Fuel pump test

[wizzer]

Hi all, hope you are getting out in the S whilst we have this fine weather. Still having problems with this intermittant lack of power and missfire. I've been through the ignition, cant find an obvious problem. Now wondering about fuel. Is there a way of testing the fuel pump for intermittant fauts?

[Julesprivate]

I'm not sure there is a way of testing anything for intermittant faults really, other than by replacement. I'm still VERY new to TVR ownership but the "yellow connector" and "wiggle test" just popped into my head so that might be worth considering. Check the fuel pump relay as I understand they are sometimes a weak point.

The only way I can think of to test the operation of the fuel pump that may have an intermittant fault would be to have an inline fuel pressure guage and a light connected to the fuel pump feed (from the relay) but that'd mean driving with your eyes on the light and the guage (so not ideal)

I KNOW this will sound stupid, so please take this as a genuine question but does it occur with lots of different fuel levels? My guage (along with many others I am sure) is wildly inaccurate and when it shows a quarter of a tank I get intermittant power loss problems as the tank is in fact nearly empty and exiting roundabouts or even hard acceleration means there isn't enough fuel to cover the pickup.

Is theer a filter in the fuel pump on an S? (I don't know but I would be interested to hear if there is)

[Roy C]

Have you investigated the TPS?

[Maffe]

Have you checked your spark leads? If oxidation/bad connetction you can get strange behaviour from the engine.
For checking fuel pump a fuel pressure device would help or just get a spare pump and try.

[wizzer]

Thanks for all your input. Throttle pot is something I hadn't thought of so will give it a go. The dreaded yellow connector was replaced sometime ago, I have tried the 'wiggle test' nothing has shown up but when I have a look at the nest of vipers under the glove box I admit I am reluctant to pull anything about. The annoying thing about it is I went out for a run this afternoon and she ran pefectly.

[Le TVR]

Fuel pumps are generally reliable. Usually get very noisy before failing. If the fuel is intermittent then it is almost 100% likely to be the supply. The fuel pump relay quite often fails due to cracked circuit board connections and these will be intermittent, eventually getting permanent.
Basic fuel pump test is to check the current draw which should be around 6A in a healthy car. Much higher than this indicates possible fuel filter blockage etc.
Intermittent faults like this are going to be electrical and there's no easy answer.

The fact that many owners consider the TPS as a "consumable" is also a good pointer...

[Julesprivate]

Le TVR said:

The fact that many owners consider the TPS as a "consumable" is also a good pointer...

That is indeed a good point. Over on the Alfa forum I used to hang out on there are countless threads on the TPS/IAC units (Throttle pot and Idle Air control) and I replaced mine twice in 5 years of ownership.

The last time it failed it was a complete PITA to diagnose as I assumed my having replaced the TPS 2 years earlier meant it was unlikely to be that. The symptoms were similar to that described (erratic idle, intermittant loss of power) which makes sense as the poor car doesn't know how much fuel to add without knowing the throttle position.

I also had to replace the MAF (Air Flow sensor) butthat exhibits different symptoms (loss of power over higher revs as the car goes into "limp home" mode.