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Help on Fuel Metering Unit Timing


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Hi Folks, apologies in advance for the long post. I have a 1974 TR6 CR engined PI car, I've just bought it for restoration, it hasn't run since the mid 80s and I'm trying to start it before I tear it apart for resto. I'm having trouble getting fuel to the injectors, consistently certainly. I've fitted new seals, brushes etc in the pump and its generating pressure of approx 138 psi, I've checked the pressure at the engine side of the pressure relief valve and I have a nice 108 psi there at the FMU. Not that its particularly relevant at this point in that they cant work without fuel but Neil Ferguson refurbished the throttle bodies and injectors for me, a beautiful job and as I say whilst I am getting some fuel up there its not consistent. There is some pulsing of the fuel lines particularly when the fuel enrichment lever on the FMU is fully on, pulling out the injector valve stem with fingernails does produce some fuel and a bit of spray sometimes and at other times just a dribble. I've put new seals in the FMU and new diaphragms in the control unit and the interface between the fuel distributor and the control unit, haven't adjusted anything in there obviously. The FMU appeared in very good condition, the seals had gone hard and the diaphragm disintegrated after 30 odd years but as I say I've replaced those, everything else in there appears in superb condition and moves smooth and freely as it should. I've cracked no 6 port fitting with the fuel pump running and there is pressure and fuel there so I deduce from that the fueling chamber in the FMU is being filled and pressurised, I've run the pump with the fitting out and I get a gush of fuel out the port, which again confirms the fueling chamber is being filled and pressurised. 

My gut feeling is that I have a problem with the FMU timing, I working on the basis of 19.35.01 P.I. Sheet 2 on the repair manual and it does not work out perfectly as I apply it. I've marked off the crankshaft pulley at 20 and 45 ATDC, at TDC and with No 6 tappets rocking I rotate the gear drive in the pedestal  anticlockwise towards the engine until the No 6 valve port moves to no crescent visible (just disappearing at the top section of the port). The manual then states that a tooth rotation more on the gear and you should be in business. I dont know how anyone would ever judge a tooth more as its deep inside the pedestal so there is no reference point even by feel but leaving that aside I have tried it 50 times in every conceivable position after the crescent disappears in the port without a comfortably correct outcome. Obviously as one replaces the pedestal on the drive it will rotate the rotor in the sleeve so its a question of positioning it so that its just out of position at TDC but just appearing with another 20 to 45 deg crank rotation. The manual states that the rotor hole should not be visible after replacing the pedestal at TDC and then to rotate the drive gear until the rotor port just starts to appear and then check where the crank position is, if its between 20 and 45 degrees happy days and off you go. The very best I can achieve with many many efforts and variations on the theme is just about inside the 45 mark, as in something like 42 or 43, a hairs breadth inside the mark in other words. This makes some kind of sense in that clearly the pedestal gear is engaging on either one tooth or the next one on the helical drive, one results in the rotor hole appearing too early (it appears when you are still at TDC) and the next one results in it appearing uncomfortably close to the limit (45 ATDC), so I can see why its happening I think, but how the hell does one get a better resolution than either one tooth or the other, its a kind of binary situation! Although I didn't like being right on the edge after many attempts with different variations I thought "well within spec is within spec) and forged ahead and trialed it to no avail. I guess I could change the alignment of the fuel rotor and drive when mating the FMU to the pedestal but I'm doing that by the book, marks aligned on the FMU rotor and flange and the drive slot in vertical on the pedestal, unless someone tells me otherwise thats as per the manual.

Maybe within spec is fine even when its marginal and the problem isn't that timing but I just don't see what else it can be myself so although I absolutely hate being beaten I have to admit I have no more credible ideas here so have to ask, any ideas? Am I misreading the manual in some way, anything else?

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Wrong timing of the MU won't stop the engine running (even if it's 180 degrees out), and it certainly won't prevent a normal fuel spray cone from forming at each injector. Forget about timing until you have a good fuel spray. BTW the diagram in some manuals is printed upside down and following it hasn't brought a fleet of cars to a halt!

If all injectors are behaving similarly, then I'd suggest two likely culprits:

1. All your non-return valves (in the union with the MU at the end of each injector line) are shot. Possible, as the original condition of the other seals etc sounds ropey. This would prevent the lines from self-bleeding. But I'd expect that at least one would work, and also you've been bleeding manually, so I'd put this in the "less likely" bucket to start with. Maybe worth blowing out all the injector lines with compressed air in case there's some crud made its way in there.

