I posted this under General Tech and this is the only other place I could think of where someone might have an idea of what's happening.

I have pulled an S5 NA 13B from a convertible which had an automatic, I put a 5 speed behind it and installed it in a Jensen Healey, using the stock S5 ECU. It fires up and runs great, until you try to rev it way up. Then the tach (a VDO) quits working. Since the tach output comes from the trailing coil/igniter I have to assume the ECU is killing the trailing ignition. It also shuts down the fuel pump ground, thus killing the pump. Since the OE pump relay runs on that weird resistor setup that works all the time when the ignition is on (I assume that's to run the pump at lower speed, thus lower pressure, thus reduced power and I have bypassed it), I am assuming that when this happens the ECU is going into 'limp mode'. I bypassed the ECU ground for the pump relay so now when this happens I lose the tach but the engine still runs.

If I shut it down and wait about 2 minutes and then restart the engine, the tach works again until the next time I try to buzz the engine way up.

I *think* the ECU will go into limp if it does not 'see' the electronic OMP. I am using the OMP and it's working, I started it on premix and watched the lines, you could see the air bubbles move through the lines until they were completely filled with oil. So I have to assume the ECU 'sees' the OMP.

I have an FSM, it is nearly useless for stuff like this. So my question: what else, other than the OMP, could make the ECU go into 'limp' mode?

 

did you put the check engine light in? or the diagnostic plugs? instead of guessing it would be much faster to check the codes...

if it is the f/p relays, you can put resistors in that circuit and it'll make the ecu happy...