PI Difficult to start after a couple of weeks.

[EGCD]

42 minutes ago, PodOne said:

Hi Steve

No expert given the present company! It will be very interesting to me and many to see a resolution of the issue here's my thoughts.

It would seem that the ignition gives good spark, the fuel pump has a good electrical supply and earth. Fuel pressure good at the MU and she idle's and runs well once started and will start ok up to a week later. Am I correct in thinking there are non return poppet valves in the MU for each line or just one serving all six? if so then given the age of the unit and modern fuel they are possibly not holding pressure in the lines which gradually empty over the week.

When you switch off could you not pull all the injectors and crack a couple of the unions say at 3 days and see if there is fuel under pressure then two more at 6 days and the last two at 9 and see if there is a noticeable difference or perhaps no fuel at all. Or will cracking two at 3 days have the effect of affecting them all? 

Just a thought while I put my coat on!

Best of luck.

Andy

 

Andy, a very good thought and I will plan to do this.

Going back to the original question in my post, I did ask for more information on the non return valves in the metering unit that I had heard about, that I presume should hold pressure in the injector hoses, but I haven't had any feedback yet.

I'll probably get the MU looked at over winter.

Steve 

[OldBob]

7 hours ago, EGCD said:

Thanks Gareth. Ill leave the car for a couple of weeks and then try a start with all injectors removed and bagged to see if I get fuel instantly, I never thought of that.

Steve

Steve,

Do an injector drip test.

Method:  after running car & making sure its running on 6 cyls,  garage car and whip out all six injectors quickly and suspend them vertically over a carboard sheet. A box works best with injectors pushed through one side (still attacehed to their fuel lines ).

Watch over next few hours and see which if any, drip, losing their fuel contents onto the cardboard.

Injectors that give a good healthy cone spray pattern can still slowly drip their contents away while parked and it leads to poor starting or starting up on just 5 cyls.

Bob

[PodOne]

Good point Bob forgot the injectors are in effect high pressure one way valves so fuel has another escape route over the long term.

Andy

[EGCD]

17 minutes ago, OldBob said:

Steve,

Do an injector drip test.

Method:  after running car & making sure its running on 6 cyls,  garage car and whip out all six injectors quickly and suspend them vertically over a carboard sheet. A box works best with injectors pushed through one side (still attacehed to their fuel lines ).

Watch over next few hours and see which if any, drip, losing their fuel contents onto the cardboard.

Injectors that give a good healthy cone spray pattern can still slowly drip their contents away while parked and it leads to poor starting or starting up on just 5 cyls.

Bob

Thanks Bob I'll try that after my next run and report back.

Steve

[Mike C]

14 hours ago, astontr6 said:

What state is your battery in when you go to start up after a winter lay up? I have found that if I have not fully charged up my battery and left it on trickle charge for a few days, it seems to make it difficult to start.

Bruce.

Thanks but the battery is perfect- the battery conditioner keeps it in good shape.

Whatever causes the TR6 long term hard starting problem is something that happens  after  months not days. Many perfectly satisfactory daily drivers become hard to start after long term storage.

For me, it's so infrequent that it's bearable, but if there is a fix I'd like to apply it.

[Rob Salisbury]

10 hours ago, EGCD said:

Andy, a very good thought and I will plan to do this.

Going back to the original question in my post, I did ask for more information on the non return valves in the metering unit that I had heard about, that I presume should hold pressure in the injector hoses, but I haven't had any feedback yet.

I'll probably get the MU looked at over winter.

Steve 

Steve, 

            The 4 straight unions and the 2 banjo unions that screw into the metering unit contain spring loaded seals that act as non return valves, you will normally get these with a reconditioned metering unit, though I have noticed that Prestige sell them individually but at £30 a pop 4 of these gets you on the way to a full recon unit.

Cheers Rob 

[astontr6]

7 hours ago, Mike C said:

Thanks but the battery is perfect- the battery conditioner keeps it in good shape.

Whatever causes the TR6 long term hard starting problem is something that happens  after  months not days. Many perfectly satisfactory daily drivers become hard to start after long term storage.

For me, it's so infrequent that it's bearable, but if there is a fix I'd like to apply it.

What about the petrol starting to degrade. I had this problem with a Strimmer? I could not get it started until I emptied the old petrol.

Bruce.

[Mike C]

1 minute ago, astontr6 said:

What about the petrol starting to degrade. I had this problem with a Strimmer? I could not get it started until I emptied the old petrol.

Bruce.

I used to have  a winter  petrol degradation problem until I started using Stabil.

The fact that the car will  start from dead cold start satisfactorily a day after a short  run indicates the fuel is now OK.

