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Old 01-20-2019, 02:27 PM   #1
Engmus
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SR20DET Miss Fire\Bucking

Hey Guys, looking for some opinions as these things are always hard to troubleshoot over the interbutts.

91 240sx\SR20 Blacktop Swap

Issue: Car bucks\misses after warming up at highway speeds. Feels like a misfire, although happens really sporadically.

Troubleshooting thus far:

TPS Reset - Good
New Fuel Filter - Good
New Spark Plugs - Good
Throttle Body\IACV Cleaned - Good
New Walbro 255 Fuel Pump - Good
Vacuum leaks - None detectable at this point, will continue to look.
Repinned CAS sensor wiring and replaced harness side plug - Good

I suspect at this point Cam Angle Sensor faulty or Igniter Faulty.

Anyone have any ideas? Things to check?
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Old 01-20-2019, 02:40 PM   #2
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sounds like a dying coilpack
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Old 01-20-2019, 02:41 PM   #3
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5k Miles ago I installed a set of SplitFire Coils, I have spare Splitfire Coil packs.
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Old 01-20-2019, 02:48 PM   #4
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clean the MAF sensor
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Old 01-20-2019, 03:00 PM   #5
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I had a similar problem, I think your next best thing to do is replace your ignition coils if you haven't already recently. I just bought a set of p2m's ignition coils for $140... very worth.
Also this is a long shot, but maybe check your brake calipers to see if they're sticking to the rotor, because that would make it feel like theres a boost leak or a misfire if its sticking bad. happened to me..
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Old 01-20-2019, 04:59 PM   #6
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What does wideband say during problems?

A misfire will show up on the wideband usually and verify it is actually a misfire
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Old 01-21-2019, 10:32 AM   #7
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Check your injectors. You might have one that is slowly starting to fail. You can do it with a multimeter, I forget what the resistance is supposed to read but they should all read about the same if they are all good so a bad one will be really apparent. I had one that was intermittently sticking closed and the reading was still way off even though it wasn't completely bad.
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Old 01-22-2019, 06:58 AM   #8
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Thanks for the ideas guys.

I cleaned my MAF and had no change, tested maf and it looks good.

This weekend i'll try swapping Coils, and check injectors.

I'll report back with my resolution when known.
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Old 01-22-2019, 11:05 AM   #9
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If your car is tuned check your rom chip. The same shit was happening on my car, I have solid mounts so the chip actually vibrated out of the ECU and was causing a faulty connection, my car would buck like crazy but idles no problem.I tried swapping MAFs, coils, plugs, etc just to find it was the damn chip.
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Old 01-23-2019, 03:48 PM   #10
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I had a really bad miss fire under load and if boost hit anything over 4psi. I replaced alt, coil packs, re did grounds, re installed CAS, adjusted TPS to factory spec and none of that worked. I Previously when first swapped the sr gapped the plugs to .028 or around that tried gapping them wider and the problem got even worse so I re gapped around .025 and all boost problems under load freeway speeds are gone no bucking or miss fire. something that simple haunted me for months until now. Hope that helps.
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Old 01-24-2019, 12:32 PM   #11
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Check grounds.

I had the one on the back of the head wiggle loose. Like mentioned above, sounds like coilpacks
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Old 01-28-2019, 01:21 PM   #12
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also if theres oil pooling by the coils can cause same issue...replace vavle cover gasket
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Old 03-08-2019, 07:50 AM   #13
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I wanted to follow up on this, my problem was my TPS.

Even though the TPS would set voltage correctly, as you opened the Throttle the voltage was all over the place, sometimes it would be fine, othertimes it would be really bad.

I replaced the TPS with a genuine unit from Nissan. Moral of the story...

Just because you check voltage on the sensor at idle, doesn't mean that as you drive the vehicle it isn't a problem, it could be somewhere between totally rekt and on the way out.

Thanks all for the input and great ideas.
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