squid_z28

Just wondering if anyone has ever had this problem with your f-body. I have the T56 tranny in my 93 lt1 z28.

It all started after getting gas one day....

When I started the car the check engine light came on and remained on. I could drive (rpm limited to 3k) however there was no speed on the speedometer. Needle just pegged to the left. After about 5 miles there was a clunking type noise (as if the clutch just engaged) and the speedometer works.

It's not possible to check a code because the system seems to be in lock mode. Aux fan is on, idle rpm is 1500, etc just like its on it's using base values for everything.
I'm picking up a new speed sensor tonight from my local chevy dealer and i'm just hoping that it's a simple fix for this problem. It's definitly intermittent and driving me crazy.

Hope everyone is having a spectacular new year and all of you near chicago, ill see you at the track.

Thanks

squid

Injuneer

What's "lock mode"? Never heard of it. How does it prevent you from scanning for codes?

Loss of signal from the VSS will set a code and turn on the SES light, and prevent your speedo from working. Appears to be an intermittent problem. I haven't seen that code cause any major problems.

squid_z28

Lock... Limp... the basic values that your computer reverts to when something is wrong. car runs, but not well.

When i put the car in accessory i cannot read the codes because the car acts as if i'm already grounding the aldl connector.

the aux fan is on, the necessary lights light up but the check engine light does not flash.

possible that I have a short in my system?

thanks

Injuneer

The PCM does not go into "lock" or "limp" mode for every little problem. "Limp" is reserved for almost a total failure of sensor inputs. Few people ever experience that mode. Yes, the PCM may make internal adjustments when it loses one sensor... reverting to preprogrammed values, or taking protective actions. But it shouldn't "lock" up and prevent you from accessing the data.

What do you mean by putting the car "in accessory"? You hook up the scanner (or short pins A & B in your 93), turn the key to "on", leave it there. Are you saying you don't get the DTC 12 handshake? You aren't possibly trying to connect while the key is in the "accessory" position? That isn't going to work.

The fans will come on full time for several "codes". The most common one is due to blowing the fuse for the AIR pump.

squid_z28

I did a little more research. First let me apologize for using incorrect terminology. It must be a pain in the butt reading my posts.

This is the experience that I am having. On a cold start my engine cranks, and will idle. The MIL is illuminated and when I drive away, stays illuminated. The car will not rev past 3k, it will either idle at 1500 RPM or not at all, the speedometer does not register a speed; but the car can be driven.
After a period of 2 - 5 miles, the speedometer kicks in and the MIL goes away. Afterwards the car runs just fine, no more limiter, no more issues with idle.

When I notice the MIL illuminated after first starting the vehicle, I kill the engine and put the key in the "ON" position where I short the data connecor and ground to make the MIL blink "1, 2, 1, 2" etc to get an idea of the Trouble Code set. HOWEVER, when the key is in the "ON" position, I cannot short the data and ground connectors because the MIL stays illuminated and does not flash at all.

This is where I am. I'm switchin clothes and going to take a look at any possible shorts to the PCM. Also I'm going to look at possible wiring problems to the ground connectors.

I appreciate the help! THANK YOU.
Sometimes these problems, when the get to be very percise tend to tick me off the most, so thanks for putting up with me. And again thank you for all the knowledge that you and this forum brings to individuals with limited knowledge such as myself.

Thanks!