Goddamn misfire
 

Alright, this stupid random misfire is driving me bonkers. I grounded the lead coil, changed plugs, set tps properly, but still... the fucker just keeps wanting to misfire... let me explain a bit more thorougly...

At idle, it rarely misfires, although, not unheard of. maybe about five times during a 2 minute period.

If you press the gas and hold it at about 1600-1700 rpm, it misfires randomly about once every 2-3 seconds. Higher rpms are perfect. Not a single misfire.

Under load, not a single misfire can be heard, and the power band feels very smooth with no hesitation whatsoever.

I'm at a loss!!! Vacuum leak? Intake leak? Boost leak???

Oh yeah, and the boost varies every once in a while. Sometimes it will go up 3/4 of the way, sometimes only 1/2. Same day, same weather, only a few hours later. I'll get an accurate boost gauge one of these days to help me determine whether or not its a problem with the instrumentation

Anyways, pls help!!

(glossary: by misfire, i mean a faint popping noise, followed by engine stumbling and bucking mildly. no particular pattern, very random)

Oh yeah, engine is a mazda crate motor with 20,000km on it.

should i try thoroughly cleaning the TB?

first of all both Rx7s I have owned has had the miss fire problem when holding the gas at those rpms....and even a little at idle....but it doesn't do it while driving and as long as the engine is running :)

so i'm not the only one *load off my mind*

But its still pissing me off lol :) and when i get my corksport exhaust, its only going to be more noticeable ;)

? misfire? as in popping noises at idle?

Fingers,
You have described my car EXACTLY. It actually frightening!! Anyways, since I know that I'm not the only one I suspect that quite a few people have this problem.

I have the same problem, but I've reduced the "misfires" by replacing the spark plug cables. It's really helped (1 to 10 - improved to about a 6, 1 being "no improvement" & 10 being "completely fixed"). But the problem still is there.

It's the same problem, at Idle it's good (happens ever so often) and at higher RPMs ( > 3500) no problem. BUT at about 1000-1500RPM I get "misfires"/pops (tach bumps up/down - < 50RPM).

I've replaced the ECU - still have the problem
Checked all the Vac. Lines
Changined the Spark Plugs

BTW - I don't know if this is a factor, but I have a 2.5" Racing Beat DP to a Racing Beat Prescilenser to custom made 2.5" pipes (No mufflers).

If anyone knows a fix please post it!

have you checked your coils?


BTW
are you still parting out the 87 T2.

yes i've checked my coils. I've improved the spark strength of my coils greatly since I started. But the induction timing light still does not work on L2. it now works perfectly on L1 and both trailing. (i HAVE tried to replace the coil, and the wires, and got the same results)... so L1 just doesnt want to use a timing light. I have no clue why.

bbbuump

im going to PM you about the T2 parts car.

Try reversing your timing light pickup on L2. Both front coils fire at the same time, its not possible for one to fire and the other not to as they are part of the same circuit. The polarity will be different from L1 to L2 and this confuses some timing lights.

Henrik
87TII

The only time I ever experience something like this is when I turn on the heater. The car sounds like it misfires and the idle drops to like 200 rpm every few seconds. When this first happened I thought I was losing a side seal, but it was just because my BAC sucks.

dude, i tried that, and i know how the system works, and trust me, i'm just as confused as you. the only other possibility is that the housing which has L2 is insufficiently grounded, and is therefore, not allowing a proper spark. but then again, why would the trailing 2 work fine?

Fark, i dunno. Its weird as shit. Any insight would be appreciated.

Looks like another symptom has been added...
when the car is not completely warmed up (1/3 of the way up the temp gauge), it seems as though it stumbles and hesitates at higher rpms under boost. Doesnt sound like detonation though. obviously, when I found out it was doing this, i immediately stopped accelerating and won't ever try to do that again til the car is completely warm.

Anyways, any opinions?

grounded the block, grounded the coils. Nothing. still misfiring slightly at idle, and frequently at 1000-2000rpm. past that, its fine. Under load, it's fine. Disconnected BAC, idle dropped. So bac is working. new plugs... ummm... i have concluded that my coil is working fine though. Tried unplugging the so-called "non working" cable, and car ran like a bag of shit... so that tells me that coil was working fine.

Anyways, still at a loss :S

hey guys, I have had the same problem and after my friend and I adjusted the timing, the car is rock solid at idle (*much* less 'misfiring'), and I was then able to set the idle lower and it was still smooth. The only problem is that even at the most backed-out point on the idle screw it's only idling at 800 or so. anyone know why that is?

I suspect after I get new wires (the ones on there are very old) and plugs, it will be running very smoothly.