Jump to content

Fuel pump overheating


Recommended Posts

Yes, that is correct, it is virtually without pressure. Installing a cooler in that line may create some resistance; not sure if this affects the pressure set by the prv. I’m sure someone knows the answer.

Waldi

Link to post
Share on other sites

I'd install it in the line between the PRV and the tank- the bulk of the returned fuel goes through it. The boot is the obvious place but the heat exchanger will reject maybe 100W into the boot space  which may cause heating  problems.

I have a diesel DMAX ute that has a small return fuel heat exchanger mounted under the vehicle alongside the chassis rail- that location works OK-although it would present additional piping problems on a TR.

Link to post
Share on other sites

Hi Mike

What do you base your comment "the bulk of the returned fuel goes through it" on?

I have no knowledge on which of the two returns does the donkey work but my logic goes that if I run at very light throttle the PRV doesn't know and still poke fuel at 105psi to the MU.

The MU must chuck most of it back?

Also I am not aware of the presssure into the PRV from the Bosche pump I would have thought the one supplied to me by Revington must be specified to be just so? 

Link to post
Share on other sites

The prv returnflow is the biggest, by far. The pump volume (flow rate) is selected for full trottle (plus some extra for wear etc). Most of the Bosch pumps supply much more than the original Lucas pump. 
The extra energy For this additional flow is part of the problem (accelerates the overheating issue).

Waldi

Link to post
Share on other sites
2 hours ago, Prefect said:

Hi Mike

What do you base your comment "the bulk of the returned fuel goes through it" on?

I have no knowledge on which of the two returns does the donkey work but my logic goes that if I run at very light throttle the PRV doesn't know and still poke fuel at 105psi to the MU.

The MU must chuck most of it back?

Also I am not aware of the presssure into the PRV from the Bosche pump I would have thought the one supplied to me by Revington must be specified to be just so? 

Peter,

 

When your Fuel Pressure was adjusted it was set via the PRV, with the test gauge at the metering unit.

So you have 105 at the Mu, meaning you will, likely have a little more at the PRV with excess sent back to tank at the PRV.

 

cheers

Guy

Link to post
Share on other sites
4 hours ago, Prefect said:

Hi Mike

What do you base your comment "the bulk of the returned fuel goes through it" on?

I have no knowledge on which of the two returns does the donkey work but my logic goes that if I run at very light throttle the PRV doesn't know and still poke fuel at 105psi to the MU.

The MU must chuck most of it back?

Also I am not aware of the presssure into the PRV from the Bosche pump I would have thought the one supplied to me by Revington must be specified to be just so? 

"The PRV chucks most of it back." The pump pump's whatever fuel it can at ,say ,105 psi. Some goes to the MU , but the bulk of the fuel goes back to the tank via the PRV return, last time I checked the numbers, the fuel returned directly from the MU to the tank was almost negligible.

This makes sure the MU always sees more or less 105 psi at its supply piping inlet. In the days before digital controls this was a common method of ensuring a supply of liquid at  a constant pressure to a device. 

If a high volume of fuel went to the MU and then returned the MU supply piping losses would come into the equation and the higher the MU demand the lower its inlet pressure. Triumph avoid this by making the MU demand small  compared to what's circulating through the pump to the PRV and being generous with the sizing of the pipe from the PRV to the MU.

 

 

 

Edited by Mike C
Link to post
Share on other sites

Hi Mike thanks for your response.

I agree the system is based on offering 105psi at the MU at all times.

  •  "The PRV chucks most of it back." The pump pump's whatever fuel it can at ,say ,105 psi. Some goes to the MU , but the bulk of the fuel goes back to the tank via the PRV return, last time I checked the numbers, the fuel returned directly from the MU to the tank was almost negligible.

Won't this depend on the work of the engine? There must be a difference in return flow between Full chat and a very  light throttle.

Someone must have witnessed / measured the flow from the PRV back to the tank? Ditto for a return from the MU??

 

 

Link to post
Share on other sites

Hi Roy

Good idea! 

Logical and not high pressure! Limited location to the Left wheel arch next to pump but I will investigate.

Thanks

 

Link to post
Share on other sites
On 6/29/2020 at 8:09 PM, roy53 said:

The best place for a cooler is between the tank and pump. ensure you have a big enough supply pipe on the cooler.

Roy

I don't agree- it's the pump that heats the fuel so the delta T on the HE will be better after the pump, and I have never found a pump that works better with extra items of equipment in its suction line.

Link to post
Share on other sites

You first need to check voltage @ pump is within spec.
Before checking system pressure you need to measure how much excess is being dumped to tank.
If the volume is sufficient then you can set PRV pressure, if required.
Setting the pressure @ idle is meaningless if the volume is too low.
 

I used an empty petrol can and a stopwatch to test.
It was over 20 years ago when I last tested a Lucas PI pump and I cannot remember the time or volume! 45 seconds? 1L 90 seconds 1.5L?
Somebody else must know? 

