I pulled the wires to the fuel pump, put the volt meter into the sockets, turned on the key and see zero voltage from the wires. So, I take the fuses out and jumped #4 and #6 and still nothing. (The other day I could hear a thunk by jumpering). Actually, I don't get much excitement today when putting the jumper on the left side of the terminals - just a faint little spark different than the other day anyway. The multi-meter I'm using has the pointed probes, but I moved them around enough with the key on that I would have made contact at some point and I verified the meter was good by reading DC voltage across the battery terminals first.

So, my question: What are the reason(s)that voltage would not be going to the wires for the pump? Is there any other fuse or something else I should be checking? Does the ECM (or ICM whatever its name) under the passenger side kick panel have any play in this?

I'm much more comfortable with mechanical than I am with electrical problems, in fact electrical problems want to make me run away as they just about short my brain out. R2

"I pulled the wires to the fuel pump, put the volt meter into the sockets, turned on the key and see zero voltage from the wires."
• That's normal. The pumps don't get power till the ECU gets timing pulses from the Ignition during cranking and running.

"So, I take the fuses out and jumped #4 and #6 and still nothing."
• That could be normal too, with the fuses out and depending on which fuse terminals you were on.
• It's not necessary to remove the fuses, and you must be jumpering the LEFT side (fuse input) terminals. For this test, fuse 6 input is just a handy voltage source. Battery voltage is always available at the input to fuses 6 thru 10.

Jumping 12V to the input of fuse 4 input is electrically the same as what the Fuel pump relay does, but it bypasses the 25A fuse and the relay, as Randy said. At that point, the voltage goes 2 ways:
1) Thru the fuse to the Tank pump (if the fuse is in place).
2) Directly to the Main pump, by way of a connector under the back seat.

"The multi-meter I'm using has the pointed probes, but I moved them around enough with the key on that I would have made contact at some point and I verified the meter was good by reading DC voltage across the battery terminals first."

I'd advise replacing the meter with a simple 12V test light. In circuits where corrosion or other high resistances can be a problem, the sensitive meter may show a nice 12V, but it won't have enough current to light a bulb.

P.S. Your '88 doesn't have the Crank Position sensor that Tony mentions. It's timing pulses come from the Hall sensor in the distributor
--
Bruce Young, '93 940-NA (current), 240s (one V8), 140s, 122s, since '63.

I'd advise replacing the meter with a simple 12V test light. In circuits where corrosion or other high resistances can be a problem, the sensitive meter may show a nice 12V, but it won't have enough current to light a bulb.

Lucid,

Thanks for posting that. I have been meaning to bring it up in answer to one post or another and keep forgetting it. It is an important point to understand while trying to solve electrical gremlins.

--
Mr. Shannon DeWolfe -- I've taken to using mister because my name misleads folks on the WWW. I am a 53 year old fat man. ;-)

Thanks for the note about the crank positioning sensor so I won't chase that rabbit.

I've got a cheap volt meter with a bulb so I'll be poking around with that.

I'm thinking with the fuses 4 and 6 jumpered I should be able to place the alligator clip into the lead and then find a good ground to see voltage, correct?

There are black and yellow wire leads into the pump - the black is probably the hot one but I'll check both hoping to get one to light.

If I get power I'm back to believing the main fuel pump died. Especially with the torque lock sound (thunk, thunk) I got the other day when I jumpered the fuses.

"I've got a cheap volt meter with a bulb so I'll be poking around with that."
•I'm not familiar with a meter & bulb combination, but assume the bulb load will prevent reading stray "ghost voltages" on the meter.

"I'm thinking with the fuses 4 and 6 jumpered I should be able to place the alligator clip into the lead and then find a good ground to see voltage, correct?"
• Not sure what "lead" you mean, but yes if 4 an 6 are jumpered on the left side contacts, the Main pump circuit should have 12V (Tank pump too if fuse 4 is in place).

"There are black and yellow wire leads into the pump - the black is probably the hot one but I'll check both hoping to get one to light."
• NO, the yellow is the hot side. Black is almost always ground in Volvo wiring.
--
Bruce Young, '93 940-NA (current), 240s (one V8), 140s, 122s, since '63.

Hi Bruce,

NO, the yellow is the hot side. Black is almost always ground in Volvo wiring. (Bold is mine.)

I certainly agree, but maybe the OP just read this post and one glaring exception to the practice:

Frustration and Confusion -- EDIT #2

In fact, maybe the aftermarket builder of all those incorrectly wired sender units also agreed black ought to be connected to the negative terminal of the pump.


--
Art Benstein near Baltimore

Q. What occurs more often in December than any other month?
A. Conception.

Hi Art,

When I wrote, "Black is almost always ground in Volvo wiring.", I had in mind the Tank pump wires outside the sender, where the hot yellow changes to hot black at the 2-pin plug.

I did have a fleeting thought about linking to that photo of your recent experience inside the sender, but ruled it out as being non-Volvo wiring.

Besides, I get dizzy looking at that nice close-up, then pondering over how the problem was fixed by "switching wires at the connector" as I believe someone claimed, when the connector has only the Hot Black and Gray Gauge wires;-)

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

Yes, the yellow/red transitions to the black of the sender's external cable at the two-pin connector. I think the reference to correcting it there was in the post where the gauge was pegged and the pump didn't work. A miswire externally.

Inside the sender, the wires were just placed into the plastic terminal holder backward, so the yellow wire, bonded to ground, went naturally to the positive terminal on the pump. The milky-colored plastic retainer for the radio noise suppression chokes and pump ring terminals needed to be unsnapped and the wires reversed inside, so they would fit in correct polarity on the pump.