2. Your fuel pump  is not performing, either because it's worn out or because it's getting low voltage (or both). Even though your pump is giving 108psi at the MU, we don't know how much volume it can deliver at that pressure. It needs to deliver 15gph at 100psi. As a crude test, direct the overflow from the PRV into some kind of container. Run the pump and record the time and amount collected. The rule of thumb from the Lucas manual is that the volume collected in 8 sec, measured in cc, and divided by 10, equals gallons per hour. If you get more than 150cc in 8 secs then you're good. Another check is what fuel pressure you see when cranking. If the wiring is at all below par (poor earth a particular problem area), the pressure will fall immediately you start to crank.

Have fun, and report back - there are plenty of people here to offer advice!

Cheers,
John 

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Thanks John, I agree both of those seem possibilities and I did think about them in passing but now that you lay it out I'll do more than think about it and do some specific tests.

1) All of the non returns leaking is a theoretical possibility given that they are the same age and made from the same materials and subject to the same conditions, but I replaced the two banjo fittings and therefore non returns (2 & 5) with new, I also tested all the others with a low pressure passing test, thats not conclusive but gets more unlikely as you say. I wont eliminate as a possibility but I'll jump to 2 initially. The fuel lines are new, again courtesy Neil Ferguson. I will re check 2 & 5 specifically on their own and see what that shows. I think I will take out and refit all of the sleeve to housing seals on the FMU and refit them if I can get them out without harm, I cant see how an error could be made there but they are common to all of the injection lines and all were replaced so maybe I could have done something stupid there.

2) The pump components look really good internally, its a fairly simple gear pump I dont think its worn out but I haven't checked its capacity to deliver volume at pressure, that's an easy check and will eliminate something else or maybe find the problem!

Its a great help to get those suggestions and to eliminate the fuel timing from the equation, thanks for the help. I'll try a few more tests and report back, might help someone else in the future who knows!

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Have you drained/cleaned the fuel tank (after 30yrs) that could be causing blockages early on in the fuel system. Also it does take a lot of cranking to get the fuel through to the injectors, ideally you need pull out the needle of each injector while someone is cranking the engine -bleeding the injectors of air, once the engine fires up it will start pulling the fuel through. If Neil hasn't, I would get him to refurb and set up the MU correctly.

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I'd try and ensure the injector lines are fully primed. I do this by:

Fresh fuel in the tank

Plugs out

Enrichment lever full on

Crank engine. Pull on the injector tips until all air clears from the line- I hold the injectors high to help vent air  and bleed into a jar until I get a good spray pattern

I then reinstall the plugs and injectors without the keeper plates and start the engine. At this stage you should be able to feel the injector pulse if you have the black nylon lines. Injectors with weak pulses can be removed and bled further by pulling on the tips over a suitable container. Don't let fuel spray near the manifold or injector port- I had a fire start once when I did this-shouldn't happen but it did.

When all injectors are clear reinstall the keeper plates.

If you can't get good spray patterns  with the bleeding process look at the MU-if your pump/PRV setup  is supplying 108 psi at the MU that's enough to bleed the injectors and get the engine idling with a good MU. 

 

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Steve, yes fuel tank has been removed and cleaned and has a decent amount of fuel in it.

Mike C, also yes enrichment lever fully on, plugs out, lots of cranking and yet not a good enough supply of fuel to bleed injectors, some fuel sputters out but not enough with any consistency to get a bleed, mostly air. It could be taken to look like a bleeding issue but its had a hell of a lot of cranking and pulling out of the injector stem and to no avail, I dont believe at this stage that its a straight bleeding problem.

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8 hours ago, JohnC said:

Wrong timing of the MU won't stop the engine running (even if it's 180 degrees out), and it certainly won't prevent a normal fuel spray cone from forming at each injector. Forget about timing until you have a good fuel spray. BTW the diagram in some manuals is printed upside down and following it hasn't brought a fleet of cars to a halt!

If all injectors are behaving similarly, then I'd suggest two likely culprits:

1. All your non-return valves (in the union with the MU at the end of each injector line) are shot. Possible, as the original condition of the other seals etc sounds ropey. This would prevent the lines from self-bleeding. But I'd expect that at least one would work, and also you've been bleeding manually, so I'd put this in the "less likely" bucket to start with. Maybe worth blowing out all the injector lines with compressed air in case there's some crud made its way in there.

2. Your fuel pump  is not performing, either because it's worn out or because it's getting low voltage (or both). Even though your pump is giving 108psi at the MU, we don't know how much volume it can deliver at that pressure. It needs to deliver 15gph at 100psi. As a crude test, direct the overflow from the PRV into some kind of container. Run the pump and record the time and amount collected. The rule of thumb from the Lucas manual is that the volume collected in 8 sec, measured in cc, and divided by 10, equals gallons per hour. If you get more than 150cc in 8 secs then you're good. Another check is what fuel pressure you see when cranking. If the wiring is at all below par (poor earth a particular problem area), the pressure will fall immediately you start to crank.

