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Misfire Under Load

 
Old 03-16-2018, 10:44 PM
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Default Misfire Under Load

Car is a 1991 Short Nose Crank, 164k Miles, COMPLETELY STOCK

Backstory
Filled up with 87 yesterday after work and headed home. Getting off the highway I did a first gear pull to about 6500 (First time i've ever gone that high on this car, idk why, guess i'm just a *****) and then heard a rattling noise. Me being super paranoid went straight to thinking detonation from the 87, but then started to think rationally and thought it could be a heat shield rattle. The one on top of the headers is solid so i felt the one near the O2 sensor area and that one what most likely my problem, it moves a **** ton with just my fingers so I felt relieved and called it a night planning to get a clamp for it the next day.
Actual Problem
Today on my way to work I was about 15 miles into my commute when I heard the car get noticeably louder, loose power, and misfire pretty bad. Sounds like a subaru so i'm guessing it probably only running on 3 cylinders. I barely has any power. It already a 1.6 and now it even slower. Idle is slightly affected, I can notice a faint jump around but the tach barely moves. At idle the car does not appear to misfire but any throttle at all with cause the misfire. The car was running strong before all of this began.
Possible Fixes?
I am thinking maybe bad O2 sensor, Timing is off, Keyway Damage(I hope not or else i'll drop a match in the gas tank), or Coil Pack

I saw no Crank Wobble

Items recently Replaced
Timing belt, water pump and front seal kit from Treasure coast miata (Front Crank Seal was not replaced due to me being a Dumbass and trying to use a tirebar to get the timing gear off and chipping the crank gear. So i'm unsure of the current keyway wear but i got a new oem SNC key with the kit. I can post a picture of the crank gear if you want to make fun of me.)
Spark plugs and wires (Both NGK)
Radiator
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Old 03-16-2018, 11:02 PM
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Start with plugs and wires . Fredb
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Old 03-16-2018, 11:07 PM
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Originally Posted by fredb View Post
Start with plugs and wires . Fredb
I replaced the plugs and wires no more than 250 miles ago
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Old 03-16-2018, 11:50 PM
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Doesn’t mean theyre good. Throw the old ones back in , if you still have them and see if if makes a difference. Fredb
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Old 03-16-2018, 11:53 PM
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Originally Posted by fredb View Post
Doesn’t mean theyre good. Throw the old ones back in , if you still have them and see if if makes a difference. Fredb
The car barely idled on the old ones. They were so old. I dont have them anymore either :/
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Old 03-17-2018, 12:19 AM
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From your description, it sounds like a single cylinder acting up . That narrows it to plugs , wires or a injector. Plugs are the cheapest place to start. Make sure the plugs are all tight and the boots are fully pushed down on both ends of the wires too. A leak down test wouldn't hurt either but I'd expect a burned valve or poor compression to idle like crap. Fredb
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Old 03-17-2018, 12:31 AM
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I did a compression test a few weeks ago. It doesn't mean much now that this happened but the numbers from cyl 1 to 4 were 190, 190, 200, 200
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Old 03-17-2018, 06:08 PM
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Broken ring.
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Old 03-17-2018, 06:57 PM
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Originally Posted by sixshooter View Post
Broken ring.
Pessimist !
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Old 03-18-2018, 12:02 AM
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So with the engine running I pulled the wire out of each Cylinder one at a time to see if one would make a difference to the sound of the car but they all made the car sound like ****. I also took the cat out to see if maybe it was clogged/fucked but it was fine. When I tried to check the timing with a timing light things got interesting. With everything hooked up and the car in diagnostic mode (Ten to Gnd) the light would not flash. I thought maybe the Harbor Freight timing light didn't work but I hooked it up to my buddies miata and it worked fine. So I went back to mine and even hooked the power terminals up to a spare battery to make sure it was getting enough power and still nothing. Then I moved the inductive clamp to a different wire to see if maybe the number 1 wire wasn't firing right and the light started working working. So I moved it up and down the wire to see if the timing light would light up at all and then it started working in a certain spot so doing the best I could, I shined the light at the crank pulley and the timing wouldn't stay in one spot. But was also not flashing nearly as fast as it was on my buddies miata. So we were thinking it could be the coil pack dying and not having enough voltage to fire the number 1 spark plug with a powerful enough spark. Tomorrow i'm going to borrow a coil pack to see if that's the problem. My buddies car is a 1.8 so i can't use his coilpack...or can I? I honestly don't know. I'll keep you posted on what happens. Thank you for the current replies and advice.
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Old 03-18-2018, 10:41 AM
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Sound like you're on the right track , no you can't use a 1.8 coil. The 1.6 coils are different . Borrow one of your buddy's plug wires and try swapping that. A bad coil should be affecting cylinders 3 as well . (I think , it's been a while since I ran wasted spark ) Fredb
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Old 03-18-2018, 12:15 PM
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One the 1.6L NA, the coil packs rarely go out. It's usually the igniter module that dies.
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Old 03-18-2018, 08:23 PM
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Well I swapped the Coil Pack and ignitor from another friends 1.6 and there is no change. But we did figure something out, The louder sound and "Subaru" sound seems to be coming from a cracked header not actually misfiring, but were not 100% about the car NOT misfiring since its still super ******* slow and still has a faint boxer sound. Might take it to a miata mechanic and ask him if he might know whats wrong with it. If you know who "Mike the Miata King” is or “Miata Mecca” is on Ebay and Youtube he is based in my area.He personally stopped working on miatas and only sells parts now but his main mechanic that helped him work on the cars opened his own shop and still works on miatas so im gonna ask him to diagnose it and i'll just fix it myself.
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Old 03-18-2018, 09:04 PM
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New plan , pull the covers and check the cam timing marks . Me thinks something has skipped a tooth. Fred
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Old 03-18-2018, 09:28 PM
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Fuel? Pressure, or **** gas.
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Old 03-23-2018, 10:20 AM
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Well after a few days of searching for local parts I got an igniter and CAS for $50, swapped them in along with a new cas o ring, and now its running normal again! Then I retiming the engine since I replaced the CAS and now it runs and idles better than it ever has! Thanks everyone for the help!

Last edited by SpaceYeti; 03-24-2018 at 12:45 PM.
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