Limited power on a VW Golf

[adpsimpson]

We picked up a 1998 diesel mk4 golf on Tuesday, which has a slight issue under high load. If you accelerate at full power for any significant length of time (> 30 seconds), or drive up a hill under full power, it will suddenly drop about 1/2 of its power, leaving it able to top out at 70mph on a flat motorway, or less up hills. The power drop is sudden and very noticeable.

It appears to remain the same until you restart the engine. Even if you drop back to low speed, the power remains reduced. As soon as you restart the engine, even if you're still at speed, it seems to recover.

It's not a speed limiter as it doesn't always happen at the same speed. So it's probably the ECU getting unhappy about something and de-rating. There's no warning lights.

Could it be a fuel or air restriction? Anyone know anything else that could make it do this? I've got a set of new filters here but have been too busy trying to fix the rear brakes (which the dealer had kindly coated in copper slip to hide the fact that there were no pads left) to fit them yet.

[evildwarf]

Check the earth strap from engine to chassis!

[adpsimpson]

Check the earth strap from engine to chassis!

Good thought, thanks.

[jeff.fn02jwa]

is it like limp home mode i would go with the earth straps to n if that not it give them a good clean with a wire brush

[adpsimpson]

Yup, exactly like a limp home mode, but only comes on in the conditions I described. Have checked the ground strap visually and it looks good, will take a multimeter to it once I finish this orange, then take it off for a scrub and re-fit it.

[slobodan]

once I finish this orange,

is that slang for something...Or are you really eating an orange?

[surfenstein]

i dont know if the vw golfs are fitted with a fuel pressure sensor,but it could be something simple like a blocked tank breather causing a vac in the tank.

[adpsimpson]

is that slang for something...Or are you really eating an orange?

No, I was actually eating an orange. Of course, if it is slang for something I don't know about, I've probably made a fool of myself.

i dont know if the vw golfs are fitted with a fuel pressure sensor,but it could be something simple like a blocked tank breather causing a vac in the tank.

I checked that, it was pretty blocked up, unblocked it but it didn't help.

[4 Runner]

Check that the Turbo boost hoss is not spilt I have jaust had to replace mine and at the same time had my MK 4 150 bhp remaped to 190 bhp very impessive and still good fuel eccomomy

[Mr Sqig]

sounds like its over boosting and going into limp home mode as if its been owned by a granny the vvt (varible vane turbo) gets gunked up and the vanes cant move quick enough causing the engine to over boost and it shuts the system down into limp home to save the engine, but you need to get it plugged on to a diag machine to read the faults out of it as that will prob tell you what it is straight away, and yes im a diesel mechanic

[dieselboy]

Wouldnt this normally be accompanied by a light on the dash?

[adpsimpson]

sounds like its over boosting and going into limp home mode as if its been owned by a granny the vvt (varible vane turbo) gets gunked up and the vanes cant move quick enough causing the engine to over boost and it shuts the system down into limp home to save the engine, but you need to get it plugged on to a diag machine to read the faults out of it as that will prob tell you what it is straight away, and yes im a diesel mechanic

Sounds the most promising yet, it's had plenty previous owners so one of them was bound to be a granny! It certainly feels like the turbo's been disabled when it happens. There's no warning lights on the dash - will a normal CAN bus reader linked to a laptop give me the codes I need?

[adpsimpson]

Wouldnt this normally be accompanied by a light on the dash?

Didn't see this, that's what I was thinking too, see my response above!

[Mr Sqig]

somtimes it might not bring a light up, cars are funny like that, any fault codes will give you a idea of where to head and being a vw will most likey tell u exactly what it is