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Vacuum leak testing, 84 Lux

Black Beauty

Black Beauty

Member
Hi,

My 84' Lux is overfuelling and I have replaced / tested everything, however, I am now convinced as much as I can be that I may have a vacuum leak as there is an odd sound from near the inlet manifold, however, I'm not really sure how I go about testing for a leak.

The vacuum pipes that go from the FPR and dampner to the throttle body have been replaced a couple years back, but are there any other smaller ones that I need to check?

I am convinced that is coming from near the inlet manifold, but I am not sure how and where to check or what tools to use?

One other thing and something I've never noticed before but may be linked, is that when I take the Oil filler cap off when the engine is running the rev's drop, thinking I was hearing things and/or it was just co-incidence I took it off again, and the revs dropped again. Does this point to an issue elsewhere?

Everything else on the car is fine, she idles' well, pulls ok except that she' does backfire when I let off the gas checking

Cheers
Spence
 
there are so many junctions, pipes and joints to check( including some under the inlet manifold ) that the only effective way to test the system is to pressurize it with smoke. Its easy to see all the leaks using smoke.

There is a brilliant tutorial on youtube I'll try find the link. Its really easy to do and 100% effective. (Apparently you can use cigar smoke but I wouldn't fancy that as a non smoker )

It is normal for the revs to drop slightly when removing the oil filla cap because believe it or not the crankcase is part of the vacuum system . You'll probably find the revs will drop slightly if you pull the oil dip stick too.
You need to check your ERG valve operation , sounds like that needs replacing

https://www.youtube.com/watch?v=FfiQ7qWiG-M
[youtube]FfiQ7qWiG-M[/youtube]
 
What convinces you that you are overfuelling? You say you have checked or replaced everything, does that include replacing the FPR? Fuel pressure at idle can be checked and should be 2 bar. If the FPR has failed shut it would give a high fuel pressure but this would cause other problems like poor starting and idling.
 
Jim,

Fpr has been replaced.

The plugs are all sooted up. I have replaced the originals with new and then got covered in black soot within 20 mins or so. I cleaned it all off and it happened straight all over again.

Peanut, where is the ERG?

Ta
 
ORIGINAL: Black Beauty

Jim,

Fpr has been replaced.

The plugs are all sooted up. I have replaced the originals with new and then got covered in black soot within 20 mins or so. I cleaned it all off and it happened straight all over again.

Peanut, where is the ERG?

Ta
Click to expand...

sorry thats me being lazy. The 944 hasn't got a ERG as such but 3 letters are quicker to type than Crankcase air/oil seperator or crankcase pressure relief system .

As you have an over-pressurized crankcase I would recommend you look at the crankcase pressure relief system.

I don't know anything about the early 944 system but looking in my Haynes it would seem that there is a filter that could be blocked. the take-off is down on the side of the block .
Hopefully someone that has taken a pre 85 engine apart can advise where it is and what needs checking

The other thing I would strongly recommend you test is the compression. You may have worn or broken rings causing the increased crancase pressure. Remove your DME and with WOT (wide open throttle) turn the engine over 10 x times for each cylinder and note the results.
 
Spense how are you getting on ?
Is Christmas getting in the way ?[:D]

I saw someone do a smoke test on their vacuum system on Youtube and they used a Cigar to blow smoke into the system through a length of hose.

Perfect for a cheapskate like Olli ![;)][:D][:D][:D] cough cough
 

ORIGINAL: peanut

Spense how are you getting on ?
Is Christmas getting in the way ?[:D]

I saw someone do a smoke test on their vacuum system on Youtube and they used a Cigar to blow smoke into the system through a length of hose.

Perfect for a cheapskate like Olli ![;)][:D][:D][:D] cough cough
Click to expand...

I broke the rotor arm dust cover whilst changing the rotor arm and dizzie cap so just waiting for new one, hence why its not moved on.

I saw that video too, i'll think i'll start off with the soapy water test first, before giving doing it more scientifically [8|]
 
The backfire and other symptoms do suggest over fueling, rather than a vac leak which tends to give high idle and lean mixture.

I know you have replaced the FPR, but it is the obvious thing, I had the same symptoms on the 2.7, cured with a new FPR.

Just a thought, is it the correct FPR - 2.5B not the later 3.0B one?
 
Mike,

Fpr was replaced with one with exactly the same code stamped on it.

I've been speaking with Tom from augment automotive over the past few days and i am going to try a matching afm and dme from a later car, which is done alot in the states and elsewhere, as a last resort.

The car does appear to have a vacuum leak or something else going on but i have yet to try the final leak test

Ultimately, its an old car that isn't used as much as it should be so Imonly have myself to blame.

Spence
 
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