Only 0.25V to the fuel pump line out of DME relay

[175K911]

Finally, after 8 years since I tore my ‘86 apart and doing a slow rebuild as a track car, I’ve got the 3.6 in and ready to fire it up. Got good oil pressure quickly with DME relay out. Plugged the relay back in, turn the key and......nothing! Engine cranks but that’s it. Pulled a fuel line at the engine, dry as a bone.

This is a 3.6 motronic with Steve Timmins’ conversion stuff. New DME relay from our host and new ecu chip from Steve Wong.

Some quick troubleshooting, the wire out of the relay to the fuel pump has 0V as it should with the key off, but only goes to 0.25V when cranking the engine. My admittedly limited electrical knowledge says I should either have 12v out or 0, so the 0.25 has me baffled.

After 8 years I was hoping for some good noises, so this is a major letdown.

[175K911]

Jumped 30 - 87b, fuel pump works just fine. Bad DME relay?

[ischmitz]

Or bad wiring or adaptation of the conversion harness to the car. Make sure the DME relay audibly clicks once you crank. There are two stages (relays) inside that black box. The first relay needs to click when you turn the key to RUN. The second (that controls the fuel pump) needs to click, once you crank, key in START.

Ingo

[175K911]

Have good spark. No fuel into cylinders? Can’t hear injectors clicking.

[ischmitz]

Hearing the injectors is virtually impossible during cranking. The 964 and 993 have the ability to fire injectors only as diagnostics through the Hammer. Even then you need to put your head almost on top of the engine block to hear the faint clicks. Once there is cranking no way you’d hear that.

You need an LED test light or a NOID light to measure pulses at the injectors.

If there are no fuel pulses you’re either missing +12V at the injectors or the DME is damaged. My bet is on bad wiring - that would explain the non-working fuel pump and the lack of injector pulses. FYI in a stock 964/993 the DME relay’s fist stage controls power to the injectors.