Link to post
Share on other sites

I agree with Mike.

A small resistance in the prv returnline is no issue. But in the suction line it can lead to cavitation (again).

and it will be more effective, despite the slightly reduced flow compared to the suction line.
Waldi

Link to post
Share on other sites
11 hours ago, Mike C said:

I don't agree- it's the pump that heats the fuel so the delta T on the HE will be better after the pump, and I have never found a pump that works better with extra items of equipment in its suction line.

thats if you think hot fuel past the pump is your problem.

 

Link to post
Share on other sites
Just now, roy53 said:

thats if you think hot fuel past the pump is your problem.

 

That's what heats up the fuel in the tank. The air/fuel HE can't cool the fuel any colder than the surrounding  atmosphere. I agree with  Waldi -if I was installing a fuel HE I'd put it in the line from the PRV to the tank.

Maybe the petrol is short circuiting- going more or less directly from the PRV return to the pump suction - with the pump's heat being  effectively concentrated in a small volume of fuel. I have an aluminum tank with the PRV return  on the passenger side edge- making sure hot fuel has to cross the tank and cool  before it get's back to the pump suction. I also have a booster pump in the wheel well under the tank that feeds the Bosch as Bosch pumps hate low/negative suction pressures. My system will work with short runs on 40+ deg C days -when the fuel in the tank will be fairly hot to start with. 

Link to post
Share on other sites
On 6/26/2020 at 9:28 AM, Adrian Steele said:

Thx Andy.  Planning to check the pressure.  Re filter, its clear and the wiring was replaced 5 years ago when I fitted the new Bosch setup from Malcom  at Prestige.  Now all I need to figure out his how to keep peas frozen in the boot!

Cold water works too, just remember to take out the boot floor grommet!

Link to post
Share on other sites

A wet rag worked for me I was off the road 30 minutes ( my mate in his MGB took my wife to the destination :(0 

I am just trying to pre empt future issues, my cooler has too small connectors to place it before the pump, I think it would rstrict the flow.

Maybe an Oil Cooler would work?

This an age old issue I dont expect a magic bullet.

 

Edited by Prefect
Link to post
Share on other sites

I wonder us the cars that use the same Bosch pumps have this issue too. Or probably better: why not?

Waldi

Possible answer: could it be because of the much lower operating pressure of the Bosch K-Jetronic (and similar systems); although an even higher amount of fuel is pumped, it is at a lower current.

 

Edited by Waldi
See above
Link to post
Share on other sites
2 hours ago, Waldi said:

I wonder us the cars that use the same Bosch pumps have this issue too. Or probably better: why not?

Waldi

Possible answer: could it be because of the much lower operating pressure of the Bosch K-Jetronic (and similar systems); although an even higher amount of fuel is pumped, it is at a lower current.

 

They're DC pumps, so the power into the fuel  is roughly volts x amps = watts. Say 12x10 = 120 watts for a Bosch pump. The K-Jetronic pumps seem to use 5 to 8 amps= 60 to 96W input.

The K-Jetronic system has a fuel  accumulator which means that the pump doesn't have to pump as much  to meet peak demand ( even then  Volvo owners say  99% of what's pumped is returned to the tank)  all the time and the injection system is pressurized when standing- avoiding vapour lock  in the PI components in the engine bay after a hot stop greatly helping warm starts.

I'll also bet the K-Jetronic designers paid a lot more attention to the pump suction piping design- one of the advantages of being a 2nd generation system

Link to post
Share on other sites

Hi Mike,
yes we agree (again:))
I know the K-Jetronic system (a bit), it was on an old Porsche 911 I had and also on a Saab Turbo. Many of these cars use the same Bosch pump (type, spec) we use, but no overheating issues, which are high in our top ten topics;)

The accumulator indeed would allow a smaller volume pump size to be used, and keept the system pressurised when not running. It also means that if your injectors dribble, All the stored fuel will leak into the manifold.

I think (not sure) Bruce uses a smaller volume Bosch pump (0-580-254-952), drawing less amps. Have not compared the pump curves yet, but if it does, that’s a proper solution (frozen peanuts and an additional cooler are just fixes).

When I selected my Bosch pump from the available curves, it had the best match (pressure, flow and current) of all types I did have datasheets from.

Cheers,

Waldi

Edit: my pump is a Bosch 0580-464-126.

I compared curves and the rated current for both pumps above is the same (@105 psi)

Edited by Waldi
Link to post
Share on other sites
On 6/1/2020 at 6:39 PM, Ashley said:

I had enjoyed ten years without any trouble from my Lucas fuel pump and was mystified by reports of the pump overheating in hot weather. Then in July of last year, on the hottest day of the summer it finally happened. With less than a quarter of a tank of fuel the pump started to scream and finally the engine cut out. Some fresh cool fuel got the car going again and all was well on the 2 hour drive home apart from a smell of petrol coming from the “tell tale” or pump overflow pipe.
I therefore exchanged the pump for another from Moss but didn’t use the car much as I was fitting new UJs to the propshaft and winter came too early for me.

