RS3RS

Just purchased a 93 Z28 with ported/polished heads and a cam swap. The previous owner never got it tuned, and it shows. On first start, it runs rough for about 20 or 30 seconds, and you have to give it gas to keep it from dying. After that, the Service Engine Soon light comes on and it will idle fine and drive pretty normal although you can tell it runs a bit rough.

I'd like to order a chip for it, since these 93s are a bit of a pain tune-wise. The issue is that he lost the paperwork and all he knows about the cam is what he messaged me:

Not exactly specific, and that's all the detail I can get out of him. Looks like Comp Cams has a lot of different options for the LT1.

So here's my question. If I take a stab at it and order a tune that is close to the cam that in it, could I expect an improvement in driveability / performance even if the specs aren't exactly the same? Even if it's not perfect, I would be happy just not having to rev it like a douche bag for 30 seconds every time I start it up. Pretty sure the neighbors hate me already.

Injuneer

I'd pull the code(s) that's turning on the SES light before going any further.... might indicate a problem not related to lack of a tune, or might indicate what needs to be corrected in the tune.

Are you sure he didn’t mean to say the Comp cam was “similar” to the GM LT4 HOT cam? That might narrow down how “mild” the cam is.

RS3RS

Thanks for the reply. I pulled the codes and got the following:

16 - Distributor ignition system (low resolution pulse)
26 - Evaporative Emission (EVAP) canister purge solenoid valve circuit

Not sure if these relate to the cam issue or if the previous owner was just using that as an excuse to hide other problems. Seems like code 16 might have to do with the opti. The car recently got a new MSI opti replacement (within the last 200 miles, I was told) that is vented.

Code 26 doesn't surprise me. The previous owner deleted the EGR.

Your guess is as good as mine. He's not the sharpest tool in the shed. I'm just trying to sort out his mess.

Injuneer

DTC 16 sets when the ECM can’t find the low resolution pulse signal from the optical cam position sensor in the Opti. If you engine starts and runs, it’s a stored code. If it was an active code the ECM would shut down the fuel system, because it couldn’t correctly time the spark. Clear the code and see if it comes back. Has nothing to do with lack of tune for the aftermarket cam.

Since you have a 93, you have to use the code list specifically for a 93. That isn’t the complete code description for a 93, it’s only for 94/95. DTC 26 in a 93 is for the quad driver module that controls:

- AIR pump relay
- EGR vacuum solenoid
- EVAP purge solenoid

Shoebox's LT1 code list, with a list for 93 on the right side:

http://shbox.com/1/Dtcs.htm

EVAP and EGR are 2 separate systems. You can eliminate the solenoid codes with a simple resistor. If you (or previous owner) have deleted the AIR pump, you can avoid the code by insuring you have a good fuse on the relay signal side of AIR pump relay. Again, nothing to do with lack of tune for the cam.

Since the engine only runs poorly cold, there’s a chance the problem is related to the ECM transitioning from open loop (cold start to 3 or 4 minutes of warm up) into closed loop. That's when the O2 sensors feedback kicks in. Or it could be related to a faulty coolant temp sensor not causing the ECM to richen the cold start A/F ratio. I would pursue those problems before getting it tuned. One way is to run an ECM data log from cold start through warmup, and a brief drive, using Scan9495 (free) software. I can review the log and look at things like the O2 sensors, coolant temp sensor and other things that might cause the problem.

Scan9495 also works on 93’s, and the author here can help sort out any installation or cable problems:

https://www.camaroz28.com/forums/com...95-lt1-874306/

Is it really an “MSI” Opti? Or is it actually an “MSD”? While the MSD is one of the most expensive available, it suffers from numerous problems, and is not recommended l

If that's all you have on the cam, tell the tuner it's a mild Comp, and hope he guesses correctly. Do not tell him it’s a “hotcam” because I am not aware of any LT1 Comp called that.

PCM of North Carolina is probably your best bet for a chip:

Camaro & Firebird V8 1986-1993 ? PCM of NC, Inc.

RS3RS

Thank you! That's extremely helpful. I'll look into everything you mentioned.

Ananta1369

RS3RS, how did everything go? Did you figure out the issue? Also, did you get a tune?

Thank you

Injuneer

Unfortunately some people ask for help, but never come back and follow up with what worked or what didn't. RS3RS has posted three different topics and never followed up on any of them.