Have fun, and report back - there are plenty of people here to offer advice!

Cheers,
John 

+1 I would also expect that the O rings in the injectors are knacked and not sealing/ not holding pressure in the injector fuel lines? In my experience: when trying to start a TR from a completely dry system> All the black injector fuel lines have to be back filled with petrol to purge as much air from them before screwing the injector on. I was shown this method 40 years ago and it has always worked for me and others that I have shown it to.

Bruce

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OK. Fuel pressure at the FMU is maintained at 108 when cranking, +/- maybe 4 psi. However on a flow trial at 108 psi into the FMU the flow rate is 83-90 ml/sec ex the PRV into the tank, I take your word for the 150 l/sec as a rule of thumb although I cant find that reference but the capacity given in the repair manual on 19.45.15 P.I. Sheet 2 is even higher than that, so either way my pump capacity seems well off in terms of volume. Given its mechanical condition I find that really puzzling but its impossible to argue with it, the fuel in the can is what it is, the volumetric flow is much lower than spec, through the PRV and recirc into the tank anyway, it might be greater on a more sophisticated test through a larger line size and not through the PRV but no way is it increasing enough to meet spec. 

So looks like there is a definite problem there then, I'll replace the pump. In the short term though (I only need to start this and have it run for a minute in order to get it registered), as the pressure is always maintained shouldn't I be able to get fuel at the injectors and bleed them? Obviously if the volumetric capacity is too low then at higher revs presumably one would run out of fuel delivery capacity but for the volumes required for starting and tickover it should work? To test that theory I tried to bleed one of the lines and did actually manage to get it bled, it took what I would consider to be ridiculous amount of time to bleed one line and did my starter no good at all but I did manage to get a nice fuel cone out of one injector and the NRV is clearly working as I can leave it for ten mins and try it again and the cone of fuel persists with no hesitation. I've started on another line but I'll have to leave the starter cool now and come back to it. Is this a valid theory, that the pressure being OK and enough to lift the injectors off their seats that if I'm patient enough all injectors will get bled and there would be enough fuel capacity to at least start?

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Hi Bruce, as per the first post, new injectors, new lines and all rubber components replaced with the exception of the NRVs in the fittings ex the FMU which test fine.

But I think your advice on the bleeding might help me, I have succeeded in getting one line bled but it took silly time and will cost me a starter if I have to do them all in the same fashion. So pre filling the injector lines with fuel through a syringe whilst I crank it over and with the pump running should shorten that line bleeding considerably. Then I'll put on the injector with the line held at high level and its fitting vertical and bleed it vertically with the injector stem held open. That's how I got the first one done but without the syringe filling, that will for sure speed things along.

Thanks, I'll come back to you and let you know.

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Hi Steve, no I haven't as I only got fuel coming through on one as yet. But I'm going to persist now and see if I can get fuel coming out them all in the same fashion and then as you say I'll try with plugs in. Right now the challenge is the length of time cranking to get any kind of bleed is really over heating the starter so putting the plugs in is only going to exacerbate that situation. 

I anticipated a good deal of cranking so before ever I started with this I bought one of those geared high torque starters, it turns it over really well (plugs in or out) and I'd say it'll be really good under normal start conditions but I'm surprised at how relatively quickly it heats up. The original of course had a much greater mass so perhaps it would cope better with sustained load, I was always going to get that overhauled anyway as a spare but I'll definitely do so now.

Thanks for the help, having another go tonight so I'll repost on progress.

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Hi TRier

Regarding your pump output (assuming its a Lucas pump?). Bear in mind the 150cc figure is based on the pump running at 13.5V. At 8V Lucas quoted zero flow. If you were cranking the engine at the time then its likely your voltage will have dropped considerably. If your voltage at the pump dropped to 11.5V your figure of 83~90cc in 8 secs is not far off.

Even 90cc (9 G/hr) at 12.5V should be enough to start the car so as k raven smith suggests I would be looking elsewhere.  

This information can be found in the Lucas service training manual (Red cover) & is worth downloading, as is the Lucas service notes (Green cover).

Regards

Alan    

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TRier, where are you located?

Lots of good advice and expertise above.  

Having read the comments and given the OK pressure (108) at the MU I'm left wondering whether the issue is a partial blockage of the fuel flow from PRV to MU core.  3 causes come to mind:

  1. A partial blockage of the fuel line between the PRV and MU.  Of has that line been cleaned out or replaced?
  2. Has the internal condition of the flexible fuel line entering the MU deteriorated and so, when fuel attempts to flow, the line limits flow?
  3. The MU likely has the small fuel filter where the primary fuel line entering the MU.  Another possible point of flow blockage.

