fuel pump brown-out?
Discussion
After a couple of intermittant hickups over the last two months, the V8S finally went non-intermittant yesterday. On the bright side, it was a nice sunny day, and barring shredded transmission this is the first break down of any sort in the last 100K miles - not a bad run. On the not-so-bright side, the outside lane of the M1 in the rush hour isn't the ideal place to find yourself stationary with no motive power. Thanks to the two truckers who held up the traffic while I rolled it onto the hard shoulder. No thanks to the twat in the black cavalier who squeazed past me at 30 mph with six inches to spare. (As it turned out, you were right, I did actually have enough time to dodge.)
Back to the problem. Symptoms were that quarter of an hour into the journey the engine would sometimes falter, sometimes cut, and sometimes not restart for a few minutes. When it cut, the engine fired and would idle at 400 rpm for a little while, but it would die as soon as I opened the throttle. I tracked the problem down to the fuel pump. Wiggling the wires at the pump seemed to help, but I suspect that was a red herring. I now reckon the problem was the fuel pump relay failing when it was hot, causing a voltage drop and sometimes going open circuit. I also think this may have been to blame for the occasional flat spot under power, if the pump was losing power from time to time.
Although it's not the same size and shape as a normal automotive 'type 86' 30 Amp relay, the pin outs look the same and I've replaced it with a standard one for now. Hopefully that'll do the job.
Oh yes, and it ran like a pig afterwards until I reset the ECU.
Anyone else had any similar symptoms, or had a fuel pump relay fail? How do you test a relay to prove it's duff? I thought perhaps I'd stick it on load for a while and see whether it played up...
Anyway, hopefully this means I'm OK for another hundred thousand miles then?
Cheers,
Peter Humphries (and a green V8S)
PS why oh why can't TVR make a reliable relay then, eh?
Back to the problem. Symptoms were that quarter of an hour into the journey the engine would sometimes falter, sometimes cut, and sometimes not restart for a few minutes. When it cut, the engine fired and would idle at 400 rpm for a little while, but it would die as soon as I opened the throttle. I tracked the problem down to the fuel pump. Wiggling the wires at the pump seemed to help, but I suspect that was a red herring. I now reckon the problem was the fuel pump relay failing when it was hot, causing a voltage drop and sometimes going open circuit. I also think this may have been to blame for the occasional flat spot under power, if the pump was losing power from time to time.
Although it's not the same size and shape as a normal automotive 'type 86' 30 Amp relay, the pin outs look the same and I've replaced it with a standard one for now. Hopefully that'll do the job.
Oh yes, and it ran like a pig afterwards until I reset the ECU.
Anyone else had any similar symptoms, or had a fuel pump relay fail? How do you test a relay to prove it's duff? I thought perhaps I'd stick it on load for a while and see whether it played up...
Anyway, hopefully this means I'm OK for another hundred thousand miles then?
Cheers,
Peter Humphries (and a green V8S)
PS why oh why can't TVR make a reliable relay then, eh?
I had a relay fail in the 350i - I think it was the fuel pump relay but I'm not too sure. Anyway it was qute catastrophic as it shorted internally which caused the relay board itself to melt and catch fire. This was my only TVR breakdown in 10 years actually, but it was a pretty big one. Luckily the fire went out almost straight away but the board needed major repair by a dealer. If there's any doubt, I would just throw the old one away and buy a new one. If TVR ever started making their own relays... it doesn't bear thinking about really, does it
I had the fuel pump on the Tasmin fail catastrophically after I hit a pothole. It just siezed, presumably due to some sediment being knocked in from the tank, or some equally daft thing.
As far as relays are concerned, you can normally rip the cover off to inspect the thing physically, clean the contacts etc., although what tends to happen is that the contacts are plated with something hard, and once its arced enough to crisp the coating, cleaning will only effect a temporary repair as the arcing then starts to vapourise the contact itself.
I design X- and Gamma- radiation warning systems at work and always rate the relays for at least 5 times the max curent I expect them to see. OK OK, so it means the cost to the client goes up, but what the hell, they Saudis have plenty of money... ;-)
On a car, of course, the relays often run at or close to the max rating anyway, albeit often briefly.
Note that inductive loads such as the horn and electric motors place an increased load on a relay, even if the 'nominal' curent is less than the relay's suggested limit the emf effects can add up.
My 390 has two 'Ignition' relays in parallel; they activate all the circuits that only get a feed when the ignition is on. They are only rated at 15A each, and both get bloody hot all the time. I had one fail in the winter of 2000/ 01, when I had the heater fan, wipers, lights and stereo all going. I just pulled a relay from elsewhere on the board to get me home, and then dicovered one had accidentally fallen into my sock next time I went to a breakers yard.
