1991 Redtop SR20DET Misfire Diagnosing

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tehetti
Posts: 1
Joined: Tue Aug 12, 2014 6:43 pm
Car: 1990 S13 240sx Hatch - SR20DET

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I have a 1991 redtop SR, swapped into an S13. I just got the car back on the road and have been dailying it, since it was sitting in my garage for 6 months after getting into an accident damaging the front RH suspension. It misfires on startup, and anytime the car is off throttle or below 2500 rpm. It is fully stock, and has all emissions from CA installed.

What I have checked:
- swapped all spark plugs, BKR6EIX, gapped to 0.035"
- checked coil pack and wires, all OK.
- compression on all cylinders are 150-170
- intake leaks (with brake clean)
- Put seafoam into fuel tank and ran for first two fillups
- fuel filter and fuel injectors (voltmeter and visual check)
- disconnected the MAF sensor and started the car, only to realize it doesn't change the misfiring. Just ran rich.
- vacuum leaks/boost leaks (doesn't seem to have any)

On any deceleration in a gear, there is a slight squeak coming from the engine every time the car afterfires. When disconnecting the TPS sensor, there was no change in idle. However the TPS has voltage through its wires.

To note: the car had no misfiring issues prior to the accident, and through the accident the engine didn't sustain any damage.

If anyone else has any other recommendations on what else to try, I'd love to know. It's currently my daily and I have to drive down to Palo Alto in the coming month for work, which is a 9 hour drive in this car.

Many thanks :cry:


CrudeTech
Posts: 1
Joined: Wed Mar 02, 2016 12:08 am
Car: 1992 Nissan 180SX Hatchback w/ SR20DET redtop manual
2014 Ford Focus w/ leaky valve cover gasket and a warranty

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I had a pretty nasty misfire this spring because of the fuel pump. It wasn't getting a good clean voltage from up front. I never bothered to diagnose it, just hardwired it with a relay. Good clean voltage straight from the battery (trunk relocation came in really handy). The pump is running full speed all the time, but it's so much stronger. I even think it fixed a rich condition. Something to do with injector duty cycle.

Had another real bad one when messing with my new MAF install. The first one was burnt. It ran so rich it was smoking through the tail pipe with a catalytic converter installed. Changed the plugs, confirmed AFR with the wideband. No more misfire.

So yeah, check spark on all four cylinders, then check fuel pressure or fuel pump voltage.

User avatar
PapaSmurf2k3
Site Admin
Posts: 18997
Joined: Thu Nov 21, 2002 3:20 pm
Car: 2017 Corvette, 2018 Focus ST, 1993 240sx truck KA Turbo.
Location: Merrimack, NH

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Make sure your engine grounds are sound. Can you verify ignition and valve timing?


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