Weird one

[Azdude]

Hello to all the volvo enthusiasts, got a weird one here, I thought that I would ask for help here because this forum has been my go to site since this 2000 s80 T6 came into my life.

This will be a long post since I want to provide the most info for the best possible diagnosis.

This vehicle ran before I did all of the following:

Head gasket, it was seeping, oil pan sealing, spots on the floor, tranny filter and service, rack and pinion swap, CV axle, etm cleaning, PCV cleaning, etc. This is not the first time I've had to mechanically time this engine so I know I got that right and I got setting the VVT correct as well. Lost a timing belt last year, so good training Re-loomed the wire harness in the engine bay. So I did take the harness loose from engine and tranny to do that, but I didn't unhook the flywheel sensor or the camshaft sensor from the harness. The flywheel sensor had some metal fillings on it so I cleaned it off, had all sensors wrapped in plastic while they were out of their respective places

Finally got everything back together and it started and ran. Idled a little rough but didn't think anything of it. Thought that fuel was a little old so in goes a can of fuel system cleaner. Put it in gear and drove for a good five miles round trip and came home. No issues

It sat for a couple of days and then I got in to go to parts store for the basics that I had used for this project, engine oil, couple of cans of throttle body cleaner etc.

Then engine just died on way home. Put tranny in neutral and it would restart put it into drive and then it ran fine all the way home. Got home and then it idled fine for a good 15 minutes, it would accept throttle up to 3-4k and then smoothly return back to idle. While that was happening I noticed that I had inverted the waste gate lines, so I shut it off and swapped them around. Restarted and checked for vacuum leaks using water in a spray bottle.. No change in rpm when I did that

Another couple of days passed, I got in to run to the doctor that is a mile down the road and I didn't even get down the block. It started with 1/4 throttle, then it idled fine, put it in gear and started down the road. Ran fine, then engine died, put tranny in neutral and restarted, once I put it back into gear the engine would start to accept the load and then suddenly die... This pattern continued until I got home,

Have fuel getting to the rail, my pressure tester doesn't fit the port but I removed the valve and visually checked output. Fuel filter swapped last year.

Put battery charger on it because I know how picky volvo can be with battery voltage, and am going to start doing the basic diagnosis but it would really help if I have some ideas of where to start and also some specs of sensor resistance and color codes of the wires because I am thinking that I would back probe from the Engine Management side to see if I can pick up any signal from the sensors etc since my scanner isn't picking up any codes nor is it capturing any live data. Tried a restart with battery charger on and engine refuses to start, so it's time to go old school and check everything a piece at a time, will double check mechanical timing and VVT settings

Have fuel getting to the rail, my pressure tester doesn't fit the port but I removed the valve and visually checked output. Fuel filter swapped last year.

Any and all help would be greatly appreciated!

I will post solution that works long term as well to help somebody else

[mikealder]

Electrical portion of the ignition switch would be a start point for this fault, next time it fails try wiggling the ignition key up and down to see if it sorts it out, if so the switch is shot - Mike

[Azdude]

Ok Mike, will check that next, just to be sure I double checked the timing and also the VVT.

[Azdude]

Checked the ignition switch, everything good. Got system voltage on all leads out. Where do I go next?

[Azdude]

Traced fault to ECU relay in engine compartment. Jumpered relay, all ECM fuses got hot, still no start.

[Azdude]

It RUNS

Here is what I did to get there. Pulled the ECM relay to see if there was system voltage on the control side of the relay, it was dead. In my prior posts I jumpered the relay on the secondary side, ETM got active when I did that. I tried to start the car and it wouldn't fire. When I jumpered system voltage from the always hot secondary to the control side plus jumpering to the other side of the secondary, turn the key and it lit up... FINALLY.

It appears that the ECM needs system voltage from the control side of the ECM relay to energize the circuits for coils and injectors.

The process that I did was chasing voltage, so a battery charger is a must, checked the ignition switch, fuses, etc..

Now the question is where is the break between the ignition and that ECM relay. Also being electrical why not a complete failure instead of intermittent up to complete failure...

[Azdude]

Update:

Chased wire for several hours, have determined that the wire from the ignition switch goes to a relay that in turn controls the ECM relay. I think that its under the dash but I have yet to figure out how to drop the relay block from under the dash

Has anyone have any ideas?

Thanks

[Azdude]

Did a good ten mile road test on the highway at highway speeds no problems with performance
Went and did surface streets and performed well there as well.

So once I can get this relay issue sorted that will make me very happy

[Azdude]

Update:

Relay / Fuse issue finally sorted. This is what I did.

Since I had the relays out, cleaned the terminals on them after I bench tested them. The sockets were cleaned as well, put the relays back in and she would almost start.. Changed the fuses, anything related to ECM, made sure terminals were clean and shiny on both the fuses and the sockets,

It now starts and runs with the key as it should. My best guess from remembering ohm's law is that there was just enough additional resistance that it dropped the voltage to the ECM below the threshold it needs.