740 1989 740T, no power to injectors.

Hey guys! I figured I'd ask here before I really started into tearing into this thing.

My 740T that I've had for a while is no longer starting. It ran great before it was mothballed for a few years. I drug it out of hibernation only to find that it won't start. I went through the basics:

Has spark
Has fuel running through the rail. The pump is on a manual switch.


Does not have any voltage feed going to any of the injectors. I checked the grounds on the fuel rail, carefully inspected the harness for rodent damage and found none. I had noticed water intrusion in the passenger compartment from sitting so I yanked the ECU. Took it apart and found water had indeed got to it. Replaced with another ECU from a good running 740 to no avail.

Any suggestions?

Radio suppression relay. It supplies power to the injectors.

shellshock said:

Any suggestions?

Click to expand...

Look at a wiring diagram.

2manyturbos said:

Radio suppression relay. It supplies power to the injectors.

Click to expand...

This. Jumper the relay to supply 12v straight to the injectors. Look at a wiring diagram, it’ll be easy.

If that doesn’t work, remove the resistor pack and file each spade connector. A corroded resistor pack is the thing that stopped my 945T from starting after sitting like 4+ years.

I agree with iHateVolvoPeople. I had the same problem with my '90 740T. Ruled out the radio suppression relay (easy to simply use a jumper to bypass). Turned out to be the resistor pack connector. Clean the spade lugs and try again.

Use a test lamp.

The boost pressure over-boost switch used on Turbo cars with LH 2.2 or it's connector can cause a no ground connection to the fuel pump relay. The radio suppression relay and/or it's connector can cause no power to the injectors.