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Discussion Starter #1
I developed a missfire and since I've replaced all plugs with ngk platinums and bought 2 new sets of plug wires. New coils. Fuel pump. Fuel filter. New injectors and I can't find the miss. It no longer throws a code but it's a very apparent missfire. It's a 99 SL. I'm also on like my third set of plugs because I replace them every time I change another part. Any help would be appreciated. Ive also replaced the ignition control module.
 

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Not sure if this is any help as it looks like you've replaced everything but my old distributor Ford FE used to misfire a bit until I put the spark wires in the proper order. The way an old soul said it, "spark can jump from wire to wire" causing odd random misfires.

I've never ran into that issue with modern cars but it could be worth looking into.

Other than that if the car is in constant misfire I would check the firing order and maybe even the crack position sensor and make sure it isn't junked up where the sensor reads from the crank pulley?

Maybe this will help!
 

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did you narrow it down to what cylinder has the misfire?

to do so, while car is running pull off one spark plug wire, and see if the idle changes.. if it does, that cylinder is good, so reconnect it, and move to the next one... repeat untill you find the one that doe snot change idle.

after you figure out what cylinder it is, make sure everything is connected good, if it is, try moving the spark plug with another known good cylinder...start it.. did the misfire move? if not.. injector I wold try next.
switch an injector with a known good one, and if the misfire moves, you know its the injector etc.
 

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did you narrow it down to what cylinder has the misfire?

to do so, while car is running pull off one spark plug wire, and see if the idle changes.. if it does, that cylinder is good, so reconnect it, and move to the next one... repeat untill you find the one that doe snot change idle.

after you figure out what cylinder it is, make sure everything is connected good, if it is, try moving the spark plug with another known good cylinder...start it.. did the misfire move? if not.. injector I wold try next.
switch an injector with a known good one, and if the misfire moves, you know its the injector etc.
+1, follow this to narrow it down.

If it started right after doing plugs and wires, it is most likely one of those two things. Maybe a plug gap is way off?
 

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SDSU Alumnus
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What was the original DTC? If you have/had a random misfire, then it could be other things than the aforementioned suggestions. A few possible culprits include vacuum leaks (more common), MAFS (dirty or faulty), or even mechanical timing (less common but more symptoms).

You may also want to specify the source and brand of the parts that were installed.
 

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Discussion Starter #6
It ended up being an injector. For some reason I decidedly to pull the front fuel rail off and I pulled each injector out and they looked like they had a little dirt or sand substance there. Which is quite weird. But I flushed everything and cleaned the rails and she's good now. My other question is are all the o2s needed or just the rear most one. I am putting a set of headers on my car and they only have 1 o2 bung.
 

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3SNY - HondaTurtleFTW
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It ended up being an injector. For some reason I decidedly to pull the front fuel rail off and I pulled each injector out and they looked like they had a little dirt or sand substance there. Which is quite weird. But I flushed everything and cleaned the rails and she's good now. My other question is are all the o2s needed or just the rear most one. I am putting a set of headers on my car and they only have 1 o2 bung.
That will throw a check engine light on your car, unless you somehow get the software and NA Chrome ecu software, since the 99 ecu is flash able.

Sent from my HD1907 using Tapatalk
 

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It ended up being an injector. For some reason I decidedly to pull the front fuel rail off and I pulled each injector out and they looked like they had a little dirt or sand substance there. Which is quite weird. But I flushed everything and cleaned the rails and she's good now. My other question is are all the o2s needed or just the rear most one. I am putting a set of headers on my car and they only have 1 o2 bung.
You mean 1 bung on each? You need at least the primary (closest to engine) O2 sensors for each bank - so 2 total. One front, and one rear. Those are used for closed loop fueling. You dont need the secondary O2s that would be after the precats as those are used to monitor the cats (and not for engine managment), but not having them will throw a CEL as mentioned above.
 
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