I live in Southern CA and I've got a '91 Z28 5.7 TPI. The first symptom occurred several months ago when it would just die and not start. Starter motor would turn it over but it would not start. After a while though it would start. There was no rhyme or reason to its behavior. Items replaced:
Fuel pump
Fuel filter
EGR valve
IAC
Fuel regulator (this item was definitely defective)
Fuel injectors
Distributor module
It runs now but according to Angel at TPIparts.com, when I describe the symptoms to him, it is going into "Limp Home Mode." Oh yeah...the current symptoms: motor dies...I can keep it running by flooring it and keeping the RPM's way up there. When the symptoms appear while driving I have to manually shift into neutral and keep the RPM's up. When in gear it hesitates like crazy...leaps all over the place (because even though I've got my foot on the pedal...the engine still starts to die out), backfires. Any input would be appreciated.

 

I`ve had ignition problems that were very similar.Finaly found a couple bad wires to distributer.Got pulled or stetched somehow and frayed them.Took hours for me and a buddy to trace them.Just a thought.

 

Were the wires attached to the module? Several mechanics insisted it's the ECM while others think that it's a bad ground or frayed ground wire. You could never get away with your car out here in La La Land (CA). Everything has to be CARB legal.

 

In true limp mode the SES light will be blinking fast and furious.
If it's not doing that, AutoZone has a nice free book with ECM trouble codes, and how to read them with a paper clip. ( really )

 

Yes, the light is blinking and I have a pro scanner. While everybody else out here in sunny CA is driving around with a cell phone glued to their ear I've got my scanner on the console and am reading the operation data. The codes that come up are MAP sensor and TPS. Both have been replaced and the symptoms still persist. Thanks anyway, though.

 

Which MAP and TPS codes ? High fail, or low fail ?

 

there is a possibility your ECM is going out. when it acts up, does the scanner still show good data?
bad grounds can cause all kinds of problems.

 

Currently I have a new ECM in the process of being shipped to me from TPIparts.com. And, actually lately, I've been so discouraged with the thing that I haven't hooked up the scanner for a while. But, in the past whenever the symptoms appear I still can get a readout on the scanner. I have been though trying to pay attention to the conditions when the symptoms appear. It seems to act up whenever it is cold outside. In the past I noticed that I got the symptoms when the motor hit 160 but lately it acts up dead cold alll the way up to 220, which is sort of pushing me towards the outside temperature having an effect on it. I checked the two grounds on the back of each cylinder head. The ground strap on the passenger side was loose so I just hooked up another one in its place. I couldn't get a wrench back there between the firewall and the head to tighten it. The other one on the driver's side is fine. Oh yeah...the problem is intermittent and often I can pull it out of the symptoms by continuing to drive it and waiting it out. The last time it went into symptomatic mode it lasted much longer than usual, did not matter what the motor temp was and the symptoms was really severe...the thing was leaping all over the place. I was putting on quite a show for other drivers.

 

I just got the new ECM installed a few minutes ago. Tomorrow I'm going to drive it to work and see what happens. If this doesn't solve the problem then it's got to be a ground. In any case I wanted to thank everyone who took the time out to post a response to my dilemma. Oh yeah...by the way, I drove it back and forth to work today with no issues. I live in southern CA in Orange County and spend a lot of time on the freeways and the car was really freaking me out when it came to long hauls around greater LA.

 

It's been almost a week since I installed the new ECM and "NO SYMPTOMS." a long time ago I should have ignored the guy from TPIparts.com and just purchased the new ECM. Not only have the symptoms disappeared but the Block Learn and Integrator are both back to a 128 reading on the scanner. Again I want to thank everybody for taking the time out to post replies.

 

My 91 Z/28 would randomly go into limp home mode and the speedometer would stop working. It would drive OK but the idle was about 1000 rpm instead of the 450 it normally was. It never tripped a code. It ended up that the ECM board was coming loose inside the case and causing problems. A new ECM fixed it.

 

Seems like there are a lot of problems with these motors. I had a similar problem a couple of years ago. The speedo would stop working and the motor would die. I thought that it had something to do with the solenoid that disconnects the torque converter when you hit the brake pedal but it was the speedo sensor telling the computer that the car was standing still. A new speedo sensor fixed this one. I really dig the car though and probably will be buried in it.