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I've recently bought a Volvo V70 I 2.4 (106 kW, gasoline, 1998), and on the way back home from the seller the car died several times when starting from a standstill, until finally a few hundred meters before my home it wouldn't start anymore. Had to have it towed (ouch), where I then started to investigate the issue.

What I've done so far:

Many people on the internet who had similar issues replaced the fuel-pump control relay to fix the issue. In fact bridging the relay let my car start again (that piece of wire went straight into the glovebox). I've ordered a replacement part and my car would start normally again and seemed to work fine at first. I've also checked the fuel pump if it still worked by disconnecting the fuel line after the filter, and a squirt of gasoline came out when turning the key.

Issues now:

I hoped the only issue would be the faulty relay, but apparently this is more complex. When I accelerate too strongly, the engine will rev down immediately and die, and most of the times will not recover. When accelerating lightly, it revs up just fine. At speed the engine keeps going, but sometimes is a little bumpy.

My Suspicions/Questions:

  • Fuel Pump: I have already bought a replacement pump. Maybe the current pump has deteriorated and killed the fuel pump relay? I'm replacing this to be on the safe side because the part is cheap enough.
  • Mass Flow Sensor: Mabye this is the culprit? Sadly I have no oscilloscope to check this whatsoever. Will try cleaning it with special cleaning spray.
  • Lambda Sensor: Could a faulty lambda sensor cause the issues? Wouldn't that light up the indicator on the dash?
  • Throttle Valve: This is a mechanical valve with a pulley system, could it be dirty and thus lag and cause issues? Does this have a sensor of sorts that could be faulty and thus cause not enough fuel to be injected?
  • Ignition system: The car has a ignition distributer. Could faulty spark plugs and/or worn distributor cause the issue?

Could any of these be the cause of the issue? What else could cause this issue?

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Seems like fuel, but you might be over-thinking it...

Cheap enough to replace the fuel filter to eliminate that.

But before I did that, I'd put a fuel pressure gauge on the injector rail and route it so you can duct tape it to the windshield, or pin it under the windshield wiper. Then duplicate the problem, observing fuel pressure. You might actually have a fuel flow problem, from a clogged filter (likely) or a failing pump (less likely).

The gauge will tell the story. If you don't want a drive with gauge hose full of fuel on your window, you can "brake stall" with the help of a friend - just don't stand in front of the vehicle. They will need to left-foot press the brake hard and simulate a launch with a medium romp on the accelerator pedal. Or, you can do the same yourself, if you can locate the gauge so it's visible when inside the vehicle.

Not everyone has a fuel pressure set with Euro adapters - and they aren't cheap. You might be able to rent one from a big retail autoparts house. Or, you can try the poor man's DIY gamble and just replace the fuel filter - it's not that much of an investment.

I suspect the pump/filter combination as it sits can only supply enough fuel flow for light acceleration. Higher demands starve the system, cause a stallout, and then it takes a while to rebuild sufficient pressure for proper injection. The relay replacement may have masked the problem, as it gave enough time for a weak flow to rebuild the injection pressure.

Occam's Razor in full effect here; I imagine your '98 Volvo has some serious mileage. The fuel filter is supposed to be replaced at regular intervals anyway. I didn't see where you replaced the filter - and honestly, I would never dare to replace a fuel pump without throwing in a new filter in every case.

If you're a "belt and suspenders" kind of person, you might just replace both the filter and the pump (since you already have it). But I'm one of those types that must know the truth, so I would go through the effort of replacing the filter first.

Indeed, it could be something more complex, but I've owned many Volvos and repaired dozens of vehicles with this exact condition. The only time I got badly stung was a Jeep that somebody shoved a shop rag into the gas tank as sabotage. The vehicle would run fine for hundreds of miles and weeks, and then stall out. Restarted fine after sitting for 30 minutes. The rag would slosh around in the fuel until it randomly covered the pick-up screen in the tank. This was one of only a few times Occam let me down. And in fairness, acceleration was not a problem. I didn't do my homework, and spent three repairs and pumps and filters and injector cleaning, before I dropped the tank and discovered the truth ...

What you have there, sir, is a mechanical fuel flow problem. I'm all in!

  • OK thank you for the comprehensive answer, I shall try replacing the filter and pump then and I'll report back when it's done! – Lukas Mar 1 at 13:28
  • Quick update: I've finally managed to remove the pump assembly after having a lot of trouble disconnecting the fuel line. Seems like I've bought the wrong pump. It fits by dimensions, but has a different power connector and different attachment mechanism for the fuel sock. – Lukas Mar 17 at 16:56
  • Did the issue persist after you replaced the filter? – SteveRacer Mar 19 at 4:04
  • A mechanic friend of mine took a look today, and we found the issue: the spark was escaping the ignition cable! Fixing it up with some gaffer tape made the issues go away, and now the car runs again. – Lukas Mar 20 at 18:08
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A mechanic friend of mine took a look at it and we found the issue when a 1cm long spark was arcing over from the ignition cable to some metal nearby.

Ignition cable charred from spark

After fixing it with some gaffer tape the engine ran without issues. It needs to be replaced and then should be good to go!

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    I'm glad you found it. I'm really surprised that didn't throw a P030x code for a misfire. – SteveRacer Mar 21 at 2:56
  • Thanks. The ELM307 bluetooth adapter couldn't connect to the car. Either the OBD port is shot, or it speaks some really old version of it that simply isn't supported by the ELM307 software. – Lukas Mar 22 at 11:49
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    I suspect the ELM307. I've had really poor luck with bluetooth code readers on 1996-2000 vehicles. Try an old-school cable type, or even borrrow one from an autoparts retailer like Autozone or Advanced Auto. (Carquest) – SteveRacer Mar 27 at 2:46

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