Just got a 91 R32 GTS4 on the road last week, and having issues with breaking up. Im going to list the mods, the symptoms, what i have done to try and fix, and where its gotten me. Thanks to all the contributors the the board for the info thus far.
I got the car a few weeks ago, but have no way of contacting the owner. I bought it through a 3rd party.
HKS Pod filter (ripped rubber)
Some kind of replacement coil loom (looks like wiring spec)
-Car breaks up above 40% throttle. If i ease into it, itll pull until about 5000RPM. Cruising at highway speeds, the exhaust had a steady tone, with a faint pop every second or so. Gas Mileage is bad, but i also dont know how these cars drink gas when driving "spiritedly".
-Hicas light comes on, after a few miles of driving. I checked the PS Fluid level, and it seemed ok. The car definitely needs an alignment though, as the wheel isn't completely straight while cruising. Going to get new tires, then have an alignment done.
Popping the hood, reveals a removed spark plug cover. The ingnitor is "mounted" to the firewall with zip ties. 3 of the 6 stock coils had heavy heavy build up on the contact points. The plugs looks black, but not terrible.
I replaced the plugs with NGK Bpr6-11. Didnt change gap (probably will go to .08 when i install the new coilpacks.)
-This made the car run "different", not def better or worse. just different.
I ordered a new complete set of Coilpacks. While i understand that probably only some of them are toasted, i figured on a 25 year old car it worth replacing them all. The packs on the car still say Nissan on them. I have no way of knowing for sure, but logic tells me at some point the previous owner bought a new set of performance coilpacks with a loom. They discarded their stock loom. When selling the car, they reinstalled the stock coilpacks, but left the new loom in because the old one was gone. The spark plug cover is in the trunk. Half of the bolts for the coilpacks are missing, some only have 2 bolts holding the pack on. None of them have all 4 bolts. All the hardware for the plug cover is gone. (the cover is in the trunk however).
-Will put in the new coilpacks, and reinstall the cover and mount the ignitor to the top of the cover. I bought new hardware from local store to remount everything
The HKS Pod filter has a large tear in the rubber part behind the filter, but before the entrance to the maf. When i give it throttle, i can hear the air being sucked into the small gap. Different sound than typical....sounds like a suction through a straw.
-Will buy a new pod filter. Will probably try and duct tape the gap in the one i have now, to see if it will help. Obviously, this is not a fix, just more of a test.
The previous owner, at some point, had a different kind of MAF in the car. I know this because they added a 2nd plug to the harness, but never removed the original plug. They pretty much Tee'd into the harness, and made it so a different MAF can simply be plugged in.
-Will, carefully, open up the harness by the MAF and remove the 2nd plug. Solder and heat shrink everything. Im sure that having the 2nd plug there is creating a decent amount of interference and noise for the ecu to have to deal with. Adapter plugs are cheap enough now, that if i ever need to switch to a Z32 or whatever, i can simply do that.
If these corrections do not fix the issue, i will move onto installing a relay for the fuel pump and getting a new fuel filter. I will probably get a new fuel filter anyway, to just know its been done.
Any tips or suggestions are welcome. Thanks ya'll