Mystery engine problem
Discussion
Hi,
I've spent three days trying to diagnose an intermittent problem with my V8:
On cornering (e.g. roundabout) either left or right it loses power only to resume normal service once straight. I tried going all the way around a roundabout and it recovered breifly part way around only to lose power again. There are a few roundabouts near me and now a lot of puzzled motorists wondering why the bowler keeps making laps of the roundabouts...
The fuel system is exactly as pre-rebuild except that:
I had to replace the fast road Facet pump with a standard one as it was worn out (I originally thought this was the cause).
The breather is now a tube running around the outside top of the tank.
I have checked:
carburetters - stripped, found clean and float level set to 1mm
fuel lines - can be blown through easily (needed lots of mints to remove faint petrol flavour that lingers for ages)
fuel filter - clear pre-filter shows a good level of fuel
blocked off fuel return but this made no difference (except that it doesn't run out of fuel when the loud pedal is used.
lamp connected in parallel with fuel pump to see whether there was an electrical problem - there wasn't
lamp connected to coil supply to see whether there was an electrical problem there too- there wasn't
jacked it up with a hi-lift to simulate extreme cornering - the engine kept running
ETA:
In the past it has run fine even on very long steep climbs, descents or side-slopes.
Any suggestions for things I haven't checked?
100SRV
I've spent three days trying to diagnose an intermittent problem with my V8:
On cornering (e.g. roundabout) either left or right it loses power only to resume normal service once straight. I tried going all the way around a roundabout and it recovered breifly part way around only to lose power again. There are a few roundabouts near me and now a lot of puzzled motorists wondering why the bowler keeps making laps of the roundabouts...
The fuel system is exactly as pre-rebuild except that:
I had to replace the fast road Facet pump with a standard one as it was worn out (I originally thought this was the cause).
The breather is now a tube running around the outside top of the tank.
I have checked:
carburetters - stripped, found clean and float level set to 1mm
fuel lines - can be blown through easily (needed lots of mints to remove faint petrol flavour that lingers for ages)
fuel filter - clear pre-filter shows a good level of fuel
blocked off fuel return but this made no difference (except that it doesn't run out of fuel when the loud pedal is used.
lamp connected in parallel with fuel pump to see whether there was an electrical problem - there wasn't
lamp connected to coil supply to see whether there was an electrical problem there too- there wasn't
jacked it up with a hi-lift to simulate extreme cornering - the engine kept running
ETA:
In the past it has run fine even on very long steep climbs, descents or side-slopes.
Any suggestions for things I haven't checked?
100SRV
Edited by 100SRV on Saturday 3rd January 16:19
Cheers cptsideways,
the electrical system is a Range Rover harness which I modified myself, the ignition is standard except for a lumenition trigger / coil driver. When it loses power it isn't like turning the ignition off, more like no fuel. I tried wiggling the ignition system wires with it jacked up (to make it lean as when cornering - no result. Also the coil supply light remained lit when the engine lost power (although this doesn't mean the coil was being triggered - I'll try that in the morning).
Thanks again - another thing to try.
100SRV
the electrical system is a Range Rover harness which I modified myself, the ignition is standard except for a lumenition trigger / coil driver. When it loses power it isn't like turning the ignition off, more like no fuel. I tried wiggling the ignition system wires with it jacked up (to make it lean as when cornering - no result. Also the coil supply light remained lit when the engine lost power (although this doesn't mean the coil was being triggered - I'll try that in the morning).
Thanks again - another thing to try.
100SRV
Hi Carl,
the tank is about half full, I did wonder about fuel slosh but I'd have thought the fuel in the float chambers would fill in for any intermittent loss of supply. Besides which it has never suffered this problem in the past - even on severe side-slopes or climbs.
100SRV
the tank is about half full, I did wonder about fuel slosh but I'd have thought the fuel in the float chambers would fill in for any intermittent loss of supply. Besides which it has never suffered this problem in the past - even on severe side-slopes or climbs.
C. Grimsley said:
Are you getting a point where all the fuel moves to one side of the tank and therefore the pump gets starved of fuel for a split second, does it make any difference if the car has a full tank of fuel?
Carl
It doesn't sound like the fuel pump runs dry...Carl
100SRV
I'd have to agree that the problem is with the fuel supply.
My guess is that the reason it originally had the fast road Facet pump in there is because the stock one was marginal on volume and so gave the possibility of cutting out by not filling the float chambers enough to allow for cornering- which you cannot replicate with a forklift unless you tie it to the forks and spin round really quickly!
To summise, I think the replacement pump isn't quite filling the float chambers.
My guess is that the reason it originally had the fast road Facet pump in there is because the stock one was marginal on volume and so gave the possibility of cutting out by not filling the float chambers enough to allow for cornering- which you cannot replicate with a forklift unless you tie it to the forks and spin round really quickly!
To summise, I think the replacement pump isn't quite filling the float chambers.
Hi,
thank you for the suggestions...
Froggie - no fuel accumulator but the pump is mounted as per Facet instructions - outlet above inlet, approx at 45° angle.
GreenV8S - I'll borrow one on Monday
BB-Q - the "normal" Facet is only a stop-gap until I can get another fast road pump on Monday. The present "normal" pump will keep it fed at full-throttle in 1st and 2nd with a slight hesitation when changing to 3rd. The fast road pump was OK unless I had BBC needles in...
If it may point out other potential causes the carburetters are 2x SU HIF 6 on a Rover V8 manifold and feed a 3.9 Rover V8. These are clean and set up as per Rover instruction manual.
