clint78z Posted September 18, 2001 Share Posted September 18, 2001 I am currently trying to trace any vacuum leaks on my L28et. I have a boost/vacuum gauge hooked up, and it currently produces 12" of vacuum at idle. I know I have a vacuum leak because it idles too high on the map referenced system. Can you guys tell me what you get for vacuum at idle?? Quote Link to comment Share on other sites More sharing options...
SleeperZ Posted September 18, 2001 Share Posted September 18, 2001 I get 9" of vacuum, but I am running an aftermarket cam in my L28ET. 12" sounds a bit low, but will a small vacuum leak cause a low manifold vacuum reading? I'm not so sure about that. Camshaft timing will certainly affect manifold vacuum, have you checked your cam gear and timing chain? Quote Link to comment Share on other sites More sharing options...
Guest Tom Scala Posted September 18, 2001 Share Posted September 18, 2001 I'm getting a little over 19"Hg. @800 RPM idle speed. Stock hydraulic P90A cam. Initial timing as well as fuel mixture has a big influence on idle vacuum. I'm running 20 deg. w/SDS & 420cc injectors FWIW. Quote Link to comment Share on other sites More sharing options...
240Z Turbo Posted September 19, 2001 Share Posted September 19, 2001 I usually saw about 15-16 in-mg at 900-1000rpm and idle. Quote Link to comment Share on other sites More sharing options...
TimZ Posted September 19, 2001 Share Posted September 19, 2001 I'm getting around 15-18" at 900rpm idle lately. I'd have to agree with SleeperZ in that it sounds more like pumping losses from the cam or cam timing. At idle, there isn't always a direct relationship between manifold pressure and idle RPM. For instance, I normally pull a higher vacuum at a fast idle than I do after the car is warmed up. That said, if you want to check for a vacuum leak, try spraying carb or brake cleaner around suspected leak areas. If there is a leak, the cleaner fluid will get sucked in, and the engine should start to stumble. This is a pretty effective way to pinpoint vacuum leaks. Quote Link to comment Share on other sites More sharing options...
Guest Anonymous Posted September 19, 2001 Share Posted September 19, 2001 Yeah, I've used Chemtool in vacuum leaks too. I repaired one Vega on the cheap for a guy, the intake was leaking, found with chemtool, well, we prepared the area plastered on silicone and then just bumped the engine. The silicone sucked into the leak and we let it dry overnight. Worked like a charm. Of course our members wouldn't do something like that .... Shadetree, Lone Quote Link to comment Share on other sites More sharing options...
clint78z Posted September 19, 2001 Author Share Posted September 19, 2001 I know there is a vacuum leak because it will idle at at 1500rpm with the throttle blade closed. So that means that I have a leak in the manifold air is getting in. The extra air is compensated with fuel because the MAP sensor is referenced off the intake manifold. I need to get an exhaust system to quiet things down so I can trace the leak. Quote Link to comment Share on other sites More sharing options...
Mike C Posted September 19, 2001 Share Posted September 19, 2001 Somebody correct me if I'm wrong, but if your motor is fuel injected still, the idle air control motor will bypass air to keep the idle speed up regardless of whether the throttle blade is cracked or closed. Quote Link to comment Share on other sites More sharing options...
clint78z Posted September 19, 2001 Author Share Posted September 19, 2001 I have a 300zxt Throttle Body with no idle bypass. The accel DFI is hooked to a map sensor which is referenced off of the intake manifold. When I pull off the brake booster hose rpm skyrocket, because the map sensor see less vacuum and compensates by adding more fuel. I have used carb cleaner on other vehicles, I have also heard of an unlit propane torch. It roars at 1500rpm but does it very smoothly, let the tracking begin. Thanx for the info. Quote Link to comment Share on other sites More sharing options...
Drax240z Posted September 19, 2001 Share Posted September 19, 2001 I find propane works a lot better than carb cleaner, which can strip paint and is quite harsh. Also its a bit easier to get into nooks and crannies because its a gas.... let us know what you find. Quote Link to comment Share on other sites More sharing options...
Guest Tim78zt Posted September 19, 2001 Share Posted September 19, 2001 I also had some vacuum leaks and now am idling around 17". I may still have a leak somewhere because it still idles at a higher RPM. My tach still doesn't work but just by ear I would say it is idling around 1100. Steve said his idles around 20", just for another point of reference. Tim78zt Quote Link to comment Share on other sites More sharing options...
Mike C Posted September 19, 2001 Share Posted September 19, 2001 Temporarily block off the power booster take off on the intake as these units seem to leak quite often. From their just check every hose and fitting. A pain, but eventually you'll find it. Quote Link to comment Share on other sites More sharing options...
Guest Anonymous Posted September 21, 2001 Share Posted September 21, 2001 my 83 zxt @ idle is a bout 21" of vacuum.. i think it is arounf 800rpm... it runs like crap until its warm... but the vacuum and stuff stays the same. Fraga Quote Link to comment Share on other sites More sharing options...
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