V8 missfire

Thanks Chris, i'm trying to contact the previous owner at the moment to establish if he used any sealant. I found red fibres in the pump which could be the o ring, but haven't seen any fuel leaks. In Austria on business at the moment so i'll investigate further when i return. Thanks again.
 
Hi all, just been reading the posts regarding V8 fuel vapourisation problems and the fact that many owners have fitted facet pumps inline. I'm starting to wounder if i should do the same. Each time i've had to remove the mechanical pump from my car i've used an old su electric pump fitted to the filter outlet to drain the fuel to below the reserve level to avoid spills and have always had a good flow. I was just woundering if i'd need to fit a pressure regulator inline with the facet or is it just a case of fitting the pump to the reserve outlet of the tank and straight onto the existing fuel line to the tap. I fitted a filter king pressure regulator/filter to my weber equipped car, along with a facet pump solid state pump (the small square one) in the boot, with a 8mm micro bore continuous copper fuel line from the tank to the bulkhead, and braid hoses linking up the lot. However i don't have a return line with that setup. I assume the pump i've described is the one used by other owners. I'd like to keep the operating pressure as low as possible to avoid leaks. I'd like some advise from anyone that has tried this conversion. I'd prefer to avoid doing this if i could but i'm running out of patients. I run a third V8 on the standard mechanical pump and have never had a problem, even in the heaviest summer traffic.
 
I also have the same problem with my 1975 3500 Auto, intermittent rough running / misfire and associated loss of performance. I'd tried the usual suspects; swapped coil for a known good spare, changed condenser, cleaned points, rotor arm, distributor cap etc. Sometimes these changes made a difference but usually only for a short time (or not at all). Along with the rough running & intermittent misfire, the vehicle developed an intermittent fault with the charging system, finally forcing me to replace the alternator. This cured the charging fault, and so far (since I only changed the alternator last night) has stopped the misfire. Would a failing voltage regulator induce these symptoms? I'm not that up to speed on vehicle electrics. The alternator is the 18ACR type with the voltage regulator built-in.

I still have the rough running to contend with but I think this is more related to fuel supply than anything electrical. The vehicle has a Facet electric fuel pump installed on the NSF inner wing, the pump is rated at 4psi. There does not appear to be a pressure regulator installed, though the Haynes manual shows a pressure range for the standard fuel pump between 3.5 and 5psi, so I'm assuming this pump would not need to be regulated? I have cleaned out the pump filter and found quite a bit of debris in there so I now have an in-line filter to fit before the pump (I'll do this tonight). I then have a 300 - 350 Mile round trip on Wednesday - Thursday for which I have to use the 3500 (the 2000TC being off the road undergoing rear end work at the moment). It'll be interesting to see how she performs! Next job is to have a full engine tune and fuel system check (including flushing the tank to remove debris). Hopefully, this should cure the remaining problem???

Cheers,
Mick
 
Hello Mick,

Hmmm, what brand of spark plugs are you using? When were they last changed? A spark plug, either fouled or on the way out can certainly give problems akin to what you have described.

As for the voltage regulator within the alternator,...when it starts to give problems or fails altogether, depending on the fault the battery could well be seriously overcharged (as has happened to me on one occassion.. :shock: ) or in the case of the latter will now discharge while driving, but it won't be the cause of the rough running etc problems that your 3500 is experiencing.

Ron.
 
Hello Ron,

Thanks for the reply and the tip regarding plugs, I'm off to the Garage just now to pull the plugs (something I should have done sooner :oops: ), so I'll let you know later. They have been in there since November 2007 which was the last full service the car had. The invoice from that service states NGK plugs but not the type used, what are the preferred plugs to use in a 3500 these days? The manual says Champion L92Y for a post 1972 car. I'll have a quick search on the forum for tips.

