1998 V70XC - New fuel pump, troubleshooted 9470674, new wiring, and odd fuel gauge behavior (problem resolved)

VolvoOwl98 · Post by **VolvoOwl98** » 23 May 2026, 22:32

Been spending the better part of the day installing a new fuel pump from VAST Tuning (DW200). Did a thorough visual inspection before putting in the new pump, got everything buttoned up, electrical connectors fastened, and the tank showed full despite being near-empty.

Took a lot of stuff apart again, re-verified wiring and that the float was well-positioned and moving freely, and put it all together again. Decided to at least try and see if it’d fire up (after I’d added 3 gallons from a jerrycan), but no

Checked 20A fuse for the fuel pump and even swapped it, no difference. Then checked the positive electrical line for the pump at the back of the car, and on position II checking between its two connections there's 7.95V, which is at least a sign of life.

Turning to pos. II yields a faint hum when listening right next to the fuel tank (in the past with the old pump it made a wrrrr sound as the fuel pump primed itself. Also cycled pos. II several times in case there was air in the system.

I did replace the fuel pump relay not too long ago and can hear a faint click from the fusebox on pos. II cycle, so hopefully it shouldn’t be that.

I have the upgraded wiring also but wanted to wait and see how the pump would go so if there was a no-start there’d be less to troubleshoot… glad I went that route lol

It being my daily makes it a high-priority to get up and running again, even if it’s an all-nighter (not too much of an issue though, already am a night owl).

Any help that anyone can pitch in with would be very much appreciated!

rrres · Post by **rrres** » 24 May 2026, 00:15

There are multiple leak points within the fuel pump unit/case, that can cause the fuel delivery system to lose pressure.

: FUEL PUMP DIAGRAM.jpg (56.1 KiB) Viewed 813 times

: 20220401_170354.jpg (134.03 KiB) Viewed 812 times

Post by **abscate** » 24 May 2026, 03:53

rrres wrote: 24 May 2026, 00:15 There are multiple leak points within the fuel pump unit/case, that can cause the fuel delivery system to lose pressure.
FUEL PUMP DIAGRAM.jpg
20220401_170354.jpg

The hive deeply appreciates the effort that went into that diagram, that’s worth 10E6 words

The fuel pump “relay” is more like a controller and turns the pump on for a few seconds at first. It should put 12 volts , full battery voltage on , during this time. You need a late night assistant to help you check thst

The fuel level resistance are measured in series so if one fails it goes open circuit which I believe if full tank

(Added part number to title thread)

VolvoOwl98 · Post by **VolvoOwl98** » 24 May 2026, 10:37

The fuel pump “relay” is more like a controller and turns the pump on for a few seconds at first. It should put 12 volts , full battery voltage on , during this time

Just measured the positive wire connector voltage with someone to turn to Pos. II, and it never reaches 12V. The multimeter shows it quickly gain power (T<1s), but it stops at 7.95V

Putting my ear right next to the pump side of the tank I can hear the faint humming sound of the fuel pump, which doesn’t stop after 2-3 seconds. I know other units are usually fairly audible when priming (the old one was easily heard for 2 seconds when the key got to Pos. II with having conversations in the car) and I have very sensitive hearing… but it is also a DeatshWerks 200 that VAST Tuning reterofitted into a new housing/unit, which are renowned as being very quiet pumps, so... not too sure.

I’d hope that it isn’t an issue with the pump considering it’s from people who deal with tuned (and very high-performance) Volvo’s. It came very well protected and the close visual inspection didn’t reveal anything awry.

VolvoOwl98 · Post by **VolvoOwl98** » 24 May 2026, 12:03

Update: I was going to use a jumper wire to test if it was the fuel pump relay, and thought "hmm, I have the old relay (which I replaced because there was some symptom I thought was caused by it, or it was a preemptive replacement... can't remember which), why don't I try it again?"

Lo and behold, it did make a difference. Still no start, still only getting 7.95V at the back when key turned to Pos. II, but now when the positive wire from the new pump is disconnected from the car, the gas gauge reads correctly!

