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TR6 Fuel Injection problem


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I have a 1971 TR6 CP fitted with the later CR fuel injection system and a Bosch pump.  I recently removed the engine and gearbox to restore the engine bay and repair several fluid leaks.  The fuel injection system was dismantled and the inlet manifolds soda cleaned.  Before dismantling the car ran perfectly.  The Bosch unit in the boot was not disturbed.  Dismantling and reassembly was done by a very skilled mechanic. 

The car now starts on the button, but runs all the time at 3,000 rpm.  If all 6 inlets are covered it ticks over perfectly!  There is clearly an air leak, but we cannot find it.  It is likely to be something really obvious that we have missed.

Has anyone else experienced the same problem?  Any suggestions as to where to look?

Thanks, Colin Caborn

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Hi Colin,

its common after cleaning the deposits out from around the butterflies on the pi system for this to happen.

3000 rpm does sound high though - but as you are able to get engine speed down by covering the inlets I think you need to measure the clearance on the butterflies.

Bob

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The fact that you are able to get the idle to normal levels by covering the inlets means the leak can only be through the throttle plates not sealing fully after the clean up. It could it be they are not fully closed when at idle. 

Gareth

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You've probably checked this, but do you still have the CP manifold?  Is there a tube with large screw connected to the manifold at the front of the engine?

If so tighten the screw and the idle speed should  drop.

If you don't have the idle air tube I'd agree with the above- you have air leakage through the throttle butterflies or throttle spindles.

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Hi Colin

it does sound like air is getting past the throttles when they should be closed

as above, this could be just from the cleaning, they are old and now don’t seal ( the dirt sealed them previously)

or it could be that the throttle mechanism isnt allowing the throttle plates to close fully

or it could be that the ‘choke’ fast idle ( if still fitted) isnt set correctly

or it could be a combination!

i’d be checking the mechanisms first as that’s easy to fix, then move on to the throttle plates and alignment of the three bodies

good luck!

steve

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5 hours ago, Mike C said:

You've probably checked this, but do you still have the CP manifold?  Is there a tube with large screw connected to the manifold at the front of the engine?

If so tighten the screw and the idle speed should  drop.

If you don't have the idle air tube I'd agree with the above- you have air leakage through the throttle butterflies or throttle spindles.

If the butterflies are open at idle this can be checked using feeler gauges under each butterfly. If fully closed at idle they should trap a .0002" gauge. But make sure that the air valve is not open too far, for correct idle speed. The butterflies must be adjusted using a air flow meter  for sync in my experience.

Bruce.

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2 hours ago, astontr6 said:

If the butterflies are open at idle this can be checked using feeler gauges under each butterfly. If fully closed at idle they should trap a .0002" gauge. But make sure that the air valve is not open too far, for correct idle speed. The butterflies must be adjusted using a air flow meter  for sync in my experience.

Bruce.

Good point Bruce, the first thing i’d do is put a flow meter on the throttle to see which are letting air past

then adjust the linkages to hopefully get them all closed/very close to closed

Colin, whereabouts are you?

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Colin,

You suggest everything is OK when all inlets are covered. Do you mean you have covered all 6 'trumpets' thereby ruling out the butterflies not closing sufficiently? That's how I understand it anyway. If so, have you lost or damaged an air tube/balance pipe plug in one of the manifolds? Have you got excessive movement in the spindle holes allowing air in? One of the 3 top connectors are letting in air (think they are 1/2" BSP ports)? Won't take much to realise 3,000 rpm.

Colin

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Thank you everybody for your valuable help. I need now to get my much more knowledgeable friend to take another look at it with your advise to help him. 

In reply to Steve, I live just outside Bedford.

I will report back when we have put your advise to the test .more to follow!

                                                             Thanks, colin.

                                                     

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Er... if it idles ok with all 6 inlets covered/ blanked the air leak is down stream of the throttle butterflies!

Check the injectors have o rings fitted

Disconnect and blank the vac hose to the servo

Check the condition of the hose to the MU

 

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