93 Z-71 355 / 485 Hp

I have just yanked the stock 350 and installed a 485 HP 355 (350 .030 overbored) in it's place. For many reasons I wanted to keep the injection, so I had to modify the stock tbi intake to adapt to the older style heads. Everything else, including the serpentine belt, ac compressor, sensors, exhaust manifolds and all bracketry was removed and reinstalled on this new engine.

My problem is that it's a pig! It's hard to start and it runs extremely rich....I would have thought it would be completely opposite. I had assumed that the stock system would not be able to supply enough fuel, but obviously this is not the case.

Brandon, 485 HP is pretty hefty, and you have to running a pretty nasty cam in her. The stock computer is going to go bonkers when you fire it up. What are the specs on the cam at .050, and what centerline are you running. I assume you are still running the stock O2 sensor as well? Do you have access to a OBD-l scanner?

JKinney, The motor was built more than 5 years ago. Up until recently it hadn't been installed into anything. It's funny you mentioned about the cam specs because when I was contemplating putting this motor in this vehicle I couldn't find my cam specs (nor did I remember). Wanting a somewhat streetable combination, I removed the front cover to check and redialed the cam at .050 baseline. I can get you this info. The O2 sensor is also stock. I have a little "Cheap-O" device that plugs into the obd connector that flashes the check engine light. Suprisingly enough it didn't put out a code. Other than this cheap-o device, I have not tryed anything else. My thoughts were to get this combination running well, then start installing headers, exhaust, intake, ignition upgrades ect. I also had the opinion that firing the motor would be challenging enough for the computer (if not impossible) as it was without the added demand of additional enhanment add on's. It should be quite a pavment ripper when done. Although currently I wouldn't dare run a stock Yugo for pink slips.

JKinney, I also forgot to mention, the hp was rated using sunoco fuel, headers, torquer 2 intake and 780 holley mech secondaries carb. I know this is not the setup that will be used, but it should give me somewhat of a baseline which to achieve when trying to get this mongrel to run on tbi.

The key you mentioned is to extract hard codes that are stored in the PCM only. It would be nice (especially for what your trying to do) to get your hands on a OBD-l scanner. It will tell you what most of the sensors are doing. The reason I asked about the cam, is I know the computer will get tangled in it's shorts if you have a lumpy cam. My interest in what you are doing, is I have contemplated putting a stroker in my 93 Z-71 as well, or that extra big block I have in my barn. With it running rich, I would suspect the O2 sensor not functioning correctly, or something is throwing off your air/fuel mixture. Keep us posted.

I would think the engine coolant temp (ECT) sensor could cause this. On a '90 I had, it got so bad I was only running on about 4 cyls and blowing lots of black smoke. New sensor fixed it right up. It's the one up front by the thermostat housing.

Forgot to add....you might try just disconnecting that ECT to test it....I think that simulates a hot engine. That's how I found my problem.
Also, with that cam's valve overlap, I would think it would throw the manifold pressure (MAP) sensor way off. Don't know what would be the best way to handle that. :2cents:

Oops....just checked the manual. Disconnecting the ECT simulates a cold engine, jumpering the terminals simulates a hot engine.

This is obviously going to be tough to figure out and I appreciate all the tips your giving. I'm going to try the tip on the sensor this weekend and I'm also gonna pick up a new O2 sensor. It certainly cant hurt.

The other night I just had a thought and it "clicked" in my head when looking thru my manual of all the sensors and their functions. I'm running a "noisy" gear drive on the motor also. Your probably thinking as I did before that, "what's that have to do with it running right" I'm wondering if the knock sensor could be picking up the geardrive noise and interpreting it as spark knock and retarding the timing? I suppose it could happen?

I don't believe this is the entire problem, but it could just be another piece of the puzzle.

There is going to be quite a bit of "wringing out the problems" but I guess that's all part of the fun right. I'm gonna look into this also this weekend and I'll let you guys know what I found out.

Your definitely onto something. I talked about trying a geardrive in my IROC a few years back (SB w/TPI), and didnt because of that very reason. Good luck!