Alright I finally got the injectors switched over! I'll put the log in with the others. Interesting to note, it seemed that with the injectors switched, the miss started off worse than before, but got better has the engine heated up. This is the opposite of before, where it tended to get worse as the engine got hotter. This may mean nothing, but I feel I should mention it.

https://drive.google.com/drive/folde...PAq38TguD09fPf

In response to Torqsplit: I have bosch III injectors on the car (yellow ones). This was brought up in the old forum in November, and became more or less the entire focus of that thread. Ultm8z helped me set new injector offsets among several other things, and I think I also adjusted the VE tables a little. It's a long thread and I can't remember everything that was done, but I think if there were issues caused by the switch to Bosch III's they would have been resolved.
It may or may not be worth mentioning that the first set of injectors that got clogged were also Bosch III's. The car has been running on III's for almost 2 years, most of which was before this began.

 

So I'm looking at the data.... I was hoping to see much leaner BLM fuel trims, indicating an injector problem on that side. The BLMs seem to be a little bit higher, but not by much (no matter which way I slice the data... latest sample, running average, running maximum). Maybe that explains your observation about the misfire being more prominent now before things get hot?

Doesn't seem to be a smoking gun justifying spending more money on injectors at this point.

I compiled the data into the attached pdf.

Shucks...

You do get some points in time where the BLM's shoot up to mid-150's in either case though. But in both cases, then it comes back down.

The only possibility is whether both sides go lean like that at the same time, such that the ECM reacting to the driver side lean-ness by adding fuel everywhere would have the same effect on the passenger side.

But if the passenger side goes lean by itself and the ECM doesn't see it, then you could have a lean misfire.

I don't know man... I'm not sure where to go from here.

 

What I do know is this: the car ran perfectly fine before. When it started missing, I removed the injectors and they were very visibly clogged, with debris in the injector baskets and piled up in the fuel rail. I remember it took a long time for me to figure it out because of the somewhat unusual nature of the misfire. That being a miss under moderate load that wasn't present at idle and cleared under heavy loads. At the time it was strikingly obvious the injectors were full of debris from a rusted sending unit. The lines were also filthy. Then I put new injectors on and let the car run a long time before trying to drive it. And when I did, the misfire was still there. It was not nearly as bad as before. But the symptoms / conditions were the same.

Knowing that something was wrong with the injectors when the symptoms began, and that the symptoms haven't changed, I am inclined to believe the injectors are still wrong.

I don't know, I was also hoping there would be some definitive proof. I could send a few injectors to be flow tested for cheap. Looks like injectorrepair.com offers $8 for a flow test or $17 for cleaning. They seem to get good reviews.

 

Yeah you may need to just bite the bullet and send them out. It doesn't look like there's anyway to get to root cause via more tunerpro data at this point.

 

As you mentioned its not present at idle or heavy load, it appears to rule out a fuel supply flow / lean out condition at full load. So I wonder what the injector flow test would reveal, 🤔 wonder if the smaller particles not caught by injector basket filters could have damaged the injectors? Even though you cleaned and blew out the fuel lines and used new fuel filter... Is an intriguing issue you are experiencing, I do not doubt Bosch 3 injectors. Have used them on my 85 the only difference they were 24lb and later use 20lb, only the fuel pressure is lower on the early C4 to compensate. Never had any issues in the 10+ years of running "reconditioned" Bosch 3 injectors in my 85, she ran great with Bosch injectors. Replaced my 91zr1 injectors with two yellow 20lb injectors per cylinder,one primary and one secondary and she runs super smooth at idle to 7000 + rpm. While most have great results with these stainless steel internals injectors, anything mechanical and electric can develop problems. Work one day not the next like a light bulb or intermittently show issues, I would think a flow test is warranted. It will reveal any issues in spray pattern or injector coil breakdown or injector pulse issues that could affect the injector during various fuel delivery requirements. Did you manage to get a long hose to confirm the fuel pressure never dropped during the times you noticed a miss? Even though you replaced the fuel pump they can start to fail intermittently, that would show similar symptoms of rough running. Had that happen on my 85 would run rough here and there but would suddenly run fine flat out, then it just died one day. Once pump was replaced she never did that again. So worth a try see if you can borrow a long fuel press gauge to stick to windscreen for a test 👍 Even a bad fuel pump relay could cause the pump to cycle off / on, while you should get an error code of low fuel pump voltage it depends where the fault is. Never showed a fault when my fuel pump was starting to fail, all depends where the ecm picks up the fuel pump voltage.
Hope to hear you solved it soon, and what it was injectors fuel pump or fuel pump wiring / relay 🤔 Think if the flow test shows a injector issue replace them for sure, if not look at fuel pump they are cheap don't forget to check the wiring connections at pump and the connector harness also the ground tab on fuel sender
​​​​​​ assembly. Good luck 🙂👍