Lessons to be leaned, then:-
1. Source some big f-off 12V DC relays and modify the wiring accordingly.
2. Wear big socks to the breakers yard.
Ian
As far as relays are concerned, you can normally rip the cover off to inspect the thing physically, clean the contacts etc., although what tends to happen is that the contacts are plated with something hard, and once its arced enough to crisp the coating, cleaning will only effect a temporary repair as the arcing then starts to vapourise the contact itself.
I design X- and Gamma- radiation warning systems at work and always rate the relays for at least 5 times the max curent I expect them to see. OK OK, so it means the cost to the client goes up, but what the hell, they Saudis have plenty of money... ;-)
On a car, of course, the relays often run at or close to the max rating anyway, albeit often briefly.
Note that inductive loads such as the horn and electric motors place an increased load on a relay, even if the 'nominal' curent is less than the relay's suggested limit the emf effects can add up.
My 390 has two 'Ignition' relays in parallel; they activate all the circuits that only get a feed when the ignition is on. They are only rated at 15A each, and both get bloody hot all the time. I had one fail in the winter of 2000/ 01, when I had the heater fan, wipers, lights and stereo all going. I just pulled a relay from elsewhere on the board to get me home, and then dicovered one had accidentally fallen into my sock next time I went to a breakers yard.
Lessons to be leaned, then:-
1. Source some big f-off 12V DC relays and modify the wiring accordingly.
2. Wear big socks to the breakers yard.
Ian
I'm worried now!
I got familiar with what fuel starvation feels like at the Oulton track day. I'd taken cans of fuel, so I could run light (I know, like it'd make any difference with me driving!) and underrestimated the amount required on two sessions.
Since then, on the road, with fullish tanks, the car is still a little 'jittery' - is this the kind of thing?
I got familiar with what fuel starvation feels like at the Oulton track day. I'd taken cans of fuel, so I could run light (I know, like it'd make any difference with me driving!) and underrestimated the amount required on two sessions.
Since then, on the road, with fullish tanks, the car is still a little 'jittery' - is this the kind of thing?
Sorry to hear the bad news Pete, 100k since last incident, well done(good servicing me thinks).
This intermittent fueling problem plagued me for two years and I must say it was the most frustrating fault i've ever had with any car
Difficuilt to diagnose as there are many things that can make the fuel pump stop (a symptom, not the cause)
After a long process of elimination it turned out to be a loose wire in a plug connector behind the dash that would break contact over large bumps and would re-connect if it felt like it, which luckily most of the time it did.Fixed in five minutes and no problems since.
Hope you haven't got this gremlin
heliox
This intermittent fueling problem plagued me for two years and I must say it was the most frustrating fault i've ever had with any car
Difficuilt to diagnose as there are many things that can make the fuel pump stop (a symptom, not the cause)
After a long process of elimination it turned out to be a loose wire in a plug connector behind the dash that would break contact over large bumps and would re-connect if it felt like it, which luckily most of the time it did.Fixed in five minutes and no problems since.
Hope you haven't got this gremlin
heliox
Final twist to the tale, the fuel pump relay has two outputs which switch on together. A changeover relay has the same size and shape but switches one of the outputs the wrong way round. With a changeover relay fitted the cars runs fine but leaves part of the ECU powered when the ignition is 'off', resulting in a flat battery overnight. What sort of idiot would do that, then? 
The only place I could find the right sort of relay was a Land Rover dealer who wanted nearly twenty quid for it. 
That's twice in 100k miles then.
Cheers,
Peter Humphries (and a green V8S)
The only place I could find the right sort of relay was a Land Rover dealer who wanted nearly twenty quid for it. That's twice in 100k miles then.
Cheers,
Peter Humphries (and a green V8S)
FWIW, I used to own a Porsche 924 Turbo which ate fuel pump relays with monotonous regularity, so it's not just TVRs. They always failed closed circuit, so you got used to removing the ignition key, hearing the pump still running, reaching under the dash and wrenching the relay out. It was an Audi part, too. So much for German invincibility.
Peter
Hope that sorts it out for the next 100K, they do seem to go as the bills for mine show it being changed twice along with the stepper motor in a matter of weeks, swiftly followed by a rewire from the ECU to stepper motor
.
Not as strange as it might seem as when you clamp the hose to the stepper motor it should tick over at around 4/500rpm (base idle) same as if the stepper is closed tight, if it comes back it may be an area to look at.
Other areas that give the same symptoms include the immobiliser (if using the pump relay as a means of control) playing up.
If it stays fixed, then congratulations on diagnosing a Tiv running fault in short order
Harry
Hope that sorts it out for the next 100K, they do seem to go as the bills for mine show it being changed twice along with the stepper motor in a matter of weeks, swiftly followed by a rewire from the ECU to stepper motor
. Not as strange as it might seem as when you clamp the hose to the stepper motor it should tick over at around 4/500rpm (base idle) same as if the stepper is closed tight, if it comes back it may be an area to look at.
Other areas that give the same symptoms include the immobiliser (if using the pump relay as a means of control) playing up.
If it stays fixed, then congratulations on diagnosing a Tiv running fault in short order
Harry
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