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John McCormack

UNUSUAL MISS/COUGH

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I took the TR6 for a 3 day 1000km run down the coast arriving home yesterday afternoon. The car was fantastic and, with a few hot sidescreen TRs down there, I had some brilliant drives.

As I was approaching my mates place on Tuesday, on a bit of a bumpy left turn into a side road the car coughed a couple of times as I accelerated away. It did it again on the next corner also a bit bumpy, one cough.

About 15 kms into a fast country drive the next day it coughed once, on a bend rather than a slow corner.

No further instances and after the second incidence and during the 480km drive home yesterday the car was wonderful.

The car has coughed randomly in the past but hasn't done it for some time.

I filled it up with BP 98 before I left home. I put 30 litres of Caltex 98 half way down the coast. The cough occurred another 200 or so kms after filling up. I had a look under the bonnet when I arrived and nothing was out of place.

Before leaving to come home I filled up with 98, can't remember the brand.

It is a stock 1970 CP PI with a Bosch pump. Never had a problem with the pump or metering unit. Pertronix ignition has been in it since I bought it.

Weather was warmish at maybe 32 degC, it is Australia approaching summer, but nothing out of the ordinary. The car didn't overheat at all even in yesterday afternoon's Sydney traffic getting to my inner city place.

Any ideas on the cause of the cough? Is it a quirk of the PI system?

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John,

Low fuel, less than a quarter tank can cause this on cornering.

Graeme

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12 minutes ago, graeme said:

John,

Low fuel, less than a quarter tank can cause this on cornering.

Graeme

Thanks Graeme. More than 20 litres, nearly half a tank, on each occasion.

It should have been OK, however fuel surge in the tank might still be it. The two corners were tight and I hit them hard, I realised late that I had to take them, and with the bumps it might have got a bit of starvation. The one the next day was again bumpy and not as tight but at higher speed with a bit less fuel.

I just saw where you are located. My wife and I stayed in Nanaimo in mid May (Maple View B&B). We saw one TR on our extensive Canada travels (which included driving all the way from Vancouver to Toronto where our son lives). It was a green TR250 in Nanaimo. We were going the other way. Probably you. 

Edited by John McCormack

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Mine has been doing this... for mine it was the fuel filter being chokka w rust from the tank.

(of course Auckland is cooler and wetter than Sydney so...)

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7 minutes ago, Mike C said:

How's the tank vent?

I'll check. It should be Ok, I did a lot of work on the tank a few years ago.

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On early fuel tanks this was a common problem of cornering with no baffles or swirl pots inside resulting in fuel climbing up the sides and away from the outlet at the bottom.

Leyland rectified this later on.

Regards Harry TR5 Nutter

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I've had this, and found the earth connection in the wiring to the fuel pump was not making a perfect connection, tightened it up and fine since. Noticed it more when over a jolt in the road. Usually just a one miss/cough once, fine on smooth roads. 

John

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John,

You report that the cough occurs on cornering; presumably you have lifted-off the throttle and then applied a little throttle as you start to negotiate the corner.

Do you get a smooth pull away from stationary - not a racing start just a very gentle pull away. If none of the above and the car coughs or judders on such slow,  low throttle starts I would suspect that the butterflies need balancing as there is uneven opening of the plates and one or more cylinders are getting a not ideal mixture.

Alan 

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3 hours ago, John McCormack said:

I'll check. It should be Ok, I did a lot of work on the tank a few years ago.

Hi John, did you coat the inside of the tank with that sealer stuff. There have been some instances of it falling off in chunks and temporarily blocking the fuel outlet.

Chris

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bumps............suggests intermittent break of circuit by the safety cut-out

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1 hour ago, Peter Cobbold said:

bumps............suggests intermittent break of circuit by the safety cut-out

+1.

To check you  can bypass the cut out by using a short piece of wire with a spade terminal each end  connected to the loom in its place.

Chris

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13 hours ago, harrytr5 said:

On early fuel tanks this was a common problem of cornering with no baffles or swirl pots inside resulting in fuel climbing up the sides and away from the outlet at the bottom.

Leyland rectified this later on.

Regards Harry TR5 Nutter

This car has an outlet each side of the tank. Put in when the Bosch pump was installed.

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7 hours ago, ChrisR-4A said:

+1.

To check you  can bypass the cut out by using a short piece of wire with a spade terminal each end  connected to the loom in its place.

Chris

These early (Feb 70) cars don't have a cut out. But a intermittent earth somewhere is a real possibility.

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12 hours ago, barkerwilliams said:

John,

You report that the cough occurs on cornering; presumably you have lifted-off the throttle and then applied a little throttle as you start to negotiate the corner.

Do you get a smooth pull away from stationary - not a racing start just a very gentle pull away. If none of the above and the car coughs or judders on such slow,  low throttle starts I would suspect that the butterflies need balancing as there is uneven opening of the plates and one or more cylinders are getting a not ideal mixture.

Alan 

Thanks Alan. The car pulls away normally. The engine performs really well in all conditions, idles nicely, good power throughout the range.

I intend having the car tuned by a Lucas PI specialist just to see if we can get a bit more out of it but I doubt this is the problem. It has occurred just a few times in 3 years of driving and as it is on bumps a poor electrical connection is likely the problem.

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19 hours ago, Mike C said:

How's the tank vent?

Thanks Mike. Just checked, all OK.

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17 hours ago, John L said:

I've had this, and found the earth connection in the wiring to the fuel pump was not making a perfect connection, tightened it up and fine since. Noticed it more when over a jolt in the road. Usually just a one miss/cough once, fine on smooth roads. 

John

The earth was tight but I pulled it off, sanded the body and terminal and retightened. I also checked the other terminals on the relay etc. Unfortunately, with such an intermittent issue I may never know whether this was the cause.

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John,

No mention of spark plugs above. My car has previously suffered from a little rough running only when  hot and that was down to spark plugs. At £20'ish a set it is not too onerous for a swap out. Indecently only buy from a reputable supplier as there are fake copies plugs out there and they have a poor lifespan.

Alan

 

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22 hours ago, barkerwilliams said:

John,

No mention of spark plugs above. My car has previously suffered from a little rough running only when  hot and that was down to spark plugs. At £20'ish a set it is not too onerous for a swap out. Indecently only buy from a reputable supplier as there are fake copies plugs out there and they have a poor lifespan.

Alan

 

A timely post Alan. I have just checked my spreadsheet of TR6 servicing and I haven't touched the tappets, plugs etc for 5,000 miles and the plugs are over 6,000 miles old. It has electronic ignition so only timing there.

The PI has not caused me any issues but I think I'll get it tuned by a specialist.

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A bit of feedback.

Quite a few of the tappets were way out. Maybe 20-25 thou gap instead of 10 thou. Only a few were correct. They all had oil in the top of the pushrod so lubrication is ok.

All the plug gaps were big, probably 30-35 thou instead of 25 thou.

The plugs were all the same colour and condition. They had a grey coating underneath some carbon buildup, which I reckon is normal for a PI that had driven a long way at speed and then through heavy traffic for the last 20 or so kms.

Timing was closer to 6 deg advanced at idle. I put it up to 11 deg and will adjust it further as I drive it.

After the adjustments the engine started immediately and idled smoothly and quietly straight away.

Trying to replicate a very intermittent issue will be almost impossible but the tune up was desperately needed. It is blowing hard here right now with some rain so a test drive will wait.

I did notice the water pump is leaking so I shall replace it soon.

Just took it for a short test drive. Much smoother and quieter, a big improvement in power especially at higher revs. Should have checked my records and done the work before the trip.

Edited by John McCormack

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