TR6 PI runs rich and bad/no idle

[MortenHoyseth]

Back with more engine/ignition/fuel issues – seems never to end J

The car fires (not easily) up, but will not idle. Unscrewing/open/lock the air supply from air manifold have no impact. The plugs are getting black/carbonized after very few minutes of running. So I guess running over-rich. I have not measured any vacuum anywhere. I’ve measured the balance of the butterflies, they are closing fine and produce fairly equal readings.

1. Since the MU is rebuild by Prestige injection, I assume the settings are right. I’m reluctant to adjust the mix on the MU. But I will if I have to.

2. Could the fuel filter on/at the Bosch pump be causing such problem, if it has gone bad. It’s not that old, though.

3. The PRV is new as well – if it allows for too much pressure (not measured) will it give an over-rich mixture? I haven’t really thought that question through, so apologies if stupid.

4. Ignition timing seems to be ok – started at 12 dgr static BTDC.

Could be air leaks on the vacuum hoses. They are all new.

Any suggestions?

Engine: ’71 2.5PI w/sprint90 cam
Ign: Flametrower, pro rebuild dizzy
Fuel: Pro rebuild MU, all new injectors, good spray, Bosch pump

[barkerwilliams]

Morten,

 

When "choke" is fully pushed in, is the metering unit enrichment / "choke" lever fully moving back or sticking on (enriching)

 

Alan

Edited April 14, 2017 by barkerwilliams

[MortenHoyseth]

Hi Alan - yes the MU rich lever is moving nicely back. New chocke cable as well, and it moves freely back/forth.

[john.r.davies]

Plus 1 for Alan's suggestion.

 

I had a very similar problem, with a Prestige M/u. Malcolm was as helopful as anyone could be, done the phone, but as Alan suggests, the problem was finally that the choke cable was kinked, it would not close fully and the choke was held open, but a millimeter or two. Disconnect the cable, make sure it closes, and try again.

I now have a small return spring on that choke lever, just in case, although I'd spot the symptoms - fine idle, but bogging down when throttle opened.

 

John

 

PS just seen your reply! You are ahead of us. J

Edited April 14, 2017 by john.r.davies

[Tim D.]

Does sound like a vacuum​ leak between the manifold and the MU leading to over enrichment at idle.

Cheers

Tim

[stuart]

Excess fuel pressure will give the same problem.

Stuart.

[Peter Cobbold]

Air leak between manifold and head?

[GT6M]

chek easy things fust

 

1, suck ont MU pipe, is it pulling links up

if not, then links joint broken, a common thing wid age ive fun oot

 

2, stik,n PRV will give rich running, as moer fuel getting in, check fuel pressure at MU end of PRV

 

3, banjo seals gon, allows constant injection

 

M

[elclem1]

Excess fuel pressure, 104psi at the MU at idle is normal. Does the MU "chatter"?

[MortenHoyseth]

Hi folks - sorry for the radio-silence from my side. Appreciate your help!

I'll get started on checking for vacuum leaks first. I've never checked fuel pressure from pump. Best checked at the main fuel feed hose at the MU? If excess fuel pressure, shouldn't the extra fuel be sent back via the return pipe? In theory.

[GT6M]

If excess fuel pressure, shouldn't the extra fuel be sent back via the return pipe? In theory.

 

Err no, cos the wee pipe that comes oot the MU is alott smaller than the inlet ,and if the PRV is letting 160+ thru, then it wont cope wid this on an idle

as v little fuel is really used at idle

 

but me loot is still on broken links !!!

 

M

Edited April 17, 2017 by GT6M

[MortenHoyseth]

When you say "suck ont MU pipe, is it pulling links up if not, then links joint broke" - is the rich-lever supposed to move when I produce vacuum at the hose going from manifold to MU? Or are you refering to internals in the MU? When I produce vacuum, no external parts are moving, but I can hear some sort of click inside the MU when I release the vacuum. I'm noob at what the vacuum does internally in both MU and vacuum unit in the breaking system.
I've borrowed a fuel pressure gauge today, and going to check that as well. The MU itself was rebuild by Prestige Inj. last summer. The vacuum unit (breaking sys) is old though. Could that influence the mixture (I guess yes) - if it's leaking?

Cheers,

Morten

[Tim D.]

You should see linkages inside the MU move when you apply vacuum.

Tim

[Peter Cobbold]

You should see linkages inside the MU move when you apply vacuum.

Tim

but you have to remove the rectangular plastic cover to see it.

But its newly reconditioned so I doubt the diaphragm has gone.

Edited April 26, 2017 by Peter Cobbold

[GT6M]

Its no the dia that goes , butt, if not replaced at re furb, this could be gon

And, whenst trying t,get the olde dia off, then the plastic screw thread bit breks off

so this why im thinking its no been replaced !!

 

its the plastick universal jointing thingy at the top end

under the dia

 

as said above, need t,tek the 4 cover screw bolts oot

screwdriver flat bit type

 

M

Edited April 26, 2017 by GT6M

[MortenHoyseth]

Thanks - you might be right regarding the links. Since I borrowed a fuel pressure gauge from a workshop nearby, and need to return it tomorrow, I decided to check fuel pressure first. The MU might still not be operating as it should, but fuel pressure first. I didn't find an adapter to fit the fuel hose connecting to the MU, so I measure at the main fuel feed hose from the boot - going to the MU. The pressure "floored" the scale on the gauge going to 145psi.