However, I don't know who made the sender (I think maybe VDO), but it was made for Volvo originally, and the same wiring colors were used whether VDO or AC supplied the uplift pumps. I'd be surprised to learn those senders fit anyone else's fuel tanks. The dizzying closeness was an attempt to show the "+" embossed from the post projecting from the pump, on the left as shown. I sure do thank Afton Crafton for noticing that reversal and helping me out with mine.



This image shows the tank pump miswired within the sender assembly.
--
Art Benstein near Baltimore

Mistakes are the portals of discovery. -James Joyce

Ahhh, sorry.. '89 was the start of the CPS
--
'75 Jeep CJ5 345Hp ChevyPwrd, two motorcycles, '85 Pickup: The '89 Volvo is the newest vehicle I own. it wasn't Volvos safety , it was Longevity that sold me http://home.no.net/ebrox/Tony's%20cars.htm

Jumpering fuse 4 to fuse 6 bypasses the 25amp fuse and the relay.

If you have the jumper in place and do not find 12v on the pump connector I would suspect that you are not providing a ground. Check under the seat to see that the ground is clean.

Randy

Under the back seat?

The negative wire that connects to the fuel pump is a screwed to the body pan under the rear seat. Easy to access on the wagons but requiring removing the seat bottom in the sedans.

Or you could check to see if it is not providing the necessary ground by giving the negative lead on your meter a good ground and seeing if you get 12v with the jumper in place.

Randy

Will check ground per your note.

I replaced the main relay in my 1988 Honda CRX this week. Same symtoms, maybe the same problem. Good luck.

Chris

What main relay?

Check the 25 amp fuse under the hood on the Drivers side fender. It's the newer style spade type. it's in a White Fuse holder. The fuse might be good but the Holder gets hot and well, shitted up.

You should still have been able to jumper out 4 and 6, I think.

What about your Fuel Pump Relay? That is another main cause of Fuel Pump failure. They can be opened and all ( not many) connections should be reflowed with additional solder. It's not an intricate piece, anyone can do it.
--
'75 Jeep CJ5 345Hp ChevyPwrd, two motorcycles, '85 Pickup: The '89 Volvo is the newest vehicle I own. it wasn't Volvos safety , it was Longevity that sold me http://home.no.net/ebrox/Tony's%20cars.htm

25 amp fuse is good via continuity check - fuse holder looks good, but I don't know how to check it. I live in the south so nothing gets rusty or crusty under the hood however I'll try to clean the contact areas. Failure occured suddenly while driving at 60 mph on a smooth highway - just shut down.

Fuel relay is good - swapped in another to prove out.

Whoa, that's a big clue, It just shut down while driving.... It could be your Crank Positioning Sensor. That sees rotation and tells the computer to send voltage to the pumps. Are you sure you didn't break a Timing Belt?

Just something else to look at. But again, the fuses should have voltage all the time.
--
'75 Jeep CJ5 345Hp ChevyPwrd, two motorcycles, '85 Pickup: The '89 Volvo is the newest vehicle I own. it wasn't Volvos safety , it was Longevity that sold me http://home.no.net/ebrox/Tony's%20cars.htm

Timing belt is good - cam rotates while looking into valve cover.
Coil has fire.
No fuel to common fuel rail - no voltage to pump. Will test ground next for fuel pump.

Does crank positioning sensor shut power off to pump? Even if I jumpered 4 and 6 fuses?

Hi there,

After one reading of this thread, I've encountered the "jumpered 4 and 6 fuses" concept several times without being convinced your method is to jumper fuse 6's voltage to fuse 4. Your wording could also mean substituting two jumpers for the fuses, which would be a valid means of eliminating the common fuse-end problems, but not accomplishing the goal of providing battery directly to the pumps bypassing the 25A fuse under hood and fuel pump relay.

Can you clarify what you're doing with the jumpers?
--
Art Benstein near Baltimore

We childproofed our homes, but they are still getting in.

I took one length of wire about 4" long and fashioned a horseshoe shape with it. I took fuse 4 out of its holder and I took fuse 6 out of its holder. I then touched one end of the wire to the left spade of fuse 4 and the other end of the wire to the left spade of fuse 6. So, no fuses were present and I called what I did with the wire "jumpering fuse 4 and 6".

Did I do it wrong or right? As stated in my original post (March 3rd perhaps) I did the same thing and heard a thunk from where the fuel pump resides, although I was crouched with my head by the drivers seat doing the jumpering. Then when I tried the same thing a couple of nights later I heard no thunk. Then I got no voltage with a multi-meter while jumpering 4 and 6.

Thanks for the clarification. You did it right.

If you start tracing the voltage at the left side of fuse 4 (while you have the jumper in place) you should know rather soon where it is failing. The back of the fuse panel there should have a red/yellow wire connected that winds up at the connector under the rear seat. The ground for the main pump is right next to it.
--
Art Benstein near Baltimore

Drive carefully. It's not only cars that can be recalled by their maker.

The fuel system is a tad complicated as I've learned here, and will not show voltage at the pump unless a series of things all go right simultaneously

But simple stuff can block fuel, clogged filter, leaking hose from the tank or a blown pump. Have you checked the pump itself? I've used jumper cables from pump to the battery, tap the battery and if you don't hear the pump whirring you know it's the pump.

(This is NOT endorsed by any reputable mechanic, if you do have a leaky fuel line from the tank and the jumpers arced under the car, this could prove disastrous)

You could take the pump out of the car to test it but now you have raw gas and sparks spewing forth. A definite no no.

On second thought while I'm a high voltage electrician and a part time pyrotech thus used to certain risk.

I would say this is a bad suggestion for this forum...


Never mind....

wait for some real experts

OK - thanks I'll wait then.