Injection Pumps - Flow and PSI

[EFA]

Need to pick the brains of the experts here......

 

I changed from a JPE in tank pump to a Bosch 909 external on a bag tank recently.

 

Both are capable of driving a fuel pressure of around 80psi if the regulator is wound right up.

 

With the Bosch pump however, my engine runs richer than Ecclestone when running at 65psi (where it has set previously with JPE pump) to the extent that the engine will not idle. Pressure has to be reduced (measured at the fuel rail) to 50psi before it'll run cleanly at low revs.

 

Also, when running at 65psi on the bosh pump and monitoring fuel pressure via the stack, hitting the loud pedal to the floor sees pressure drop to 56psi momentarily.

 

So the equally high presssure, faster flow rate pump actually cannot sustain the pressure on demand, but over pressurises the system when running at the previously calibrated pressure.

 

Confused??? So am I.

 

What i do know is that the Bosch has a significantly higher litres/hour rating than the JPE (lucas) pump (160l/hr ves 125l/hr). Other than that there is no difference.

 

So do i need a full remap?

 

Or is it by chance I have another problem.

 

I have checked the coolenmt temp and air temp sensors report correct values to the ECU, and I have checked the calibration of the throttle pot has not moved.

 

Other than crank enrichment and coolant temp vs fuel maps (MBE Easimap4 or a 956ECU) is there anything else I could have overlooked?

 

Oh and forgot to mention that when i fitted the Bosch pump, without adjusting the regulator, the pressure increased 10psi so its already effectively backed down 10psi.....- is this a clue???

 

Fat Arn

Visit the K2 RUM site

See the Lotus Seven Club 4 Counties Area Website here

 

 

Edited by - fat arnie on 9 Sep 2002 00:15:43

[Peter Carmichael]

Fuel pumps deliver a combination of pressure and flow. The more pressure you ask of them, the less flow they produce. The pump is running constantly, so if the engine is idling and has low demand, the fuel pressure regulator is having to dump all the fuel back to the tank.

 

It sounds like your fuel pressure regulator is not up to the flow of the new pump. I reckon that when you are seeing 65psi at idle and gentle running, the FPR is actually set for 56psi and is swamped, so the indicated pressure is high. When the engine takes a lot of fuel - acceleration fueliing - the fuel bypass back to the tank is reduced because more is going into the injectors, bringing the FPR back into its working range for flow - you see the true set pressure.

 

It sounds like you need a bigger FPR. Until you get it, your fuel pressure is going to be very difficult to predict - it should be rock steady at all times.

 

Your car still went like a train though.

[Tony Martyr]

I agree with Peter, not his first staement but his technical diagnosis.

Pumps produce flow and the system downstream creates the pressure. The regulator has to be matched to the pump in terms of flow and it sounds as if yours is not. You also need to make sure that the return line to the tank doesnt create a back pressure with the increased flow

[Swiss_Tony]

Arnie

This sounds like the beginnings of an excuse!

What you need is a lovely pair of carbs

 

James

 

 

P17HPC The K2RUM EATER!

[Swiss_Tony]

Arnie

 

If K2RUM is "Back on the road and faster than ever"

What happened at Brooklands?

 

James

 

 

P17HPC The K2RUM EATER!

[Peter Carmichael]

Tony,

 

The hint of my opening statement was that the pressure and flow are interrelated. You can't have the one without the other. Pumps have a characteristic "pressure vs. flow rate" curve.

[Mike Biddle]

Arnie, I specialise in high pressure pumps, and both peter and Tony are correct in diagnosing the pressure regulator as the most likely problem here, i,e, it cannot handle the higher flow.

 

It is also possibe that the return line could cause a problem if it is too small. As fuel goes through the line, fricton will reduce it's velocity unless there is enough pressure to maintain it. In any given size of line, the more flow you introduce, the more pressure you will need to maintain a given velocity, and the smaller the line the greater the pressure required for the same flow. Length of line is also important. Pressure regulators can sometimes be "confused" by too much pressure in the dump line, and while I very much doubt this is a factor here, it might pay to try a bigger return line before buying a new regulator.

 

If you can give me the pump performance curve, estmate of injector consumption at idle, and ID + length of the feed and return lines (might as well check both) I will take a look at it for you.

 

Did you change to a bigger capacity filter as well?

 

Regards, Mike.

 

 

[Marius]

@Mike: specialised in high-pressure oil pumps I bet......

 

Another possibility: the ex-JPE pump had been placed IN tank so below fuel-level. The external BOSCH-pump (I guess) has now been placed above fuel-level, isn´t it ? The BOSCH pressure pumps are normally not suited to "pull" the fuel from the bag-tank so might make a difference in flow/pressure, too. But I´m not an expert though. Just had to fit a catch-tank and a second pump in order to submit enough fuel to the pressure pump.

 

Doesn´t K2RUM throw flames now when being overfuelled ???? Nice extra-gimmick for Le Mans 2003... 😬

 

Marius

[Tony Martyr]

Peter - I know-I know but I feel my sole purpose in life now is to keep you syntactically correct and to restrain your more exuberant technical postings lest they confuse the gentle reader. Perhaps a short piece on the different charactoristics of positive displacement and centrifical pumps as used in car engines should be your next subject - clearly some members get confused - not on this posting I hasten to add