Rough running when accelerating. (again)

[GTXGTXGTX]

My 87 GTX had fuel starvation problems back in February which turned out to be the dreaded rotten filler neck. I replaced the neck and got all the rust out of the tank, cleaned the mesh filter on the lift pump, replaced the fuel filter in the engine bay and it has run perfectly for the last nine months. Now the symptoms (rough running when accelerating, and going up hills etc) have returned abruptly. I have checked the tank and there is some very minor specs of non rust dirt at the bottom but nowhere enough to block or partially block the mesh on the lift pump

Any ideas what the problem could be? Lift pump appears to be the original. Could it be dying?

Thanks

[scrumpyone]

After changing my filler neck I still had problems. Ended up with a new tank, all fuel lines & swirl pot replaced.

[mark1gls]

If the main pump gets noisier when you have the problem then the lift pump is dying.
For the cost of a replacement it may be worth to try a new one and keep the old one as a spare. You will properly need to replace the rubber fuel hose which connects the lift pump to the sender, just make sure the filter at the bottom of the lift pump is the same height as the original one or it will sit to high or to low in the fuel tank.
I also had to fit 2 new fuel hose clips as the old ones was the crush type of clamp.

[GTXGTXGTX]

Thanks Mark
I have a new lift pump. I bought it last time I had problems but did not fit it as in the short term the new filler neck seemed to solve problem. I will fit it and see if it helps. You are right, I will need to shorten the fuel hose to ensure the pump sits at the same level as the old one.
Cheers for the advice.

[GTXGTXGTX]

This is driving me mad. The new lift pump did not help unfortunately. . Maybe its not a fuel issue.
Everything is perfect until I accelerate, at more or less exactly 3000 revs the engine starts to run rough and lacks power. its fine at lower revs. I had a similar problem last year. I changed the filler neck last year and all was ok for a few months, tank is clean, fuel filter changed twice, new lift pump.
Maybe its ignition, HT leads less than a year old, plugs new, cap and rotor arm approx. 2000 miles.

Any suggestions appreciated.

thanks

[bensspares]

Distributor vacuum advance diaphragm ?

[james butler]

Distributor vacuum advance diaphragm ?

good call, or the vacuum pipe may have come off/split.

[big_wig_074]

check the timing on the engine (not the distributor, the cam timing) I had a similar issue, I had paid a garage to do a cambelt change for me and they had used the wrong marks on the cam wheel. it was about 30 degrees out! ran fine (ish) at lower end but hit a brick wall later on up the revs. I will be doing my own from now on. you need to take the cam cover off to do this to see where the cam lobes are, and a screw driver in no1 spark plug hole to check tdc. there is a guide somewhere, probably one of rubjohnnys finest.

[mark1gls]

Are you running on super unleaded petrol or normal unleaded?

You need to set up the timing for the right type of petrol, I find super unleaded gives my car smoother power delivery and tick over.

[GTXGTXGTX]

Thanks for the suggestions. Will check these out.