Hello all my 3rd gen friends.

I have a 1991 Camaro Z28 5.7 TPI that have started running rough.

I have in the winter time changed heads, cam, ported the intake, edelbrock high flow runners, bigger TB, distributor cap and rotor, plugwires, headers, bigger injectors, removed the A.I.R pump and made a new true dual 2.5" exhaust system. It has also had the chip / prom replaced to one that fits my setup.

The car ran great for about 20 miles and then it started to have some issues.
The tachometer starts to jump up a lot and the car stumbles every time the tach is jumping. The wideband / AFR gauge is jumping and shows a different number every time that happens.
I have a video of it but dont know how to upload it.
I have tried to change the coil, ignition control module with no luck.
Something i think is strange is when i put back the stock chip / prom then the tach is not jumping but the car does not start.

Anyone have any ides?
And i apologize if this is hard to read, English is not my first language.

 

Sounds fuel related... 20 minutes running fine after a winter break with upgrades? Have you tried testing the fuel pressure? Would be nice if you could connect a scanner tool and see what the BLM's are reporting. I would think that you're running in the 140's - 150's.

I would pop in the other prom and go from there...?

 

Did the new chip disable the VATS? Maybe when you put the stock chip back in, the VATS may be kicking in and keeping the car from starting.

I agree with Bennett... if you can get a scanner on it and capture the running data when the issue happens, that'd probably tell you a lot. Otherwise its just guessing.

Or if you have a Windows laptop... get a USB to ALDL OBD1 cable and download Tunerpro RT.

 

The biggest problem is that i dont have anything to scan i with or know anyone that has it. And here in Sweden i dont know if i can get anything to scan it with if i dont order from the USA and that takes maby a month to get. I will order one but would like to solve this mystery asap😂
The engine have maby just over 1 hour of runtime on it. But only 20miles driven.

No the VATS should be connected still.

Can it really be fuel when the tach is jumping up? Should it not jump down instead if it was something wrong with the fuel system / pressure?

And i have tried to put the stock prom back and with it in place the car wont start. The only thing i notice is with the stock one is in the car the tach is not jumping around when i crank it like it is with the new prom

 

Also, a quick and easy check. When you put the ignition on, do you get a double blink from the SES, service engine light? This signifies if the ECM is engaging or not. Also, might be worth jumping the OBD and seeing if you get any codes?

 

I get the service light to turn on, then of and then on again until i crank the engine over then it goes of.
I have heard of that but am not sure how to do that. I will look in on how to do that and come back with results.
Im kind of new to this TPI stuff so i have a bit of learning to do. I have worked more on older cars with carbs before and not fuel injection cars.

 

I have looked if i have any codes now and the only thing i get is that 12 code that it is supposed to have.