Re-wiring Fuel Pump
Discussion
Hi all,
As I’ve only got 11.5v at the fuel pump with the engine running, I have decided to re-wire it.
Rather than unpick all the existing loom, I will run new cables directly from the battery via a relay (which will be triggered via the original pump cables).
I’m thinking of putting the relay in the cubby hole behind the passenger seat, and drilling a hole through the cubbyhole, for running the cables to the pump.
My question is- is the body tub “double thickness” in this area, or has anyone got any better ideas?
Many thanks.
As I’ve only got 11.5v at the fuel pump with the engine running, I have decided to re-wire it.
Rather than unpick all the existing loom, I will run new cables directly from the battery via a relay (which will be triggered via the original pump cables).
I’m thinking of putting the relay in the cubby hole behind the passenger seat, and drilling a hole through the cubbyhole, for running the cables to the pump.
My question is- is the body tub “double thickness” in this area, or has anyone got any better ideas?
Many thanks.
I wouldn’t use the existing cables at all as they are not great and have multiple connectors.
just run a new one from the inertia switch at the front of the car, I believe the yellow cable from it goes to the pump but double check this.
I ran some new cables under the centre console and drilled a hole near the top above the fuel pump area, pretty easy to do. I provided the pump with a direct negative from the battery too.
I ran some 2.5 mm heat resistant single cores we use at work which from memory are rated at 25 amps but I’d probably use a 2 core automotive cable for neatness sake if I did it again.
just run a new one from the inertia switch at the front of the car, I believe the yellow cable from it goes to the pump but double check this.
I ran some new cables under the centre console and drilled a hole near the top above the fuel pump area, pretty easy to do. I provided the pump with a direct negative from the battery too.
I ran some 2.5 mm heat resistant single cores we use at work which from memory are rated at 25 amps but I’d probably use a 2 core automotive cable for neatness sake if I did it again.
Edited by Belle427 on Saturday 11th June 09:32
Sir Paolo said:
................As I’ve only got 11.5v at the fuel pump with the engine running, I have decided to re-wire it.......
Rather than adding a 'fix' would it not be better to trace where the loss is?Do the same voltage check at each stage through that circuit Starting at fuse 13, fuel pump relay pin 30, then pin 87, Black Loop-back connector, connector where the wire colour changes from black to yellow/black, Immobiliser, Inertia switch, connector in the passenger side 'B' pillar.
If you are loosing volts in one of those many circuits then the likelihood is that other circuits will also be corroded and would benefit from the same clean you will give to this circuit.
Steve
Steve_D said:
Sir Paolo said:
................As I’ve only got 11.5v at the fuel pump with the engine running, I have decided to re-wire it.......
Rather than adding a 'fix' would it not be better to trace where the loss is?Do the same voltage check at each stage through that circuit Starting at fuse 13, fuel pump relay pin 30, then pin 87, Black Loop-back connector, connector where the wire colour changes from black to yellow/black, Immobiliser, Inertia switch, connector in the passenger side 'B' pillar.
If you are loosing volts in one of those many circuits then the likelihood is that other circuits will also be corroded and would benefit from the same clean you will give to this circuit.
Steve
Check voltages at all critical circuits and rectify all volt-drops found
2.5 to 3 volts volt-drop along any part of the fuel pump circuit is massive
Polly Grigora said:
Was going to post the very same comments
Check voltages at all critical circuits and rectify all volt-drops found
2.5 to 3 volts volt-drop along any part of the fuel pump circuit is massive
It’s a valid point, and I did consider that.Check voltages at all critical circuits and rectify all volt-drops found
2.5 to 3 volts volt-drop along any part of the fuel pump circuit is massive
However, with the potential number of failure points and degradation of the original loom, running new cables seemed the best option.
Fully understand your thoughts and they're good but you could regret them later
There's always a chance that all other circuits are good but this is an unknown at present
Determining what is causing the volt-drop matters much
If volt-drop is caused by a poor main positive supply to the fusebox it does need attention
If volt-drop is caused by a fusebox internal fault and is only present in the fuel pump circuit then it can be bypassed but you would still be taking a chance as corrosion or bad termination points within the fusebox will possibly overheat, short out other circuits and possibly start burning
Any volt-drop present in any circuit is a big problem because heat is generated at the cause of the volt-drop and heat can cause burning to take place which in turn can start a fire
Yes, It's a proper pain of a job at times to prove what's wrong but that is what the job is all about
There's always a chance that all other circuits are good but this is an unknown at present
Determining what is causing the volt-drop matters much
If volt-drop is caused by a poor main positive supply to the fusebox it does need attention
If volt-drop is caused by a fusebox internal fault and is only present in the fuel pump circuit then it can be bypassed but you would still be taking a chance as corrosion or bad termination points within the fusebox will possibly overheat, short out other circuits and possibly start burning
Any volt-drop present in any circuit is a big problem because heat is generated at the cause of the volt-drop and heat can cause burning to take place which in turn can start a fire
Yes, It's a proper pain of a job at times to prove what's wrong but that is what the job is all about
Hi Polly,
You are absolutely right!
I’m regretting it already - I fitted new cables from battery to a new relay, and now the fuel pump won’t even run.
And it only turns over on the starter if I put the fob in the steering column!
I checked all the connections for continuity- no joy.
So I put it all back together how it was- still no joy.
Does anyone want a Chim, before I torch it?
You are absolutely right!
I’m regretting it already - I fitted new cables from battery to a new relay, and now the fuel pump won’t even run.
