I've tracked my '91 240 DL no-start problem to fuel delivery. First, I replaced the fuel filter to start with a clean slate. When turning the key to the 'on' position, I can hear the fuel pump relay click in the passenger footwell, and I can hear the in-tank pump priming. I confirmed this also by jumping the relay block as well as the #4 and #6 fuses. In no case have I heard the external main pump turn on with the key. I thought before I hassled with the main pump, I'd check for voltage. With the key on, I did not get 12 volts to either the black or yellow wires (I only had my test light with me at the time - no volt meter). Does the main pump get power from someplace other than the fuel relay that powers the in-tank pump? Keep in mind, this was only with the key in the 'on' position. Must the engine be cranking before the main pump energizes? I'd like to narrow this down before I start throwing parts at it.

Short version: in-tank pump is working - exterior pump apparently is not. Is a new pump certainly in my future?

To "hotwire" the Main pump by itself, remove fuse 4 and jumper from 6 to the LEFT fuse 4 contact. That goes straight to the main pump. (With fuse 4 IN, voltage also goes to tank pump.)

"Does the main pump get power from someplace other than the fuel relay that powers the in-tank pump?"
• No -- what varies is when (under what conditions) the ECU energizes the Fuel relay, which it does by activating the coil ground path (Terminal 86/2).

"Keep in mind, this was only with the key in the 'on' position. Must the engine be cranking before the main pump energizes?"
• Except for the brief "buzz/prime" when Key is first turned on, the ECU requires timing pulses from the Ignition CU. This is for both cranking and running.
(Basic safety: No ignition signal=no fuel pumped.)

Bruce Young

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Here's an update and a request for assistance:

Jumping at the fuse terminals does not energize the main pump. However, applying battery voltage directly to the pump itself will energize the pump, and the car will start and run. While the car was running, I checked for voltage at the wires going to the main pump, and did not find any. This seems to point to a problem with the main pump circuit. Does the ignition also get its signal from the crank sensor, like the main pump? I ask, because I'm obviously getting spark. If the ignition does not receive a signal from the crank sensor, then that could definitely be the culprit.

A quick summary: 1991 240 no-start due to fuel delivery; Relay engages and runs the in-tank pump with key on; main pump does not energize when engine is cranking, but works fine when 12 volts is delivered directly to it.

Looks like I need to start working backwards from the main pump. Where to next?

Jumping at the fuse terminals does not energize the main pump. However, applying battery voltage directly to the pump itself will energize the pump, and the car will start and run.
• Voltage must be getting to fuse 4 if the tank pump runs (earlier post), so there must be an open circuit between the fuse 4 input (left contact) and the Main pump.

The diagram shows 2 separate in-line connectors between the fuse contact and the pump. I think one of these is under the rear seat, but don't know about the other.

Get the back seat out (no fun -- you need to push back and then pull up while still pushing), find that y/r wire connector, see if jumpered power is there at the mid-point, and go from there.

I suppose even the push-on terminal at fuse 4, where the power takes off for the pump, could be suspect -- but that should be 2 wires (1 in and 1 out) in a single female terminal, because there are 3 male push-ons for each fuse -- only 1 input and 2 outputs.

When looking at a fuse from the side, with the wires in your right, the bottom-most terminal runs under the fuse to the hot INPUT side (Left fuse contact). The two top terminals connect to the fused OUTPUT side (Right fuse contact).

Does the ignition also get its signal from the crank sensor, like the main pump? I ask, because I'm obviously getting spark. If the ignition does not receive a signal from the crank sensor, then that could definitely be the culprit.
• Only the ignition gets the RPM signal. It then relays a "copy" to the FI ECU to allow fuel system operation. If the engine runs, the RPM sender and ignition are OK. I'd say you've isolated your problem to a single circuit path.
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Bruce Young
'93 940-NA (current), 240s (one V8), 140s, 122s, since '63.

Thanks. I found the connector under the rear seat, and I can energize the pump by applying 12v there, and I don't get any power to it while the engine is running (I started it and let it run by manually energizing the pump, then looking for 12v at that connection), so that connector seems to be ok. From there, the wires run to the transmission/drive shaft tunnel, so I'll begin the hunt for the mystery connection.

As a side note, shortly before the no-start problem occurred, after starting the car (to check the brakes), I had no power to the radio, windows or a/c controls (I briefly touched on this on my first post in a different thread). About an hour later, I started the car and everything worked fine. Could these be related, or point to a more specific problem?

This isn't my car, and it's not the owner's primary car, so I'm spending time on it as I can. Thanks for all the help.

Andy, I was asking Art Benstein about that circuit and he says:
"My 91 WDM shows two connectors in the path. The one, we figure is the one under the seat, but the second one may be a four-holer above the driver's toes leading to the harness next to the rocker. It contains green/white, yellow, black, and our red/yellow suspect. The other three circuits are for rear defroster and both sides of the differential speedo sensor."

Hope this helps. I'll be away till the 12th.

Bruce
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Bruce Young
'93 940-NA (current), 240s (one V8), 140s, 122s, since '63.

I found the problem yesterday. The four-hole connector above the brake pedal had somehow completely separated. I guess if I had started from the fuse panel and worked towards the pump, I'd have found it sooner, rather than vice versa. Thanks so much for the assist. Now, back to replacing the front brake rotors, which was the original task. It's a shame the brake lines must be disconnected to do this.

lines are soft you wont need disconnect to pull rotor

Thanks for the response. I never seemed to get any activity from the main pump at ANY point (turning key on, etc.), so that seems to point to a bad pump. I'll pull the fuse and jump it to be sure. If the pump doesn't energize, I'll check for voltage at the wires and replace the pump if I get voltage.