TR6 PI - running very rich

[MortenHoyseth]

TR6 PI running rich

Hopefully my last post amongst a few due to post-engine-rebuild issues I’ve had. I have hope to actually drive the TR6 during summer. Problem now is that it is running VERY rich – soot on plugs building up at an impressive pace, and from the tail pipe black smoke.

It gets too much fuel, but I do not know why.

1. PRV checked and gives about 106psi
2. MU rebuild by Prestige Injection – run 3 km since rebuild. Not fiddled with it.
3. All injectors are new and checked.
4. Ignition is not perfect, but ok, static 12 dgr BTDC.
5. No air leaks in the hose from manifold to MU. New hose, clamps tight.
6. Brake servo vacuum seems ok, but blanked off the connection on the manifold to be sure.
7. The engine has recently been rebuilt by Moss – compression good. High lift Sprint90 cam.
8. Dizzy rebuild by Dist. Doc.
9. MU timing has been checked ok multiple times.

I have not done anything with the MU.
Could the return pipe be blocked? I’ve disconnected it and blanked the return hose, then put on a new hose going in to a bottle – no change in engine behavior. When idling there is certainly fuel being sent back via the return hose. The butterflies – I know they are not perfectly in sync. I’ve measured, when idling, vacuum, and they are not too bad. I’m not sure how much this will influence the fuel consumption.

Any suggestions are VERY welcome J

Fun fact – had a local car mechanic over, and he said that he had never seen a car with that much extra fuel coming in, looking by the black smoke from the tail pipe. Sadly

[barkerwilliams]

Morten,

 

 

A carb with a blocked air filter will still deliver the correct'ish fuel/air ratio - just less of it. A PI has the air and fuel totally independent and the MU will inject the same amount of fuel even if the air flow is restricted. Try the car (stationary) with the large pipe disconnected between the air filter and the manifold

 

The only way the injectors deliver too much fuel is if the MU sends too much to the injectors

 

The most common cause of excess fuel delivery is the choke cable sticking. Is the MU lever back home towards the front bulkhead? Don't look, get you finger in there and push!!

 

Then it is vacuum, have you measured and are you getting 7" or better at a slow tick over (PI's do not have good vacuum)? Apart from the choke the only control for the amount of fuel delivered is the vacuum. Only measure the vacuum on the MU feed pipe.

 

If the vacuum is good, and the air filter is OK then I would suggest it is either the fuel pressure or the MU.

 

Have you set the fuel pressure 106psi?

 

How long ago was the MU overhauled, and has it stood "dry" with no petrol in it for some time?

 

 

 

Alan

Edited July 6, 2017 by barkerwilliams

[Peter Cobbold]

Morten,

Try the tongue test to check MU diaphragm is OK.

http://www.tr-register.co.uk/forums/index.php?showtopic=34963&st=0&p=261520&hl=tongue&&do=findComment&comment=261520

 

Give the PRV a really good thump with ignition on...it might have stuck shut since you last measured the pressure?

 

Theres an inner diaphragm between the MU 'castle' and the rotor block. It rots when fuel is left in it for months.

 

It must be something very obviously wrong !

Peter

[barkerwilliams]

Morten.

 

I see Norway is to ban petrol powered cars by 2025, you had better get this car on the road soon!!

 

Alan

Edited July 6, 2017 by barkerwilliams

[HSM]

For extreme over fueling apart from vac. diaphragm & high fuel pressure

my next check would be to measure the datum track settings, for TR6

they should be .058' to .002' of an inch. Advise google Lucas shuttle

metering for information on how to do this.

 

Harvey S.Maitland

[Mike C]

You have probably checked this already, but are sure that the fuel enrichment lever is correctly set and is not sticking?

[MortenHoyseth]

Alan - regarding petrol powered cars in Norway - spot on, I better get the car running now

1) Peter - I disconnected the vacuum hose at the manifold, put on a manual vacuum pump with a meeter, and the vacuum holds and seems very stable. when the Vacuum is released, a click can be heard from the MU. So it sounds ok?
2) Also when idling, if I pull the chocke / rich mix lever, the idle is even worse and engine stops. So at least it does seem to work.
3) I have tried to disconnect the hose in front of the manifold (at the idle adjustment screw) going to the air filter/manifold - no difference.
4) I'll try to tap the PRV - it might be stuck.
5) Alan - the MU was rebuild/overhauled some years back, and it has been dry for hm - 3 years or so. It might be something there.
6) Alan - when you refer to measuring vacuum (7"), I just pop of the hose from manifold to MU, at the mainifold end, pop on an measuring device and start the engine and measure at idle? Is this correct?

Next steps is
a) Test points 4 and 6 above.
Take the MU off and see if there are things there I can check, and if not send it away for check.

Sounds reasonable?

