mattyp716

I have a 2004 RX-8 MT with roughly 130k miles on the clock. I got the car around 10 months ago and it ran fine after doing all the regular maintenance needed. Around 4 months ago it began having trouble starting, so I replaced the original starter motor with a more powerful one and that seemed to solve the issue.

Now recently it is throwing a CEL saying there is a misfire. Even with the powerful starter motor and a powerful battery, it struggles to start even when at a cool temperature (not cold, live in Florida). My mechanic suspects it might be the ECU/PCM causing the misfire but I have never heard that issue before.

I have replaced the sparks, the leads, the coils are fine, I have cleaned the ESS and the MAF, and it has a gutted cat. The engine was rebuilt not too long ago and I believe the compression is fine. I have done all the ECU/PCM resets that I know of and still misfires. When putting the inductive timing light on the leads, one coil fails to spark, even when switching around the coils, the same one consistently will not spark (I believe it is #1).

Sorry for the wall of text but does anyone have an idea what this could be before I spend a windfall on getting a new ECU/PCM and programming? (which might not be the problem)

200.mph

iTrader: (9)

you need new coils

mattyp716

Could it really be as simple as that? My mechanic said the coils are fine, I'm not sure how he checked them though.

200.mph

iTrader: (9)

the ignition in the rx8 is kind of a weak point. many will say 30k miles is the most you get out of the system. i would replace mine every spring (non dd car). a flashing cel is a misfire and 99% of the time its ignition related. its best to change all four plugs, wires, coiles together.

mattyp716

I will go ahead and change them but I'm not sure if I wrote that correctly, to elaborate:

The coil that is in position 1 will not fire, even when moving a coil from say position 3 to position 1, the coil that fired in position 3 will now not fire in position 1. And the opposite is true also, the coil that didn't work in position 1 now works in position 3.

200.mph

iTrader: (9)

oh well thats a different story. not sure but i would check the harness for that coil

DAT2RTR

Now the real fun begins

RIWWP

iTrader: (2)

2 possibilities:

1: The rare answer is you might have a harness problem specific to that coil.

2: More likely, the discharge route for the electrical pulse is busted. Like if you move the coils, but the plug wire for position 1 is broken, or it's not actually clipped onto the plug, or the plug it's clipped on to is internally damaged (it happens, especially if the wrong tools are used for installation). In other words, the coil is charging up fine, but there is no complete path back to the battery or alternator for that coil's charge to let go. If it was all coils, i'd say it's a grounding point. Just one coil and the only unique path is plug wire and plug (and harness noted in option 1)

wcs

iTrader: (2)

How are you determining the coils are or are not firing?

You can buy a HEI Ignition tester from Amazon cheap.
TeamRX8 has a thread somewhere on it and how too.

Also if I recall corectly only the Trailing Coils fire during cranking.
... maybe someone else could confirm or flame me on this last point.

mattyp716

What would you recommend doing RIWWP? Getting all new coils and leads? Or do you think it's worth looking into a new harness?

mattyp716

wcs, It was a month or so ago now so my memory might be a little hazy but I took it to my mechanic and he used an inductive timing light on each of the leads and it showed that it wasn't sparking, or sparked intermittently.

RIWWP

iTrader: (2)

First, check the plugs to make sure they all work right. Then check the wires to make sure that they are completely seated on each plug and each coil. That's the cheap/free options, and also the most likely source of the problem.

If you know how to use a multimeter, you can use that to help validate plug wire integrity and spark plug internal integrity.

If that doesn't solve it, move your multimeter to the coil harnesses, and test to see that all 4 harness connectors are reading the same for all pins.

You will uncover the problem somewhere in there, and only then would I bother making purchases to address the problem found.

If no found problem, then i'd revisit the symptoms, carefully paying attention to make sure that I understood them correctly and there isn't any other consideration that was missed.

wcs

iTrader: (2)

Ya I've used that trick as well.
I don't think it's as reliable as using the correct tool.

Here's the thread I was referring to -->> https://www.rx8club.com/series-i-do-...-wires-222641/

RIWWP

iTrader: (2)

A timing light tests the coil, the wire, and the plug all at once. If it works on a timing light, then all 3 work fine.

But if you have a problem, a timing light doesn't identify which of the 3 pieces is the problem. The spark tester WCS pointed out tests the coil and the wire, but not the spark plug. But between the two tools, it's easy to narrow down, swapping wires on coils as needed, or confirming that the wires and coils are fine so it must be the plug.

mattyp716

Thanks for the help RIWWP, I'll test it out later when I get some time to work on it. Hoping for it to be something minor.

mattyp716

And thanks for the link WCS, that's extremely helpful.