Engine Help Please!

[vroom]

Can anybody help with the following?

My 4.0 L Chim occasionally (once every 10 outings), loses power for about 5 seconds and then returns to normal.

It's very sudden in nature, driving a long in top & power instantly drops. I also lose idle when it happens (unless I keep foot on the accelerator).

The last time it did it, I could smell the Cats working overtime. As soon as the fault cleared, smell disappeared.

If I switch off & then restart the engine the fault clears.

It feels like I’m losing a complete bank of injectors, but I'm not too sure. I've tried to induce the fault by applying pressure to all the electrical connectors. / moving cables, but to no avail.

Would love to sort it so I can drive with confidence…
Thanks

Nick.

[Russlarc]

Its not the old air lock in the petrol tank prob.

If I fill the griff up to the top of the tank with fuel a vacuum occurs between filler cap and petrol.

Fuel is staved from some of the cylinders and engine misfires or conks out. Exactly as discribed

'Once every 10 outings maybe the frequency of a fuel stop'

I never fill to the top now although some old PH threads suggest drilling a small hole in the filler cap.

[qube]

Mine suffers from this very rarely as well, does it happen at all engine temps or around 50 degrees mark ?
It too sounds like the engine is dieing and won't throttle up to all cylinders, with a strong smell,once the alarm is reset the car drives off like it never happened.
Try taking the petrol cap off and listen for an excessive hiss from the tank like a whoosh of air, if there is then the tank is not venting properly, i've cut a small piece out of the gasket of my fuel cap which helps greatly. I've also cleaned the stepper motor ,changed the spark plugs ,cap ,leads, throttle sensor, potentiometer, fuel rail temp sensor,lambda sensors and coil ,looking back on the past TVRSH from the last owner the car has suffered with this problem for a few years but never diagnosed, but the problem comes back intermittently and then dissappears. Has anybody else has had this problem and solved it.

[HarryW]

Can't comment on the specifics of the fault but I fairly recently had similar symptoms where on a run it would die for 5 secs then come back an hour or so later it was completely dead . Turned out that the rotor arm disintegrated into three bits and dust. Probably not your problem as its running now but the fact that it comes back and smells strongly (of petrol??) could mean its not sparking for that period and is electrical?
As Shpub will probably post, if you can recreate it on the move then a rolling road may be cheaper in the long run than changing bits to find out whats it's not

Harry

[shpub]

quote:
Its not the old air lock in the petrol tank prob.

If I fill the griff up to the top of the tank with fuel a vacuum occurs between filler cap and petrol.

Fuel is staved from some of the cylinders and engine misfires or conks out. Exactly as discribed

'Once every 10 outings maybe the frequency of a fuel stop'

I never fill to the top now although some old PH threads suggest drilling a small hole in the filler cap.

If it is this then get the venting through the carbon cannister sorted out. Drilling holes, cutting gaskets just cure the symptom not the problem. In some cases this can be caused by a bent pipe behind the tank or a perished one. It could also be caused by a carbon cannister fuel of fuel or water which is not ideal. There is also this myth about the hiss from the tank. Some hiss is normal. Big hiss followed by clanking as the tank shrinks isn't.

It can also be caused by many other problems. Try gummed, knackered injectors. Bad connections, defective fuel pumps, blocked fuel filter and ignition faults. Problems with fuel pressure regulators. This is a swine to check out and often a rolling road is the quick and easy way. This month's Sprint has an article on an intermittent problem I had on the Griff that turned out to be a combination of four minor issues all combining. And yes Harry you were right

Steve

[shpub]

quote:
Mine suffers from this very rarely as well, does it happen at all engine temps or around 50 degrees mark ?
It too sounds like the engine is dieing and won't throttle up to all cylinders, with a strong smell,once the alarm is reset the car drives off like it never happened.

That could be an immobiliser problem killing or strangling the pump so there is not enough pressure and engine dies. Resetting alarm restores normality. Or the fuel pump relay. Or the ECU....

This can also be caused by gummed/dead injectors where the spray pattern is screwed up. I would not advise chnaging those on spec at £78 each. Again they can be cleaned and the spray pattern looked at to see if there are issues.

[GreenV8S]

quote:
Mine suffers from this very rarely as well, does it happen at all engine temps or around 50 degrees mark ?
It too sounds like the engine is dieing and won't throttle up to all cylinders, with a strong smell,once the alarm is reset the car drives off like it never happened.
Try taking the petrol cap off and listen for an excessive hiss from the tank like a whoosh of air, if there is then the tank is not venting properly, i've cut a small piece out of the gasket of my fuel cap which helps greatly. I've also cleaned the stepper motor ,changed the spark plugs ,cap ,leads, throttle sensor, potentiometer, fuel rail temp sensor,lambda sensors and coil ,looking back on the past TVRSH from the last owner the car has suffered with this problem for a few years but never diagnosed, but the problem comes back intermittently and then dissappears. Has anybody else has had this problem and solved it.

Sounds kind of similar to the symptoms from a dodgy fuel pump relay. Especially if it happens say fifteen minutes into a journey, and goes away at random after a few seconds or minutes. If this is the problem it will eventually leave you stranded, so I suggest you get hold of a spare fuel pump relay now just in case. You can get them from a TVR or LandRover dealer, about £18, ouch.

Cheers,
Peter Humphries (and a green V8S)

[vroom]

Thanks for the advice,

The CAT smell was of rotten eggs as opposed to fuel.

The car was nice & warm & about 1/4 of a tank of fuel +/- 1/4 of tank due to gauge accuracy (I suppose could be empty then...).

I just had a new rotor arm - also found in numerous parts recently - so can rule out that one.

[dodger(rwalker1)]

Cat blockage??

[vroom]

I hope not!

I'm hoping the smell was the CAT working hard to compensate for the over / under fueling when the fault occured.

The reason I reckon is that my vectra has a aux. air pump which is switched on when the engine is cold. It blows cold air into the exhaust manifold (before the CAT). It has the effect of making the CAT work harder & gets it up to temp a lot quicker, so it is more effective (or something like that). I note that it really stinks when the pump is running!

I might try & pull the fuel pump relay when the engine is running to see if I can get the fault to occur - process of elimination I suppose.

Fingers crossed...

[M@H]

quote:

There is also this myth about the hiss from the tank. Some hiss is normal. Big hiss followed by clanking as the tank shrinks isn't.

is this the "someones locked in the boot" type clanking noise ?? as I hear it every few days and have been too shy to ask...