A check engine light recently came on for code P0446 on my 2000 S10 4.3L. I have one of the cheapo code readers that plug into the OBD port and that is how I read the code. The simple solution would be to throw a $30 evap vent solenoid at this but I am not sure that is the problem.
The truck recently went in to the shop for three things that might play into this, both at the same time. I had the fuel pump replaced. The fuel line coming out of the pump was leaking and spraying fuel all over the top of the tank. There was a noticeable odor of course and that is why the truck went into the shop. The dreaded intake manifold gasket had been leaking coolant for a while but was manageable. Then is seemed an injector was sticking open so I had both the intake gasket and fuel injection spider replaced. So it went in for fuel related problems at the tank and at the injectors. Obviously all the stuff on top of the intake had to come out.
The truck runs fine throughout 99% of driving conditions but has two obvious issues. There is a noticeable misfire at idle. You can hear that poofing sound out the exhaust while it is sitting and idling. It is fine under normal acceleration and driving. The other issue is at high throttle/high power conditions such as when accelerating quickly or passing. The engine will cut out and lose ALL power, creating a strong bucking feeling. It returns to normal when you let off the gas.
I have felt like the HVAC system switches modes such as from normal to defrost or the temp changes when climbing hills as well. I know these are vacuum controlled so am wondering where to start, especially considering all the variables that might be in play here.
I am not getting any misfire codes or pending codes for misfire. It has been driven several hundred miles since this started so shouldn’t be an issue with not enough start cycles or mileage.
I checked the vacuum lines and wiring connections . There weren’t any any obvious problems. I figure I will pickup a can of starter fluid to spray around the lines and see if I can notice a difference in how it runs to detect a vacuum leak. It seems to run fine when cold but starts misfiring and sputtering at idle once warmed up. It isn’t a high idle or anything with a lean misfire like you hear with vacuum leaks.
Is this possibly just the vapor canister purge valve? I figured this wouldn’t cause running issues and just create excess emissions. I have been told to just replace the gas cap because these are cheap and that might be the issue. The seal on mine looks fine but this might not be a bad idea. I don’t see this causing the misfiring I am experiencing though so want to narrow this down before throwing money at it.
I concur w/post above, p0446 indicates a vent valve/circuit problem, not purge valve. Could be the prior work dislodged the vent valve’s electrical connector, or a vent related hose is being pinched. One reason that valve is used by the computer is to verify the truck’s evap system is not leaking fumes to atmosphere. I’m guessing a test vacuum is created in the evap system, then opening the vent valve to measure how quickly the vacuum subsides. If the vacuum (negative pressure) doesn’t subside towards zero quickly enough, the drivetrain computer thinks the valve’s functionality is suspect. Other possibilities of course, like the evap pressure sensor is inaccurate.
I don’t fully understand purpose of vent valve I guess. Can think of two purposes, but there may be others…
Purpose 1: During re-fueling fumes at top of gas tank are pushed into charcoal canister. The gasoline stays inside canister, and air cleaned of gasoline leaves canister (to atmosphere) via vent valve?
Purpose 2: When car is driving down the road gasoline inside canister fumes is pulled out (by engine vacuum) through purge valve into engine. In order for gasoline to exit canister and go into engine, air must come into canister to replace lost gasoline, and that air comes in through the vent valve? It seems like you’d want to have filtered air for that.
I always clear the code at least once to see if it is what I call a “phantom code” or an actual problem. My girlfriend used to have a car like this. I would clear the code at least twice before taking it seriously. There were so many times the check engine light came on for random problems. You would clear the code and that code would never return but a completely different and unrelated one would show. That car was GM Daewoo garbage and is gone now. I figure in addition to all the other problems, something electrical must have been wrong.
Anyway, I cleared the code on this one. It showed right back up shortly after clearing so I figured I had a real problem and not just a “phantom code” as I call it. So, I went to the parts store and bought the vent valve/solenoid assembly. It looks like this is an easy swap but the weather has been crap or I have been busy so didn’t feel like messing with it. Anyway, the new part is sitting in the box and I can see that the code is no more and there is no more check engine light. It just went away on its own.
I am not sure what happened or if I should replace the part or just leave it alone for now. I do have one idea… I was paying for gas at a busy station with cash so didn’t want to have to go back in for change. I figured out how much gas I thought I needed and gave them that much money so it would just shut off. Anyway, I come back out and start filling. I wasn’t paying a lot of attention but the pump didn’t turn off when it was full. Gas had just started to pour out the filler tube from being overfilled when I hit my money limit and the pump shut off. I know overfilling can damage the evap system and wonder if maybe gas that ended up where it shouldn’t have eventually vaporized and the problem resolved.
I am just wondering if I should return the part or not. I figure I will hang onto it for a few more weeks just in case but don’t know if I need to be worried about this or not.
