Vacuum leak(?)

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Vacuum leak(?)

Post by kruiik on Mon Jul 26, 2010 12:12 am

Symptoms,
- slightly wandering idle rpm (~800-1000rpm)
- earlier almost stalled every now and then (something what i've done fixed this...)
- CO emissions are over the approved limit (in Finland)
- lack of power (well, duh 103kw...)
- slowly descending rpm's after full throttle acceleration, when clutch pressed

What has been done,
- ISV Cleaned - and tested that it works
- Throttle Body and it's connections tested
- all hoses with ISV and air intake pressure tested - no leaks
- When idle was wandering, power for ISV removed to make a note that idle RPM risen a little, but was steady after that

what is going to be done,
A) spray "startpilot" to vacuum side of engine to try and locate the vacuum leak
B) (hopefully not) replace all vacuum tubes if case A fails
C) if B fails, dismantle intake manifold and start rebuilding there

All pointing to vacuum leak - but i really have hard time figurin where - all the parts have been tested separately and seem to be tight.

Any clues where "abnormal" leak would be? Sound seems to be coming somewhere "under" the ISV, behind the engine block.

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Re: Vacuum leak(?)

Post by $küll on Mon Jul 26, 2010 12:56 pm

i would first try to disconnect the lambda probe, to see if there is any difference.

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Re: Vacuum leak(?)

Post by kruiik on Mon Jul 26, 2010 1:37 pm

doh, forgot to mention that there is a clear "sshhh" sound when accelerating rapidly. So yes, there is a vacuum leak for sure - pinpointed it somewhere _under_ the throttle body and intake manifold, but still unclear where.

Lambdaprobe didnt make much difference, and it's replaced to brand new and it still works the same.

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Re: Vacuum leak(?)

Post by $küll on Mon Jul 26, 2010 3:48 pm

is the lambda bosch or chinese?

you cant have a hidden leak, or it is a manifold seal, or the rubber from the k-jet head to the throttle body.

i dont think you could hear a leak in the small hoses...
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Re: Vacuum leak(?)

Post by kruiik on Mon Jul 26, 2010 5:58 pm

Lambda is original from Bosch.

You mean the leak would be between intake manifold and engine or between throttle body and intake manifold?

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Re: Vacuum leak(?)

Post by $küll on Mon Jul 26, 2010 6:21 pm

yes somewhere there, because the suction is bigger than anywhere else. the big rubber duct from the k-jet head to the throttle body is also known for leaks. i had one too...
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Re: Vacuum leak(?)

Post by kruiik on Mon Jul 26, 2010 6:36 pm

Big rubber tube is in good condition, already dismantled all rubbers and only one was a bit cracked but wasnt cracked through - and it is replaced already.

If "start pilot"-trick doesnt help - need to remove intake manifold, i suppose..

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Re: Vacuum leak(?)

Post by $küll on Mon Jul 26, 2010 10:46 pm

your brakes work ok?

do you have the air conditioning?
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Re: Vacuum leak(?)

Post by kruiik on Mon Jul 26, 2010 11:39 pm

Brakes work really good, no problem with those.

And i do have Air conditioning as well.

Still unsure where the leak is, i guess it's time to remove intake manifold Sad

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Re: Vacuum leak(?)

Post by $küll on Mon Jul 26, 2010 11:47 pm

take a look at the pipe that goes from the vacuum line for the brakes, to the air conditioning inner recirculation.

this pipe goes from the valve near the brake drum into the gaitor where the AC pipes go inside the firewall. maybe this line is disconnected...
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Re: Vacuum leak(?)

Post by kruiik on Tue Jul 27, 2010 12:48 pm

nope, wasnt that pipe either, pressuretested it and no leaks Sad

i remove throttle body and checked intake manifold underneath with enlarging mirror, and rubbed it clean - no clear cracks. Throttlebody's seal is in mint condition as well...

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Re: Vacuum leak(?)

Post by Elektrik on Mon Feb 21, 2011 1:42 am

The same problem here. I have vacuum leaks somewhere, lambda sensor outputs 0.35v on idle and 0.05v on throttle. RPM jumps over 1000 to ~450. on idle, on throttle everything seems fine, since the sound as turbo from engine Smile There is a lot of smoke as on idle, same on throttle. "eats" too much petrol. Also I noted, that when RPMs is jumping the brake seems not to be working at full capacity. Where I have to search for a problem ? I've changed all the tubes, big rubber tube seems in good condition, no cracks. Thanks.
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Re: Vacuum leak(?)

Post by $küll on Mon Feb 21, 2011 9:38 am

Elektrik: first, welcome to the compi forum Smile

second, have you tried to disconnect the lambda? when you do so, the engine goes into safe mode, and uses programmed values for the lambda.

it is naturall that the brakes dont work if the rpm are on 450, because the engine itself makes the vacuum that boosts the brake drum.

check the tube that goes from the drum to the intake manifold, check if it is connected well and if there are any cracks on the L shaped rubber connector.
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Re: Vacuum leak(?)

Post by Elektrik on Sun Apr 10, 2011 6:17 pm

$küll wrote:Elektrik: first, welcome to the compi forum Smile

second, have you tried to disconnect the lambda? when you do so, the engine goes into safe mode, and uses programmed values for the lambda.

it is naturall that the brakes dont work if the rpm are on 450, because the engine itself makes the vacuum that boosts the brake drum.

check the tube that goes from the drum to the intake manifold, check if it is connected well and if there are any cracks on the L shaped rubber connector.

Yes, I've tried to disconnect lambda sensor - no difference, same, just error that no lambda detectec occours in ECU, and as you said eingine goes into safe mode.
Checked the L connector - in perfect condition. Checked WOT (wide open throttle) switch - works perfectly. Everything seems fine in electric side - when disconnect Idle valve - engine raises rpm and falls into safe mode with error in ecu. When I disconnect differential pressure regulator - engine almost cuts off, and falls with error in ecu. Where else can be the problem ?
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Re: Vacuum leak(?)

Post by mle on Wed Aug 24, 2011 10:41 pm

I have very similar symptoms to kruiik, except wandering idle (mine is quite stable). Occasionally engine stalls just for a sec during driving, feels like it goes to lean. Not sure, but it feels it depends on temperature, I was driving today early in the morning, and nothing, Compe worked like charm. But when I was driving again afternoon, it stalled every now and then. I can't think anything else which could cause it.

I have replaced most of the easy parts: spark plugs, distributor rotor & cap, all filters. I have cleaned ISV, I also blocked hose that goes from throttle body to charcoal filter. I have looked all hoses, all looks good. Haven't pressure tested those though. I'm soon running out of ideas what to look next. Maybe AEB then... Smile

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Re: Vacuum leak(?)

Post by $küll on Thu Aug 25, 2011 12:12 pm

try changing the water temp sensor or look at the connector, maybe you will find dodgy wires...
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Re: Vacuum leak(?)

Post by mle on Thu Aug 25, 2011 1:42 pm

Temp sensors and wires are next things to look at. I'm also thinking if it could be fuel pump, I've been told that k-jet needs quite high pressure to work right. Fuel pump could also give symptoms depending on temperature.

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