It doesnt run quite right though. I've yet to do the ignition rotor for the lack of tools at my apartment. I'm hoping that'll fix the tugging and hesitating sensation under hard accel. Stuff like this makes megasquirt suck sometimes.

Todd has said that with a stock ignition and high boost, the combustion front can be "blown out" by the pressure. This necessitated upgrading to a better coil and possibly the MSD box...

I believe I was experiencing that with the fouled plugs. It is more likely to occur with a crappy tune at a lower boost level than it would normally occur. Once I get my shit together I should be good for a few more psi with the stock components.

When it comes time, I think I'll stick one of the MSD coils in there.

get a coil from a e32 or e34 M30

Datalog your RPM signal and timing and post it up. Lets start there and be sure that you have a clean RPM signal.

I did do a datalog a few nights ago. I need to download megalog viewer and check it out. I'll post it up ASAP.

You can also just post up your datalog and I can look at it or email it to me.

number of different causes of misfires.

first thing is the condition of all the parts, cap, rotor, wires.

two, as power goes up, combustion pressures go up, and the voltage required to jump the plug gap goes up.

solutions:

1. plug gap, smaller plug gap takes less power to fire. although the chance of firing the plug, and not igniting the a/f mixture goes up.

2. wire routing. the spark plug wires should be routed so they are away from each other, and any of the other signal wires for ecu's etc. crossfiring between cylinders is very very bad, its like advancing the timing 90degrees....

3. mixture. gasoline is easiest to ignite, in a narrow a/f range, if its too rich or too lean its hard to get the mixture to burn. so too rich, is too rich.