P6 V8 manifolds and loss of power

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Nick666

Nick666

Active Member
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Somerset/Dorset border
Hi -
OK I know almost nothing about V8s except I'm obsessed with the sound, so bear with me! Two questions:

First:
Recently bought a S2a 109 which has a V8 which I'm told is from a Rover P6. It keeps losing power, tends to happen at speed (60ish) but don't know if that's relevant, basically starts sputtering and the power drops completely, and doesn't recover (but doesn't die completely) until you pull over, but pretty much as soon as you do it's just fine again. I half wondered if this could be from sucking crap up from the fuel tank, which blocks the fuel flow but falls away again when there's little suction? Any suggestions welcomed anyway!
[UPDATE - now happened at lower speeds as well, was only doing c.35 today]

Second: [solved]
The entire exhaust system is pretty much shot so looking as though it needs a new one - question is, where the exhaust manifold fits to the block, is that always the same for a Rover V8? I'm kinda assuming it is and the variation in manifolds (e.g. RR, SD1, Defender etc) is due to the other bits / obstructions around the engine in various vehicles?

Or have I got that all wrong? Kinda guessing I'll need to get a custom system made but it'd be handy if at least the flanges were standard!
 
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I don't know much about the P6 based V8 specifically but for the first problem I'd check for a worn fuel pump or poor connection to it. Once you get above a certain speed the fuel pump can't supply enough fuel and the engine will drain the float chamber. It's only once you slow down that the pump can keep the engine running and refill the float chamber.
 
Thanks this does mirror what I heard elsewhere as well - I am a bit confused now though, as today it did it at about 35mph and hadn't been going for long so either it's getting worse or it was just coincidence it was all at >50 before. Also now having to use the 'cold start' to get it going and it just isn't that cold yet.
 
Nick666 said:
Thanks this does mirror what I heard elsewhere as well - I am a bit confused now though, as today it did it at about 35mph and hadn't been going for long so either it's getting worse or it was just coincidence it was all at >50 before. Also now having to use the 'cold start' to get it going and it just isn't that cold yet.
Click to expand...
your first issue does sound like fuel starvation
 
The other thing to check is whether the flexible fuel lines have started to delaminate inside (due to the higher ethanol in petrol nowadays). It could be enough to block the fuel line slightly/occasionally.
 
Sigh, only just had time to do a tiny bit of checking and to bodge up a throttle return spring - keeps it nicely in line though at least so no stress on the linkages.

And no crud or water at all in the tank. BUT I did notice that the P6 has a return flow to the fuel tank, which this does not. Still don't know how much flow the pump's putting out right now (although a brief look suggested it wasn't firehose pressure anyway) but considering it sounds like HIF6 carbs only want about 3-4 psi wondering whether it might not actually be the opposite, and the carbs are overflowing. I'll work on that separately but clearly something that'll want looking at.

Obviously, my tank doesn't have the return already, or indeed the blank where one could be added - so seems like the options are:

1) swap for a diesel tank with the extra hole already in there (£120 I don't want to spend?)
2) find a sender that's compatible but has a return built in (the current one is the six-screw version so it'd be nice to have one that just swaps straight out...)
3) drill a hole and fit one of the diesel return pipes.
4) find a different route to plumb the return back in somehow - I can't think of any way to do that so it works, was thinking some kind of swirl pot but can't make it work in my head...

Welcome suggestions!
 
Have sourced a diesel return pipe so going to plumb one of these in - shame it doesn't have a blank fitted but not exactly an impossible task to fit! Now to be super clever and avoid disturbing the neighbours with loud noises like blowing my eyebrows off with sparks...
 
My 101 return on tank is just an elbow soldered to the top of the tank.You could make up a plate with an elbow soldered on drill hole in top of tank and screw plate on with a gasket.
 
How does it attach through tank?If youve replaced exhaust manifold make sure you use manifold gaskets early v8 didnt have them and can cause cracked manifold usually on left bank im told,just got my head back today po fitted long reach plugs and number 8 snapped
 
Two screws. Not replaced the manifold yet - first three companies I approached didn't reply! You'd think they didn't want custom. Got Powerflow going to look at it once I've sorted the fuelling situation (hopefully), good tip, will make sure they put some gaskets on for sure, but think the existing rust collection has gaskets there though right? (can't think what else those'd be if not gaskets)
IMG_20170916_175518717_HDR.jpg
 
Looking at pic on phone so screens small do you mean the lock tabs on bolts can't see if there's a gasket between manifold and head
 
If its a standard 3.5 why are you changing exhaust system?
You're first post does sound like fuel starvation I would fit return with external electric pump
If return is not fitted now and engine runs where from carbs will it return from
Cheers Rob
 
Another thought fuel starvation under power can be due to floats problem in carbs not letting enough fuel in
 
If you do fit a return, it needs to be smaller than the feed or fit a restriction in the line. Surprised p6 had a return. Sd1 didn't. Think they both used su
 
cooltide said:
If you do fit a return, it needs to be smaller than the feed or fit a restriction in the line. Surprised p6 had a return. Sd1 didn't. Think they both used su
Click to expand...

My thoughts as well my 101 is a year 75 on strombergs so has return from carbs and yes return is smaller but shouldnt make a lot of difference as floats control fuel level in carbs the return doesnt it just reduces pressure from electric pump
Meant to say don't know if sus on p6 had return or electric pump if manual lift pump no return needed as run by engine speed
 
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Thanks both! SUs on P6 definitely had a return, came off the banjo from the driver's side carb. And an electric pump. Will put something in the return line (won't hurt anyway right?). Doing that first as it was meant to be there and relatively easy/cheap to try. A replacement pump is the next on the list, followed by having the carbs refurbed then the ignition system replaced. [Right now both the ignition system and pump are unknowns, having been installed by POs.]
 
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