Resealing Plenum

[pincher]

I did a search but it's a bit sickly at the moment

I still have, after all this time, my erratic idle problem - not a bad as it was previously but it is still noticeably there.

Latest theory is a suspected air leak at the rear of the plenum, which seems feasible to me so my question is, once I have removed the plenum what is the most tried and trusted way of resealing it?

[mgjc]

Search on the internet for Hylomar Blue, it works very well indeed. I did mine about 6 weeks back after replacing with ACT carbon trumpets.

Just clean trumpet base and plenum first - make sure there is no debris still attached so you get a proper seal. Then apply a thin line to both and then bolt down to about 15 Lbf.Ft.

After that you should be good to go.

[haircutmike]

Unfortunatrly there is more to erratic idle then resealing the plenum.

It is unlikely to be that but to reseal is only a 15 minute job.

Could be,

Throttle position sensor
Stepper
weak mixture at idle
AN other fault.

Just keep plugging away till succesfull!

I disconnected my stepper when the engine was hot and I now have a steady idle, downside is that it doesn't idle when stone cold and needs a couple of minutes of warming first.

[Simon says]

You have the fuel pressure reg pipe connected I take it? situated at the far end of the plenum on the stepper mount housing

[pincher]

haircutmike said:

Unfortunatrly there is more to erratic idle then resealing the plenum.

Tell me about it! I have tried all sorts - swapped out the stepper motor and AFM for known good ones (Del's ), tried resetting the ECU - all to no avail.

I have a Speedo Control Unit to try after the plenum fix - would have done it before but I can't get the dash off

I had a service at Castle yesterday and asked them to have a look at the idle - could see him squirting liquid around the plenum area so presume that is how they diagnosed a potential air leak at the rear.

[pincher]

mgjc said:

Search on the internet for Hylomar Blue

That's the stuff - couldn't remember what it was called!

[pincher]

Simon says said:

You have the fuel pressure reg pipe connected I take it? situated at the far end of the plenum on the stepper mount housing

Yes, is connected.

[haircutmike]

Simon says said:

You have the fuel pressure reg pipe connected I take it? situated at the far end of the plenum on the stepper mount housing

Some wally left mine off after an engine rebuild!..............Oh yeh, that was me!

[rev-erend]

Wurth RTV silicon is simply the best ..

[John042]

I manufactured a gasket together with Hylomar. The casting is not exactly a precision one. Cheers John042.

[Simon says]

rev-erend said:

Wurth RTV silicon is simply the best ..

That's the one I use although Hylomar is ideal for this kind of deal, just a heads up if you use a silicone sealer make sure its oxygen sensor friendly as many are not(the vinegar smelling stuff is bad) and turns them pink at the tip and poisons them most automotive silicone is Lambda/Oxygen sensor friendly nowadays inc Wurth you should not have to resort to making gaskets to seal the plenum I have certainly never had problems with sealing and I have 2 joins as I am using the plenum spacer just make sure the surfaces are oil free spotless & nick/burr free

Edited by Simon says on Tuesday 19th June 15:53

[redgriff500]

Sealed mine today... a mate works at L Rover and came around with the factory manual.

The factory uses Loctite thread sealant.

[pincher]

pincher said:

Simon says said:

You have the fuel pressure reg pipe connected I take it? situated at the far end of the plenum on the stepper mount housing

Yes, is connected.

Just got round to taking the plenum cover off and disconnected the pipe and noticed that it has a 1cm split where it attaches to the regulator - I'm now thinking that this could be a(nother) reason why my revs are shonky?

ETA - pic of the hose where it attaches to the FPR;

Edited by pincher on Monday 25th June 18:16

[900T-R]

Might well be a contributory factor - you don't need a lot of false air to get the poor old thing confused. Cut the end off, put it back again & if it doesn't make any difference at least you'll feel better about eliminating another possible gotcha.

[Simon says]

Unmetered air leaks are always a bad thing.

[pincher]

I really hope that this is the main cause and once I have resealed the plenum, my woes will be over - it's getting very tiresome pulling up to a set of traffic lights or zebra crossing with 1600 revs on the go, in neutral

Will report back tomorrow on whether I have fixed it.

[carsy]

Mine did this at one point in the past and yes it was the pipe you are referring to had come off the stepper. Put back on and sorted so keep your fingers crossed.

[rev-erend]

Congratulations

[pincher]

Well, it's better but I wouldn't say it's fixed completely. Think I might have another go at resealing when I am back from Le Mans and if that doesn't work, give it to someone until is is fixed permanently.

[haircutmike]

I've pulled one apart without sealent and it was running OK.

I would look elsewhere.