512TR intermittent CEL

Without logging onto the Motronic and doing some diagnostics, at least knowing what error is being set, it is all just guess work as to the cause. But in my experience it never hurts to clean the grounds for the Motronic. They are located on the cylinder heads towards the back, on top, between the intake manifold and the parting line. If you pull the air-flow-meter off you can access easily, one 5mm and one 6mm bolt, 1-6 is on the right head and 7-12 on the left. However, your best bet is to find out what is setting the light

 

twice when I started the engine only half the engine would fire but when I shut it down & restarted it the whole engine would then fire

Wierd

 

I'd consider checking/replacing the relays to each ECU and fuel pump, as well as inspecting/replacing the crank sensors and their connections.

Your 512TR is running Motronic 2.7? Should be easy to display those error codes on your dash if so.

 

1212 on M2.7 for 348's, 355's, and Mondial T's is a lambda issue (O2 sensor and/or MAF and/or coolant temp sensor). Perhaps this holds true for 512 TR's running M2.7 as well.

You swapped the O2's from side to side, but the trouble code remained on your 1-6 side, so I'd rule out O2's being the problem because your swap didn't trigger a 7-12 bank 1212 code.

If 512 TR's have twin MAF's then you could swap them to sort of repeat the same test above, but I'd suspect that what you really have is a coolant temp sensor gone bad (causing you to run too rich which triggers the O2 1212 code) or a fuel pressure regulator gone bad (causing you to be too rich again).

To test the FPRs, pull off the black vacuum hose (easily comes off by pulling with one hand; simple test) to the FPR, rub your finger on each end, and sniff your finger for the scent of fuel. Fuel smell in a vacuum hose means the FPR has failed.

Easy to replace.