Jim

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Hi all, thanks for the help and suggestions. Have made some progress, with a combination of the suggestions, leaving the pump running, bleeding the injectors from a height and pre filling the lines it actually bled relatively easy, now I have a nice cone of fuel from each injector, lovely shape and maintained there even after turning off the pump and letting the thing lie for a bit. Having gotten to that point I've put plugs in, have spark at each plug. So I've spun it over with full fuel enrichment and I'm not getting it to fire, can alternate between backfires through the exhaust or at the inlet by advancing or retarding the distributor timing but at no point could I say its close to firing other than I guess backfires show some life! 

I notice a couple of things which wouldn't help here and I'll investigate tomorrow evening but if you have any suggestions on new info its appreciated. Its nearly 40 years since I looked at a spark but I would say these aren't quite as blue as I'd like and that's given there are new plugs, new condenser, new leads, new cap, new rotor, new points and a new 12 V coil (with a 12V supply not through the ballast wire), its not a bad spark I would think but not dead clean blue. The other thing I note is that the vacuum piping between the throttle bodies is not gas tight, its intact but quite slack on the connections, I think I'll change those in case they are leaking inwards and making the mixture too lean. I've static timed it at 10 deg BTDC. Actually the other thing I noticed when static timing it is that there is quite a lot of backlash in the rotor shaft, not sloppy laterally but back lash as in when its engaged in the drive I'd say it can be rotated back and forth by maybe 15+ deg (dist shaft rotation). Ultimately that's not great but as its rotation in one direction once its timed approaching from the right direction the backlash wouldn't stop it starting I wouldn't think? 

I've packed in for tonight but thanks for all the suggestions, progress made!

Edited by TRier
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Hi Jim, I'm in Ireland, in Kildare a little south of Dublin.

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Hi Alan, I'd say that's accurate enough, there is a voltage drop and of approximately the order you outline. I think things have moved along now past the pump worries, its probably not brilliant but definitely good enough for the short term purpose here which is just to get a start. I have fuel and fire now, I'd be confident enough fuel, fire I need to look a bit  more at to be confident but after that maybe now heading for a question mark over whether they occur at the right time. 

Thanks for the input.

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Thanks, I think that does have an effect.

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Is that Neil? Yes the manifolds were in poor condition, there is a lot of things in poor condition in this poor ole car, for now :). I cant comment on the efficacy of the FMU in terms of the set up of the control unit but it looks unmolested and the distributor part of it looks really good, it was actually dry when I took it off and no residue in it, yes the diaphragm at the control end was perished but I'd expect that. I did change it and all the other seals as a matter of course, it seems to be good and now its sequentially sending pulses of fuel to the injectors and certainly visually everything looks good, internally there was no discernable wear or marks and everything moves very smoothly. I am concerned though that at no time can I get this 20-45 deg ATDC for the appearance of port 6 on the rotor, as per the original post thats always effectively visible at TDC or else at something like 50 deg ATDC. Is that significant?

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Hey folks, just for a laugh. If Neil (I'm assuming k_raven_smith is Neil) thought the manifolds/throttle bodies were bad, look at the clutch master cylinder!:o This car needed to find a friend!

Clutch crystals.jpg

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49 minutes ago, TRier said:

Hi Alan, I'd say that's accurate enough, there is a voltage drop and of approximately the order you outline. I think things have moved along now past the pump worries, its probably not brilliant but definitely good enough for the short term purpose here which is just to get a start. I have fuel and fire now, I'd be confident enough fuel, fire I need to look a bit  more at to be confident but after that maybe now heading for a question mark over whether they occur at the right time. 

Thanks for the input.

Congratulations on making good progress. Any air leaks in the inlet manifold and connected piping will make the car very hard to start. With regard to your sparks -whenever I see Lucas components in any electrical system I start fault finding  by checking all relevant earths.

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4 hours ago, super6al said:

Hi TRier

Regarding your pump output (assuming its a Lucas pump?). Bear in mind the 150cc figure is based on the pump running at 13.5V. At 8V Lucas quoted zero flow. If you were cranking the engine at the time then its likely your voltage will have dropped considerably. If your voltage at the pump dropped to 11.5V your figure of 83~90cc in 8 secs is not far off.

Even 90cc (9 G/hr) at 12.5V should be enough to start the car so as k raven smith suggests I would be looking elsewhere.  

This information can be found in the Lucas service training manual (Red cover) & is worth downloading, as is the Lucas service notes (Green cover).

Regards

Alan    

Thanks Alan, I just downloaded that green book and the timing process in that is different to the repair manual. I'm going to re do it as per the green book and give it a try, I'll let you know.

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