Cheers,
Mick
 
Hello Mick,

Funny thing with the plugs. The recommended plug for all the P6Bs post 1972 is Champion L92YC. I had always used these up until the original 3.5 was replaced by a 4.6. I always cleaned and gapped them every 6000 miles and replaced them every 12,000 miles.

They never gave me problems,...however a friend of mine, a fellow P6B owner used to have problems with these plugs, rough running and misfire. He used NGK plugs without problems. On one occassion I thought that I too would give the NGK plugs a try. Rough running and misfire was the result.. :shock: Back to the Champions!

The only major difference with our cars, even though they are both 1974 models is in the CR. Mine is (was) a 10.5 :1 while the other is a 9.25 : 1.

What is the CR of your engine Mick? Looking forward to knowing what you find..!

Ron.
 
Hi Ron,

Plugs are NGK BP5HS; took out # 1 plug, looks to be normal with light grey deposits as per the book. However, as a matter of course I will change the plugs over on my way to Shropshire today (got to return the Exchange alternator to Wins, so I can get a new set there). We'll see which ones Geoff recommends.

This Engine was fully rebuilt 7500 Miles ago and is a 9.5:1 CR Engine.

Before the electric fuel pump was installed, she ran as sweet as a nut. I never had problems with vapour lock or rough running. I've just installed the inline filter between the tank and the pump, so we'll see if that makes any difference.

All the same, this will be an interesting journey!

Cheers,
Mick
 
Lads, I'm hoping to return form Autria Friday and desperately want to get the car running so i've decided to fit a low pressure electric pump on the inner wing to overcome the problems. I think i have a spare reserve tap to fuel pump line in the workshop so i've planned to cut this pipe near the pump, bend both sides 90deg and attach 2 braid hoses up to the pump, which hopefully i'll be able to get 90deg unions for. This way i'll be able to maintain as standard looking a system as possible, and it'll be easily reversible. Failing that i'll disconnect the mechanical pump, leave it in place, and attach my braid hoses over the existing metal pipes without cutting them. I could make a small bracket to support the line to the filter as this is currently done by the pump. I also plan to fit an inertia cutout switch inside the front panel, operating a relay, to cut the pump in the event of a shunt. Doing it this way will avoid unreversible changes to the car and will also retain the reserve. I would prefer to keep the pump away from the front of the car/hot exhaust by putting it under the floor at the back but as well as the problems stated above, the car is broken down outside my house 30miles from my main workshop so i need an easy solution. Any views/advice on my plans? Good or bad idea?
Cheers, Dave.
 
I fully support the pump mod you propose. It should be a much better solution. But don't be surprised if it doesn't completely cure your problem. I still think your observation of gunk / sealer in the system is a likely cause. Problem with this sort of thing is that you are often looking at the cumulative effect of a lot of minor problems, each of which on its own isn't sufficient but taken together....

Chris
 
Chris, thanks for your support and words of caution. The previous owner has assured me that the fuel lines were cleaned through with compressed air a few months ago so i'll do the same before fitting the new pump. My first priority is to get her to run so i can at least get her back to my workshop, or even drive her onto the transporter. I'll give her a shakedown close to home so that i can tow her in for more work if the worst happens. A friend of mine has now suggested removing the mechanical pump, fitting a blank plate to the block, and plumbing in at that point. He suggested finding a pump small enough to fit to the block, with some form of heat insulation, in place of the old pump, to make the modification almost invisable. This is wishfull thinking though! The previous owner of this car went to great lengths to keep the car original so i don't want to undo his work. I think an inline filter might be an idea if i have room to fit one. I also have to replace the fuel sender unit so i'll have an opertunity to get some gunk out of the tank while i'm at it. At the moment i suspect that the sender could be the source of the sealer if it was replaced in the past. I'll have a look on the net for a suitable pump and hopefully start work at the weekend if i ever manage to get out of Austria!!
 
