Fuel pump testing sequence
10-09-2018, 09:25 PM
#1
Three Wheelin'
Thread Starter
Fuel pump testing sequence
I have no fuel from the pump to the fuel rails. tested the fuse and pump relay and swapped out with others
and still no fuel. I jumped 87 and 30 at the pump relay, and touched the pump: I can hear that it is trying to work, and
it is straining, in a sense, if that makes any sense, and it gets warm. so this is not a power issue.
fuel filter was replaced on 01/17.
what is my next step??
and still no fuel. I jumped 87 and 30 at the pump relay, and touched the pump: I can hear that it is trying to work, and
it is straining, in a sense, if that makes any sense, and it gets warm. so this is not a power issue.
fuel filter was replaced on 01/17.
what is my next step??
10-09-2018, 10:46 PM
#2
Rennlist Member
How have you checked for fuel at the rail - opened a union carefully up there? Possibilitiies are a blocked filter (unlikely), pump jammed (seen that myself), in-tank pump blocked (heard of that), or a hose failure somewhere.
Check the Amps being pulled at the pump fuse - I see 7A with a single external pump, using a digital ammeter that plugs into the fuse socket -
https://www.google.com.au/search?q=d...iSQTvL7xkI70M:
. When my pump jammed, at the suggestion of SWMBO (she who must be obeyed), I applied reverse polarity to the pump terminals and it spat (past tense of spit) out something small and resumed normal service.
I would make a remote pump switch using 6-8 ft of 2 core flex, male spade tags one end to plug into the 30 & 87 sockets at the relay, and a momentary switch at the other. Have a fire extinguisher handy. Crack open the filter outlet a bit - gravity should feed some fuel out. Enable the pump briefly and see what you get - should be a significant spray. If not, crack open the pump outlet (to the filter) and try again. If still no flow, sounds like the pump is a problem. Close that connection, clamp the hose tank->pump, disconnect hose from pump, relax the clamp and you should get a gravity fuel flow....
Tales of in-tank pump failures commonly tell of hose failure in the tanks feeding pieces into the external pump, or causing it to overload and fail.
jp 83 Euro S AT 57k
Check the Amps being pulled at the pump fuse - I see 7A with a single external pump, using a digital ammeter that plugs into the fuse socket -
https://www.google.com.au/search?q=d...iSQTvL7xkI70M:
. When my pump jammed, at the suggestion of SWMBO (she who must be obeyed), I applied reverse polarity to the pump terminals and it spat (past tense of spit) out something small and resumed normal service.
I would make a remote pump switch using 6-8 ft of 2 core flex, male spade tags one end to plug into the 30 & 87 sockets at the relay, and a momentary switch at the other. Have a fire extinguisher handy. Crack open the filter outlet a bit - gravity should feed some fuel out. Enable the pump briefly and see what you get - should be a significant spray. If not, crack open the pump outlet (to the filter) and try again. If still no flow, sounds like the pump is a problem. Close that connection, clamp the hose tank->pump, disconnect hose from pump, relax the clamp and you should get a gravity fuel flow....
Tales of in-tank pump failures commonly tell of hose failure in the tanks feeding pieces into the external pump, or causing it to overload and fail.
jp 83 Euro S AT 57k
10-10-2018, 04:06 AM
#3
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After you have confirmed no fuel flow from the main pump as per JP above, then the most likely culprit is that the main pump is blocked with debris due to a failed connecting hose for the two-piece in-tank pump. (This, based upon your description that you hear the pump trying to work.)
Have you "serviced" the in-tank pump? If not, search for in-tank pump threads.
The only failures of the main pump I've encountered with 90+ is debris from the in-tank pump seizing the main pump.
If your pump is still trying, then after fixing the in-tank pump, reversing polarity (again as per JP) may clear the pump with no long-term effect.
Have you "serviced" the in-tank pump? If not, search for in-tank pump threads.
The only failures of the main pump I've encountered with 90+ is debris from the in-tank pump seizing the main pump.
If your pump is still trying, then after fixing the in-tank pump, reversing polarity (again as per JP) may clear the pump with no long-term effect.
10-10-2018, 08:31 AM
#4
Three Wheelin'
Thread Starter
I did crack a fitting at rail and no fuel.
will search regarding in tank pump. many replace with a strainer? since it is VERY hot (near 100 yesterday) here most of the
year, I would prefer to keep the in tank to avoid vapor lock??
will search regarding in tank pump. many replace with a strainer? since it is VERY hot (near 100 yesterday) here most of the
year, I would prefer to keep the in tank to avoid vapor lock??
