Fuel temperature and possibly worn efi pump issues?

[sowen]

This is something that's been in my head for the last few days since getting my turbo'd Rover P6 back on the road. After the mot I drove to work, about 25 miles motorway and B roads. Most of it was gentle cruising, but after 20 miles I noticed it felt like the engine was cutting out under boost. Got to work fine and left it all day.

On the way home it progressively got worse to the point that it felt like it was stuttering on cruise on the motorway. I took it out for a hard blast yesterday with a pressure gauge attached to the fuel rail for 15 miles and it was fine, but today I did the same route to work and back and it faltered at exactly the same places as it did on Friday. I saw the pressure was dropping under load, and the last 10 miles to home the pressure was fluctuating and wouldn't rise more than about 2psi above base pressure of about 40psi.

I left it for a few hours before draining the fuel tank which was still warm, not hot, but definitely not cold, as I'd expect with an efi system pumping fuel front to back. The fuel tank is located above the back axle in the boot, and the boot floor immediately below the tank was warm.

Previously I've had lots of trouble with fuel supply and cavitation, and am beginning to think that the high pressure pump, an unbranded 044 inline type, may have become damaged and as the fuel warms up it's losing it's pumping ability? After turning it off the fuel rail still holds 40psi pressure which I believe they should do.

Is this a feasible scenario? I'm hoping replacing the pump with a new one should sort it, and should I look into fitting a fuel cooler too?

[Phil H]

Is there a swirl pot (or similar arrangement) anywhere in the system, feeding the HP pump or is it just taking a tap from the bottom of the tank? Could the return line be causing aeration of the fuel (i.e. just returning the fuel to the top of the tank somewhere)?

Are the fuel lines insulated when in the engine bay? Slightly extreme, but Jaguar used the aircon system to keep the fuel cool on the V12 XJ-S but a 5.3l V12 generates an awful lot of heat although virtually all OEM fuel systems tend to have some sort of heat sleeving on the lines when they're in the engine bay.

[sowen]

Aug 6, 2018 6:43:41 GMT Phil H said:

Is there a swirl pot (or similar arrangement) anywhere in the system, feeding the HP pump or is it just taking a tap from the bottom of the tank? Could the return line be causing aeration of the fuel (i.e. just returning the fuel to the top of the tank somewhere)?

I have two 1/2" feeds from the bottom of either side of the tank which are fed into the top of a small reservoir mounted low down. This reservoir feeds the pump from another 1/2" hose, then it's 3/8" hose to the front along the transmission tunnel inside and joins directly onto the fuel rail which is just above the footwell. The return line follows the same routing to the back, but re-enters the tank through the original sender unit which is located in the bottom offset from the centre alongside the axle, with a 90 degree elbow pointing at the centre of the tank. I very much doubt it's causing aeration in the tank, or at least I really hope that's not the issue?

Aug 6, 2018 6:43:41 GMT Phil H said:

Are the fuel lines insulated when in the engine bay? Slightly extreme, but Jaguar used the aircon system to keep the fuel cool on the V12 XJ-S but a 5.3l V12 generates an awful lot of heat although virtually all OEM fuel systems tend to have some sort of heat sleeving on the lines when they're in the engine bay.

Fuel lines are not insulated and it is a tiny engine bay, but they are short where they exit the tunnel/footwell area which is just below the manifold and fuel rail. The exhaust system is on the other side completely seperate from the induction side. The fuel tank sits just above the back axle inside the boot, so I'm thinking heat is also rising in there too?

The fuel pump I've got has been in a couple of my projects in the past, is unbranded and has been run dry on the odd occasion being used as a sucker pump above a tank so I'm thinking that it's just worn and struggling to pump warm fuel at pressure? I am thinking of adding heat insulation around the fuel tank and axle to reduce the heat coming up, as with most cars the fuel tank is external and would have airflow around it to help take away some heat?

[Phil H]

I’m thinking, based on your description, that the heat source is likely the pump that’s both failing to pump enough juice, and acting as a heater too.

Bit like I’ve just had a starter motor do to me recently - battery power just seemed to heat up the cabling and motor rather than do the useful work of turning the engine.

[sowen]

What makes me convinced it's getting warm and failing is that on the two trips I did of the same route, the rate and timing of failure was almost exactly the same like I was repeating the journey. My initial thoughts were that if it was the fuel pump failing surely it just wouldn't create the pressure all of the time, but only seems to do it when hot? This also makes me think that I've had similar issues in the past with fuel supply problems on my Rover, and that pump could be partly responsible for the numerous breakdowns and waiting for it to cool down before continuing?

The lightbulb moment was remembering I used to have carburettor icing problems on my Land Rover, and that would start at exactly the same point passing under a bridge every time and clear on the same straight stretch of road without fail!

[npp]

I had a very similar scenario in my Elise which was indeed traced back to a faulty fuel pump - it would cut out on a hot day. Letting the car cool down or putting some fresh, cooler, fuel in would cure it for a while and then it would come back. No problems on short drives or colder days.

Had an expensive racing-spec fuel pump fitted last year which solved the problem, even on very hot trackdays.

[silver63]

From experience generally when fuel pumps get hot they draw more amps.Is there any way you could temporarily wire an ammeter into the circuit viewable from inside the car and observe readings when fault occurs?

[sowen]

Aug 7, 2018 5:43:10 GMT npp said:

I had a very similar scenario in my Elise which was indeed traced back to a faulty fuel pump - it would cut out on a hot day. Letting the car cool down or putting some fresh, cooler, fuel in would cure it for a while and then it would come back. No problems on short drives or colder days.

Had an expensive racing-spec fuel pump fitted last year which solved the problem, even on very hot trackdays.

Yeah that sounds a bit like what I'm getting. Can't say for colder days, they just don't happen anymore

Aug 7, 2018 7:25:12 GMT silver63 said:

From experience generally when fuel pumps get hot they draw more amps.Is there any way you could temporarily wire an ammeter into the circuit viewable from inside the car and observe readings when fault occurs?

I could, and that's not such a bad idea, just that I'm on a time limit to get the car done for RRG and thoroughly tested. It's blocked up with the tank drained awaiting new fittings to fit the new fuel pump before pressing into commuting duties again

[swampy442]

Could you not adapt a fuel cooler from say, a diesel VAG car and use that in the return line? They have a flat mounted cooler mounted on the floor

[sowen]

Aug 29, 2018 7:42:15 GMT swampy442 said:

Could you not adapt a fuel cooler from say, a diesel VAG car and use that in the return line? They have a flat mounted cooler mounted on the floor

I've been eyeing up the fuel cooler on my Rover 75 before I scrap it, but since replacing the fuel pump I've not had any issues. It's been driven further and the fuel has remained cool, though I am running nearer a full tank now.

[swampy442]

Good news

[froggy]

The cheap O44 usually last a few yrs at best , I went through a couple on one car in five yrs and have replaced the one on another car after three yrs. I went over to in tank pump o n both cars now .