Hi all, just been on the net looking for a suitable electric fuel pump to fit in the engine bay and have hit a problem. I found a list of pumps, and chose 3 possible units as follows: SS500 or SS501 Cube pump, with 2.0-4.0psi/25 gals/hr and 3.0-4.5psi/30 gals/hr respectively. Or the 60104 posi-flow pump 1.5-4psi/25 gals/hr. The posi-flow is the neatest looking pump and should be easy to mount. There is also a filter inlet unit available and a non return outlet, both of which just screw into the pump. However, several sites i have looked at mention that the pump has to be mounted within 8" of the tank. This seems to apply to all the facet pumps. However, while searching for a pump i found a part number for an engine bay mounted electric fuel pump for pre '86 PAS equipped carb range rovers. When i searched the part number a facet pump came up. In the pump data sheets a dry prime figure of 300mm is quoted for the facet, leading me to think it should still work in the engine bay. My other alternative is an SU type pump, but these are quite bulky. Does anyone know of a small SU type pump or should i stick with facet. If i stick with facet i think i'll go with the posi flow. Any comments?
PS: What size/type are the treads on the original fuel line to pump connection?
Regards,
Dave.
 
Hi all, just to keep you all up to date on my long running fuel saga! My plans to fit the pump under the bonnet have been scrapped. It's amazing how the mind can create space under a P6 bonnet when your thousands of miles from the car! I couldn't find a suitable location so I now plan to fit it at the back. However I'm also considering fitting a reserve tap before the pump, at the back so i can keep this feature. I found a hose/pipe specialist to supply the correct connections to bridge between the original fuel lines once the mechanical pump is removed, so that the system will still look close to standard. Have to go off on business again monday but may try (er indoors permitting) to sort it out before i go. Have trailered her back to my workshop so at least now i have try conditions to work in.
Will keep you all posted.
Regards,
Dave.
 
Hi all,
I finally got around to fitting the facet pump this week. I mounted it close to the tank outlets, connected to the reserve line. Dispite the fact that the mechanical pump had been fully rebuilt the engine had refused to run. I cut the reserve line and joined the pump to the tank with a short length of hose, and ran about 2 feet of steel braid fuel line to a position where i could safely rejoin the original line (space near the pump for a joint was very tight). I left the rest of the fuel system as it was (including the mechanical pump). Once I fitted the electric pump it fired instantly and ran perfectly. After a few seconds of running I shut the electric pump down and she continued to run, and has done since (drove about 15 miles last night). I'm going to try running it like this and see how i get on, only using the facet if I run into problems. Have a lot of driving to do this weekend so I'll let you know how it goes.
Regards,
Dave
 
Hi all,
after 4 days, 150 miles and 2 shows, the missfire has returned. I felt some hessitation saturday evening on my way home, however it soon cleared. However, today after about 6 miles the car started to missfire at idle and I had to blip the throttle to keep it running. I switch on the facet, which apart from making noise, did no good. I limped the car home (it went ok over 1500 rpm) and it promptly died. I let it cool and fired it up and all seemed well again. However, after standing for several hours it ran like a pig again. I had it running on reserve with and without the electric pump, and it barely ticked over at 500rpm, then i switched to main feed and after about 30 seconds the idle went back to normal and it sounded like a V8 again. This lasted for about a further 30 seconds and then died, refusing to start again until i put it back on reserve feed and fired up the electric pump (though again it ran like a dog). So the situation at the moment is: It'll start and run like a dog on reserve. Switching to the main feed has no effect for about 45 seconds, then she runs perfectly for about 30 seconds and then dies. Won't start on main feed, won't start on reserve without the electric pump. What is going on here??? Earlier in this post chrisyork mentioned the o-ring in the reserve tap, could this be my problem? Funny thing is I can always draw the fuel out with my old su pump when i need to drain the tank.
Regards,
Dave
 
Well it still sounds like a fuel supply problem doesn't it. The implication is that there is an intermittant blockage. The switching to main tank and everything being ok for a few seconds sounds to me like you are using a fuel lines worth of fuel and then there is no more forthcoming. That implies both inlets in the tank are being blocked by a "floater"! But I wouldn't put huge amounts of money on that!

