Engine holding back at speed

[pstruck]

Bit of an odd thing happened to the V8S tonight. In top gear accelerating to, ahem (some undisclosed three figure speed ) and the engine seemed to suddenly hold back. It felt as though I had lifted of the gas, but I hadn't. Almost like hitting a rev/speed limiter.

It doesn't seem to be rev related as I can exceed the sort of revs I was doing in lower gears and it doesn't happen. Tried it a second time, same speed in top gear and it happened again. Same thing.

Anyone have any ideas as to what might be causing this.

[deeen]

Caravan brakes binding?

[Leadfoot]

Sounds like fuel starvation. Tank almost empty, filter need changing, vent (line?) clogged.........?
Or could be ignition. HT lead(s?) or coil breaking down under load, Dizzy's moved changing the timing, vac advance pipe or module loose/fallen off?
Electrical. Block earthing strap failing?
Loads of things it *might* be!

Edited to add: Inlet pipe collapsing under the vacuum?



>> Edited by Leadfoot on Tuesday 6th July 22:50

[GreenV8S]

Could be a problem just about anywhere in the fuel and ignition systems, but these are exactly the symptoms I get when the throttle pot is starting to give out. For some reason mine generally seem to wear out in the full throttle position, go figure.

[JoolzB]

I had similar symptons in my S3, TVR replaced a valve and it solved the problem, just another possibility??

[snowy1101]

I had exactly the same problem, and replacing HT lead cured it.

[pstruck]

Thanks for the suggestions chaps.

Fuel tank was three quarters full and car has just had full service.

It wasn't a gradual effect, but quite sudden and at virtually the same speed each time it happened. My first thoughts were HT leads or TP, so I'll check them first. Don't want to end up spending loads replacing bits that don't need replacing. It's not like I am doing that sort of speed very often!

[matty_boy]

I ran out of petrol a couple of weeks ago (looked like a right plonker, and spotted a few unfriendly hand gestures... mind you, someone did stop and gave me a lift the petrol station).

Anyway, since then, I'm experiencing similar problems. It feels as though the engine is being suffocated, like it's being held back when I go for full throttle - difficult to explain, but it's a similar sensation to when I ran out of petrol!

Any ideas? Someone suggested an air blockage or a sort of silt stirred up in the system, but no idea how to sort it.

Symptoms seem similar, so could these problems have a related solution?

[wedget]

snowy1101 said:

I had exactly the same problem, and replacing HT lead cured it.

I had exactly that, i tried everthing and it was a combination of me dropping a spark plug b4 fitting it and a dodgy HT lead that i had inspected and it looked perfect but wasnt, also try changing the fuel filter and general tune up/ injection cleaner

>> Edited by wedget on Wednesday 7th July 09:08

[wedget]

matty_boy said:

I ran out of petrol a couple of weeks ago (looked like a right plonker, and spotted a few unfriendly hand gestures... mind you, someone did stop and gave me a lift the petrol station). Anyway, since then, I'm experiencing similar problems. It feels as though the engine is being suffocated, like it's being held back when I go for full throttle - difficult to explain, but it's a similar sensation to when I ran out of petrol! Any ideas? Someone suggested an air blockage or a sort of silt stirred up in the system, but no idea how to sort it. Symptoms seem similar, so could these problems have a related solution?

Put in some good quality injection/ fuel system cleaner and go for a long run, i hade the same problem and it cured it after two tanks

[RUSSELLM]

Had a similar thing on a deisel car, faulty fuel punp, sucking in air or something or other

I dunno

[Horse_Apple]

matty_boy said:

I ran out of petrol a couple of weeks ago (looked like a right plonker, and spotted a few unfriendly hand gestures... mind you, someone did stop and gave me a lift the petrol station). Anyway, since then, I'm experiencing similar problems. It feels as though the engine is being suffocated, like it's being held back when I go for full throttle - difficult to explain, but it's a similar sensation to when I ran out of petrol! Any ideas? Someone suggested an air blockage or a sort of silt stirred up in the system, but no idea how to sort it. Symptoms seem similar, so could these problems have a related solution?

Hi. There is a danger that when you run out of fuel you end up sucking up all the muck in the bottom of the tank and shove it into the fuel system. It should be stopped by the filter, but there could be a build up in the lines.

Applying a bit of back pressure into the tank from the filter may clear a blockage of residue.

I am paranoid about this issue and will always fill the tank when it hits the half way mark.

[z_chromozone]

Horse_Apple said:

matty_boy said: I ran out of petrol a couple of weeks ago (looked like a right plonker, and spotted a few unfriendly hand gestures... mind you, someone did stop and gave me a lift the petrol station). Anyway, since then, I'm experiencing similar problems. It feels as though the engine is being suffocated, like it's being held back when I go for full throttle - difficult to explain, but it's a similar sensation to when I ran out of petrol! Any ideas? Someone suggested an air blockage or a sort of silt stirred up in the system, but no idea how to sort it. Symptoms seem similar, so could these problems have a related solution? Hi. There is a danger that when you run out of fuel you end up sucking up all the muck in the bottom of the tank and shove it into the fuel system. It should be stopped by the filter, but there could be a build up in the lines. Applying a bit of back pressure into the tank from the filter may clear a blockage of residue. I am paranoid about this issue and will always fill the tank when it hits the half way mark.

Paranoid , you only get 20 L in if you fill at half empty. Try three inline filters, that should put your mind at rest.

[matty_boy]

I'm a bit thick when it comes to cars, so I need to be told things in layman's terms.

"Put in some good quality injection/fuel system cleaner and go for a long run, i had the same problem and it cured it after two tanks."

- OK, I can just about understand this. Do I just get this stuff from Halfords or something?

But this... "Applying a bit of back pressure into the tank from the filter may clear a blockage of residue."

- How do I do this?

Cheers, guys.

Matt

[wedget]

If you got to Halfrauds and get some injection cleaner cost around 5-12 quid, You may want to try complete fuel system cleaner, Put it in with your fuel next time you fill up, I personally only half fill the tank. then go for a nice long drive, Repeat as necesary, As for the back pressure cant help there also if you have not changed the fuel filter for a couple of years may be worth changing only cost about a fiver. try canging the plugs and leads as well, as problem may only get worse, Did on mine. also a general tune up is next on the list, shop around and try to avoid the mobile type, this should cost around £40 also dont know about your engine but your tappets may need adjusting if your engine is a bit rattly.

[stigproducts]

I had the same problem, a different engine, someone suggested it was the quality of the fuel I was using. Sure enough on the next tank the problem went away and hasn't been back.

I find BP is the best stuff. With a tuned car the variations in fuel you can by can make a difference to running apparently.

Try a tank full of Optimat (or whatever its called)

[Horse_Apple]

z_chromozone said:

Paranoid , you only get 20 L in if you fill at half empty. Try three inline filters, that should put your mind at rest.

I certainly hope I am paranoid, otherwise everyone really is out to get me!!!!!!!!!