V70 petrol: Fuel starvation only when hot.Advice needed

[CSCUK]

Hi.
Help needed to diagnose fuel starvation fault on 1999 v70 2.5 petrol.

Fault description:
Starts from cold first turn of key.
Engine revs normally when I press the accelerator until engine hot.
Once engine has reached normal operating temperature if I attempt to rev the engine it dies immediately then will not start again until cold, once cold again engine will start and rev normally again.

I have renewed the fuel filter but it has made no difference whatsoever.

Back story of pattern of use of the vehicle prior to fault starting.
(this may give a clue to what is wrong)
I only use the v70 from June to late autumn as a surf wagon which I live in at whatever beach I'm surfing.
Between late autumn and June I take it off the road. Every June it starts first turn of key and then drives hundreds of miles to beaches without any issues.
Same story June 2023.

First occurrence of fault.
After being parked for a month at a beach I did a routine start and ran the engine until hot.
When hot I tried to rev the engine and it immediately died, although it stayed running (just) and each time I tried to rev it would almost completely die, but just manage to keep ticking over.

To fix this I used fuel system cleaner and poured the bottle into the tank before starting from cold.
When it reached normal operating temperature I very slowly pressed the accelerator to try to rev it (I'd already discovered that if I pressed fast it immediately died)
The slow pressing of the accelerator gradually increased the revs to higher revs without it dying, so I did this repeatedly until it was revving higher and higher.

Then I tried pressing the accelerator fast.
It revved without dying, but with a distinct pause between the press of the accelerator and revving, like it initially missed firing and then caught up and revved.
I continued revving it in this way until the fuel starvation completely cleared and it started revving completely normally again, no matter how fast I hit the pedal!
So I think cool, fault fixed, I can continue rolling.

Fast forward to late autumn and another beach.
It's now a month from when I had arrived at this beach, hoping to ride the majestic waves rolling in from the deep ocean swells off the coast of Africa.
Seriously awesome rides.

I do a monthly routine start and it was back to the exact same fault of dying once hot (despite it still having the fuel system cleaner in the tank!)

I walk into the local village and ask a mechanic at a garage what he thinks. The mechanic says it sounds like a blocked fuel filter. He says it may have gone worse coz of the fuel thickening over the months the car wasn't used. He says the 95 octane e10 fuel has a tendency to thicken with age.

I jump on a bus and get to a bigger village with a garage that sells 99 octane fuel. I fill a fuel can and take it back to my fuel-starved surf wagon.
I tank the 99 octane, start it cold then slowly rev it until the fuel starvation fault completely clears (exactly as it had done when I used the fuel system cleaner to clear it!)

Going by this, I only needed to have bought 99 octane fuel and not fuel system cleaner. Although the fuel system cleaner was still on board so could have helped?

Once it's revving normally I drive to a garage and fill the tank with 99 octane.
I then drive hundreds of miles stopping for varying lengths of time, (but never longer then two days) after all stops the wagon starts first time without fail, whether starting from cold or starting from hot.

It's now late late autumn and the nights are lasting 14 hours.
It's time to begin the journey home.

Certain that the fuel starvation fault is 100% fixed I drive the 300+ miles home (starting the wagon from hot a few times along the way without any stalling or dying)
It revs and performs perfectly the whole drive home.

Arrive home late autumn and park the wagon. Disconnect battery.

Last week I attempted a routine start and it's fuel starvation fault is back, and if anything it's worse than at the beach, because now it dies completely when revved instead of dying but still ticking over (albeit only just) like at the beach.
I thought changing the fuel filter would have fixed this but it has made no difference at all.

Yes, the fuel starvation fault can be temporarily fixed by slowly revving the engine until it builds up to higher revs for long enough to clear the fuel starvation (as I've described doing on two successive occasions)
but there must be something mechanically wrong for this fuel starvation to keep reoccurring.

I have previously left the wagon unstarted for long periods of time without it ever causing this fuel starvation problem,
including an 8 month period after which the wagon started and revved normally when hot, after not having been started for 8 months!

Appreciate help in identifying cause of this fuel starvation caused, or worsened, by leaving vehicle unstarted for long periods.

KRS

[SteveSarre]

Hi KRS

What exact model do you have?

If you put your reg into https://www.opieoils.co.uk/ it will give you some useful info which you could post back here.