Since this has probably reached your seriously aggravating threshold i think I might start by removing the tank from the car (quite easy). Then have the float and feeds assembly out of the tank and examine everything very carefully. You should be able to get a new float and feeds assembly if required, they're not common but they are around. If the inside of the tank looks anything other than in perfect condition I'd be inclined to replace it with one from a scrapper. There's no reason a 2nd hand tank should have suffered external corrosion. The only debate is whether the inside might have suffered through having been stood with petrol in for too long. Petrol is hygroscopic, plus you have the effect of atmospheric heating and cooling drawing water vapour (we are in England!) into the tank.

Chris
 
Chris, thanks again for your input. The good news is that I have a new sender/pick up set to fit (the sender unit failed before I bought the car). I'm starting to wounder if the two are connected. The strange thing is that any time I have a problem I find that I can draw fuel through the system no problem with my old SU pump connected to the filter outlet. I assume that the fact that the facet is a push pump that it doesn't have enough suction to overcome the restriction. I think I might rebuild the reserve tap as well while the tank is drained just in case. One owner here is still trying to convence me that the problem is vapour lock, but surely that would clear when the car is cold.
Regards,
Dave
 
Hello Dave,

To second what Chris stated,...it does indeed sound like a fuel supply problem, but there is no guarantee that it is. By all means renew the "O" ring within the fuel reserve tap, but I doubt it will make any difference at all.

The fuel tank sender unit is removable without the need to remove the tank from the car, should you prefer to do it that way.

I would doubt very much that your car would be suffering from vapour lock when it is cold, although it has happened to my P6B,...but that was down to the fuel, not the car.

Ron.
 
Thanks Ron, I'll start by removing and checking the sender/pick up, though I find it strange that both the reserve and main lines could be effected at the same time, especially as the fault is intermittant. I've started to look at the fuel tap because it is the common item between the two supplies. I also notice that the facet didn't seem to speed up, indicating, in my mind, that she's getting fuel. Is there some kind of a gauze around the outlets in the tank that could be dirty that would effect both at once? Any further advice would be very welcome, I'm chasing this problem with 10 months now :( .
Regards,
Dave
 
Hello Dave,

The main line protrudes up into the tank from the sender unit for a couple of inches and has no gauze cover of any kind, rather it is just the bare metal pipe. The reserve line on the other hand does indeed have a gauze cover, in the shape of a dome which sits right on the base of the sender unit, reaching up barely an inch.

Unless you have a major blockage in the fuel filter itself?? I assume you changed this one?

I run a clear fuel filter at the base of the tank on the main line before the electric fuel pump. Any debris coming through is easy to spot, and is trapped there so as to not clog up the fuel pumps.

It could be an ignition problem,...misfires are common in that regard when things start to play up.

Ron.
 
Hi Ron, due to the location of my fuel pump (very close to the tank outlet) I had no space to fit a standard inline filter, however I have fitted the standard facet inline filter that comes in the form of a pipe union. The main fuel filter was replaced by the previous owner just before i got the car, and i can draw fuel up through it easily (I've emptied the tank several times by undoing the outlet side of the filter and attaching a length of hose and a pump - which has always generated a good flow). I've been through the entire ignition system and i'm happy with it. It's definately a fuel delivery issue, as before i fitted the facet the carbs and filter were not getting any fuel (though i could still draw it through the system). I already rebuilt the old ac pump, primed the system up through the filter with the su, and tried starting it, which only resulted in a splutter (and a dry filter). Maybe i should fit the old su pump permanently! I'll try removing the filter outlet and have a look see how the facet performs pumping fuel out, It's fitted to the reserve line by the way. If both pumps are struggling, how can I pump 3 gallons out of the system in a few minutes with the su?
Regards,
Dave
 
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