2002 Mercury Grand Marquis
4.6L 8 cylinder engine
No modifications; original engine/transmission
Approx. 225,000 miles


Check Engine Light – Code P0465 (Evap System Leak/Small Leak./Vacuum Leak)


I have replaced the gas cap (with an aftermarket cap).


History: A few weeks ago I started my car (engine was cold) and about 20 seconds later put the car in reverse to back down my driveway. The car felt as if it was going to stall out, then revved high, and then felt like it was going to stall out again. I put the car back in park and let it warm up for about 2 minutes. I went in reverse and the problem didn’t happen again. I drove off with no problem, but about 10 minutes later while driving, my Check Engine Light came back on (after previously being reset) – same code P0456. This hesitation/almost stalling problem ONLY happens if I do not let the car start up for about 1-2 minutes, and does not happen all the time (even if I do not let it start up).


History: The other day I started my car and I noticed it had a small “miss”. I said to myself that the Check Engine Light was going to come on any second (after previously being reset), and sure it enough it did - Same code – P0456.


My mechanic has told me that the P0456 code means there is a leak in the Evap System, and he needs to run a “smoke” test to find the leak. He says this code has NOTHING to do with engine performance or will make the engine run differently. My question to him was, then why does the Check Engine Light come on after I have experienced some engine performance issues as described above. He told me if I am having difficulty like I say (as if I am making it up); the Check Engine Light code would give the code for engine misfire/need coils replaced.



Any ideas? I feel as if there is a small vacuum leak under the hood, and perhaps the Evap System is not the issue. Does the P0456 code also come on if there is a vacuum leak, say associated with the Intake?

Note: I have had to replace coils within the last 6 months since the coils I have no are CHEAP AFTERMARKET coils (I couldn’t afford to replace all of them with the Ford coils). But, whenever they needed replacing, the Check Engine Light would give the appropriate code, tell me the cylinder of the misfire, and I would replace the coil and fix the problem easily.



I should also note the engine runs great on the highway/local, but does have a slight (very slight) hesitation at times. This I attribute to the cheap coils. Perhaps the coils suck, but are not totally bad as if to illuminate the Check Engine Light, although I don’t know if it works like that (either they are good or they are bad, nothing in between?).