My car randomly shuts off about once a week when im sitting at a red light or sitting in a drive thru for last couple years.
But now the smog check guy says i have a minor sensor issue preventing me from passing smog. He said drive 200mi with battery unplugged. But i can't get 10mi down highway before it dies mid upshift
From there, i learned that slowly speeding up works decent, but aggressive acceleration causes shut down mid upshift. (Automatic transmission)
What could be the issue?
Its a retired 2009 ford crown vic chp with tons of loose wires, no sparking im aware of. No starting issues, no engine noises.
Any thoughts?
Never drive a car with the battery disconnected, for one, unless you enjoy fried electronics.
Also throughout last couple years, random acceleration while stopped for half a sec. I always had foot on brake though. Ive only owned vehicle for 2 years
If your mechanic is claiming that there's a problem with a sensor, he should be able to tell you exactly which one. OBDII is very good at telling you what problems are in the engine. On top of that, instead of "driving around without a battery"- they should be very capable of resetting all of the codes to start over.
I'd suggest finding a more competent mechanic.
My very first, brand new out of the show room automobile, a Fiat 128 did that: no one knew the answer back then. 
wae
SuperDork
6/18/19 7:15 a.m.
Is it possible your guy meant to unplug the battery for a while then hook it back up and drive it for 200 miles? If there was a sensor issue, that would effectively clear the code and then put the car through all the various system tests to make it emissions ready assuming that the issue was a transient one. Trying to turn it off and on again is a pretty cheap and easy fix that does occasionally work for minor issues and flaky sensors to limp them along until they fail all the way.
Something that was sending enough bad data to shut the car down, though, probably wouldn't be fixed by simulating a catastrophic power failure and if it were a sensor issue causing that, it would be awfully likely to set a code that might give you a general area in which to start looking.
I had a Ford van -- check that, two Ford vans -- that exhibited a similar issue. If I was extremely gentle to the throttle, moving it no more than about a quarter of an inch from idle, everything was pretty much okay. Any further than that and it would cough and spit. No stalling, but it wasn't going anywhere, either. Both times it was related to air getting around the MAF because the air cleaner assembly on those things was designed by Satan himself and is really difficult to get back together and sealed up after removal. That may or may not have anything to do with your problem, but I find it cathartic to relate the story, so there you go.
Troubleshooting any ford should start with cleaning the MAF and checking for any unmetered air. They are just super sensitive to it and will display all sorts of bad behavior if the pcm gets incorrect info from the MAF.
My smog guy said to take off the power cable on the battery for 5 minutes , that zeros out the computer,
hook it back up and drive 50 miles to have the computer reset.
In reply to californiamilleghia :
Just out of curiosity- why can't your smog guy clear the codes and reset the module themselves?
Are all smog guys dumb? Where i live doesnt have emissions testing so i dont have any first hand experience. But from this thread 2 out of 2 smog guys are dumb.
wae
SuperDork
6/18/19 8:10 a.m.
In reply to gearheadmb :
I'm going to guess that there's some sort of rule that is preventing them from doing that? It does seem kind of dumb
Disconnecting the battery doesn't reset codes on ODB2 systems, need a scan tool for that. Most of the parts stores have code readers, have them read it to see what it says is wrong or at least what the code is.
Tyler H said:
Buy this OBD2 bluetooth interface. Download Torque Pro.
Post your codes and freeze frame data.
Exactly. Use the tool to let the car tell you what is wrong. Fix that problem, and enjoy. If a mechanic is suggesting that codes need to be cleared, that's an immediate indication that there IS a code that needs fixed. Not that it just needs cleared and it will go away- something is wrong and needs fixed.
Not sure why mechanics want to ignore that feature.
gearheadmb said:
Are all smog guys dumb?
Yes.
Well, maybe that is the wrong word. Not technically proficient. If they were, they wouldn't working at a testing station.
Sorry for late response, or simply thank you. I need to turn on email notifications. I will aork on the jssue per your advice.
On another note, i drove with battery disconnected for about 7miles, 20min or so. Didnt help, but i didnt try disconnecting the battery for 5 min with car off.
My next measure, when ive cleared my agenda, will be to check it out with the code reader, try the battery disconnect, and use code reader again every day to when code reappears, see if i can pass smog and fix after, bc ive been driving without registration or insurance for too long
Vigo
MegaDork
10/1/19 9:24 p.m.
Not technically proficient. If they were, they wouldn't working at a testing station.
Yeah, it seems most places have it in common that whatever their state mandated fees are for compliance inspections don't end up being particularly profitable for shops, so they tend to assign the lowest-paid person they can get away with to do it.
