Is it possible the TBI needs to be cleaned up? I don't know much about TBI's quite yet, but I'm planning on rebuilding mine just to make sure it's squared away. It's my understanding they get carbon build up over time and I can only imagine that it could affect performance?
Might be a simple suggestion? Kit runs bout $31 on RockAuto; might be worth a shot?
If the TBI couldn't be the culprit, can anyone explain why? I picture a choked up TBI in the same light as maybe a gunked up carb?
The TBI may need to be cleaned and rebuilt. ANYTHING can wear out.
Not real likely. They're less-complex than a 1920-era carburetor. No tiny fuel passages, no tiny air bleeds, the only drillings are for vacuum nipples and large fuel passages. Small passages are more-likely to plug than large ones.
TBI is about as reliable as it gets. Actual throttle-body faults are rare. Most problems are solved with aerosol carb spray on the throttle blades and the idle air control passage--or the problem is a bolt-on--the TPS sensor, the IAC motor and pintle assembly, etc.
Actually now that I'm re-reading this, I see that the OP replaced the injector spider with a BWD brand unit a couple years back. That would be my number one suspect here. It would be nice if someone could confirm a way to diagnose that properly (and I'd be interested to learn) but if I were going to fire the parts cannon, that's the direction I'd fire it in.
I'd start with measuring exhaust-runner temperature looking for a cool exhaust near the port. Cool means that cylinder isn't firing.
If that doesn't work, a simple cylinder-balance test, using professional equipment...or more-likely, a test light connected to ground, with the pointy end lightly greased and slid between the plug wire and the distributor boot. Shorts the spark to a single cylinder. Any cylinder that doesn't drop manifold vacuum (or doesn't drop it as much as the other cylinders do when shorted) is suspect.
I honestly don't know the difference between TBI or Spider Injection!
TBI injects the fuel ahead of the intake manifold. the air/fuel mix flow through the intake manifold, into the ports, past the intake valve. The intake manifold is "wet" with fuel. there is only one or two injectors, the engine cylinders share the injector(s)
Spider injection injects the fuel at the transition between intake manifold and cylinder head port. 99% of the intake manifold never touches gasoline. The intake manifold is "dry". Each cylinder has it's own injector--no sharing. The injectors are tied together in a plumbing nightmare to a central control system. An eight cylinder engine has eight "legs", thus "spider".
The updated system uses eight individual electric-solenoid injectors instead of the eight tied-together spider injection system.
I replaced a little over two years ago and and have put 60,000+ miles on them sense.
"I" would be considering replacing at least the primary O2 sensors.
But the voltage seems to be with the correct range. Is it possible for them to be bad and still give off the correct voltage?
Yes. Which is why I asked about cross-counts. If the voltage is good, AND the cross-counts are good...the O2 sensor is
probably OK.
I had an O2 sensor that worked great at low speed. Voltage AND cross-counts looked wonderful. At highway speed, the sensor gave me a false-lean indication, so the computer went pig-rich. Took me a long time to figure that out. A thirteen-dollar O2 sensor solved the problem completely--but not until I had a dozen hour of labor into testing EVERYTHING else.
