RX744CSP

iTrader: (4)

Story so far: the Jensenator (1974 Jensen Healey) has an 5 normally aspirated 13B which, due to an electronic OMP problem, was going into 'limp mode. I swapped another OMP onto it and it happened again. I decided to swap a Series 4 (1986-1988) mechanical OMP and ECU into my car and get rid of the limp mode thing once and for all. So I mated the S5 harness to the S4 ECU, swapped on an S4 front cover and OMP, etc.

The wiring is almost exactly the same between the two; there are two wires whose colors do not match but their functions are clear and after much research (I have both the S4 and S5 wiring diagrams) they were connected. With the exception of the MAF, MAP and TPS sensors, everything is the same; I have the correct TPS and MAP, the S5 MAF is compatible with the S4 ECU (been done lots of times and I got the straight lowdown on how to connect it). I now have everything I need: spark at the plugs, tach operation, +5V reference to the sensors, +12V at the injectors etc but I don't have injector pulse. Dammit.

I clipped one of the signal wires to a primary injector, connected an LED ('noid light') between +12V and the signal wire, when I switch on the ignition I get a momentary blip but no injector pulse when turning the engine over. I have checked wires, ohmed wires and checked continuity till I am dizzy.

I keep coming back to a ground issue, AFAIK I have all the grounds, well, grounded. The ECU ground wires for each connector are grounded to the engine harness which in turn is grounded to the engine which is in turn grounded to the ECU mounting bolts. I verified them all with a DVOM but I keep thinking I missed something simple.

Another thing: the S5 ECU has a tachometer input from the trailing coil, the S4 does not show anything like this on the wiring diagram.

Any ideas out there?

Black Hearts

iTrader: (23)

hmm, i had a similar situation(about no injector pulse)

turns out the injectors were gumed and the stock ground wasnt enough to release them. so we jumped the ecu grounding points and heard the injectors click.
fired her up and bam smoke everywhere....good ole rotary =)

i know it prob isnt near what your looking for but its worth a try.

RX744CSP

iTrader: (4)

Update: a local bud has done a pinout on other ECUs and suggested that I double check 3G which he says is the injector ground. Did so; the ground tests good with a DVOM. But I intend to go back through the grounds again, couldn't hurt.

I keep wondering something: I realize the S4 and S5 trailing coil pack is different. On an S5, the tachometer signal from the trailing coil (blue/yellow wire) also goes to the ECU. On an S4, the tach lead does not; it goes directly to the tach trigger lead.

So my question: where does the S4 ECU get its engine RPM signal from, if not the trailing coil/igniter? BTW, one of the two wires that is different between S4 and S5 wiring is a blue/red wire to the trailing coil. Mebbe that means I need an S4 trailing coil. Any ideas?