'93 240 won't start

If the fuel pump is getting power but isn't running, I'd say the problem is obvious.

Hmmmm, I'm going to go out on a limb here.

Tell them to check the fuel pump.

So why would it run with the test equipment connected but not without?

So why would it run with the test equipment connected but not without?

As suggested by other replies:- Presence or absence of connected diagnostic equipment notwithstanding, if the main fuel pump is getting proper power (ground and +ve) properly delivered to its input terminals when it ought to be getting power, but, is not running, then the main fuel pump has an issue that means it needs to be substituted, even if only temporarily, before any further diagnostics can be carried out.

I have to confess to some bafflement as to why with the diagnostic equipment and new battery connected, the pump runs (it's obviously getting a 12v supply), but, with diagnostic stuff removed (pump allegedly still getting a 12v supply when it should), it doesn't run, that makes no sense at all.

Clutching at straws mode on

Did the garage reinstall your battery as well? Are all the fuses properly seated and the ends clean, perhaps the new battery they tried was managing somehow to get a bit more current to the pump during engine cranking, enabling it to start and run, whereas your battery can't?

Clutching at straws mode off

Best wishes, Ken Phillips

Something bad in the wiring harness that the test equipment bridged? Incorrect reassembly after removing the testing equipment?

I just talked to the mechanics. Seems there's an undocumented relay up behind the glovebox that is fried. This might account for my wife having smelled something burning (a point I hadn't mentioned here earlier).

They're waiting for the relay to arrive and will see if that fixes the problem.

Ken, your bafflement is shared.

See my earlier post regarding the discovery of the shop manual undocumented relay. Methinks we're on the right trail here.

I had previously checked all the fuses, especially the #6. I long ago replaced those bloody ceramic units with Buss AGPs, glass fuses with stainless (?) ends. End of the corrosion problems. BTW, I heard those are no longer available. Go see your local auto store. I got some last week.

I suspect a Bosch relay is a LOT cheaper than a genuwine Bosch fuel pump.

Keep tuned to this station for further developments. Film at 11:00.

Well now, I just got the car back. Turns out there was a genuwine Volvo relay, #898151 which was fried. That's the one up behind the glovebox. The spark coil had also arced somewhere along the way and needed replaced.

Damages?

1. Relay: plus labor;
2. Spark coil: plus to change it;
3. New 75 month battery:
4. Tow in: ;
5. Two days of trying to figure out what the hell was going on: 7.

All told, I'm satisfied. I sure could never have figured that out myself. To those who responded to my earlier posts, thanks.

Chuck Fiedler Nothing but Volvo since 1974

I question whether the pump was actually recieving 12V *under load* or if there was simply 12V measured at the wires to the pump with the pump disconnected. Connect a car battery to a multimeter through a 1 megohm resistor and you'll measure 12V, but apply any sort of load to it and the voltage will drop to zero because of the high resistance.

Relay is about 50 bucks, or free to resolder which is usually all it needs. Fuel pump was around $260 last time I bought one.