I need major assistance. My car is stranded in a parking lot since yesterday. Been using the car since morning. Started in the morning easily. Ran absolutely fine. Stop for lunch and 1/2 hour later can't start the car. Car cranks strongly but engine just won't start typical of a hot no start problem.

Based on the FAQ, the possible culprit are either the ECT or the radio supression relay as

1. Battery only 2 weeks old. Voltage 12.37 with no surface charge.
2. Fuel injection relay replaced 3 yrs ago due to no start, I opened the current one - looks ok, no cracks in the circuit
3. Power stage replaced 2 yrs ago due to intermittent engine cut off
4. Hall sensor replaced last yr as the connector broke

Thinking of common things first I suspected the RSR, went to my parts guy and had a look at the manual. My RSR is on the strut tower behind the PS reservoir. I have another relay near the battery which is for the fan as the wires go the radiator's side tank. Can't swap as both have diff part no. 2nd bad news, both are not to specs. The parts no. don't match to what's given in the manual. The old RSR in a bosh relay no. 0 332 204 151 with 5 spade terminals. Got myself a new correct RSR relay with 4 round type terminal.

Some idiot mechanic (before I had the car) had extensively modified the wiring as evident by missing multiconnectors and patches of electrical tape here and there connecting the wires and incorrect relays. The old RSR had 4 wires coming in with 1 unused center terminal - it also had spades instead plugs. The multiconnector for the RSR was also missing. With a small nose plier I modified the terminals and reconnected it to the new relay using the same previous order (in hindsight BIG mistake). Tried starting the car, NO crank at all AND I saw SMOKE from the engine. The ground wire was fried to a crisp!!

Inspected the wiring configuration. there's 4 wires which are to the best I could follow
1 grounded to the strut
2 going somewhere towards the radiator
3 going to the started motor
4 towards the engine block

Help from the brickboard is my only hope to get her started again before I resort to towing her to a workshop. Questions are

Is my new RSR still OK? Did I do serious damage to other unknown parts? Does anyone know which wires goes to which relay terminal? Is it possible to bypass the relay just to get my car back?

My top priority is to drive the car back to a secure place which is home and sort out the rest at my own leisure. Sorry for the long post. Any advice is much appreciated. Thanks so much in advance.

Aslan

89' 740 B230E K-jetronic (with auxillary air valve)

Went back to the car and inspected the wiring

Relay behind PS - wires go to 1. ground 2. starter motor (I think, round thing near tranny housing) 3. runs under the fuel distributor with a a bunch of other wires 4. to the fan in front of condensor. All 4 wires are black in colour

Relay near battery - one red one blue and two black 1. to battery terminal 2. to sensor in the radiator side tank. 3 and 4 runs together in a sheath joining other wires towards the strut power. Lost it from there.

Now I'm really confused as to which relay is which. Any help appreciated

My 91 740 turbo had an erratic starting problem(crank yet no start). I switched the electric cooling fan relay with the radio suppresion relay. Car has been running fine since, Electric fan doesnt work. Hope this helps. Jack

Thanks for the suggestion Jack. Unfortunately both the old relays were not identical in terms of part no. I did try switching one with the other just in case I was lucky but car didn't even crank with the switch. That's why I went looking for a new relay. I believe some models did came with identical relays, not sure if mine WAS supposed to. Thanks anyway