The wiring at the connectors looks the same between the old and the new, and IIRC did too at the pump. But it's a piece to the puzzle nonetheless

VolvoOwl98 · Post by **VolvoOwl98** » 24 May 2026, 12:52

Update #2 and summary of current status:

I reconnected the old fuel pump and had someone turn to Pos. II. Pump primed itself (and squirted out a bit of fuel)

Current status of things:
- New fuel pump from VAST is installed
- Faint constant hum sound from pump side of tank when key turned to Pos. II
- No start
- Positive fuel pump wire connected, gas gauge reads incorrectly (full tank)
- Disconnecting positive wire, fuel gauge now reads correctly
- Measuring constant 7.95 (8) volts at the positive wire in the car, never reaches 12V when key turned to Pos. II
- Old pump primes just fine when connected to car power
- Used jumper wire on pins 15 and 87, key to Pos. II, still read 7.95 volts without going up to 12
- Reading pin 15 in fuse box for relay, seeing 12.05V that goes down to 11.88V power there

I have the upgraded wiring to pair with the DeatshWerks 200 pump, but it should still be able to run on the stock wiring receiving 12V power (just not as efficiently as with the better wiring installed).

The fuel level resistance are measured in series so if one fails it goes open circuit which I believe if full tank

So potentially something with the wiring of the pump is messed up?

I'm rather regretting not testing the new pump before putting it in... I don't have a current (lol) way to supply a constant 12V (unless I make one) which is why I didn't test it beforehand, that and I also had trust that a unit from a tuning company wouldn't have issues (which could still be the case).

Current order of function thinking is that if the new pump isn't able to receive 12V to prime, it can't build initial pressure, and it also wouldn't receive the 12V needed to turn over and run when the key is turned to Pos. III. And with the old pump, maybe it's just being a freak of engineering and somehow being able to run on 8V??

So my thinking is, issue from the battery to the fuel pump relay?

Hopefully with this progress things will be able to be sorted out soon... at this point I'm more running on adrenaline to combat the tiredness of being sick

Post by **abscate** » 24 May 2026, 15:37

I had the grey connector burn on my fuel pump on the kat. Start tracing the voltage back from the pump and find where you are losing voltage. I don’t think 8 volts will run the car

VolvoOwl98 · Post by **VolvoOwl98** » 24 May 2026, 15:52

I had the grey connector burn on my fuel pump on the kat. Start tracing the voltage back from the pump and find where you are losing voltage. I don’t think 8 volts will run the car

Thankfully the gray connector on Saskia looks fine. With the help of the thread here:viewtopic.php?t=52252 I checked all other electrical things in the engine bay pertaining to the fuel pump and they cleared no problem, so I think at this point the only thing that can be done is replace the wiring with the upgrade kit and hope for the best

Vova585 · Post by **Vova585** » 24 May 2026, 20:27

I think at this point you narrowed it down to positive 12v power supply wire. If you are only getting 7-8v there-corrosion, partially broken wire are your suspects. If with disconnected supply plug to the pump you are still reading 7v (measuring between positive supply and separate chassy ground/preferably at battery post)- your issue is corrosion. Even 1-2 strings of cooper should be able to give you 12v reading. Best next move- find correct wiring diagram for your car(alldata diy is $30 per month, Mitchell diy...or maybe someone here can suggest free resource). Examine the diagram and try to see if there is an intermediate connection between relay and pump. Examine that and test on both sides(middle probe lead, t-pin not to change the variable/unless it is sitting in a puddle of water or all green from corrosion). Good luck

VolvoOwl98 · Post by **VolvoOwl98** » 25 May 2026, 00:03

Best next move- find correct wiring diagram for your car(alldata diy is $30 per month, Mitchell diy...or maybe someone here can suggest free resource). Examine the diagram and try to see if there is an intermediate connection between relay and pump

I had puttered around for a bit looking for that, the most I came up with was this info I found in VIDA (I don't have a disk of the electronic wiring... at least not yet):

I spent a little time checking Haynes Pro, but that didn't yield any new information. Currently finishing up the installation of the new wiring (will make separate write-up for that when able), so hopefully bypassing the car's positive and drawing power from the battery will be sufficient (also makes it easier to service in the future).