BAD2000TA

iTrader: (6)

OK, I'm having a problem with my freshly built 383 LS1 (3.905" bore, 4.00" stroke, 224/230, .610/.605 114lsa cam). It's got a noticable miss or two and I'm trying to identify the problem. The plugs are new NGK TR55's, wires are new MSD 8.5mm's.

I bought a little spark indicator probe. It lights up when you hold to a spark plug wire. Anyways, on cylinders 1, 2, 3, 4, & 7 it shows a very consisent spark. However, on cylinders 5 & 6, it's very intermittent. Spark.spark.spark...........spark.spark.spark..... ......spark.spark.spark. About a second-to-second and a half gap between the sparks.

Would this possibly indicate that the coils are going bad? Or, is a coil either good or bad - no in between. Please help!!

Brian

LS1MCSS

iTrader: (18)

Swap one of the coils that you think might be going bad to different location and check the spark. If the results are the same, then the coils are bad. If not, you may have a set of bad plug wires.

Haans249

iTrader: (24)

I would first swap the wires lol, thats a little easier. I highly doubt its the coils. If you werent having any problems before, I don't think they'll suddenly have any problems now. Also, make sure the wires are seated properly.

blkbird

iTrader: (28)

Ive had three of my coils go bad. That was at about 30k miles.

99blancoSS

iTrader: (115)

swapping the coils around is quick and easy, great idea to try and isolate.

flirtnwithdisaster

iTrader: (6)

I would think it would be more of a ground or a sensor problem. 5 and 6 being across from each other I would pull the plugs and run a compression ck. Then ck the plugs to see if they are gassed or not. could be a vacum leak. I know you said the spark is irregular.

99blancoSS

iTrader: (115)

The easiest thing for him to do is turn 2 10mm bolts counterclockwise and swap the coils to another location. This will tell him immediately if its the coil or the location. then you work from there. Try the easiest first.

BAD2000TA

iTrader: (6)

I was planning on swapping the coils around later tonight. That was my next step. Just looking for some options to try. Very frustrating......

Thanks for the responses.

99blancoSS

iTrader: (115)

Sorry for your troubles but it shouid be fairly easy to isloate. You have the coil harness that connnects to the main harness with a 7 pin connector. There are only a few places for it to get messed up. Coils can go bad, it's unusual but it can happen.

Haans249

iTrader: (24)

Disconnecting two wires and switching their places i would think is the easiest thing to do, you don't even need to turn bolts. Plus, its possible that the wires weren't seated properly on the coils as well, so that would be another thing to check before you start moving things around.

Then the most logical step would be to move the coils. It would be really unlikely they went bad if the coils would work just fine one day, shut off the car, swap out plugs and wires, then suddenly they don't work anymore. Work backwards, by starting with the wires.

BAD2000TA

iTrader: (6)

No, it's not like that. I had a Comp 918 spring fail in #4 cylinder. Piston hit the valve, broke the valve head off, blew the piston apart, broke the rod in half, punched two holes in the block.

This is my new engine: 2004 LS6 block, 3.905" Mahle forged pistons (-6cc reliefs), 4.00" SCAT forged crank, SCAT H-Beam forged connecting rods, LS6 heads (.020 milled), Comp Cams 224/230, .610"/.605" 114 LSA, Patriot Gold valve springs and retainers.

So, the coil was still firing at the dead cylinder for a while (tried getting the car back to the house). The spark plug was smashed, along with the chamber. My thought now is that maybe by firing a million times at a dead plug, maybe that did some damage to the coil? Sound logical?

My point is that it wasn't like I was driving one day, then the next it wasn't working.

Lt1Porsche

iTrader: (6)

There is not much of a difference to the coil when you compare firing a live plug vs firing a dead plug. It doesnt matter to the coil. So no damage there. And parts DO just all of a sudden stop working. Thats what happens when they go bad. Make sure all your plugs and wires are tight. Moving plug wires around is stupid. If everything is tight. Move the coil pack around with a properly working coil. If the problem moves to the new cylinder, replace the coil. If the problem continues on the old cylinder check continuity between the coil and the pcm and make sure all harnesses are tight. There are no sensors or grounds that will drop a single cylinder. So if continuity is good with the engine off and with the engine running and continuity remains constant even when misfire occurs you need to have the PCM reflashed or get a new one.

flirtnwithdisaster

iTrader: (6)

explain why you have a engine that is running great. put under a load and it started missising. Ckd for spark it would hit every once in a while. swaped coil did not fix. Figured I might have a bad pcm. Turned out it was a crank sensor. Could have been a place on the relucter ring that was causing it not to reconize the pulse but replaced sensor and bam it started firing. So don't ever say it is not a ground or sensor until you have been there.

BAD2000TA

iTrader: (6)

That's very interesting. I've always thought that if the crank sensor was bad it would either throw a code or not fire at all. Very interesting......(wonder how much a crank sensor is???)

flirtnwithdisaster

iTrader: (6)

I would not go out and buy one until I checked all other options. This is a case that I had 2 weeks ago. I could not believe that this could have happen but it did.

Lt1Porsche

iTrader: (6)

A bad crank sensor would not make just one cylinder misfire. It would be a random misfire across multiple cylinders. If you have a general cylinder or 2 that are misfiring constantly then the problems are directly related to those cylinders not something like a crank sensor. He has cylinders 5 and 6 specificly randomly misifring not a random misifre under load. thats the difference. Also its not that the cylinder only has a misfire but the coil is losing spark as well so its either losing ground from the PCM or the coil is just not firing.

Lt1Porsche

iTrader: (6)

Oh and I have been there. Multiple times.

flirtnwithdisaster

iTrader: (6)

Is it just a luck of the draw or is it odd that the firing order is 18736542 and you see what is next to each other the #6 and the #5 if there is a problem with the reluctor ring or sensor it would affect these 2 cyls or in the PCM

Lt1Porsche

iTrader: (6)

The reluctor ring definitely possible. But not the sensor. If the sensor is malfunctioning it will more than likely misfire on other cylinders rather than only 5 and 6.

Haans249

iTrader: (24)

How do you know that it is only those two cylinders that are misfiring? It is not the reluctor ring, thats stupid, the motor wouldn't even fire.

Have you done a CASE relearn? I bet you haven't, and if you haven't, you'll have misfiring issues. You need a tuning program or the tech 5 to conduct the crank sensor relearn procedure. Do this first, and I'm pretty sure it'll fix your problem since you have a freshly built motor in there.

This will fix your issue.