Hesitation at 2.500rpm

[cureton]

Hi,

Griffith 430 here, all original. Noticed some hesitation/stuttering around 2.500rpm. Suspected the spark plug extenders, changed to new ones and also changed the ignition cables same time. All fine, no hesitation, smooth as a cat. Took car out 2 weeks later (nothing changed within) and same hesitation again. As we hear issues about new extenders getting faulty I took out all extenders and put some heat sleeves instead. Made no difference, same hesitation.
Ecu-mate shows fault Code 68 Road Speed Sensor. Could this cause the hesitation or what could be the likely culprit for my problem?

Thanks for any pointers.

[Corky]

As old Griffith owner (at 45-50k) I had a similar issue, and after lots of diagnosis it turned out to be the camshaft, I had initially thought was an electrical issue, hopefully other owners will also give their views.

[blitzracing]

It won't be the speed sensor, it only affects the idle.

[thicksliced]

Four or five years ago at around 75,000 miles my 430 developed a similar fault. I was convinced it was electrical but found nothing. Eventually it wouldn't rev beyond 2500 ish rpm and it turned out to be the inner lining of the air intake that was becoming detached and choking the engine.
Might be worth a look.

[cureton]

Thanks for the pointers so far. Forgot to say spark plugs are new too. Road speed sensor doesn't cause the problem-thanks Blitz. It revs well beyond 2500rpm, it is just this kind of misfire around 2500, not below. Will now go through things like distributor, rotor arm, coil etc.

[blitzracing]

Failing HT can show up under certain load conditions as when the throttle is wide open the combustion pressures are high, so it needs a higher voltage to ignite the spark, so it maybe simply you have the throttle open further at 2500 than other revs. For some reason there is not a tendency to hold a TVR are WOT for any length of time on the public highway.

[cureton]

To hold a TVR at WOT over a certain lenght of time is less of a problem on German motorways . But the misfire is mainly apparent around 2.500rpm at little or gentle load. On harder acceleration it is not there or at least not noticeable. So can't be lack of fuel supply or something.

[davep]

Might be worth getting your injectors tested, cleaned and balanced.

[blitzracing]

Injector cleaner you put in the petrol does work reasonably well, I used some on an old Toyota before removing the injectors, and all the brown gunk at the tip of the nozzle was soft and coming away. Another process for engine cleaning is Terraclean. Not tried it myself, but worth a watch:

https://www.youtube.com/watch?v=wiViPKIoG68

[blitzracing]

Just a thought, a worn out track on the throttle pot can cause it to drop the fuelling as it passes that point and the output voltage drops. If you are lucky it will Throw a TPS / AFM error as the software is programmed to recognise you cant have a high AFM flow if the throttle is shut

[cureton]

Hi Blitz, thanks for the pointer. Connected ECU-mate and did a few gentle sweeps with the pedal from closed to full. Voltage does not show any erratic drop-outs.