I have a 94 Camaro Z28 that doesn't run very well.

When I start it, it sounds like only 2 or 3 cylinders are firing. When it finally starts, it runs rough if you gun it until 2,000 rpm or so, runs smooth above that. After it warms up (5 min or so) I can’t get it above 2,000 rpm with out it dying.

I used Datamasters Diagnostics via Obd1 and it popped several DTC’s:

16 - A low resolution pulse was not detected by ECM within 720 high resolution timing pulses.
22 - Throttle position sensor (TPS) voltage was under 0.23 volts when the engine was running.
34 - MAP sensor signal voltage was too low (high vacuum) when engine speed was under 700 RPM, or when TPS was greater than 20% with an engine speed above 700 RPM.
41 - Electronic spark timing (EST) circuit voltage was above 4.6 volts when engine speed was under 1500 RPM. Circuit - open or shorted to ground during engine run.
42 - PCM did not detect any EST signal within 84 crankshaft revolutions. Circuit - open or shorted to ground during engine run.
46 – Fuel Enable - Vehicle anti-theft system (VATS) failure.

Any help on what to look at first, or maybe a website to look at that might tell me what needs to be replaced per code would be greatly appreciated.

Thanks
Kevin

 

Several unrelated codes are often from a defective alternator. Either it is putting out voltage too low to maintain a good level in the battery or the diodes are leaking and allowing too much AC to pass into the DC system and causing the PCM to flake out.

Since this is very easy to check and rule out as the cause of the problem I suggest you check the voltage across the battery with a meter set to DC and confirm it's about 14 volts DC while the engine is running.

Now set the meter to AC and check from ground to the main output terminal of the alternator. It should be at or less than 0.03 VAC. Any higher, the diodes are defective.

It's also a good idea to check the grounds at the block above the starter, at the ICM, the radiator support and at the frame. As well as the passenger inner fender. And the positive cluster as well. Don't just wiggle them to see that they are tight, remove them and clean them and the contact point as well.

 

Thanks for the help; I checked voltage at the battery (13.9) and the alternator (0.03) and I would say that both checked out.
As far as the grounds, I unconnected and wire brushed until shinny the negative at the battery, block, passenger inner fender, and the radiator supports. I am not familiar with the positive cluster, and I thought the ICM was on top of the manifold, but there is no ground so I’m sure I’m wrong. Maybe you could try to explain where they are?
I thought we were on to something with the ground. Ever since I got the car (36k miles ago) when I start it the first revolution is very slow. I had to replace the battery, and even with new battery had the same problem, but It always started so I just lived with it.
After cleaning the grounds the car seemed to run better. It ran a lot better though 2k. I drove it around the block, but after about a half of a block it tried to die if I touched the gas. When I got back I cleared the codes and retested it. It popped 3 codes. Two of the same codes:
16 - A low resolution pulse was not detected by ECM within 720 high resolution timing pulses.
41 - Electronic spark timing (EST) circuit voltage was above 4.6 volts when engine speed was under 1500 RPM. Circuit - open or shorted to ground during engine run.
And a new code:
51 - PROM error.

Any help would be greatly appreciated.

Kevin