Whatever causes this problem only affects the starting after a long period of inactivity. Draining of the injector lines after the MU could be a possible cause-I've never checked whether it occurs more often with low fuel levels in the tank.

Since I've started using Stabil I've left the tank full over winter and the engine does seem to be easier to start than I recall from earlier times. Before that I let the tank run down for winter , refilling with fresh fuel in spring.

[john.r.davies]

ECGD

You describe the symptoms precisely: "Symptoms are that the engine spins up fine, but wont catch until at least 3 cranks of about 15 seconds, and then it only fires on a couple of cylinders and requires chasing with the starter spinning before the others kick in."

This implies some drain down of fuel from the injectors, so that the lines contain air.    Air is compressible, and will be ejected from the nozzles, but only in small quantities each time they are pressurised.   As that is completed and fuel arrives at the injectors, that cylinder will fire.   I don't think any of the other explanations are sufficient.

In turn this implies that the injectors seal imperfectly, but I think you have replaced them, so maybe you can't blame them.   It may be a small leak in the M/u.   I have M/us adjusted for 2.5L and 2L, and the latter suffers from this, but not the 2.5 version.      Your DPO replaced the M/u in 2006?   does this one have all-Viton - alcohol resistant - seals?

Meanwhile, leave the pump on for longer before starting, to ensure full pressurisation and use the choke lever for longer.

John

[astontr6]

1 hour ago, Mike C said:

I used to have  a winter  petrol degradation problem until I started using Stabil.

The fact that the car will  start from dead cold start satisfactorily a day after a short  run indicates the fuel is now OK.

Whatever causes this problem only affects the starting after a long period of inactivity. Draining of the injector lines after the MU could be a possible cause-I've never checked whether it occurs more often with low fuel levels in the tank.

Since I've started using Stabil I've left the tank full over winter and the engine does seem to be easier to start than I recall from earlier times. Before that I let the tank run down for winter , refilling with fresh fuel in spring.

Drain down of the injector lines is a problem as I have suffered from this. I overcame this by re-O ringing the injectors with some special O rings made from a green Viton material. I took a bit of arm twisting to get him to supply them on their own but it has cured the problem of drain down. My injector lines will start to pulse as soon as the engine is cranked. I have the odd one that does not go straight away.

Bruce

[Mike C]

15 minutes ago, astontr6 said:

Drain down of the injector lines is a problem as I have suffered from this. I overcame this by re-O ringing the injectors with some special O rings made from a green Viton material. I took a bit of arm twisting to get him to supply them on their own but it has cured the problem of drain down. My injector lines will start to pulse as soon as the engine is cranked. I have the odd one that does not go straight away.

Bruce

Thanks, I'll keep this in mind for my next injector service.

Last time I did a major injection system bleed , I seem to recall the air in the injector lines was reluctant to move until I pulled the tips- I believe the air volume was large enough and its pressure high enough to absorb the slow speed petrol pulses from the MU without opening the tips and  admitting extra fuel into the lines.

If there is a significant drain down of the injector lines during long periods of inactivity this may be why it's so hard to reestablish fuel flow.

 

Edited November 3, 2022 by Mike C

[Waldi]

Did anyone on here connect a pressure gauge in the line from pump to MU, and then leave it there after a run?

What is considered a “normal” rate of pressure reduction? 

Cheers,
Waldi

[john.r.davies]

I have a pressure sensor just before the M/u and a read out guage on the dash.  Pressure is 100-105psi on start up, and drifts down to 95 when warm.   And, as I'm using wide open throttle on circuit, then it may drop to less than 90.

Would others consider this unusual, or a problem?

I've also monitored the temperatures in my rather complex fuel system, complex because I have a swirl pot, to prevent surge admitting air into the system when the tank not full.   "Temp tabs" on lifter pump, swirl pot and PRV do not register, but one on the main pump shows that it gets to 37-40C.    Has anyone else done likewise, and what did you find?

John

[JohnC]

Hope you've solved the problem, but if not...

The only thing that stands out to me is the braided injector lines. Having said that, I have no hypothesis as to how they would be a problem over weeks. As you say, they have (only) been cast as a likely suspect in hot starting problems. But how about this: Replace them with white (translucent) lines. That way you know the braiding isn't a problem *and* you can see if one or more lines develop an air lock (and how big). I've done this, and I can tell you that air locks of 1-2" are no problem. More, and you'll likely get the engine starting on less than six cylinders, or only after long cranking.

It may not solve your problem (but it might), but it will allow you to eliminate or not whether petrol leakage is a problem.