So from what I've understood this is far to much. 110psi is what I'm aiming for, right?
I haven't tried to adjust the PRV before (up for tomorrow), but seems quite simple just via a screw.

Just to verify - the fuel feed (from bosch pump/filter) goes into a T-joint; one goes to the MU (where I measured) and the other goes to via the PRV to a return pipe/hose to the tank. So the PRV will need to be adjusted to set the trigger point at about 110psi, thus send more fuel back to the tank in my case.Is my understanding correct?

Cheers - and thanks for all your help!

[Peter Cobbold]

Thanks - you might be right regarding the links. Since I borrowed a fuel pressure gauge from a workshop nearby, and need to return it tomorrow, I decided to check fuel pressure first. The MU might still not be operating as it should, but fuel pressure first. I didn't find an adapter to fit the fuel hose connecting to the MU, so I measure at the main fuel feed hose from the boot - going to the MU. The pressure "floored" the scale on the gauge going to 145psi.

So from what I've understood this is far to much. 110psi is what I'm aiming for, right?

I haven't tried to adjust the PRV before (up for tomorrow), but seems quite simple just via a screw.

 

Just to verify - the fuel feed (from bosch pump/filter) goes into a T-joint; one goes to the MU (where I measured) and the other goes to via the PRV to a return pipe/hose to the tank. So the PRV will need to be adjusted to set the trigger point at about 110psi, thus send more fuel back to the tank in my case.Is my understanding correct?

 

Cheers - and thanks for all your help!

Morten, Yes that's right. 145+ is far too much and it will run stinky rich. You've found the problem. Its probably the PRV needs adjusting. But check the hose back to the tank from the PRV is open - there's another thread at present where that appears to have blocked.

Peter

[MortenHoyseth]

The PRV fitted (don't recall where I bought it a few years back) was stuck- no way I could adjust with the square plastic hole in the end. So I put in an old PRV, it measured about 95psi, adjusted it to about 108psi. So far so good. Couldn't get the car starting, but it might just be that I need to bleed the injectors. I'll be back.

[GT6M]

Errrr its no just a case of turning a screw

its wot has med the PRV go this high

 

If just turning a screw t,let pressure ga doon,

then wots gonna happen when the problemo bit of sheite thats most likely in there

decides t,ga on holiday, ans, yer fuel pressure drops back to being v v low

 

Ye need t,tek the PRV t,bits and clean it oot

then re assemble in CORRECT order

 

IMPORTANT, whilst yeev got the PRV in bits,

 

IF there is sheite int PRV, and after its been cleaned, an pressure tested

its back t,normal, then fine

 

Butt, mek yer self a Screwdriver that will fit perfectly into the slots,

and mek sure its a tight fit, an goes in a good 1/4 inch

 

there are 4 slots,or like a + and if just useing a badly fitting driver

then it can, an most likely will, round the edges oft cross adjuster

as a normal screwdriver is tapered

this need modded so its parrallel for a bit, and right width too,

 

tek time t,mod a screwdriver.

 

fit, check PSI, adjust if needed,

wid a biit of luk, it wont need adjusted

 

It maybe sheite, or it may well be some ones upped it

cos the olde pump was down on PSI, so upped pressure t,try an compensate

butt this is useless, as pressure will be farrrrr to low at WOT an revs

 

M

[GT6M]

Ahaaa, chukl,n to me self

 

The PRV fitted (don't recall where I bought it a few years back) was stuck- no way I could adjust with the square plastic hole in the end

 

this is wot im on aboot above

ive had so so many wid ruined PRV adjuster ends, done by folk wid no the right Tool

 

IF ye doo bugger it up, can be adjusted frae other end !!!

 

M

[MortenHoyseth]

Hi - allright - got the fuel pressure right (measured at the PRV in the boot) - well approx 108psi. But back to start for me. I can't get it to start at all. It was challenging before as well. But I've been trough the entire system - ignition, mu, electrical, fuel...Think I've gone blind on it now Asked TR club in Norway for on-site help.
In know fuel is coming through - after bleeding the injectors, all give a nice spray of fuel. I'm back to suspecting that it's something odd with the distributor. The strobe light is triggered nicely on the lead from coil to dizzy, but it is not triggered on any of the leads to the plugs from dizzy. Going crazy with this.

[oldtuckunder]

Well if you have signal on the king lead it says points, condensor, coil are fine, but nothing out to the plugs means either the king lead isn't plugged into the cap, the cap is tracking out, the wobbly graphite bit in the cap isn't contacting the rotor arm or the rotor arm is shorting out. From your distributor problems last year you must have spares a pleanty, change them one at time and isolate. NB it is possible to get a weak signal on the king lead but not enough oomph to make a plug spark under compression, but I think you should see a strobe signal. Unless you have bought some of those fancy new 10mm diameter plug leads that a number of people are now hawking around, in which case its almost impossible to get a signal from them. I know keep a spare thin long plug lead in with the timing light for these occasions!

[DaveN]

Rotor arm and or the cap! Change them both!

Get them from the distributor doctor.

[Waldi]

To see if the king lead signal is strong enough you can install one of the spark plug leads directly in the coil, put a sparkplug in the cap and hold it to Earth (engine). You should get a nice blue spark.

[oldtuckunder]

Rotor arm and or the cap! Change them both!

 

 

One at a time!