Edited July 7, 2017 by MortenHoyseth

[MortenHoyseth]

Mike - as far as I can see with the MU fiten on the pedestal, the enrichment lever is returning fully to base position (towards the fire wall).

[MortenHoyseth]

Alan, regarding measuring the vacuum. On the manifold: I blanked off the servo hose and disconnected the hose in front to air filter. Disconnected the hose to the MU at the MU side, and put in a measuring device. Then fired up. Very uneven idle (as "always) but:

1. Vacuum needle (on the measuring device) was jumping from 0-5 inHg constantly a few times pr. sec. Is this normal or should it be at a steady level? I did not touch the trottle during this.

2. I now seemed to have more control over idle rpm with the idle adjustment screw on the manifold - I could easily get it to 1000rpm. This morning with all hoses on, no way it would go above 600rpm. I didn't think that much about it when in the garage, so I'm not sure if I blanked off the vacuum hose to the MU or left it fully open while adjusting the screw.

Anyway, regarding (1) - is this correct behaviour? I have little experience with this, but very keep on learning/understanding

[Mike C]

If the enrichment lever is returning fully towards the firewall with the cable connected , and has about 6mm free play at the cable end with the enriching knob fully in, then it's working OK. If there's no free play, the setting on the excess fuel lever cam needs adjusting (0.15-0.2mm).

[MortenHoyseth]

Hi Mike - the enrichment lever seems ok, there is certainly free play. I'll measure it.

[barkerwilliams]

Morten,

 

"...I blanked off the servo hose...."

 

​But what if the servo is leaking? Best to have fitted a T piece into MU hose and measure when the engine is in a working configuration. But yes normal reading is quite intermittent as each cylinder pulls and the needle goes berserk.

 

You should be able to guestimate a reading, it is 7 inches'ish, as long as it is in the ballpark. However you wrote 0 to 5" that seems a little low, but the gauges you (and I) use are probably not calibrated. Have you checked the throttle body interconnecting rubber pipes for leaks - often they are not fitted with clips and can leak. The injector to throttle body plastic holder and O ring can also leak and reduce vacuum, a liberal coating of red rubber grease always helps.

 

There are different configurations of metering unit whether TR6 or saloon, mostly the main spring differs. If you do send it away for checkout then make sure you advise the workshop that the car is a TR6 PI, and specify what camshaft you have and possibly which style of throttle body you have - the one or two interconnecting balance pipes. I have in the back of my mind that the balance pipes arrangement affects the idle vacuum - not too sure but it does no harm to let the workshop know.

 

The engine should stall when the large idle screw is fully home. If not then the engine (two or more cylinders) is getting air from somewhere else. Air can enter and mess up idling via the from throttle body to head gasket leaking, throttle body balance tubes leaking, butterflies not synchronised, air leak around injectors, possibly but unlikely from a servo air leak. There is also an unused vacuum hose connection that used to go (but was never used) to the distributer advance and should be properly sealed with a blanking cap.

 

I hope to hear you are on the road soon.

 

Alan

Edited July 7, 2017 by barkerwilliams

[Waldi]

Morten,

A lower vacuum results in an increased dosage of fuel, but you know that probably, so it is important to get this right first. Vacuum leaks are hard to detect, but a spray of WD-40 at potential leak points, like the interconnecting tubes or the gasket between TB and cilinderhead will detect leakages: as soon as the enginespeed increases, you have a leak. Since you are already running rich, I 'm not sure if this will work very well, but worth a try. Spray a little on a butterfly first to test if this method will increase rpm.

Good luck with the challenge.

Be carefull with the hot exhaust manifold and downpipes.

Waldi

[k_raven_smith]

Hi. Send me the metering unit

[barkerwilliams]

There is an offer you shouldn't refuse.

 

Alan

[MortenHoyseth]

Neil/k_raven_smith - an offer I cannot refuse Thanks. I'll send you a personal message.

[Nick Jones]

Did you tell Neil that you were using the Sprint 90 cam so he could calibrate the MU accordingly? A longer duration cam will usually produce less manifold vacuum than the standard one especially at low rpms, increasing the fuel delivery, so the MU needs to be calibrated accordingly.

 

Nick

[MortenHoyseth]

Nick, good point - I haven't done that yet, but I will provide all relevant specs.

[Guest ntc]

The mu can only be set by Neil ( good call) if everything else is right.

[astontr6]

TR6 PI running rich

 

Hopefully my last post amongst a few due to post-engine-rebuild issues I’ve had. I have hope to actually drive the TR6 during summer. Problem now is that it is running VERY rich – soot on plugs building up at an impressive pace, and from the tail pipe black smoke.

 

It gets too much fuel, but I do not know why.

