Power loss over bumpos

[TR5tar]

Apologies if this is a common problem and has been covered elsewhere on the forum.

 

Pushing along at a steady 50-55 recently, I crossed over some recessed train track which made the car bounce up and down a bit. Then, just for a 3-4 seconds, I lost power, although the engine didn't cut out. The car had plenty of fuel in it, so there was no issue there, but someone I spoke to about the problem thought that it could have been the fuel pump. I've not had the problem since, but then I haven't gone over any major bumps at speed since. Is this something that others have experienced? Is it a sign of something more serious to come? Is it something that I can cure (other than going more slowly over bumps)?

 

Thanks, DC

[PJM]

Loose electrical connection somewhere? Pump connections, relay, earth, inertia switch, fuse?

[TR5tar]

Thanks PJM. I think all your suggestions are a possibility, and I did wonder about the connections, but I think what the chap who mentioned the fuel pump was getting at was something about the magnets in the pump, but I don't understand pumps enough to know how they work and what part the magnets play.

 

By the way, in case anyone was wondering what a "bumpo" of the title is, it's a bump that you go over and at the same time shout "Ooo", not a typo, honest.

 

DC

[Rodbr]

What car? What carbs? type of fuel pump?

 

[North London Mike]

Just a thought............

 

Wheels off the ground ?

[graeme]

What car? What carbs? type of fuel pump?

 

 

Could be a TR5, clue in the posters username.

 

Graeme

[TR5tar]

Yes, TR5, so no carbs, PI. I don't think the wheels were off the ground, but it was more of a bump than I was expecting.

 

Thanks, Darren

[roy53]

It's only TR5 prices that fly

 

ROY

[Rodbr]

Graeme,

He could have been driving something else, so your comment is not really helpful in any way.

 

Hi Darren,

How much fuel was in the tank, perhaps your fuel became airbourne and the pump got a gulp of fumes insufficient to stop the engine but total lack of power momentarily till pump started on fuel not fumes.

[Peter Cobbold]

Inertia switch. Doing what its supposed to do but rather too enthusiastically.

[TR5tar]

Hi Rodbr,

 

I was on just over 3/4 of a tank when this happened. I try never to run with less than half a tank, as I'd heard that this could cause problems on a TR5. And so, I don't think it was lack of fuel that caused this particular problem, but thanks for the thought.

 

Hi Peter,

 

I must confess I don't know what an inertia switch is. Is it a safety device which cuts the flow of fuel if the car is in an accident? If so, then I'm beginning to see how this might have caused the lack of power. You say that it's being a bit over enthusiastic. Does that suggest that it's faulty? Is it something I should be concerned about, or is it quite a common thing?

 

Thanks, Darren

Edited September 22, 2014 by TR5tar

[Peter Cobbold]

Darren, The inertia switch cuts the electrical feed to the fuel pump in the event of a collision- so we dont get 100psi fuel sprayed around. Its a grey plastic cylinder next to the wiper motor on the nearside bulkhead. Normally a button on the top pops up when the cut out has been activated. But yours might not have been triggered hard enough to do that. It has given problems on TR6s, cutting out when drivng normally, and a modern substitue has been found.

So.....if your cutting out recurrs when attacking that railway line again then try connecting the two wires at its base together making sure you insulate them from earthing to the body ! If that stops the cutting out then you have found the problem. If not then you have the fun of finding some other fault ! Intermittent faults can be infuriating so having a reliable way of triggering it will help.

Peter

[Kiwifrog]

If I remember correctly inside the inertia switch is a heavy ball bearing held into contact with 2 electrical contacts by a weak spring, therfore a big bump could momentarly cause the bearing to bounce and lose contact for a fraction of a second stop the pump causing low fuel pressure and the problems you describe.

 

Not something I would personally worry about, although if I were you I would make myself familar with the cutout switch and how to reset it in case next time it pops all the way up.

 

Cheers

 

Alan

Edited September 22, 2014 by Kiwifrog

[TR5tar]

 

Thanks Peter, Alan.

 

This inertia switch certainly sounds like the culprit, and is definitely something I need to be familiar with in case I need to reset it. I've been out to try to locate it, following your guidance Peter, and found a black cylinder with a red, rubber cap in on it, located on the bulkhead, near side. Pictures attached. Is this it?

 

Thanks Darren

Edited September 22, 2014 by TR5tar

[ST TR5]

TR5's we're not fitted with inertia switches

Cheers Sean.

[stuart]

The one in the photo is an aftermarket fitting so check the connections to it.

Stuart.

[TR Mitch]

Inertia switch. Doing what its supposed to do but rather too enthusiastically.

 

The inertia switch does not usually reset itself, that could be potentially very dangerous. You have to push the button to get it back and I doubt they suffer from intermittent connection otherwise there'd be dozens of modern cars coughing along our bumpy roads.

 

The switch looks very familiar to me (see this post). I think the problem lies elsewhere, perhaps the pump, although I believe there is a decent Bosch pump in the set up on your car

[Peter Cobbold]

Inertia switch. Doing what its supposed to do but rather too enthusiastically.

 

The inertia switch does not usually reset itself, that could be potentially very dangerous. You have to push the button to get it back and I doubt they suffer from intermittent connection otherwise there'd be dozens of modern cars coughing along our bumpy roads.

 

The switch looks very familiar to me (see this post). I think the problem lies elsewhere, perhaps the pump, although I believe there is a decent Bosch pump in the set up on your car

MIne would break the circuit without tripping the button - and without going over bumps. Nasty. I would have replaced it with a modern if I still ran PI.

Darren's looks like its at an earlier stage f failure owhen it trips briefly and then remakes. But its not the same type as the 6's.

[TR5tar]

Thanks ST TR5, Stuart, Mitch and Peter. Although we may not have conclusively got to the bottom of what caused the problem, I've learned something useful and important with this discussion of the inertia switch. At least if I get the problem again, with a total loss of power, the inertia switch is the first thing I'll try.

 

I have to say, I've quite surprised myself by locating the switch (thanks to Peter's direction). I felt sure I'd get several posts telling me the photo was of something entirely different.

 

Darren

[brucer]

Have you tried changing the fuse in the pump circuit? I have had 2 fuses that have had intermittent/poor connections in the end cap.

 

Bruce

[Peter Cobbold]

Thanks ST TR5, Stuart, Mitch and Peter. Although we may not have conclusively got to the bottom of what caused the problem, I've learned something useful and important with this discussion of the inertia switch. At least if I get the problem again, with a total loss of power, the inertia switch is the first thing I'll try.

 

I have to say, I've quite surprised myself by locating the switch (thanks to Peter's direction). I felt sure I'd get several posts telling me the photo was of something entirely different.

 

Darren

You found it even with my wrong instructions ! Had to say that in case other 5 owners are looking for a grey plastic cylinder.

Peter