Hey Guys,

Long time lurker here, finally got another Z and decided to post. (And yes, I did search)

I have a couple running condition problems with the 94 Z28 6M I just picked up yesterday. I've put 250 miles on it and it's been talking to me... I was hoping you guys could help me decipher what it's been saying.

1.) It has a low rpm, low load stumble when cruising occaisionally.
2.) It has a mid rpm, high load stumble/cut out when accelerating. Again, occaisionally.
3.) It breaks up over 4800 RPM or so.
4.) SES light is on, sometimes. But it doesn't blink, just steady.

So... I know I should scan it. I have a cable for my old OBD2 car, but am waiting on the OBD1 cable. Autozone can't scan OBD1, so I gotta wait.

So here's my guesses:
1.) Poss EGR (but that's usually just off idle, right?)? Opti? Dirty TB?
2.) Bad wires? Coil? Opti?
3.) Fuel filter? Dirty injectors? Opti?

I see a recurring item there... I hope I'm wrong.

Right now it has a pretty severe exhaust leak at the rear of the driver's manifold. The very last bolt is missing, discovered it before I started the car this AM. Hopefully it just fell out and it's not broken. That may be causing it to run a bit rich, but it doesn't smell rich. Car idles high, too. Like at 1200 RPMs.

I have to wait til this weekend to check things out, but I'm looking for a little input to see if I'm on the right track. I was planning an oil change, TB cleaning, and general inspection for Saturday morning. Will problly need a complete tune up, as I think the wires are factory original...

So what do you guys think?

TIA!

 

C'mon... Nobody has any help to offer?

I went under it this morning and it has MSD wires on it, so at least those aren't the original ones. I also had it running in the dark garage last night and didn't see any fireworks.

Could the problem be the ICM? It seems to only happen when it's warmed up. And the mid rpm stumble happens under mild acceleration, it also makes my manifold exhaust leak go away while it's happening and the tone of the exhaust changes.

Any help would be appreciated.

 

i think your first investment with the new car should be a repair manual. it will tell you how to probe all of the sensors and what all of the readings should be. i would not go and replace anything until you know its bad, or unless you know that its lived its life. the ICM typically will work or it wont. dont let everyone give you the "opti scare." opti's work and the work good for the most part... just keep them dry.

congrats on the new toy

 

Picked up the *shudder* Haynes manual for it at Autozone last night. Keeping an eye on eBay for the real thing.

Thanks, it'll be fun once I iron out all the wrinkles.

 

Well it sounds like ignition to me, and could likely be the opti, because it happens at low, middle and high RPM. Before shelling out for an Opti, or anything else for that mater, I would do two things:

1- Buy a shop manual.

2- Get it scanned, or buy a scan tool.

I know its a hassle but An Opti for you car goes for well over 300 bucks, and the above would be a minimal investment in comparison.

 

Here's the "real thing" on EBay:

http://cgi.ebay.com/ebaymotors/1994-...spagenameZWDVW

No, I'm not the seller, just trying to help you out. This guy always sells the 93-95 books...never see the 96 factory manual.

As for all your possible causes for stumbling...yes, yes, yes, yes. It could all contribute. I, myself am a victim of stumbling, and if you do a search for "stumbling" or "hesitation", you'll see your not alone by any means.

Me, changed plugs, wires, opti. I scanned mine and showed a "slow switching", "slow to heat up" driver side O2. This is weird, since it's relatively new when I installed my headers, but will target that first.

Keep the board updated if you fix your stumbling issues...there's lot of us out there that would like to know.

 

Scan it. Header bolt is probably stripped or something. I guess exhaust leak already did enough damage to O2's, that even quicker fouled plugs, which causes miss. So, fixing leak + changing plugs/wires and O2's in my opinion will do alot for your car. Clean MAF, replace fuel filter, etc.

 

Great suggestions guys, thanks. keep 'em coming!

Funny thing, I had that auction in my watch list already. But I got my 91 Custom Cruiser FSM for 15 bucks and my 96 Fleetwood FSM for like 40 on ebay, so I'ma keep watching for them.

Another scary thing I noticed from the PO was that he changed the injector fuses in the underhood box near the driver's headlight to 15 amps. They are supposed to be 7.5 amps. I don't know why he did that... I was afraid to change them back right before I took it to work. I'll have to check it this weekend.

I have ordered the "half" cable (I already have an OBD1 swap cable) from www.akmcables.com and am just waiting for it to arrive so I can scan it with Tunercat.

I'm aware at the cost of the opti and would like that to be last on my list of replacements... I come from the B & D car world, so I am very familiar with this drivetrain. He11, I even put a T56 in my Fleetwood.

Thanks guys, post if ya think of anything else. And I'll keep you posted if I fix it.