Are all your dash lights working when you first turn on the key?
Does the engine fault code light go out when the engine starts?
Do you have a code reader ?
When were the spark plugs last changed?

Depending on your model, if you have a distributor cap and rotor, when were they last changed?

Hope that helps,
Steve

[CSCUK]

Thanks for replying.
The motor is a B5252S 10 valve
2,435cc petrol.
All dash lights work normally when ignition turned on and fault code light goes out when engine starts.
I don't have a code reader.
The plugs haven't been changed in a while but it's annual mileages are relatively low.
I've never changed the distributor and rotor.
I've attached a pic of the distributor, it may have electronic ignition system.

[Luxobarge]

Totally Agree with SteveSarre's comments and questions above. Although you think the fault is fuel starvation (and it might be) it sounds to me as if this is an assumption, without any actual empirical evidence. Poor HT ignition performance often displays these symptoms, and much of this is easy and cheap to check and rectify, so I agree with him, start here.

I'd recommend removing the distributor and cleaning it internally, especially the contacts, and replacing it and the rotor if it's in any way worn or damaged or showing signs of age. In fact, I'd recommend changing it anyway if it's never been done. Same with the spark plugs, I'd at least inspect and clean them, and ideally replace them if they are now quite old - irrespective of mileage. You also need to think about the HT leads, a good way of doing a decent check on these is to remove the big black spark plug cover and run the car in the dark - tickover will be fine. In total darkness you may see some stray sparks here and there, if so then they probably need replacing too. If there are no stray sparks, they are *probably* ok.

Having gained some confidence in the HT side of the ignition, you could turn to some proper diagnosis of the fuel system. It's quite possible that you're right, and it's a fuel feed problem, so the first thing to do is pop a fuel pressure guage on the schrader valve on the fuel rail and see what pressure you're getting, and under what conditions. I can't remember what pressure you should see here, others will be able to advise. I'm surprised that your "mechanic" didn't do this, it's quite simple and a guage is cheap. If you're getting the correct fuel pressure then it's highly unlikely that it's a fuel feed problem.

If you do come up with a fuel pressure issue then I'd suspect either fuel pump or fuel pump relay, neither are too difficult to deal with.

If all of the above doesn't sort it, I'd also be wanting to check for fault codes, even if the EML isn't on, but I seem to recall that this isn't straightforward with the 10V engine. Others on here will be able to advise how this can be done (a normal OBDII code reader won't work, I believe).

Hope this helps

[Bob Meadows]

The distributor cap is screwed on for this engine type:~

Quite easily removed but the lower fastener is hidden- but accessible.
Worth removing and cleaning or renewing if needed.
The rotor arm is also held in place by screws and serviced as above/or renewed.
That is the easy bit so worth doing.
Bob.

[CSCUK]

Thanks guys. I'll start working through everything suggested until it's fixed.

[SteveSarre]

Definitely remove distributor cap and rotor arm and see if they have significant deposits.
Almost certainly worth refitting new, unless in very good condition.

Then see if that helps, and proceed to other items as time allows.

HTH
Steve

[SteveSarre]

When the engine is cold, the injection system adds extra fuel to the mix.
(Which is what the choke does on older non injection engines). That makes it easier for the spark to ignite the air/fuel mix.

As the distributor cap, rotor arm and spark plug wires deteriorate, they become less able to generate and to pass a strong spark to each cylinder.

As spark plugs deteriorate, the electrode gaps increase and that also makes it more difficult for the spark to jump across and ignite the air/fuel mix.

When the engine warms up, less extra fuel is added, and you may reach a point at which the spark doesn't ignite the mix correctly. When that happens, you feel the engine misfire and lose power.

All because the ignition components had deteriorated.

[DaveNP]

I had similar with my car a few years back, it wasn't until I replaced the plugs, leads, distributor cap and arm 'just to be sure', that I found that one of the spark plug leads was shorting from the cap part inside the cylinder head. Struck me as odd because it was fine in the cold and damp when I would expect an electrical problem.

[duke1]

hi this sounds very familiar to me and took a day or 6 to find!just change the little water temperature sender housed alongside the thermostat and cheap when i bought one at partsmonster.com this not only give signal to the temp gauge but also signal to ecu so it knows when fuel mixture needs a response to keep mixture correct,this signal loss is common on our model and comes with age,long live the 850!