2000 1.8 FM 2 kit @ 7 psi...MISFIRE HELP!!!
 

whats up guys, I'm John, new to this forum and needing all the info I can get on my recent miata purchase. It's a 2000 miata special edition with the old style fm 2 link kit running about 6 psi. I am having VERY intermittent problems with misfiring under boost. No ck engine light, new magnecor wires and ngk plugs at .030 gap, compression good, also brand new coils from mazda. Whats left to check, auxiliary injectors? My afr goes way lean from time to time. There is no rhyme or reason why it does what it does. Sometimes it pulls great and sometimes it just runs like shit. Has anyone ever dealt with a similar issue? I know this is the noob thread so if I need to move it somewhere else just tell me where. thanks in advance

Maybe the fuel pump is on its way out. Do you have a fuel pressure gauge you can watch while driving? I assume since you say auxiliary injectors that you don't have an AFPR?

What size injectors are you using.

My FPR is stock, I don't have a clue what the aux. injector size is. Note this car uses 4 stock injectors as well as 4 bosch injectors that are fabbed onto the upper mani.

I was leaning towards a bad pump as well, I have not been able to check FP while running as I would have to run a T fitting and a gauge, which I don't have. I am running the old style fm2 link kit. The car does not like to go into boost when cold, has anyone ever seen a fuel pump issue get better after 30 min of driving? I sure haven't. I have already changed the fuel filter with no change. The car has a walbro pump already. Think about this..... the car will misfire under boost and immediately my afr goes lean, now if I am losing spark that dead cylinder will essentially become an air pump and cause super lean afr's, correct? I am thinking of going to coil on plug for shits and giggles and see what happens. Maby I simply don't have enough spark Kv? thoughts? :idea:

No car "likes" going into boost when cold. If I were you, I'd narrow the gap on the plugs to like .025" and see what happens.

I will try that and see what happens, if it improves at least I will have narrowed it down to an ignition problem vs a fuel delivery problem.

If you were having a misfire, your AFR would go rich as the mixture is not igniting. I had this problem when going up to 11-12psi. I fixed that by gapping the plugs down to .020. If it's going lean on you, I'd still say it's fuel related.

I had to gap my plugs to .025 for 12psi with the FM2 kit. Also check the fuel filter if you think the pump is good.

messiahx, O2 sensors measure oxygen content, not unburned fuel, therefore if I had a mixture that was not igniting it would read lean. Very little oxygen in the exhasut gas = a rich reading, high oxygen = lean.

djp0623, already changed filter with no change, the filter was not clogged either.

I had a plug gap issues awhile back. The misfiring was happening at above 5k roms and at WOT. The misfire would range from a slight hesitation in the rev range to feeling/sounding like I had the car in neutral and bouncing off launch control. I did some datalogs but I had a bad WB02 at the time so AFR readings were useless.

Read this thread and see if it describes your problem

https://www.miataturbo.net/forum/t36757/

that thread sounds a lot like mine except for the fact that my car will continue to skip at IDLE after a longer 2nd 3rd 4th gear boost pull. I can rev the car up a few times and it usually clears up. This makes me think it is ignition related, the fm link only operates under boost. I have issues out of boost as well as in boost. I still have not ruled out a shitted up aux. injector. The car was sent to the paint shop so I can't do anything else to it until I get it back. I'm going to get some new ngks, gap em to .020 or so and get back to y'all.

bad injector is really standing out to me. My dad's pontiac had a dead injector before. We swapped out a lot of ignition related parts before we went to fuel and it was a dead injector. It drove like shit in the cold.

check that your harmonic balancer bolt is torqued up to the correct tension, if not pull off your harmonic balancer & check that it is not out of round where it goes onto the crank & also check the crank for wear where the balancer bolts up, if there is wear the harmonic balancer/ striker plate will move under load ie boost & you will loose ignition causing misfires. This was the problem with mine & chewed out my crank needing me to replace it therefore warranting a full build, i hope its not the case BUT its easy to check just by checking the balancer bolt & if it has the correct torque on it.