 

Thanks for all the help guys, I do think I'm gonna go and get them flow tested. I'm thinking about only sending 4? I don't have lots of money to be playing around with, and considering tunerpro showed similar results on both banks I would think they're all in similar condition. I'm not 100% sure, It'll probably be a couple days before I get everything in order to send them out so if y'all have any thoughts let me know.
Alternatively I could just get them cleaned outright. The company says they will include before / after flow data so I can see if they were in fact clogged. Maybe I could send 4 to get cleaned and if the flow pattern improved send the other 4?
I'm trying to save some money but ultimately I'll do what needs to be done even if it's not the cheapest. Let me know what you guys think. I'll be away for a couple days, then I can get everything underway.

Once I do get the injectors cleaned, I won't be putting them back on the car until I can do something about the lines. Not sure what to do there, short of making new ones. If the injectors are clogged, evidently the particles were small enough to make it through the fuel filter and injector baskets.

 

If getting them cleaned / reconditioned, do all so you have confirmed flow matching and fully tried and tested injectors. that way you can eliminate them as the cause of your problems, I got a reconditioned set of Bosch 3 from FIC for my 85. They worked great for many years, FIC have reconditioned ones for $229.... However a flow test or clean will quickly show up any issues and save a hundred 🤔

Yes flush the fuel lines and fit a new filter, do confirm your fuel pressure does not drop of at any time. A long hose and pressure gauge is cheap, put onto windscreen to ensure you don't have any fuel pump issue. Remember I had a fuel pump cause similar issues, would idle fine but run rough and would occasionally run great at full throttle till it gave up and left me stranded. If the filter on pump is damaged the pump could ingest debris have varying flows, if your fuel pressure is confirmed to be stable then you can look elsewhere. The injectors are batch fired one bank at a time I believe from memory of TPI engines, Does anyone have an old set of working injectors for him to try?

I Have 16x 20lb accel injectors which had a couple of secondary injectors coils short, which blew the injector fuse however they got me over a hundred miles home when I replaced the fuse. There must be many with working spare injectors? Being in Aust the postage would be more than they are worth lol, have a link below for the FIC 22 lb Bosch 3 reconditioned injectors. Many here have used FIC with great reviews.
Yes it will be cheaper to get your newish set cleaned and tested I would get them all done to be sure 👍

https://fuelinjectorconnection.com/p...sch-design-iii

 

Sorry for the gap in posts, I've been away the past couple of days. I think I'll go through with getting these reconditioned. I'll do a better job cleaning the fuel lines, however long that may take. I've been busy this summer and don't have a lot of money budgeted for the corvette, so it may be awhile before I get all this done. As a result I likely won't post the results in this thread just because it will probably be dead and forgotten by then.
If the injectors come back and the flow data indicates they were clean when I sent them in, or if the problem persists after reinstallation, I'll get a better hose for my fuel pressure gauge and find out what the running pressure is.

If anyone has anything else to add, I'd be happy to hear it.

Thanks for all the help, I'm feeling a lot more confident now having gone through the car again and having created a plan of action for this. Hopefully I'll have it ready to go before the end of the summer.

 

Keen to hear if you find the cause, I have a similar issue with my '93. Starts and runs fine when cold but when up to temp it breaks up around 2000rpm, if you drive through this with heavy throttle it takes off.