Hope this helps
John

[Tom B]

I have a 1970 TR6 and it behaved just like the OP – difficulty starting. I did some work on the injectors that others may find useful/informative.

The thread on the injector to the fuel lines is ¼” BSPP. The flat is also ¼” Whitworth (13.34 mm) which is why it is difficult to find a suitable spanner in your toolchest (I had one at the bottom..)

The car has a mix of injectors 73125 A,D and E plus one Injector, 73045A, which is different to the others in that the flat on the injector is not 1/4" Whitworth but probably 3/8" Whitworth (18mm).

If you run through air from a compressor it will be damp. The bodies seem to rust quite easily so it is best that they are re-installed and used promptly after refurbishment

The O-rings are available from Polymax (the go to place for O rings)

4.47mm ID x 1.78mm CS FKM (Viton) 75  BS008V75

17.12mm ID x 2.62mm CS FKM (Viton) 75  BS115V75

(Suitable for Gasoline (including high alcohol content) temp range -10C to +150C)

I replaced all the O rings as I was uncertain of the heritage. The larger ring is for the insulator blocks and the smaller for the injector. I use a bit of silicon grease to aid installation. (I appreciate that will wash off with the petrol but it makes life easier during re-assembly)

Some had filters in the body some didn’t. When I have the strength I may look around to see if there are any suitable replacements.

The ring at the bottom of the injector near the tip that flies off when you remove (advice from a previous poster on performing this operation in a plastic bag is extremely good) is known in engineering circles as a “snap ring”. I have not tried to buy any but a search on that term brings up appropriate results.

The injector pressure was set at 51 +/-1psi. I tried various ways to set/measure the pressure but the one that worked the best was also the simplest. I have a cheap “H***s” compressor (actually it works quite well) that has a digital display. I made up an adapter from a ¼” BSPP cone fitting and an old Schrader valve with the guts removed (shown in the photograph) and powered it from a battery. It quickly pumps up to pressure and when connected to the injector gives a good display of the pressure. Because the compressor runs off a piston, and the pressure is modulated slightly, the injector happily puffs away about 3 times/second. We therefore have a dynamic measurement (as recommended by another poster).

I did the injectors in turn and didn’t allow the fuel lines to drain (they were supported upright). After each injector replacement the engine was started and run until all cylinders were firing. If this is followed there should be no need to “bleed” the air out. I did notice that as each one was re-set the starting became easier. If the poppet valve pressure is too low (as some of mine were) then the sealing against fuel draining away is poorer. The “before” injector opening pressures were 26, 53.5, 53, 39.5, 37.5, 40 – quite a variation. However, when running, I have to say the engine seemed rather good, but the starting was poor. It seems better now I have re-set the injectors but time will tell.

[EGCD]

On 11/2/2022 at 9:48 PM, OldBob said:

Steve,

Do an injector drip test.

Method:  after running car & making sure its running on 6 cyls,  garage car and whip out all six injectors quickly and suspend them vertically over a carboard sheet. A box works best with injectors pushed through one side (still attacehed to their fuel lines ).

Watch over next few hours and see which if any, drip, losing their fuel contents onto the cardboard.

Injectors that give a good healthy cone spray pattern can still slowly drip their contents away while parked and it leads to poor starting or starting up on just 5 cyls.

Bob

Thanks Bob, I tried that today, and after shutting down after a good run I took out all the injectors, and wrapped blue tissue around each needle valve to soak up any leaking petrol. I monitored them over the next few hours and there was no sign of any dripping from the injectors.

After about 6 hours, I gently pulled out each needle slightly against the spring pressure, and no fuel came out.

I can only assume that the pressure had dissipated and drained back through the Metering Unit.

For how long is it reasonable for some fuel pressure to be maintained in the injector hose after shutdown?

[EGCD]

On 11/3/2022 at 8:34 AM, Rob Salisbury said:

Steve, 

            The 4 straight unions and the 2 banjo unions that screw into the metering unit contain spring loaded seals that act as non return valves, you will normally get these with a reconditioned metering unit, though I have noticed that Prestige sell them individually but at £30 a pop 4 of these gets you on the way to a full recon unit.

Cheers Rob 

Thanks Rob, looks like I might be going down that route.

Steve

[EGCD]

On 11/2/2022 at 6:42 AM, Mk2 Chopper said:

Have you tried turning the engine over with the injectors removed and see if they spray straight away or are taking time to fill back up? 

A couple of other thing I didn't see was checking the tappets/ valve clearances and the throttle plates/sync. It's critical on a PI to set these both up as changes in vacuum at idle will change the mixture. 

I would have to agree that apart from that you've done everything else to resolve, and really it's only the MU left to look at should those couple of checks not prove to make any difference. 

