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Vacume Leak In R33 Gtst

Crans

By Crans,
in Engines & Forced Induction

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Crans

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After many many problem with my skyline i finaly found a vacume leak which i was hoping was the cause of my lean idle, lag and super richness on boost. I removed the charcole canister which is brocken and the car seams to run slightly better. Idle is still lean lag is still there but actual driving of the car feels alittle better.

After parkig the car in my drive way after testing how it went I noticed when i pressed the brake pedal the rpm droped. So I pressed it multiply times and the rpm dropped below 500 nearly stalling the car.

Any ideas here? Is this another air leak?

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jarrod83 Community Regular

jarrod83

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sorry to hear that my borrowed intercooler didnt solve your problem dude, i still feel you need a real turbo for response :P

Have you had any change in the behaviour of the braking.. how do ur brakes feel compared to the other silver skyline?? Sorry to say the check valve stops boost entering the brake system so its unlikely to be your problem unless your check valve is broken. Generally if your car goes to stall when you press the brake your brake booster has a leak in the diaphragm.

The brake booster has vacuum pressure on both sides of the diaphragm, when you press the brake pedal in, it lets in atmospheric air pressure into one side of the diaphraghm , the unbalance in the pressures gives you your brake boost. Maybe check your brake lines and get a vacuum tester and check the vacuum at the end of the brake line with the brake pedal both pressed and depressed.. id be keen to check mine as well as its one of the only few places i havent checked for my small air leaks. I think the engine would get a small amount of air from the brake system when the brake is released as the atmospheric air pressure side of the diagraghm gets repressured to vaccum.

Apparently your car can also stall from a few other things in the brake system, like blocked lines, split hoses and a master cylinder leak.. but i dont really see how with my limited knowledge, hopefully an actual mechanic can give us some additional information.. i only learn these things as things on my car break and im looking for answers:P

Jarrod

INSTASKID Newbie

INSTASKID

Posted
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I have seen this happen on many older cars, pressing the brake pedal repeatedly will either make the engine rev, or stall.

I would check the lines going to the booster and the booster itself as Jarrod mentioned. Listen for a vacuum sound when you depress the brake, that's the booster, you should only hear it while applying pressure. If you still hear vacuum when the brake is depressed and stationary, that could indicate a leak.

Laz

Crans Mentor

Crans

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wtf is wrong with 16-19 on idle

For starters, I am using an rb20 ECU, a 0 on any cell on the fuel map is a theoretical Stoich so yeah it may go slightly leaner but not the constant 17-19 i was getting on the way to work today. So i either have a leak, or yeah may be an electrical problem. I might check for voltage drops on the injectors.

Crans Mentor

Crans

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Little update on this problem.

I have disconnected my narrow band sensor and fed my Techedge widebands narrowband sim output into the loom. Car is running a lot better mostly sticking at around 14.9arf Still at idle tho its hitting mega lean and slowly moving back to 14.9afr.

I should not have had to replace the sensor as its only a year old. I think it may have been damaged by being too close to the turbo.

Back to the lean idle problem I am thinking there are 2 possible problems.

1. I do in fact still have an air leak. And now that the closed loop is working properly it is able to bring the afrs back to where they should be.

2. My idle needs to be reset.

Will continue to play with it.

lachlanw Veteran

lachlanw

Posted
Posted

afr shouldnt be a constant number at idle i hope you realise . it should swing from rich to lean and back again repeatidly . and i hope its fully warm when your doing this

every time you release the brake pedal you are letting more air into the plenum than the ecu wants in there . hance idle changes

Crans Mentor

Crans

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Yes I know when in closed loop the afr should swing rich to lean to rich etc. If you knew exactly how it worked then you would know that anything richer that stoich is seen as rich by the ecu and anything leaner than stoich in seen as lean by the ecu. Meaning the rich to lean to rich swinging should all be very very close to stoich. When monitoring using a wideband you don't actually see the swinging like you would a narrowband guage all you see is a twitch in the numbers/graph.

When having the idle issue my idle is sitting at lean no swinging nothing like that. And yes of course the car has been warmed up first.

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