Lambda problem? Please help!

[KRIMZON]

hey folks, just finished doing a top end rebuild on my 80 2.8 V6q....it runs great, but it still has a minor issue which it's always had since i've owned it...

There seems to be a power lag that happens when you open up the taps, it's quite hard to explain but i'll try.

Obviously i'm not gonna push the car by any means at the moment while it's all setting in....but a nice 100mile run to cornwall and back yesterday certainly helped bring it to life.

ok, typical senario...

In 3rd bring it up 3500rpm, change to 4th, put foot down (not to hard but enough to pick up speed at a reasonable pace) car pulls great for a second then the car pulls it selfs back with a low drone from the exhaust like its struggling for air for about half a second then picks up again rapidly to 3500/4000rpm, change to 5th, then same senario as above??? I hope that explained it alrite

Timing is spot on, all fuel lines are clear, has new fuel filter....well anything you would do in a top end rebuild and a service has been done except....the valves, buckets, cam bearings and what not were solid and perfect....the only issue for the action of a top end rebuild was a oil leak from the head gaskets....engine is now water/oil/bloody tight...so no worries there.

When I got the car the catalytic converters were'nt there which is fine as I would removed them anyway. Both lambda sensors are there and had white-ish coating on them. Would these need to be removed/replaced?? Or is it a possible MAF sensor problem? I have no understanding on any of the sensors really, which looks f**king stupid as I type that bad hay ho.

Sorry for the long winded explaination. Any other ideas welcome.

Regards
Jay

[4v6]

Whiteish coating on the lambdas indicates silicon contamination to me.
Could have been burned in the engine somehow and poisons them.

Iif theyre just ordinary o2 sensors, you can test them by using a digital voltmeter set on its lowest reading to measure the signal coming from them whilst the engines running.
It should flick from 0 to 1 volt (dc) very quickly.
Itll go something like, 0.459-0.121-0.204-0.608-0.453 and so on.
If its just giving a static unchanging reading then its knackered, but get the engine warm first and take the reading from the signal wire ( not the heaters!) and ground.

[Martc]

I suggest getting it hooked up to vag com and get the codes read, should indicate a sensor issue.

[A_N_Other]

You could try unplugging the Lambda sensors - car should run fine without (not use them to trim the fuel if they're disconnected)
Personally, I'd expect Lambda sensor problem to show up in a steady state - problems at idle or shocking fuel economy, rather than in a transient condition.

Might be MAF problem though - you could try unplugging that and seeing if the problem improves or gets worse.

VAGCOM is definately a good idea to see if there are any codes though (you should get a couple if you unplug stuff too!)

[KRIMZON]

Cheers guys, local specialist Vehicles quoted me around £45+ VAT to hook it up to there Computer...is that about normal? If so....SV here I come.

[thesoundcriminals]

any ideasr I got the car now and its still there. I seems to be getting worse feels like a fuleing issue. help

[Phil Payne]

Originally Posted by KRIMZON

Cheers guys, local specialist Vehicles quoted me around £45+ VAT to hook it up to there Computer...is that about normal? If so....SV here I come.

It's usually charged at 1/2 hour's labour, but it's generally not worth it for lambda sensors. They last (at most) about 40k miles - if you've no record of them being changed in that time, swap 'em.

They don't break - they just wear out. Inexorably and inevitably.