Horrible Missfire...has me perplexed
 

Hey guys, I posted this on M.net too but thought you all might also have some insight....Last weekend it was the throwout bearing and slave that I had to replace and now this, grrrr its annoying.

So I was on my way to work today. Car seemingly fine for about 15min of driving. I was cruising at 70mph and all of the sudden the car starts to missfire BADLY. Feels like its running on 3 maybe 2 cylinders. The car will still run and will decelerate while in gear just fine, but if you try to maintain speed it misses horribly, and when I accelerate it takes about 40% throttle just to get any kinda forward motion and still with a terrible missfire. Car will rev pretty well in neutral but will not hold steady rpm, it idles but with a huge missfire and barely stays running @ about 200rpm. It honestly sounds like one or more of the cylinders is not firing, I recently changed my coil pack to a low mile unit and its been fine. Here are the list of things I am going to check tonight when I get off...

1. Test Coil Pack
2. Check Coolant Temp Sensor
3. Replace Plugs ( they are 5k old )
4. Check/Test CAS

Just so you guys know Im still running my stock 1.6L ecu. Normally when something like this happens its an IC pipe or something that has come loose. I checked all my IC connections and they seem to be tight, so I dont believe there to be a leak there. I took off the AFM and the turbo compressor blades are not damaged in any way so thats not what it is. I was thinking that it could be fouled plugs, or bad gas. I filled up about 15 miles ago and then this problem arose...however I was nearly empty when I filled up so I would think that If it was water in the gas I would have seen problems right away. It is possible that the plugs are fouled too, the wires are about 15k old and are NGK so I wouldnt expect them to be bad already. Any help would be great, give me ideas so I can check all this stuff tonight. Thanks guys.

Probably improperly fitting tires, I'd say. ;)

Sorry, I have nothing useful to add.

LOL, yeah those damn tires fucked everything up.

Maybe a split coupler.

So let me get this straight, the misfire happened suddenly and at a consistant pace on the highway. Since then it has been doing this the entire time you are driving?

I dont know if fuel pumps go bad suddenly, but check your fuel pressure and make sure its not leaking fuel. Check your timing with a timing light. Check your main fuses, check for intake system leaks ... but i find this doubtful as you werent even boosting at the time.

If that doesnt reveal anything, there are only so many things that could go bad suddenly including CAS, AFM, and ECU.

Something in my gut tells me you have an AFM issue. People in the MS section could tell you how to test it with a multimeter.

could be, i checked them all and they seemed to be fine, Ill know more when I can get the car home and take a look at it.

Yes these things can be sneaky.

well I thought about the AFM, so I took it off to have a look at it. It had a little oil residue on it but thats it.

Did you throw a code?

lol my engine light is always on;) has been for 4 years.

well reset it and drive for a bit and see what codes it throws! It would almost definitely tell you about a MAF failure

update :

Car runs fine under boost at anything over ~30% throttle, but when asked to idle or run under 30% throttle it just runs like shit. It will not idle w/o me keeping my foot on the gas, and sounds like its on 2 cylinder until I give it more gas then it runs fine. It also decelerates fine too.....I dont get it

https://www.miataturbo.net/forums/sh...ighlight=alive

Sounds very familiar

Ahhhh, yeah I can pull apart the AFM tonight and see whats going on with it. I am still running my stock ecu but its possible that the AFM just took a shit, it is 20 years old now.

i had a similiar problem when i blew out the peice of broomstick i had pluging up my aic check your hoses for vacuum leaks as well as you couplers. also it couldnt hurt to pull the plugs and make sure they are straight. FPR hose, AIC, leak on AFM, coupler, plugs, how much throttle boost do you need before the peiburg goes out. i have a 190 here if it turns out to be your fp let me know.

Check your fuel pressure regulator for a diaphram leak... I suspect your are sucking fuel through the vacuum line into the intake manifold.... uber rich without boost = misfire.

The FPR seems to be fine, the line is dry and devoid of any fuel.

I just fixed it, the little bolt that held down the spring in the AFM was somehow gone. So i just tightened the spring and put a little bolt in it and VIOLA! The car now runs better than it ever has. I think it was loosening over time and this morning it just went VERY loose and thats why it wouldnt idle or anything. But yeah, I actually made the spring a little more tight than it was originally so now it runs a little more lean under full boost, which is good since it was running pig rich for a long time

I had a feeling it might be the AFM ... and no i dont check this site 80 thousand times a day, I just happened to get home a few minutes after your post :P

haha, its all good man. Thanks for your help I appreciate it. I was so fucking pissed that I couldnt figure it out, then it came to me. Im so so so smart guys, I really am:gay: