try swapping the coils before you test with cleaned plugs

 

If one coil is bad, plugs in either 1-7-6-4 or 5-8-3-2 are different to the other circuit. If both ones are bad, all the plugs would have same colour, or they'd atleast differ in the above fashion.

Since I have fouled plugs on 5-6-7-8 only, I don't see how replacing coils, output stages, distributors or their attached hardware would help?

 

Still doesn't matter. The injectors are batch fired. That mean they all fire at the same time. You should not see any difference from one side of the engine to the other.

It's got to be cam related.

 

But they're batch per cylinder bank, right? What if there's a problem in ⅝ injector ciruit only?

 

No, on your car they are all in parallel. But they have seperate 12v feeds for 12v from W13 on the central electric. Check d.c resistance from W13 to each set. One set feeds Cyl 1-4 ther other 5-8.

There may be a higher resistance in one path...

There are junction points where each set of four injector feeds are joined into one wire that
goes to W13.

 

Update, seems like atleast my oxygen sensor is shot. It shows value of 0.05-0.10V (lean) and doesn't fluctuate at all.

I temporarily set the coding plug to non-cat and the car seems to run better other than idle which dropped, but that's probably because I don't have the potentiometer to set the idle mixture.

Gonna get a new sensor and see how it changes things. Testing this stuff is kinda slow though because it takes time for the boxes to adapt to new sensor conditions.

 

Okay, the oxygen sensor was a symptom, not the cause.

The car runs pretty good after the ecu's have been disconnected, but after adaptation kicks in it gets back to bad.

So, either adaptation instruments are bad (o2 sensor, MAF), or there's something in the fuel injection causing trouble which causes adaptation to think the car is running lean. o2 and MAF are both new or new'ish components, so I'll leave them alone for now.

Since I've timed the cams recently with 32V'er, I'm hesitant to blame cam timing on this. I can't rule out even mismatched set of cams though, since I didn't check the cast numbers when I installed them .

On the other stuff, I've been focusing on the bank that is running rich without much luck, but what about the other bank? The plugs are somewhat whiter than cream coffee, indicating burn on the lean side. What could cause this? Can FPR/dampers affect this in any way?

 

I'm not sure if I'm clearing anything up here, but it seems to me there's some mixing up of spark vs fuel when talking about cylinders & banks.

Each coil feeds one bank, so the passenger-side coil feeds cylinders 1-4, while the driver's-side coil feeds cylinders 5-8. Check page 343/418 of the PET if you don't believe me. So as far as electricity and spark go, if a coil is not firing, you'd see the evidence of it in cyls 1-4 or in cyls 5-8.

However, if the ignition monitoring relay in a MY89+ car sees that one bank was not firing properly, it will shut down the injectors to half of the cylinders (not the coil!) of each bank (I don't recall which cyls, maybe 5-8-3-2?)... the dreaded 4-cylinder mode that I've been wrestling with.

So Aatos, if you have fouled plugs in the driver's-side cylinder bank (cyls 5-8), then you may have an ignition problem on that side. Replace the coil, wire to distributor, distributor, cap, and spark plug wires. If they are firing but running leaner or richer than the other side, something in the fuel/intake system.

Good luck!!

 

Sorry, you are mistaken. If you look at the circuit diagram, it clearly shows "coil/distributor left" driving cylinders 3,6,5,2 with 1,4,6,7 driven from the other coil/distributor.

 

Umm last time I looked that statement was not true.... there is one coil per distributor... each distributor has 2spark leads running to the opposing bank...