mr.mustang214

iTrader: (8)

So my 93 z28 recently started acting up a bit. If any of you have followed my build thread you may know i'm tracking down a rich issue on the drivers side. However, even with this the car still ran good. Last Saturday I drove it to a car show. Sat in the sun for the majority of the day (usually it's in the garage at home). Was roughly a 90 degree day with high humidity. Started the car to drive home and all seemed well. As i'm driving i notice it just feels gutless. The more I continue to drive I notice it sounds completely different, kind of like it's missing. Get it home and let it cool off. Haven't touched it again until last night. Pulled the ICM and coil off and had the ICM tested at Oreilly's. Of course it tested fine, but doesn't mean it's not acting up when it gets hot.

So put the ICM and coil back on. pulled all 8 plugs and double checked wires. Everything looks good. Go for a quick drive and seems to be running ok. Sure enough about 10 minutes into the drive starts doing the same thing. gutless and sounds like it's missing, but it still drives. I went ahead and ordered an AC delco ICM on Amazon and some heat sink to apply when I replace it. While i'm waiting on that to get here do you all have any advice or suggestions on what I could test that may be causing this issue?? I do have a ALDL cable and scan9495 (though i haven't really used it yet) that i could run some data logs if that would help. I just dont really know what i'm looking for

SS RRR

iTrader: (2)

Unplug your O2's and drive it around again. See what happens. Could also be a fuel pump issue. Check pressure without vacuum to fuel pressure regulator when it's acting up. Usually ICM's either work or they do not. You can test the coil:

http://shbox.com/1/4th_gen_tech2.html#opti_test

mr.mustang214

iTrader: (8)

What should i look for when driving with o2s unplugged? Will check fuel pressure as well. Checked it about a month ago for tuning but doesn't mean the pump isnt quitting on me. And i will definitely test the coil. Have been through shbox's website a few times but didn't notice that. Appreciate the help!

BALLSS

as SS...says the ICM generally is a work or fail.

having a FP gauge with a hose long enough to tape gauge to windshield so you can see what FP is when symptom occurs and at SUSTAINED WOT.

have the coil checked ....and don't rule out Opti

testing before blindly replacing parts is easier on your wallet...

fire up that scan software you have and check for any codes

SS RRR

iTrader: (2)

To see if it stops acting up. Driving while engine is cold the PCM is in open loop and does not use any sensor input. Once the engine is at operating temperature the PCM will go into closed loop and start making adjustments with sensor input. If you have faulty O2's it could cause the problems you are experiencing. Unplugging the sensors forces the PCM into open loop regardless of engine temp. If it runs fine while in open loop with the engine warm then most likely your O2's are bad. When is the last time they were changed?

mr.mustang214

iTrader: (8)

Makes sense. They were actually just replaced two months ago because I had to do a heated o2 conversion for tuning since it's a 93. I will try this for sure

mr.mustang214

iTrader: (8)

Ok couple things I've been able to check. Did the icm and opti harness test and everything came out good. Also checked fuel pressure at idle without vacuum and was 43.5 on the dot.

Also scanned for codes and there's nothing. Tomorrow I plan on running a data log to post on here to see if you all may notice something.

mr.mustang214

iTrader: (8)

Alright, took it for a drive and recorded data. It's just such an odd issue to me becuase it seems to idle fine, then you hit about 1500-2000 rpms and you can feel it sputter just slightly. I also noticed some backfires that I didn't get before this issue. If anyone could look at the file and just let me know if anything stands out i would greatly appreciate it. Just dont know if i need to just pull the opti and check it out or what.

mr.mustang214

iTrader: (8)

Anyone??

SS RRR

iTrader: (2)

Did you unplug the O2's and drive around until after the car got to operating temp? Can you read live data with that? If so, did you notice of the O2's were switching voltage quickly?

mr.mustang214

iTrader: (8)

Yep, o2s looked healthy while I was viewing the data. i attached the .csv file with everything in it. The numbers varied rapidly which from my understanding is how they are supposed to operate.

I haven't unplugged them yet just because i wanted to get a log with all the data first. I can still try that if it seems like they aren't operating properly

SS RRR

iTrader: (2)

You need to unplug them, drive around and see if your car acts up.

mr.mustang214

iTrader: (8)

Well... I'm embarrassed but I finally found it. Somehow I had missed a spot on the wire for cylinder 5. Was cracked right by the header. Put a replacement wire on an everything cleared up. I do appreciate everyone's input! This stuff can get frustrating for sure

SS RRR

iTrader: (2)

How did you find it? One easy way is to run the engine with the hood up in the dark, rev and see if you can see arcing anywhere on primaries/manifolds.

mr.mustang214

iTrader: (8)

I sent my data log to Solomon as well and he said the issue was in the drivers side alone. Which all along it has ran rich on the drivers side (possible leaky injector), but he said the readings were all over the place and showing very lean as well. So I just decided to double check everything on that side again just to make sure it wasn't something obvious. Sure enough, it was.

I went ahead and ordered a whole new set of plug wires just to be safe. I will definitely remember to run it in the dark to look for any arcing. That would have solved my problem from the get go, but this is my first LT1 and i'm learning as I go. This forum and shbox's website have been a tremendous help. All along I've been told to never buy an LT1 for that "shitty optispark." But this car was just too good of a deal to pass up, and truly hasn't given me that much trouble.