And it only turns over on the starter if I put the fob in the steering column!
I checked all the connections for continuity- no joy.
So I put it all back together how it was- still no joy.
Does anyone want a Chim, before I torch it?
Hi all,
By way of an update (and as some of you clever ones out there in PH land have guessed, this thread is linked to the one on Ignition Coil Voltage) - the introduced non-start problem was traced to fuse 13 which had blown.
This of course is the fuel pump and CDL feed.
Interestingly enough, by putting new contacts on the fuel pump, using new spade connectors, I now have an extra 0.5v at the pump - to 12v in total.
This has also reduced the misfire/hiccup at 4.5k rpm, and more importantly, the engine now pulls through this zone onto 6k where it didn’t want to do previously
By way of an update (and as some of you clever ones out there in PH land have guessed, this thread is linked to the one on Ignition Coil Voltage) - the introduced non-start problem was traced to fuse 13 which had blown.
This of course is the fuel pump and CDL feed.
Interestingly enough, by putting new contacts on the fuel pump, using new spade connectors, I now have an extra 0.5v at the pump - to 12v in total.
This has also reduced the misfire/hiccup at 4.5k rpm, and more importantly, the engine now pulls through this zone onto 6k where it didn’t want to do previously
Sir Paolo said:
Hi all,
By way of an update (and as some of you clever ones out there in PH land have guessed, this thread is linked to the one on Ignition Coil Voltage) - the introduced non-start problem was traced to fuse 13 which had blown.
This of course is the fuel pump and CDL feed.
Interestingly enough, by putting new contacts on the fuel pump, using new spade connectors, I now have an extra 0.5v at the pump - to 12v in total.
This has also reduced the misfire/hiccup at 4.5k rpm, and more importantly, the engine now pulls through this zone onto 6k where it didn’t want to do previously
You use the word reduced- this is a worry if its still there at all as an engine that leans out under high loads can damage the piston crown due to lack of cooling fuel when temperatures are at there highest. The stock pump has a good capacity reserve so Id be surprised if .5 of a volt would have much effect TBH but as pump fuel load varied the voltage drop may have increased. The only way to really see if the engine is leaning out is to monitor the lambda probe outputs that needs plug connectors for the lambdas and long leads with a test meter that can be read by a passenger as you drive the car flat out. The lambda probe outputs normally cycle between 0 and about 1.2 volts up to 3400 RPM or less than 2/3 throttle. Above this they should read at least 1.2 volts constantly. If they drop to 0, then the car is running less than 14.7;1 AFR which is too lean for full load. Problem is now that an ignition misfire is also picked up as a lean mixture by the lambdas so may give you a false reading but its a good place to start. To be 100 percent sure you need to put a pressure meter on the fuel rail take off (serp engines) then peak load the engine and see if the pressure drops. Difficult to say the least without a rolling road, Of course lack of fuel can be something as simple as a kinked fuel line or blocked fuel filter apart from grotty connections on the pump. By way of an update (and as some of you clever ones out there in PH land have guessed, this thread is linked to the one on Ignition Coil Voltage) - the introduced non-start problem was traced to fuse 13 which had blown.
This of course is the fuel pump and CDL feed.
Interestingly enough, by putting new contacts on the fuel pump, using new spade connectors, I now have an extra 0.5v at the pump - to 12v in total.
This has also reduced the misfire/hiccup at 4.5k rpm, and more importantly, the engine now pulls through this zone onto 6k where it didn’t want to do previously
Ignition wise- the RV8 is a hard environment because you are asking for 4 sparks per engine cycle unlike a 4 cylinder engine at 2 so it means the coils dwell period is very short, and once you hit about 4000 RPM the HT voltages start to drop off significantly even on a perfect system. The combination of a high power coil and careful dwell control in the ignition amp means the system has enough headroom to maintain spark even at higher RPM as long as you don't mess about with it and everything is in good condition. Measurement of the actual HT voltages is difficult without specialist equipment like the old style Crypton or Sun engine tuners found still in classic car garages, but there is a wealth of information available if you look at the waveforms on all the plug leads when trying to trace a misfire.
Hi Blitz,
Many thanks for your detailed advice.
I do fully understand that a lean mixture under load could be unhealthy for an engine, so I make sure that I don’t go above 3.5k rpm unless I’m testing it.
It is odd that it is somewhat erratic in nature.
Sometimes this misfire will manifest itself at 3.5k rpm, and others at 4.5k rpm.
The idle seems to be affected too, as when coming to a standstill, it almost stalls, before settling down.
Yet, bizarrely this seemed to improve a bit on a run last night.
I do have Rover Gauge, but I’m not very familiar with all the readings, but maybe if I had a passenger they could view it and see what the Lamdba is telling me(?).
I have also considered a rolling road session which should of course be able to diagnose the issue while replicating being driven under load.
Many thanks for your detailed advice.
I do fully understand that a lean mixture under load could be unhealthy for an engine, so I make sure that I don’t go above 3.5k rpm unless I’m testing it.
It is odd that it is somewhat erratic in nature.
Sometimes this misfire will manifest itself at 3.5k rpm, and others at 4.5k rpm.
The idle seems to be affected too, as when coming to a standstill, it almost stalls, before settling down.
Yet, bizarrely this seemed to improve a bit on a run last night.
I do have Rover Gauge, but I’m not very familiar with all the readings, but maybe if I had a passenger they could view it and see what the Lamdba is telling me(?).
I have also considered a rolling road session which should of course be able to diagnose the issue while replicating being driven under load.
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