 

1. PRV checked and gives about 106psi
2. MU rebuild by Prestige Injection – run 3 km since rebuild. Not fiddled with it.
3. All injectors are new and checked.
4. Ignition is not perfect, but ok, static 12 dgr BTDC.
5. No air leaks in the hose from manifold to MU. New hose, clamps tight.
6. Brake servo vacuum seems ok, but blanked off the connection on the manifold to be sure.
7. The engine has recently been rebuilt by Moss – compression good. High lift Sprint90 cam.
8. Dizzy rebuild by Dist. Doc.
9. MU timing has been checked ok multiple times.

I have not done anything with the MU.

Could the return pipe be blocked? I’ve disconnected it and blanked the return hose, then put on a new hose going in to a bottle – no change in engine behavior. When idling there is certainly fuel being sent back via the return hose. The butterflies – I know they are not perfectly in sync. I’ve measured, when idling, vacuum, and they are not too bad. I’m not sure how much this will influence the fuel consumption.

 

Any suggestions are VERY welcome J

 

Fun fact – had a local car mechanic over, and he said that he had never seen a car with that much extra fuel coming in, looking by the black smoke from the tail pipe. Sadly

Sorry to hear about your troubles! Is your car a CP or CR? Have you got the right M/U?

That cam that you have got, is a top end performer and if you have the right M/U, you may still have trouble as it may only be set up on a rolling road with a selection of fuel cams by substitution? I have to say that I would not use the Sprint 90 cam but only use the old BL ST cam S2 which does not cause fuelling problems, same as the old SAH 357 and pulls from 1500 RPM+. Where as I suspect that your cam only pulls from 2500 RPM+?

The other 2 things that I would do is:fuel pressure test, with the engine running at the M/U and connect a vacuum gauge to the manifold servo spigot ONLY with the servo pipe unit disconnected and advise us of the readings, at different revs.

Apart from that are you certain that you have no air leaks? I also assume that you have a gas flowed head and an extractor exhaust manifold to go with the Sprint 90 cam?

 

Bruce.

[Nick Jones]

Bruce raises another good point here.

 

TR tradition has it that the MU should be bench set using the Hartridge machine, not tuned on the car. However, this presupposes that you know the curve it needs setting to. In the case of an entirely standard engine (including exhaust system and air filter) this is not completely unreasonable thinking. However, given that the MU is using manifold pressure to infer the incoming air flow rather than measuring the actual mass airflow (which is effectively what a carburettor does), anything that changes the engines pumping ability (valve clearances, blocked air filter, different air filter, different exhaust) affects the apparent load that the MU sees. So unless your "standard" engine happens to accurately match the template Triump/Lucas used your bench set MU won't be completely right.

 

For a non-standard cam, especially where other mods are involved, the metering curve will be a guess. Possibly a highly educated guess, but still a guess. Should be possible to get pretty close, certainly much better than you are now, but best results require a rolling road tune with someone who knows how to set up a Lucas PI metering unit. There are not many of them....

 

Nick

[MortenHoyseth]

Hi folks - just a quick update. My MU is on its way to Neil. I figured, better let an expert look at it, rather than me ruin it. If it was set incorrect, then GREAT, if it was all set correct - then I can eliminate the MU from the list of potential sources.
I'll update this thread when I get it back.

QUESTION: anyone experienced air entering via the injector holes? The injectors with the plastic screw-on seems tight, but the ones with push-on (or whatever they are called, they don't have threads) I suspect is not air tight.The O-ring outside the plastic is tight, but there might be leaks between the plastic and the injector itself. Far fetched?

[HSM]

I have never experienced any problems in air entering around the injectors

with either push in or screw in types, correctly set up metering unit should

cure your over fueling problem.

 

 

Harvey S.Maitland

[BlueTR3A-5EKT]

The mu can only be set by Neil ( good call) if everything else is right.

Did I miss something

Cylinder compressions?

Peter W

[astontr6]

Hi folks - just a quick update. My MU is on its way to Neil. I figured, better let an expert look at it, rather than me ruin it. If it was set incorrect, then GREAT, if it was all set correct - then I can eliminate the MU from the list of potential sources.

I'll update this thread when I get it back.

 

QUESTION: anyone experienced air entering via the injector holes? The injectors with the plastic screw-on seems tight, but the ones with push-on (or whatever they are called, they don't have threads) I suspect is not air tight.The O-ring outside the plastic is tight, but there might be leaks between the plastic and the injector itself. Far fetched?

Morten,

 

You have not given an answer to what your inlet manifold vacuum pressures are or whether your car is a CP or CR type. As you have gone for a Sprint 90 cam, from memory, I think that I have got it right? that you have to use a CP M/U even if the car was a CR type. Other may have to correct me on this? I prefer the screw on nylon bushes for the injectors as I know then they are air tight.

 

Bruce.