Injector Replacement Detonation Blues

[Talamascan]

This thread started out as a discussion about injector replacement but now has kinda morphed so I'm starting a new thread.

I had a bad OEM injector on my 93J and my mechanic first tried flushing the system (which worked once before) but that had no effect this time, so I had him do the dremal method (i.e. no pulling of the upper intake plennum) to replace the thing with a remand injector. Everything went as planned and the car runs better than ever with one big exception, namely that it now pings consistantly on medium load throttle inputs (not so much on light or full throttle). Swimshark and Yoda came to the rescue by indicating that ethanol erodes the OEM injectors used on pre-95 models of our engines, but, after reviewing the recommended website, I suspect that what they might really have been saying is that the ethanol is the probable reason my old injector failed at only 100K.

Anyway, I've refilled my tank with premium from a different station and the pinging remains quite pronounced and, most importantly, hard to avoid on my daily commute. So, Swimshark/Yoda, assuming you see this, as for the ethanol issue, I'm wondering how its presence in the fuel would cause detonation even assuming it erodes our injectors. As for other possible culprits, could my MAF or 02 sensors have been injured by the flush and cause a lean condition? Could my knock sensor have been knocked off line by a simple flush, or could it be something as -- err -- obvious as my fuel filter being clogged from the flush?

I know that the simple answer to all of these questions is "could be, " but anyone who has actually suffered something similar is particularly encouraged to provide their experience. I'm particularly interested in hearing from anyone who has had a clogged fuel filter and suffered detonation as a result.

[yodawill2000]

Is the water temp normal ?
I'm thinking if the only thing changed was the injector, It may be the culprit.
Same cc rating as OEM ?

[Talamascan]

Yeah, I'm beginning to fear that as well.

Water temp is normal (a bit below the mid line at full operating temp). I know that the 300ZXTT OEM injectors are rated at 370cc but what are ours?

[yodawill2000]

Flow Rate : 270ccmin at 3 BAR - 80% Duty Cycle

[Talamascan]

The mechanic confirmed both that the remand injector has the correct flow rate and that the kit came with new upper and bottom O rings (which he installed). He also confirmed what I should have known, namely that the flush would not flow through the fuel filter.

[Talamascan]

Dollars to doughnuts I gotts myself a bad injector on board.

[swimshark]

by pinging do you mean its bucking or is it throwing a det sensor code? if it throws a det sensor code it will switch to a safety map and run super rich.

[Talamascan]

The car doesn't buck, throw warning lights or run rich.

Ever since I put the remand injector in lat week, the car has suffered from audible detonation at medium throttle imputs. Other than that, it runs great; idle is good, full throttle is good and the car shuts right on and right off.

Monday my mechanic: 1) removed the remand injector and put a new OEM injector in its place, 2) replaced the spark plug (which looked fine), 3) cleaned out the MAF, 4) checked the fuel pressure (which was fine) and 5) checked all the ground wires, all of which resulted in ZERO improvement with the detonation or anything else.

On top of that, my mechanic says can no longer get any code readings from the computer on his scanner so now he thinks that the ecu is the ultimate culprit, which I think may not be the case since the car is obviously communicating with the computer and visa versa pretty well except for during specific throttle applications.

Anyone have experience with bad ecu's in our cars, cuz that sure seems like an expensive proposition, particularly since ours differ from the 300zx.

[Talamascan]

If it's not the ecu, that raises the obvious question of why it's not pulling timing or switching to a rich mode every time the darn engine starts detonating. I suppose the knock sensor could have decided that this was THE perfect time to suddenly go MIA, leaving the ecu in the dark, but even then, it seems like the 02 sensor would signal a lean condition to the ecu and I'd get a trouble light.

Even if dremeling of the upper plenum caused a hole letting excess air into a cylinder, seems like the ecu would compensate and I'd get a crappy idle.

Sigh

[Talamascan]

Picked up some carb cleaner and sprayed all around the engine, and there are no vacume leaks. Taking the poor car to a different mechanic tomorrow. This one has me stumped.

[Talamascan]

Still further to my annoying problem (which amazingly has yet to manifest a "check engine" light on my dash), in researching on the 300zx forum, it turns out to be the case with their ECUs' that, while a faulty exhaust gas sensor circuit reading on either bank will trigger such a light, the same is not true with regard to a faulty detonation sensor circuit reading. How interesting and how odd at the same time.