Pump is now on cotton reel mounts to reduce noise but there is an aluminium strap in case the mount fails and the earth is to the chassis.
I will drain the tank tomorrow and see whether there is any debris in there but the pickup gauze was clear. If it was fuel slosh I would have expected the float bowls to take care of this whilst cornering. The float level was checked and set to 1.0mm which is pretty much where it was before.
Many thanks for the suggestions.
100SRV
thank you for the suggestions...
Froggie - no fuel accumulator but the pump is mounted as per Facet instructions - outlet above inlet, approx at 45° angle.
GreenV8S - I'll borrow one on Monday
BB-Q - the "normal" Facet is only a stop-gap until I can get another fast road pump on Monday. The present "normal" pump will keep it fed at full-throttle in 1st and 2nd with a slight hesitation when changing to 3rd. The fast road pump was OK unless I had BBC needles in...
If it may point out other potential causes the carburetters are 2x SU HIF 6 on a Rover V8 manifold and feed a 3.9 Rover V8. These are clean and set up as per Rover instruction manual.
Pump is now on cotton reel mounts to reduce noise but there is an aluminium strap in case the mount fails and the earth is to the chassis.
I will drain the tank tomorrow and see whether there is any debris in there but the pickup gauze was clear. If it was fuel slosh I would have expected the float bowls to take care of this whilst cornering. The float level was checked and set to 1.0mm which is pretty much where it was before.
Many thanks for the suggestions.
100SRV
It would help if you told us what the carb is. Let me take a wild guess...Edelbrock 500
Mine would stumble when turning right, only figured out what was going on when I added a lambda sensor - It would go massivley rich, therefore I concluded that it was fuel sloshing out of the float chamber into the venturi.
Mine would stumble when turning right, only figured out what was going on when I added a lambda sensor - It would go massivley rich, therefore I concluded that it was fuel sloshing out of the float chamber into the venturi.
100SRV said:
If it was fuel slosh I would have expected the float bowls to take care of this whilst cornering.
The HIF are extremely good at coping with cornering forces and I doubt the problem is there. More likely imo is fuel surge in the tank. The engine would run using the contents of the float chamber, but depending how much power you're using this might only last seconds. The fuel pressure test should show whether this is the problem.
Hi,
many thanks for the suggestions...I've been fiddling with the car this morning and it is definitely dropping onto four cylinders when cornering, it makes no difference whether it is part or closed throttle (too much traffic for full throttle at the moment!). Question is how do I tell which carburetter is at fault? The engine runs badly for a couple of seconds and recovers just as quickly.
Note that the Rover inlet manifold is arranged so that the LH carburetter feeds 1, 4, 6 and 7 and the RH carb feeds the others.
Keep the ideas coming!
100SRV
many thanks for the suggestions...I've been fiddling with the car this morning and it is definitely dropping onto four cylinders when cornering, it makes no difference whether it is part or closed throttle (too much traffic for full throttle at the moment!). Question is how do I tell which carburetter is at fault? The engine runs badly for a couple of seconds and recovers just as quickly.
Note that the Rover inlet manifold is arranged so that the LH carburetter feeds 1, 4, 6 and 7 and the RH carb feeds the others.
Keep the ideas coming!
100SRV
Hi,
Oakdale - float chamber vents are not blocked.
I took it for a good blast tonight - roads very quiet (folks scared of the cold?) - observations:
1. It is running rich at idle.
2. It does not lose power as often, when it did it was when:
a. just finishing a right turn out of a tee junction
b. tight left turn off a roundabout
c. entering a roundabout at 12'o'clock position to exit at 9 o'clock it lost power at about the 6' o'clock position
I have ordered a new "fast road" Facet solid state pump to replace the present "road" item, when this is fitted I will remove the block from the return line restrictor. I will also correct the mixture then see whether the fault persists.
crustyfur2000 - I like the coil idea but it definitely drops onto four cylinders and I have a distributor / coil ignition system so a failure there should kill all eight cylinders. Out of interest can I use a "gold" Lucas performance coil with Lumention? I'm sure I've read that this is a good thing to have.
On the upside I trust the car enough to take it on a long excursion on a cold and frosty night - a big improvement as on Saturday I was reluctant to leave the estate!
100SRV
100SRV
Oakdale - float chamber vents are not blocked.
I took it for a good blast tonight - roads very quiet (folks scared of the cold?) - observations:
1. It is running rich at idle.
2. It does not lose power as often, when it did it was when:
a. just finishing a right turn out of a tee junction
b. tight left turn off a roundabout
c. entering a roundabout at 12'o'clock position to exit at 9 o'clock it lost power at about the 6' o'clock position
I have ordered a new "fast road" Facet solid state pump to replace the present "road" item, when this is fitted I will remove the block from the return line restrictor. I will also correct the mixture then see whether the fault persists.
crustyfur2000 - I like the coil idea but it definitely drops onto four cylinders and I have a distributor / coil ignition system so a failure there should kill all eight cylinders. Out of interest can I use a "gold" Lucas performance coil with Lumention? I'm sure I've read that this is a good thing to have.
On the upside I trust the car enough to take it on a long excursion on a cold and frosty night - a big improvement as on Saturday I was reluctant to leave the estate!
100SRV
100SRV
Probably not relevant here but there was a reported case of an engine losing power on turns which was finally tracked down to an electrical multi-connector between engine and wiring loom being pulled slightly in its socket as the engine shifted with the cornering forces.
The movement was enough to break a connection or two which was of course remade when the cornering forces ceased.
The movement was enough to break a connection or two which was of course remade when the cornering forces ceased.
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