Chasing down a misfire

[andyf]

This is a bit long winded but please bear with me, I want to try and give you all the details because I am struggling with this big time.

The car is a TR7 with the 2.0 engine. The problems started at the beginning of the year, when under load particularly up steep hills I thought I could detect a slight misfire. This has got gradually worse during the year until now when it is at times almost undriveable. The symptoms are that it will drive ok until I reach an incline or if I stamp on the accelerator, when it misfires. If I am driving normally and accelerate slowly it is usually ok, but push my foot to the floor and it misfires immediately. I have done the following:
Replaced plugs, ignition leads, dissy cap, rotor arm, coil.
Cleaned earths and replaced main battery earth cable.
Changed connectors on LT coil wires and back of alternator.
Swapped out distributor for a spare including bypassing the electronic ignition and reverting back to points.
Swapped carbs (twin SU) for a spare set and replaced rubber mountings.
Replaced all breather hoses from carbs to cam cover.
Had the carbs set up and timing done using carbalancer / timing light.

Another problem I have is that a recon alternator I fitted last year has the ignition warning light glowing intermittantly over the summer which I have largely ignored (apart from removing the multi block on the back and replacing the connectors). I was going to worry about this later once I sorted the misfire, but do you think these could be related? The voltmeter reads about 1/2 when the light glows and nearer 3/4 when it behaves. I don't know if I imagined it but it may have felt better when the light went out when I drove at the weekend. Is this possible or am I clutching at straws?

Sorry for rambling on but this is doing my head in, any ideas would be greatly appreciated.

[sprintmini]

Is the fuel pumped to the engine or sucked there,I.e where is the fuel pump located?
Could be a soft fuel line which closes up when the fuel is being dragged through,although if the fuel is being pumped from the rear then that's unlikely.
It sounds like fuel starvation rather than electrical to me but I'm no TR expert,in fact I'm to an expert full stop.
Has the car been used on a regular basis?
Maybe the fuel has gone off leaving that residue in the fuel lines which will block them up eventually.

[andyf]

Hi SM, the cars used regularly at weekends so the fuel is fine and I have replaced the fuel hoses (forgot to mention them) and it had a new tank 2 years ago. The pump is a block mounted mechanical one just under the carbs.

[Seth]

What oil are you using in the carbs?

Also, is the vacuum advance working correctly?

[retrowrongun]

Does it have a vacuum advance attached to the dizzy ,usually worth checking also if missing under load and often overlooked

edited just to say see someone has already suggested this but would definately check it 

[andyf]

Yep, vacuum advance working, I even swapped complete distributors over including the advance. I have always run 20/50 dashpot oil in it (I`ve had the car years) but I did empty the pots and used 3 in 1 just to try it but it made no noticeable difference.
Something else I didn`t mention is that compression etc is ok, a mechanic friend had a vacuum gauge on the engine and gave it a clean bill of health.

Can you see why this is doing my head in.

[sprintmini]

I would take the pump off and check that out,if it's mechanical the diaphragm may have split or it could just have had its day.
If they are similar to the BL pumps on minis they are fairly cheap to buy.
I know spending more money is to always the best idea but it sounds like a fuel starvation problem once the pump is under load.

[sprintmini]

Or failing replacing the pump try turning the engine over and see how much fuel it pumps.....no forget that it's under load where the problem lies,I'm just thinking out loud.

[sprintmini]

Any joy mate?

[omega]

as you seam to have done most of the electrical I think I would do a compression check as maybe its a valve problem.

[Deleted]

Check the filter in the top of the fuel pump followed by sorting out the Terminator short.

DO you have an aftermarket plastic fuel filter fitted if you do where is it?

[ChasR]

I would be tempted to say it is a fuelling problem. Have you checked the fuel pump out at all?

I was going to say you may float chamber issue although you are now on another set of carbs?

What brand of rotor arm and coil is fitted to your car?

[sprintmini]

Wasn't there a mention in the press about NOS rotor arms breaking down when fitted?
But I'm inclined to think its a fuel starvation problem as the engine seems to run ok on idle and part throttle,surely if it was electrical then it would show on part throttle as well!!

[Jizmondo Scrotmondo]

I had a similar problem but obviously, my engine is fuel injected. It turned out that the Head Gasket had burnt out between cylinders 1&2. I'd defo get it compression checked.

[retrowrongun]

If its fuel as you think then maybe worth removing fuel pump and checking the pad on the pump lever arm and also the cam itself to make sure it isn't worn badly , grasping at straws but worth checking ....
Also maybe worth fitting an inline fuel pressure gauge and checking what's happening whilst driving

on a different tangent have you had a leak down test done as could be knackered valve seats ?

[andyf]

Thanks all for the thoughts. I haven`t checked out the fuel pump at all because its the one thing I haven`t got a spare for knocking around so that will be next on the list because I was thinking that way myself. I don`t have an in line filter but it had a new petrol tank 2 years ago. According to my mates vacuum gauge(?) the engine is healthy, no valve or compression issues showing up.

The rotor arm & coil are all intermotor and yes, some of the stuff coming through now are renowned for being rubbish but they made absolutely no difference when changed so I am assuming that even if it is faulty new stock, it would too big a coincidence for it to give exactly the same symptoms.

I am going to have a play over the weekend and I will let you all know what happens, thanks for all the suggestions.

[andyf]

Sorry DP