Gareth

Today was the first start for 10 days. Before starting, I removed all the injectors, and gently wrapped the ends in blue tissue to soak up any fuel.

30 sec pump running to prime the MU. After a 20 sec crank, no sign of any fuel from any of the injectors. After another 20 sec crank fuel showed from injectors 3 and 4. After a third 20 sec fuel showing on 2, 3, 4 and 6. It took a forth 20 sec crank to get fuel coming from all injectors.

I then refitted the injectors and the engine started within a few seconds.

With the other results I think this confirms pretty much that the MU unions/seals/valves need looking at.

Steve

[Mk2 Chopper]

Just thinking out loud here, but if your getting drain down on most injectors, the only place for the fuel to go is back to the rotor and finally out through the return line. 

So it would be interesting to remove that pipe at the MU and observe it continue to flow sometime after the engine has been off. 

Gareth

[Steves_TR6]

Really interesting thread as my car does exactly the same thing !

injectors were refurbished by Neil F so i trust them, but the MU came with the car 10 years ago so os suspect.

i do also have braided lines……

steve

[Tom B]

2 hours ago, Steves_TR6 said:

Really interesting thread as my car does exactly the same thing !

injectors were refurbished by Neil F so i trust them, but the MU came with the car 10 years ago so os suspect.

i do also have braided lines……

steve

Steve,

My suspicion is that the injectors need checking every few years. Springs deteriorate, surfaces get worn etc... One of the injectors I took out was leaking fuel which can't help the starting issue.

Tom

[Spit_2.5PI]

On 11/8/2022 at 10:20 PM, EGCD said:

30 sec pump running to prime the MU. After a 20 sec crank, no sign of any fuel from any of the injectors. After another 20 sec crank fuel showed from injectors 3 and 4. After a third 20 sec fuel showing on 2, 3, 4 and 6. It took a forth 20 sec crank to get fuel coming from all injectors.

I then refitted the injectors and the engine started within a few seconds.

With the other results I think this confirms pretty much that the MU unions/seals/valves need looking at.

Steve

4 hours ago, Steves_TR6 said:

Really interesting thread as my car does exactly the same thing !

injectors were refurbished by Neil F so i trust them, but the MU came with the car 10 years ago so os suspect.

i do also have braided lines……

steve

Yes, mine too! Mine is all KMI circa 2005 and I suspect the internals are pre-ethanol. I've changed the injector seals to Viton - no difference. The fact that none of the injectors have fuel tells me that it's the MU which is the common factor.

One little thing mine does - if I start it for just a few minutes or less, in other words I don't let the engine get warm. Then stop and leave it for several days, it will start on the button. None of this 20- 30- 40-seconds cranking nonsense! Do yours do this, Steve and Steve?

Cheers, Richard

[John L]

I have a very similar issue, I did take the 4 none return valves apart, seems impossible to do the other 2, and turned the rubber bung over in the none return valve, just turn the spring around and lets the rubber plug come loose, they were very marked, but the biggest issue here is the untidiness of the machining of the seat that the rubber is expected to seal on, I think it did improve for a while but is bad again now.  I too have the metal braided hoses, and these must hold a larger quantity of fuel in them compared to the black nylon pipes, perhaps this is more relevant than it appears, the injectors have had the viton seals by Mike Bilney.

Perhaps it could be the o rings and the fit of the rotor and shuttle that is allowing some creep back of the fuel, again once been run and left for a few days it starts fine.

John 

[Peter Cobbold]

On the other hand if the shuttle fit is a little loose it would allow fuel to pressurise the injector hoses without cranking.

[EGCD]

A bit more progress today.

First undid the injector hoses for #1 and #6 at the MU as these were the easiest to get to. 

Both hoses were pretty full with fuel, which I wasn't expecting, but I've no idea of course if the hoses were completely full.

Inspected the NRVs in the unions and they both seemed ok, holding pressure, and passed a simple tongue suck test, albeit for only a short time.

Made up a simple rig for checking the injector blow off pressure using an inflator compressor with a digital pressure gauge (uncalibrated) as previously suggested. #1 blows off at 44 psig and #6 at 54 psig.

NRV union, braided hose and injector assemblys for #1 and #6 leak checked with toungue suck test and no leaks identified.

However when I was about to refit the NRV unions in the MU I noticed the O ring seal in #6 port was partly disintegrated and obstructing the port slightly. It's possibly always been like that or maybe deteriorated over the 16 years since the MU was fitted, or been attacked by E5 fuel over the years. 

Need to check the others now. Good job it's winter and not using the car.

Steve