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Re: EVAP CEL specailists! Help Please, repaced Canister! Posted by Ari [Email]  (#2847) [Profile/Gallery]
(more from Ari) on Thu, 10 Apr 2008 05:56:10
In Reply to: EVAP CEL specailists! Help Please, repaced Canister!, Steve, Wed, 9 Apr 2008 21:34:28 Members do not see ads below this line. - Help Keep This Site Online - Signup |
Not a specialist, but I drove past a Holiday Inn Express on the way to work.
From all of the descriptions, the system is working properly. The canister either leaks or it doesn't. The fuel tank either holds pressure or it doesn't. The valve opens or it doesn't.
The basic tests I see are the Engine on not ticking - holds vacuum. OK, the valve is working and the line is intact. Next, you get 'pulses' in the vacuum when the valve is ticking. OK, the valve is opening and closing. The fact that you can suck on the line from the tank and not pull vacuum is interesting but inconclusive.
My analysis - the valve is wired correctly and working correctly, and the hoses from the valve to the intake are OK. Diagnosis - you have a vacuum leak, either in the tank or Other Than the Evap system. Huh?
The Evap system works by opening the valve at specific times in the engine cycle. The diagnostics work by noting the difference in engine fuel flow requirements when the valve is open (extra air flowing) and closed (normal air flow). However, that system can only operate in a limited range.
If you have an air leak at the tank, you'll pull more air from the tank when the valve is open than expected. The EVAP system will signal this just like a missing gas cap. You test on pulling vacuum from the tank is inconclusive - depending on the amount of fuel in the tank (and therefore air) it can be very hard to suck all that air out. You might try the vacuum test on the tank with a full tank of gas - minimal amount of air. My guess is that you've got a leak at a fitting at the tank that is letting in air. When the EVAP valve opens, you get more air than it should, and the CEL is triggered.
The other option is that you have a vacuum leak elsewhere in the system. This effectively 'biases up' the amount of air in the system. Yes, as a '95 you have a MAP sensor, so all air is metered air, but leaks can still throw things off. The EVAP is essentially a measured air leak, but if you've got others elsewhere in the system, it may push the EVAP fault detection out of its comfort zone.
So I'd start with the tank - make sure it isn't leaking. As a simple test, run the car for about 5 -10 minutes with a half tank of gas or so, shut it down, and pull off the gas cap. If you don't hear any whoosh of air coming in, suspect an air leak at the tank. Fill the tank with gas and see if you can pull a vacuum at the canister line. If you can't, suspect the tank. And while you're at it, inspect ALL other vacuum lines for leaks. How do your spark plugs look? If you've got one or more vacuum leaks elsewhere in the system, you may be running a little lean.
posted by 192.249....
, Thu, 10 Apr 2008 05:56:10 <-- Viewing This Message, Fri, 11 Apr 2008 07:18:40
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