10-10-2018, 10:15 AM
#6
Rennlist Member
The definitive thread is probably this one , our saga is at post #87. Whatever you decide, I would advise adding a narrow hose clamp to the tank fitting before trying to unscrew the pump or strainer.
How many miles on the car? Fuel pumps do fail, but new ones are not necessarily up to the standards of the originals. At a minimum refresh the intank pump or replace with a strainer, and then run a flow-test per WSM -- that will tell you how healthy the main pump is.
10-10-2018, 11:08 AM
#7
Rennlist Member
Vapour lock has nothing to do with a problem with the in-tank pump and everything to do with heat soak with a hot engine [i.e. you stop for fuel after run in hot conditions and then find you cannot start the car until things cool down a bit- that is vapour lock. If I was having a run in the middle of summer at the gas station I used to open the hood as soon as I shut the engine down.
As has been stated pull the main pump and give it an instantaneous pulse of reverse voltage and if you are lucky it will spit the culprit out.- even better if you can reverse flush with some diesel fuel but once the pump is spinning chances are it is problem solved [or a new pump].
As has been stated the likely root cause will be failure of the in tank hose. Roger does a little kit from GB to cover this. If the hose has failed there is no reason to believe the in tank pump is toast. I have pulled one to ;pieces and rebuilt it and it works but I have not put it into service. There were no signs of wear on the pump internals albeit it would be difficult to tell if there was short of components in pieces.
As Jim says some folks feel the in tank is not needed as they have removed and replaced with a strainer- I know I had problems under certain extreme conditions with a low fuel level and extreme cornering in an autocross event on a somewhat hot [for the time of the year] day. Most of the time you will probably get by without but...? The irony is that it is probably easier and cheaper to wreck the main pump by cavitation [should it happen] than it is to replace the in tank pump
As has been stated pull the main pump and give it an instantaneous pulse of reverse voltage and if you are lucky it will spit the culprit out.- even better if you can reverse flush with some diesel fuel but once the pump is spinning chances are it is problem solved [or a new pump].
As has been stated the likely root cause will be failure of the in tank hose. Roger does a little kit from GB to cover this. If the hose has failed there is no reason to believe the in tank pump is toast. I have pulled one to ;pieces and rebuilt it and it works but I have not put it into service. There were no signs of wear on the pump internals albeit it would be difficult to tell if there was short of components in pieces.
As Jim says some folks feel the in tank is not needed as they have removed and replaced with a strainer- I know I had problems under certain extreme conditions with a low fuel level and extreme cornering in an autocross event on a somewhat hot [for the time of the year] day. Most of the time you will probably get by without but...? The irony is that it is probably easier and cheaper to wreck the main pump by cavitation [should it happen] than it is to replace the in tank pump
Last edited by FredR; 10-10-2018 at 02:14 PM.
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10-10-2018, 12:21 PM
#8
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Before anyone decides “scientifically” that they cannot delete the (broken) in-tank pump, I recommend the following procedure:
- sit down in a comfortable chair
- have two shots of your favorite numbing agent
- call your preferred 928 parts supplier and get a quote on a new in-tank pump.
This procedure may result in reformulation of your theory.
- sit down in a comfortable chair
- have two shots of your favorite numbing agent
- call your preferred 928 parts supplier and get a quote on a new in-tank pump.
This procedure may result in reformulation of your theory.
10-10-2018, 01:03 PM
#9
Three Wheelin'
Thread Starter
Before anyone decides “scientifically” that they cannot delete the (broken) in-tank pump, I recommend the following procedure:=left
- sit down in a comfortable chair=left
- have two shots of your favorite numbing agent
- sit down in a comfortable chair=left
- have two shots of your favorite numbing agent
-removed the sending unit, and inside the tank looks spotless
-drained the tank, and took out the in tank pump. the hose does not appear to have deteriorated at all, but
you can see, it was nearly split in two
could this mean there is no debris in my main pump, and that my issue was that the in tank pump was sucking air?
what is the proper and safe way to clean the filter
10-10-2018, 02:07 PM
#10
Rennlist Member
That is the classic failure- the hose hardens with petrol exposure, it cracks and little bits of the hardened rubber brake off and snag the main pump.
What most folks do not understand is that the clearance between the impeller and the volute is tiny on small pumps like these otherwise the efficiency takes a huge dump. The size of particle that jams a pump is such that in part in can get between the impeller and the volute- then it jams. A smaller particle will pass through and a larger one will tend to bounce around but go nowhere.
