Car holding back under acceleration

[philippo]

Hi

Just be out for a drive ('98 500) and something I'd noticed before seems to have become much more marked.

Under light or medium acceleration as the car hits about 3500rpm, it feels as if the engine is holding back or I'm lifting off slightly. It doesn't sound like a misfire and it's less noticeable under heavy acceleration though I suspect it's still there. Given it always occurs at the same revs and whether in 2nd, 3rd or 4th (haven't tried really in 1st or 5th) I suspect ignition related and my immediate guess would be coil.

Before I start replacing parts I'd be most grateful for people's views.

Cheers

Philip

[bigdods]

AFM ? Ive recently had both my other cars (not the TVR though) show exactly this lack of power under acceleration, pulling back etc. Turned out in both cases to be dodgy AFM. You should find you can easily test this by removing the electrical connection from the AFM which will push the ECU to a default map - you wont get full power but if the AFM is the problem you wont get the pulling back any more.

Of course Im no mechanic, but the above helped me prove the fault on my other cars, I am assuming the same would apply to the TVR.

Im sure other wiser heads will be along to help shortly !

[tvr4ever]

philippo said:

Hi

Just be out for a drive ('98 500) and something I'd noticed before seems to have become much more marked.

Under light or medium acceleration as the car hits about 3500rpm, it feels as if the engine is holding back or I'm lifting off slightly. It doesn't sound like a misfire and it's less noticeable under heavy acceleration though I suspect it's still there. Given it always occurs at the same revs and whether in 2nd, 3rd or 4th (haven't tried really in 1st or 5th) I suspect ignition related and my immediate guess would be coil.

Before I start replacing parts I'd be most grateful for people's views.

Cheers

Philip

I would guess the ignition amplifier module judging from the symptoms you describe.
One thing you can try is see if the 2 small brass bolts holding the ignition amplifier module to the housing are not loose. These bolts are vital for grounding the module, if they are not secure the module will act-up like yours. You could unbolt the module, clean it, and then re-apply thermal conducting paste to the rear of the module.
The paste is like the one used for installing computer chips, very important this step, it's to ensure that the heat from the module can transfer away from it.

This did the trick for me.

Fred

Edited by tvr4ever on Sunday 24th September 15:35

Edited by tvr4ever on Sunday 24th September 15:35

[GreenV8S]

Ignition problems usually show up worse under full throttle in my experience.

[philippo]

Thanks for suggestions.

Ignition amplifier bolts are very secure.

I'm skeptical that it could be the AFM as the problem arises at identical revs under light, medium, and I've now establised hard acceleration.

Reading a thread on TVRCC about a misfire I'm convincing myself that I have maybe a cylinder cutting out above 3500rpm, so a faulty ht lead could be to blame. One night this weekend I'll run revs up with bonnet lifted and see if it reveals anything.

Cheers

Philip

[philippo]

Problem fixed. Turned out to be a duff plug. At least put it this way, after fitting new set of plugs car, car goes like a steam train. Strange, old set only had 4000 miles and were 18 months old.

Happy New Year to all.

Philip

[tgriff]

coil amplifier
change it
Steve