If it is working ok now, leave the old one alone. If it starts acting up again, you could remove old one and compare it to new one on work-bench. apply voltage to activate, you may learn the old one isn’t opening and closing consistently like the new one does.
The computer won’t allow a faulty vent valve w/o complaint b/c it needs it to work correctly to do the test that verifies the evap system is leak free. My OBD I Corolla has an evap system, but it has no way to test it is leak free on its own. That’s tested as part of the state’s emissions testing process. You are experiencing one the joys of OBD II … lol …
This is good to know. This problem is obviously unrelated to my overfill event. I am wondering about the fact I had the fuel pump replaced recently or maybe this is all a coincidence.
Anyway, I am thinking I might have an iffy crank position sensor. I talked to a few folks and they seem to think this might be the cause of my misfires at idle or under heavy acceleration.
I also notice it seems to take a little more cranking than any of my other cars to start. Again, this goes along with a crank sensor. I just assumed it was all the fuel system problems but the fuel pump, regulator, filter, and GM spider injector system were all replaced at the last service. It is maybe a little better as it doesn’t have to wait to build fuel pressure when it was leaking but still noticeable compared to anything else I own.
Again, I have NO CODES for the crank sensor or anything else now. I have a friend who wants to hookup his $1000 diagnostic computer for me so figure I will take him up on this offer. I don’t know what this will show if there are no codes/no pending codes for anything like this but it is worth a try.
I guess it could also be some strange electrical gremlin like the corroded solenoid wire on the 1997 F250 that drove me nuts with good voltage readings but that couldn’t handle the amps. Dealing with no so obvious problems like this is probably the most frustrating thing about having older vehicles around.
Yes, you can hear it missing at idle. It seems to run fine under “normal” driving but if you really accelerate hard, it begins misfiring quite noticeably. I am wondering if that fact that is is likely not misfiring 99% of the time is why no codes are showing. Shouldn’t there be a pending code though?
Could be the engine is running overly lean. Symptom may be showing up more at idle and under acceleration. Suggest to obtain a fuel trim test. Not sure if a faulty vent valve could cause a lean mixture, but if you have a way to block it temporarily, might be worth a try. Note that blocking air from entering evap system could conceivably cause gas tank to collapse as fuel level dropped, so only a brief experiment. I’m guessing that’s not the problem; instead you have some sort of vacuum system leak, pcv system problem, or egr problem. Any weirdness in the brakes? If so, could indicate the power brake booster is leaking vacuum.
I would expect misfire codes, but the misfire-code algorithm may not set any codes until the problem has persisted for a certain number of miles, or it becomes more severe.
In the way of misery loves company, I noticed the other day my truck’s idle has become a little wobbly … lol …
The misfires seem to have gone away but the check engine light came back on. I was going to read the code and replace the vent valve if it was the P0446, figuring it was wearing out or being “sticky” intermittently but the code and light vanished before I had the chance. Either way, if it comes back, I will read the code ASAP and replace the vent valve with the one I still have on hand if is the same code.
Basically you can hear it misfiring out the tailpipe when it is acting up. You hear that poof of the misfires. It has done it once under heavy acceleration and I have tried repeating the conditions but the problem is also quite random. I was hoping I could get it to do it every time so if I took it to the shop, I could duplicate it with ease. Unfortunately that is not the case. I have had several suggestions about the crank position sensor so plan to replace that if I replace the vent valve and this doesn’t stop.
I thought I was maybe having some type of vacuum issue as well. I see that has been suggested above. I noticed the HVAC switched modes under heavy acceleration going uphill once where I might have been slightly lugging the engine. It was like on normal vent, then the defroster switched on. As soon as the loading was over with, it switched back to normal a few seconds later. Again, I have tried to duplicate that behavior as well and it hasn’t done it in quite a while. The HVAC stuff is vacuum actuated of course so figured that might be an issue.
Either way, I suspect the code will return and I will read it ASAP, then change the vent valve if that is what it is and see what happens from there.
Sorry you are having those difficulties, frustrating. On the other hand it’s a bit of a mystery story, and people read mystery books and watch mystery movies all the time for entertainment. You’ve got that on the plus side of the ledger I’m guessing the vent valve issue is not related to the misfiring, and the misfiring is most likely some sort of ignition system problem. Your truck isn’t configured with a distributor I presume.
The 4.3L from this era DOES use a distributor and is not coil on plug. It is a 2000 but my 1997 and 1999 modular fords are coil on plug. I bought the top end line at Oreilly, AutoZone, or whatever. Apparently parts store brand parts are not well-liked here so maybe that is the problem. Again, I didn’t opt for the cheaper grade which was an option.
I replaced the plugs, wires, cap/rotor, and the coil when I was having some ignition problems several years back and it was due on mileage for sure. There is probably way more time on these new components than mileage as of now if that matters.
The fuel system was also just gone through. The pump/sending unit was just replaced, the upper intake gasket replaced, the spider injector and pressure regulator replaced, etc. as well while they were in there.