At the end of March and the beginning of lock down I filled the car up and then left it until a couple of weeks ago. Finally when out for a drive in the glorious weather but after 25 mins the car started to suffer from fuel starvation problems above 2500 rpm and the pump started to change it’s tune. The pump was hot to the touch so I looked into why the new pump might be overheating.

I borrowed an in-line pressure tester from a local classic garage and found that I was only get 75 psi at the MU. When I tried to adjust the PRV the best I could get was 80 psi before the adjustment screw went loose. I therefore replaced the PRV with the diaphragm type supplied by Remington as it seemed to be an improvement and I fitted the braided fuel line in the hope that this would finally remove the smell of fuel from the boot. ( At least that’s what the good man at Revington assured me.)

With the new set up the pressure at the MU was only 90psi, so I fitted the test line directly to the pump. The pump was only putting out 95 psi.

On calling Moss they were very good and sent out a new pump under warranty. I have just fitted the new pump.

The inline test shows that it is putting out 105 psi at the pump, which is giving me 98 psi at the MU.

Took the car to fill up with fuel as it was at about 1/3 and then went for a twenty minute drive. All was well until the last couple of minutes when the pump started to change it’s tune and the car cut out as I coasted into my drive. ( V lucky!)

Once again the fuel pump was hot to touch.

Does anyone have any thoughts on this?
 

On hearing that my friend’s Landrover was suffering from carb ice I wondered if the garages were still using winter fuel as low demand due to Corona Virus had not used up their stocks.

By the way the car is an early PI and does have a drop of 1 volt at the pump from the battery, however wiring the battery directly to the pump only increases the pressure by 5 psi. I have also put an air line on the MU return pipe and can hear it blow out in the tank. I assume that the return pipe to the tank from the T at the PRV is clear as it tried to empty the tank when I changed PRVs.

 

On 6/1/2020 at 6:39 PM, Ashley said:

I had enjoyed ten years without any trouble from my Lucas fuel pump and was mystified by reports of the pump overheating in hot weather. Then in July of last year, on the hottest day of the summer it finally happened. With less than a quarter of a tank of fuel the pump started to scream and finally the engine cut out. Some fresh cool fuel got the car going again and all was well on the 2 hour drive home apart from a smell of petrol coming from the “tell tale” or pump overflow pipe.
I therefore exchanged the pump for another from Moss but didn’t use the car much as I was fitting new UJs to the propshaft and winter came too early for me.

At the end of March and the beginning of lock down I filled the car up and then left it until a couple of weeks ago. Finally when out for a drive in the glorious weather but after 25 mins the car started to suffer from fuel starvation problems above 2500 rpm and the pump started to change it’s tune. The pump was hot to the touch so I looked into why the new pump might be overheating.

I borrowed an in-line pressure tester from a local classic garage and found that I was only get 75 psi at the MU. When I tried to adjust the PRV the best I could get was 80 psi before the adjustment screw went loose. I therefore replaced the PRV with the diaphragm type supplied by Remington as it seemed to be an improvement and I fitted the braided fuel line in the hope that this would finally remove the smell of fuel from the boot. ( At least that’s what the good man at Revington assured me.)

With the new set up the pressure at the MU was only 90psi, so I fitted the test line directly to the pump. The pump was only putting out 95 psi.

On calling Moss they were very good and sent out a new pump under warranty. I have just fitted the new pump.

The inline test shows that it is putting out 105 psi at the pump, which is giving me 98 psi at the MU.

Took the car to fill up with fuel as it was at about 1/3 and then went for a twenty minute drive. All was well until the last couple of minutes when the pump started to change it’s tune and the car cut out as I coasted into my drive. ( V lucky!)

Once again the fuel pump was hot to touch.

Does anyone have any thoughts on this?
 

On hearing that my friend’s Landrover was suffering from carb ice I wondered if the garages were still using winter fuel as low demand due to Corona Virus had not used up their stocks.

By the way the car is an early PI and does have a drop of 1 volt at the pump from the battery, however wiring the battery directly to the pump only increases the pressure by 5 psi. I have also put an air line on the MU return pipe and can hear it blow out in the tank. I assume that the return pipe to the tank from the T at the PRV is clear as it tried to empty the tank when I changed PRVs.

Hi Ashley,

What is the running current in Amps at the pump and what size is the feed wire to the pump? BL modified the size of wire in summer 72! Are the inertia s/w contacts clean?

Bruce.

Link to post
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Reply to this topic...

×   Pasted as rich text.   Restore formatting

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

Loading...
×
×
  • Create New...

Important Information

Please familiarise yourself with our Terms and Conditions. By using this site, you agree to the following: Terms of Use.