1998 V70 T5; problem hot starting & occasional brief power loss at speed

evdrive · Post by **evdrive** » 27 Aug 2019, 05:41

Background: 337k miles on her, new clutch & new turbo in the past 5 months, all new vacuum lines, plugs & wires & cap/rotor replaced in the past 8 months, very recently a new purge valve & new ECT & new thermostat trying to solve the problem.

Symptoms: After driving for an hour or so (enough to get things hot) if I have to make a short stop (for gas or groceries) less than a few hours when starting back up the engine will light up just fine, revs will initially go up past 1k, but then they will start dropping and the engine will shake. It'll keep shaking sometimes for up to 30 secs and will sometimes stall. I can't give it gas at all during this time or it will die. If I'm patient it will eventually catch and revs will pop back up over 1k before settling into a normal idle. This can sometimes go thru that cycle more than once trying to get it to settle into normal. If I try to drive before it normalizes then it'll jerk and lose power when pressing the throttle and usually stall. It's almost a similar feeling as when the turbo went out. The original turbo's wastegate valve started leaking and it couldn't hold boost before I replaced it and driving with it like that I had to keep revs no higher than 2500, but since replacement that's been fine. According to my boost gauge it'll hit 12-13lbs when I get into it. But the loss of power has a similar feeling like it just cuts out. Other than the starting issue it will also very occasionally have that power cut while driving at steady state driving (60-70mph). Not a sustained cut, but it can be felt. Tipping in the throttle it'll jerk a little and slow instead of speed up. If I just lay off the gas and coast for a bit it'll normalize and drive fine and I can even getting into boost and accelerate after those instances.

I'm at a loss as to what's causing this. Initially I thought a vacuum leak, but I've looked thru all the hoses and even cleaned the MAF and idle control valve with no change. Since I've had the car I've replaced a ton of stuff fixing the things that go wrong; fuel pump relay 2x's, fuel pump (@200k+), crank position sensor, hazards switch, door switches, throttle cable, intercooler piping & hoses, shocks & struts, control arms, tie rods, cv axles, the recent turbo & clutch, and much more. I thought it was air related, but I haven't crossed off fuel related. Could it be the pump is starting to go? I know it's something that's affected by heat or maybe it's something that's not releasing pressure unless it sits long enough. It starts up just fine after sitting overnight or the 8-9 hrs I'm at work and doesn't show any of those symptoms other than that occasional at speed one.

Please let me know if you've got any ideas! Thanks you for taking the time!

Post by **misha** » 27 Aug 2019, 06:22

I hope that fuel pump relays you replaced weren't aftermarket.
What about fuel filter?
To me....it sounds like ocassional fuel pressure loss.
Maf could be the culprit also...it's connector is more common.

evdrive · Post by **evdrive** » 27 Aug 2019, 06:29

Good point on the relay. I thought I got a Volvo one, but I'll look. I might make a jumper and use that to test when the engine's hot. I just got a fuel filter that I was going to throw in there. The MAF is original so that could be it. How long do MAF's last before failure?

Post by **misha** » 27 Aug 2019, 06:59

Ect too must be Volvo oe or at least Vernet.
Ect connector is also prone to failure and corrosion...so check that also on wiring loom side.
In my experience about Maf....it's connector is more prone to failure that actual Maf.
You will need a little precise screwdriver to minimize the gaps in the connector.
They usually fail when SAS valve become stuck open and let water and moisture from exhaust condensation throw air filter.
Otherwise....if air filter is changed at least at half of recommended interval it will last a long,long time.
If you suspect the maf is bad....when problem occures again....disconnect it's connector and drive it a bit like that and see if problem disappears.
Cap & rotor must be Bosch,plugs...Volvo or cheap copper ones(NGK or Bosch) properly gapped.
Turbo engines don't like fancy plugs.
Is check engine light on?

evdrive · Post by **evdrive** » 27 Aug 2019, 07:21

No CEL, Bosch & NGK cap/rotor/plugs, ECT is a Volvo.

I'll check the ECT wiring and the MAF connector!

Post by **misha** » 27 Aug 2019, 08:04

Are NGK copper plugs properly gapped since they have wrong gap out of the box?
Proper gap is essential for turbo engines.

evdrive · Post by **evdrive** » 27 Aug 2019, 08:22

I gapped them when I swapped them out about 4 months ago.

evdrive · Post by **evdrive** » 27 Aug 2019, 08:23

If they weren't gapped right then I'd have issues when getting into boost. It would start breaking up.

evdrive · Post by **evdrive** » 27 Aug 2019, 08:24

When it happens on the hwy is when I'm just cruising at very part throttle.

Post by **abscate** » 27 Aug 2019, 10:06

Unplug the turbo control valve and drive it around. It should drive like a 160HP Volvo, smooth and powerful, but without the thrill of boost.

If it doesn't, forget about the turbo and find your induction leak.

To diagnose fuel side, start with measuring the Fuel pressure at the rail with a good quality gauge. No "I have fuel at the rail" or "it spurts" or other useless non-diagnostics.