2006 FX4 level 2
 

Hi.
Occasionally my 2006 FX4 will turn over but won't start unless I disconnect the battery for an extended period of time. Then it will start and run just fine for a few days and do it again. It seems to be happening more often as time goes on. Any help would be greatly appreciated. Thanks.

Welcome to the forum

Not much to go on

Any flashing light on the dash when this happens?

Does engine turn slower than normal?

Next time it happens have a can of Quick Start(ether) handy
You want to spray some into the intake, so.............
You can pull off power brake vacuum hose and spray some down the hose, then put it back on
Pull out air cleaner and spray some in the Air Tube, it won't hurt MAF sensor
Pull off air tube at intake and spray some in the intake

Then crank engine, this is the 50/50 test
If it starts and then dies you have a fuel problem
If it doesn't start then its a Spark problem
50/50 instant results

Thanks RonD. Engine runs after the battery being disconnected since yesterday. Reconnected this morning and she fired right up. Running completely normal now. Based on what its been doing it'll likely do it again before the end of the week. Could it be a PAT issue?

Yes, but PATS module(in the dash) will flash the "Theft Light"(padlock icon) if the PATS key is not recognized
So watch if the theft light comes on with key on, and then goes OFF, if so then not a PATS issue, key was recognized

And PATS will also disable starter motor if triggered, so if engine cranks its not as likely to be a PATS issue, still could be but gets to be pretty long odds if starter still works

50/50 test tells you if its a fuel or a spark issue, so narrows it down quite a bit

Computer monitors both system, and will turn on the CEL if it sees a problem

But it doesn't have a fuel pressure sensor, so if fuel pump is not coming on it wouldn't know that, it can see if pump is getting 12volts but not that it starts to work

It also can't see Spark, it can see if coil is plugged in, but not that its sparking, but there are 3 separate coils in the coil pack, all 3 failing at the same time would be very long odds

And it could be a computer problem, so no CELs because computer is no longer "sane", lol

The Crank sensor is a long shot but not a no shot
In a 50/50 test engine would not fire/start so a no Spark issue, crank sensor times spark so no crank sensor pulse = no spark

It wouldn't start again. I checked and she had spark. I replaced the crank sensor, that didn't do it. I resigned myself to changing the fuel pump and that seemed to do the trick. Thanks again for the advice RonD.

Good work

Thanks for posting the final FIX, fingers crossed