Thus plenty of reason to be optimistic that the in-tank pump may still work and easy to check now that it is out. Same for the main pump.
The bit on the entry of the in tank pump is not a filter- it is a strainer- just give it a brush with an old tooth brush [no toothpaste!].
What most folks do not understand is that the clearance between the impeller and the volute is tiny on small pumps like these otherwise the efficiency takes a huge dump. The size of particle that jams a pump is such that in part in can get between the impeller and the volute- then it jams. A smaller particle will pass through and a larger one will tend to bounce around but go nowhere.
Thus plenty of reason to be optimistic that the in-tank pump may still work and easy to check now that it is out. Same for the main pump.
The bit on the entry of the in tank pump is not a filter- it is a strainer- just give it a brush with an old tooth brush [no toothpaste!].
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Chopperharris (05-06-2023)
10-10-2018, 02:17 PM
#11
Three Wheelin'
Thread Starter
^^^^^^^^^^^^^^^^^^
since the hose break is on the output side of the in tank pump, I assume you are talking about little bits getting
into the main pump??
in tank pump bench tests fine; all good there. was going to play with the main pump, but since it is 28 years old,
have decided to replace. roger sells a hose kit for the split hose, so I think problem is (soon to be) resolved.
does the hose just split in a moment, or does this evolve over time??
since the hose break is on the output side of the in tank pump, I assume you are talking about little bits getting
into the main pump??
in tank pump bench tests fine; all good there. was going to play with the main pump, but since it is 28 years old,
have decided to replace. roger sells a hose kit for the split hose, so I think problem is (soon to be) resolved.
That is the classic failure- the hose hardens with petrol exposure, it cracks and little bits of the hardened rubber brake off and snag the main pump.
10-10-2018, 02:37 PM
#12
Rennlist Member
^^^^^^^^^^^^^^^^^^
since the hose break is on the output side of the in tank pump, I assume you are talking about little bits getting
into the main pump??
in tank pump bench tests fine; all good there. was going to play with the main pump, but since it is 28 years old,
have decided to replace. roger sells a hose kit for the split hose, so I think problem is (soon to be) resolved.
does the hose just split in a moment, or does this evolve over time??
since the hose break is on the output side of the in tank pump, I assume you are talking about little bits getting
into the main pump??
in tank pump bench tests fine; all good there. was going to play with the main pump, but since it is 28 years old,
have decided to replace. roger sells a hose kit for the split hose, so I think problem is (soon to be) resolved.
does the hose just split in a moment, or does this evolve over time??
Good to know the in-tank is still functional.
10-10-2018, 04:46 PM
#13
Three Wheelin'
Thread Starter
can someone explain what effects can happen when the in tank hose is severed? the pump will still be sucking fuel,
but it will just be recirculating into the tank, so the main pump is receiving fuel via gravity only. but it would seem that
the amount of fuel to main pump is decreased?? if that is true, then the main pump will not be able to feed the fuel rails
at maximum capacity? I am wondering if this could cause a lean situation with fuel pressure not up to par??
but it will just be recirculating into the tank, so the main pump is receiving fuel via gravity only. but it would seem that
the amount of fuel to main pump is decreased?? if that is true, then the main pump will not be able to feed the fuel rails
at maximum capacity? I am wondering if this could cause a lean situation with fuel pressure not up to par??
10-10-2018, 05:28 PM
#14
Rennlist Member
If the in tank pump is still working then the fuel delivery will perform just like a system where the in-tank pump has been removed [i.e. no pressure on the suction to the main pump].
If the main pump reaches a point where it cavitates then the discharge head developed will drop and then it is a question of whether there is sufficient head left to satisfy the controller. I remember being advised many years ago that one sign of the in-tank hose having failed might be a slight reduction of top end power
If the main pump reaches a point where it cavitates then the discharge head developed will drop and then it is a question of whether there is sufficient head left to satisfy the controller. I remember being advised many years ago that one sign of the in-tank hose having failed might be a slight reduction of top end power
10-10-2018, 05:39 PM
#15
Three Wheelin'
Thread Starter
one sign of the in-tank hose having failed might be a slight reduction of top end power
acceleration and pitch of the car, and cornering, the delivery would be varied. at times the cut could be near closed, and other times more open.
I am trying to discern, is whether fuel pressure to the rails was also varied???
FWIW: surprisingly, the in tank hose still feels supple??