Different Cylinders Missing, Thinking Injectors

[ThisIsSparTTa]

A quick background, I bought my 91 TT about 1500 miles ago, and it now has 166k miles. When I did, my local Z shop identified a bad injector on 6 that I had him go ahead and do via the dremel method. I have no baseline for comparison, but after this she was running pretty solid and had lots of good pull.

Previous owner didn't understand what had been done to the car, but here's what I've found, if it helps: Intake, Flashed ECU, Boost at 14 PSI, AFC, Down-pipes, performance cats and catbacks.

About a month ago she starts to run really rough. Initially it was backfiring, low power, etc. Initially, did a power balance did test and found problems on 3 and 6, also when playing with the PTU sub-harness I found that the engine nearly died. I cut the engine to visually inspect the PTU sub-harness, and after it wouldn't crank, I played with sub-harness some more and it cranked again. At this point, without changing anything it was running normally again (no backfiring), so I chalked it up to a problem with the PTU-subharness that needed to get fixed. A few days later it started running like crap again, doing the same stuff minus the backfiring.

First thing I did was cut the PTU-subharness connector and directly solder the wires together per advice from my local Z club and Z shop owner. I no longer get the engine dying etc when moving the cable. Also, for future, I check the voltage on all the coil connectors and was getting ~13V, so I think they're getting power.

However, engine is still running terrible. Now power balance is failing on 3 AND 5, but 6 seems to be okay. The spark plugs were in an unknown state anyways, and likely had at least 20k on them based on when the previous owner did their last batch of maintenance, so I got some PFR6B-11Bs (which is what it had previously), and replaced them. Problems remained on 3 and 5, basically the same behavior.

Swapped coil pack with 3 and 2 (opposite sides) and problem remained on 3, and 2 seemed fine. Also quickly tried 2's coil pack connection on 3, and it didn't seem to do anything. Didn't bother swapping 5 after this. As I noted above, I also measured all 6 coil pack connectors and found them to be have ~13V on the left and middle terminal.

I ohmed the front 4 injectors (didn't feel like pulling balance bar tonight), and 1= 24ohms (high, yes I know), 3 = 45ohms, 2 = 12ohms, 4 = 14ohms. I will note that listening to 5 with a mechanics scope sounded VERY weak compared to the others. 3 did sound okay.

Where I'm at right now, I think its time to replace all 6 injectors (I'll just replace the one already done to be sure since I'll have it off, and it was having an issue initially on power balance test). However, I think it is weird that the problem moved from 6 to 5, which is the only thing that makes me hesitate. I think its pretty clear 3 needs a new injector, 1 is a little high, and 5 also looks like a bad one. One last quick note, I checked ECU after problems began, and there were no codes, haven't tried again since then. Is there anything else you guys think I should give a shot first? Any other advice?

Thanks for the long read, figured it would be easier to give all the information you guys always ask for up front rather than in pieces.

[t.mcginley.jr]

Definitely sounds like a new set of injectors is necessary. When any of the injectors start failing, it's only a matter of time before other ones do, as you can tell with the weird issues you're having.

You might as well pull the plenum to make the job easier. While you're in there, you can go ahead and replace all the fuel lines with fresh ones. You can also do the throttle body coolant bypass if it wasn't already done. When you replace the injectors, make sure to get new lower intake seals and o-rings:

http://www.z1motorsports.com/product_in ... ucts_id=47

Also you should verify which injectors you actually have in there, are they stock or higher flow?

[ThisIsSparTTa]

....

Also you should verify which injectors you actually have in there, are they stock or higher flow?

Thanks for the confirmation!

And your question is a million dollar (okay, ~$600) question. I was going to make up a second thread once I got the confidence to go through with the injectors. The purple on the injector is very dark, very similar to the 555cc shown here: http://z32.wikispaces.com/Fuel+Injector . But, then the article goes on to say that the lighter purple 370CC turns darker purple pretty quickly. It goes on to talk about the dots, but I didn't see any dots on the 4 that I was able to get to. The injector definitely isn't brown/green like they describe the older 370CCs to discolor to.

I'm game for going to a the 550CC if I do have the 370CC, even if it requires an ECU flash, but I wanted to do some more research on that first.

[t.mcginley.jr]

You mentioned in the original post that it has a flashed ECU. Is there any sticker or indication on the ECU itself that says what size injectors it's tuned for? There might also be a sticker on the eprom chip itself, but you would have to open up the ECU to check.

It's kind of hard/not accurate to go by color because of the large variety of injectors available. Do you know if they are new or old style injectors though? Old style will have very square connectors, whereas newer style will have more oval shaped connectors.

[ThisIsSparTTa]

You mentioned in the original post that it has a flashed ECU. Is there any sticker or indication on the ECU itself that says what size injectors it's tuned for? There might also be a sticker on the eprom chip itself, but you would have to open up the ECU to check.

It's kind of hard/not accurate to go by color because of the large variety of injectors available. Do you know if they are new or old style injectors though? Old style will have very square connectors, whereas newer style will have more oval shaped connectors.

I'm fairly confident in them being the old style being that its a 91, the connector looks like the old style, and the angle that the injector connector had. I'll have to recheck the ECU when I get home. I know it has Jim Wolf's name stickered on it, so that's a good thought to see if there's more info.

I'll try to take some pics of the injector soon, but they're probably not going to be great due to the location of the injector. I may still decide to make another thread because I have a couple of other questions about going for larger injectors that I wasn't finding last night, but I need a chance to do some more research first.

[ThisIsSparTTa]

Update for anyone following along, I checked out my ECU and EEPROM and pulled the following 2 pics off it from when it was flashed. I didn't see any information on there that indicated the injector size to me, but I've emailed Jim Wolf through his website hoping that they can pull up information from maybe a serial number or other that will tell me what injector size they flashed the ECU for. If interested here's pics:

[t.mcginley.jr]

That's surprising that the injector size isn't on any of those stickers. Since it isn't I'm leaning towards them being stock injectors, but hopefully JWT can look it up.

[ThisIsSparTTa]

JWT got back to me in a little over 12 hours, with a response that helps me out tons. Kudos to them!

The JWT program number on the label on the EPROM (9450J.D2C) is for a 1990-94 300ZX-TT with 555cc injectors (early style not later yellow 608cc) and a single Pop Charger filter set up (one filter in front of the MAF and the factory "Y" pipe behind it).

Great news for me! I can just drop in replacement 555ccs, and not have to worry about the rest of the things that come with upgrading injectors.

[t.mcginley.jr]

Nice!! It's always fun learning that you actually have more upgrades than you thought haha

[ThisIsSparTTa]

Yea...but I've had a ton of free time at work today, and I'm finding the 555CC injectors are $1200 per 6, which is a bit shocking. Considering they would not be pintle-less, its looking like it would almost be cheaper to go with a newer style pintle-less, even with whatever adapter I'd need plus another ECU flash for whatever size I ended up with (615 or 740, maybe). Plus the fact that basically all gas stations have ethanol now, its probably only a matter of time before the injectors crap out again, and I don't want to be spending that kind of money on injectors any time soon. I'm probably going to do some more research, and then get people's opinions of my different options. This is looking like more money than I was thinking I would need to spend, and if I'm going to do it, I'd rather put in something that's going to last longer.