Im trying to get my 87 GTA running properly for some time now.
its a 5.7L auto, new distibutor, ign module , IAC, TPS, O2 sensor, AFR remaned LT1 injectors 2yrs now(all in spec when cold/ hot), MAP, plugs and wires 3 yrs old, 1yr old walbro 255lph pump.
Problem is I can get the car to run and idle great for around 20-30 min but after that it starts acting up, major surging until it stalls.
It can run for a while but if I turn the car off for 5 mins after a drive it starts with the surging.
Seems like it happens once it warms up, Im using the EBL with a WB O2 as well and everything seems to read out fine at first.
With the surging, the WB reads that it runs very lean to lean 20:1 - 16:1.
2 Things I can only think of would be injectors are leaking or coolant sensor unless someone else has encounterd this before.
Im running out of things to check and ideas, any help would be appreciated.
Thanks

 

Egr valve, Vacuum leak, tp/iac sensors just a few i would check

 

EGR is removed, no vacuum leaks confirmed...TPS and IAC are new and working properly. Tested with voltameter and shows that its running proper on the EBL Whats up software.
Consider it only happens after the car runs for around 20 - 30 mins, before that the engine runs great.

 

at 20:1 your engine would not be running. Check for exhaust leaks infront of that WB. Or if you have AIR, make sure it goes off while in closed loop, should not be pumping air into the manifolds while in closed loop. I feel you are getting a false lean condition. Double check those things, if you still have a lean condition. Check your fuel filter...or just replace it. Also check your Coolant temp sensor. And as stated before check for vaccuum leaks. Lean is either not enuff fuel, or too much air coming in.

 

AIR tubes are cut off and air pump is removed.
I have no exhaust leaks at all, its solid.
I have a new CTS delco I can install but the one I have is Neihoff reads fine fan kicks on etc...
There are no vacuum leaks, its confirmed checked...
I dont remember changing the fuel filter although like I said it runs great for 20 -30 min then starts leaning out surging.
The fuel regulator reads 43psi bang even when the engine dies.

 

Injectors maybe? Sometimes they don't cause a problem until they get warmed up. I know you said you checked for vacuum leaks, but surging is a classic sign of that problem.

 

When the surging starts, are you at a light throttle cruise? Are you idling when it starts to happen? when exactly does it start to surge? after the surging starts is it only at idle, or light throttle cruise, or both?

 

For sure. I confirmed that first before moving on (vacuum leaks), BTW thanks for the replies I appreciate any ideas.
Could the injectors get too hot and no be able to handle the pressure, get clogged under stress?

 

If anything they may be getting too hot and may increase the resistance of the injector coil causing the injector pintle to not open as far as it should or possibly not at all making it run lean, but this is unlikely. I would check all the resistance of the injectors when the car is warmed up, should be about 13-16 ohms if i remember correctly. If they are over or below that spec. replace the injectors. Also did you use any RTV when you installed your o2? could have got some on it and it could be messing up your o2 readings. Just a thought. Another thought that comes to mind is the VSS (vehicle speed sensor) if you have a scan tool or winALDL you can see the VSS and confirm it matches the speed you are going or is very close. In fact on Mitchell this is the first thing it says to check when diagnosing a surging condition before moving on to any other possibility so it must be a big deal when it comes to surging problems especially at cruise.