Sputtering at low rpm and massive loss of power, sudden onset and persistent

Question

Vehicle:

• 1994 Nissan Sentra
• GA16DE engine
• 4-speed automatic transmission
• 298,400 km

Recent Work (3 months ago):

• spark plugs
• spark plug cables
• distributor rotor
• distributor cap
• cleaned K&N reusable air filter
• cleaned MAF sensor
• taped up superficial cracks in the air intake tube (with electrical tape)

Symptoms:

Car's been running great ("better than ever") for the past 3 months. Saturday night while I was returning home, the car started sputtering when I stopped at a traffic light and has been down a lot of power (I'd say 50%) throughout the RPM range. The car shakes at idle, and it's worse when in gear at parking lot speeds, the transmission still upshifts and downshifts when you would expect it to and there are no unusual engine sounds. It feels like a persistent misfire.

I was running low on fuel when this started, and I was on my way to a fuel station (I thought I may have pushed the fuel too far and suffering fuel starvation). Filling up didn't fix the issue, but it did reveal I had 1.3L left in the tank (there's usually 3-5L left when I fill up).

Troubleshooting done:

• battery reads fine (12.6V with car off)
• alternator seems fine (14.0V at battery terminals with car on)
• nothing obvious is disconnected
• air filter looks fine

I suspect I may have aspirated gunk from the bottom of the tank which may have obstructed the fuel filter. I picked one up and will install it after a quick lunch. My question is: what else could it be? Specifically, ever since those new parts went on 3 months ago, I've been hearing a whine at high rpms. I didn't think anything of it, could it be the air intake gasket leaking?

Update #1: Changed fuel filter, read spark plugs and performed compression test. Spark plugs read fine (to me), compression test was even (130-140 psi) across all 4 cylinders, test drive showed slight improvement, but still down a bunch of power and shakes at parking lot speeds.

Update #2: Performed the water sizzle test and found a dead cylinder (#1), then confirmed it with a surface thermometer. In the amount of time the other three cylinders were getting up to 140C, #1 was still sitting at 40C. Timing light confirmed all 4 cylinders are getting strong regular spark, so it's most likely a fuel thing. Bad injector or bad electrical connection to the injector?

Update #3: Removed upper plenum, air intake hose and throttle body in order to access and detach the fuel rail. Disconnected all 4 injectors and performed resistance test: #1 reads open, #2 and #3 are reading higher than spec, #4 is reading way higher than spec. I'll be replacing the entire set. Question: the friggin little plastic clips that hold the electrical connectors onto the injectors snapped. Just the clip part, not the overmold part. Any suggestions besides zipties?

Answer 1

Swap your injectors on cylinder 1 with another cylinder. That will tell you whether the injector is dead/clogged or if it is the wiring going to the injector. Typically it's not too bad to remove an injector on these engines, certainly DIYable. If cylinder #1 starts firing with the injector from the other cylinder, you know you don't have a wiring issue.

Great work getting this far on the diagnosis!

Answer 2

As Paulster2 suggested, it was a dead cylinder, caused by a faulty fuel injector (see question update #2 and #3). As suggested by Justinm410, the injectors aren't too bad to reach on this engine and are definitely DIYable. I did have to take the intake manifold, throttle body and air intake off in order to have good access to the fuel rail, just to do the electrical troubleshooting.

The fuel injectors on this engine are pressed through the fuel rail and only held on by a little horseshoe clip, itself held on by 2 Phillips screws. Y'all can probably imagine what happened when I tried to remove these screws after 23 years and 298,400 km. Yup, the Phillips head got chewed up pretty good as the screw was seized in place. I used locking pliers to crack them loose and then unthreaded them. I replaced them with thread-matched bolts with a hex head, my favourite.

As for the electrical connectors for the fuel injectors, the plastic clips snapped off all 4, I now have zipties holding those connectors on. Nothing says DIY mechanic like zipties. I only ended up replacing the single faulty injector, I'll do the other ones if and when they go. I have my eye on #4.

And now, to go for an extended test drive, as I missed my little baby this week. :)