I just bought a 1990 740 and it's a great car when it runs, its perfect. The problem is when it gets warmed up like after a lengthy trip of at least 15-20 minutes it will not start back up until it cools off. Has anyone ever come across this problem before?

 

I would try to replace the coolant temp sensor.Thats what it sounds like to me.I have seen that many times with these cars.

 

Have same problem with 1990, 740 GL. Hot soak problems are very common with high mileage 700/900 models. I have replaced a defective fuel pump relay, coolant temp. sensor and fuel pump check valve and cleaned the ignition coil. The fuel pressure is ok and I get sparks but problem still there. I plan to change the RPM sensor next. Good luck and don't give up.

 

I changed the rpm sensor, it was in poor shape. Still same problem. This evening I switched the radio suppression relay with the cooler fan relay and the car now starts right away. Figures, the problem is the easiest to fix and the least expensive. I just ordered 2 new relays from eEuropeanparts.

 

That would have been my next guess.Those cars were weird some of them had those relays and some didn't.Thats why I didn't suggest that first.Im glad you got it figured out.The speed sensor would have given you problems soon if it was in bad shape.

 

I replaced the radio suppression relay and it didn't help. I have just ordered a new speed sensor, hopefully this will correct it.

 

Let me know how you make out.

 

try fuel and radio relays

 

I finally replaced the speed sensor (it was lost in transit) it worked! It runs beautiful now.

 

Im glad you got it fixed.