The truck was running fine today and I changed the oil and filter which is completely unrelated to all of this of course.
Any noticeable oil leaks? Like from the valve cover gaskets? You mentioned you replaced the intake manifold gasket, which is a good idea to replace proactively, common air leak source, but if the valve covers have a leak, they can also allow air to get sucked into the engine via the pcv system, creating a lean-misfire. This sort of leak is often affected by engine compartment temperature, so it might not leak much when the engine is cold, but as the engine warms it begins to leak air, and the resultant engine stumbles.
As far as the distributor, it sounds like you’ve already replaced most of the related common failure parts, but one idea, check the distributor shaft for sideways play. There should be very little to none. If there’s sideways movement, it can affect the ignition system, even if it an electronic point-less version.
Thanks. I will check for sideways play on that shaft today. Will also pickup a can of starter fluid to spray around under the hood to see if I can find a vacuum leak. I don’t think that would show a problem with the valve cover gaskets though.
One thing I know is an issue is that the oil pan gasket is leaking. This is something that requires the engine be completely removed from the truck. It isn’t a stamped steel pan that can be replaced but a large cast aluminum structural component of the engine on the 4.3L. I once ran over some road debris at night that put a crack in the oil pan. I got a used one on hand and planned to replace it until I realized the job this would be. I ended up draining all the oil and letting it sit empty a few days. Then I cleaned up and roughed up the oil pan. I used some thin sheet aluminum and JB Weld to patch the crack. I thought this was the leak point at first but it isn’t. Honestly I think the old oil pan is fine but since I have a used one on hand, it will be replaced if I ever need to pull the engine for a clutch or something like that. The leak is not serious. I could probably go a full oil change and be down a quart if I didn’t add any but I do check it and add from time to time. It is easier and cheaper to do this than have the entire engine pulled. Mine is 2WD but I understand this is a lot easier in 4WD models.
I am debating just changing the crank sensor as several have suggested that as a cause of this. It seems like it should stumble under acceleration all the time if a vacuum problem. If I floor it, it will seem like it is ready to take on the world and then just cuts all power like I hit the rev or speed limiter. Of course I am not near either of those limits. The only code I have had is P0446 which seems to be unrelated to these problems. Of course there was the code that showed and cleared before I was able to read it.
My own truck’s idle has gotten steadily worse, ok when engine is cold, but misfires at idle when warm. Some indications of ignition system problems, so replaced plug wires and distributor cap, both of which had clearly seen better days. One plug wire measured as an open circuit in fact. No improvement … lol … In my truck’s case the engine runs perfectly cold, and even when warm its rapid acceleration is perfect. I’m now thinking the actual problem is the carb’s idle-circuit, gunked up.
As far as your truck, this sort of problem, pretty good chance it is either spark or fuel. Make a guess. If guess doesn’t pan out, try the other one, hopefully that method will eventually lead to a solution. I think the starter fluid idea to check for vacuum leaks is a good one. If there were a valve cover vacuum leak I think this method would find it; but a valve cover vacuum leak big enough to cause your symptoms seems pretty unlikely. In your truck’s case the most likely air leak problematic-location is the air path from the air cleaner to the throttle body, including the throttle body gasket. After that, cracks in vacuum hoses and connections, and leaky vacuum actuated devices. If you have a vacuum advance gadget on your distributor, make sure it is working correctly and not leaking vacuum. I expect however a 2000 truck, even if equipped with distributor, still doesn’t have a vacuum advance unit. My Corolla’s distributor has no vacuum advance unit, all timing is done electronically.
I continue to wonder about the p0446, but have no theory how a faulty evap vent valve could cause the engine to perform poorly. If you could figure out a way to temporarily plug it off, might be worth the time to do the experiment. Short term experiment only of course.
So what else? hmmm …
You may have to bite the bullet and replace the crank sensor, might help.
An exhaust system restriction could explain the poor acceleration, but less likely explanation for the idle misfires. You may have to consider you have two problems, not one.
If you think a valve cover gasket or oil pan gasket is allowing extra air via the pcv system, maybe you could plug that air path into the engine off temporarily, see if it helps.
I am thinking I might have two problems as you say. My truck is actually running BETTER over time so don’t know what that is all about. I am still going to keep an eye on things and read the code as soon as a light comes back on. If the evap solenoid, I will replace it as I have one in the box.
People keep saying it is likely the crank sensor so I don’t know. Either way, it runs fine just going down the road and I haven’t really had any misfire issues lately. I have tried to re-create the problem under heavy acceleration and it won’t happen. If I replace the solenoid first and that doesn’t help, the crank sensor will be next.
I will try the starter fluid trick for vacuum leaks.
I’m guessing the vent valve issue is not related to the misfiring, and the misfiring is most likely some sort of ignition system problem. Your truck isn’t configured with a distributor I presume.