Sorry i’m advance, it’s a long read but i’m trying to include every detail to help and i appreciate all responses. I’m a girl who knows nothing about cars. I bought a 2016 mustang gt back in jan of this year and i’ve never had a problem with it, it’s been so great and was in great condition. One evening while driving home i got an engine coolant temperature warning. It was an issue i wanted solved immediately so the first shop i called was big o tires, it was around 5:30 on a friday so most other shops were already closed and i work mon-fri i needed the issue fixed asap, but i explained the warning and they said they could look at it the next day. Next day comes and they say the thermostat needed replacing so they replaced that along with an oil change. Once it was time to leave the shop i started the car and got a long crank, so i tried again.. same thing. I walk back in and ask why it’s cranking long and a technician came out with me and of course third times a charm and it works fine so i say whatever, maybe it was a one off issue. Next day comes around and it cranks fine up until the evening and it does the same thing and i’m getting pretty annoyed at that point. I called them and said it’s still long cranking and they have me come in again. I go in, they inspect the car and the proceed to say nothing is wrong and it’s because my key fob is dirty and to clean it. They said the alternator battery and starter were all fine. I had it professionally cleaned and still had the long crank issue, clearly the key fob story was a load of bs. Few days go by and I take it to another shop, he took the time to look at the car and said the only thing that could possible be wrong is the purge valve is getting stuck either open or closed, something along the lines of that i apologize i don’t 100% remember what he said, but he said he put some type of liquid on it to help. A good 3 weeks go by with no issue and i’m thinking wow that must have worked and was relieved … only yet for it to happen again tonight. The car has no check engine light and i’m unable to duplicate the issue for anyone because the long crank happens at random. I feel like i’m at a dead end here and nobody can help me and im going crazy. i’m desperate to get this problem fixed and big o tires doesn’t seem to wanna help me anymore even though my car no problems until visiting their shop. To me it sounds like something THEY did because again i never had a single crank issue before. I really wanna take care of this car as it’s my dream car i had been saving up for. Any insight or advice? the best i can describe it is that when i start the car i get a long maybe 6-7 second crank before it starts up, so the car DOES always start up but the crank is extremely long and again just happens at complete random.
Car Diagnosis
- Thread starter j.2016
- Start date
manicmechanic007
5 Year Member
Just know that places like tire shops have mechanics but low powered ones
Most of us got our start at a tire shop, me included
They are just not highly trained (yet)
Long crank times can happen for a few reasons
Slow to build fuel pressure is one of the main causes
Try cycling the key on and off once or twice before you actually hit start
That will prime the fuel system in case the pump is weak
Buy yourself a cheap 40 dollar scan tool that runs PIDS for your 2016
Have you tried a "flood clear start" when this is happening?
Most of us got our start at a tire shop, me included
They are just not highly trained (yet)
Long crank times can happen for a few reasons
Slow to build fuel pressure is one of the main causes
Try cycling the key on and off once or twice before you actually hit start
That will prime the fuel system in case the pump is weak
Buy yourself a cheap 40 dollar scan tool that runs PIDS for your 2016
Have you tried a "flood clear start" when this is happening?
I'll try and break this down some:
Symptoms:
Long crank (5–8 seconds) before the engine fires.
Intermittent — more common after a hot soak or sitting a short time.
No CEL or only EVAP-related codes (e.g., P0456 small leak, purge valve stuck open).
Some owners report this showing up after cooling system or intake work (thermostat, MAF cleaning, etc.).
Vehicle always starts, just delayed.
A dirty key fob does not cause long cranking.
If the car unlocks/starts normally, it’s not a PATS issue.
Don’t waste time or money here.
With engine off: Battery should read 12.4–12.6 V.
During crank: Voltage should not drop below 10 V.
With engine running: Charging system should hold 13.5–14.5 V.
A weak battery or dragging starter can cause long cranks, especially after the car is hot.
Turn the key to ON (don’t start).
Listen at the rear of the car for a 1–2 second hum (fuel pump priming).
No sound? Possible fuel pump relay, fuse, or pump issue.
Rail pressure should build to about 55–60 PSI at key-on prime.
After shutoff, pressure should hold for several minutes.
If it bleeds down quickly, possible bad pump check valve, leaky injector, or faulty fuel pressure regulator.
Shop can confirm with a fuel pressure gauge if you don’t have one.
A stuck-open purge valve allows raw vapors into the intake during startup, which causes a rich mix and long crank.
Quick test: unplug the purge valve’s electrical connector and try starting for a few days. If issue disappears, replace purge valve. (~$40–60 part, easy DIY swap).
Inspect purge lines for cracks, loose fittings, or disconnections (common after cooling system or MAF work).
A weak or failing crank sensor can delay spark signal during crank.
Usually throws a CEL, but intermittent failure is possible.
Shop can scope/test the CKP signal during crank if basics check out.
Leaky injector – check for fuel smell, rich exhaust, or fuel in oil.
PCM tune mismatch – if engine or ECU swap was done (for example 2001 vs 2002 ECU differences), confirm PCM, harness, and sensors match. The 2016 GT has MAF-integrated IAT; if wiring is wrong, sensor data may not reach PCM.
Replacing the purge valve solenoid.
Fixing fuel pressure bleed-down (bad check valve in pump or leaky injectors).
Addressing weak battery causing slow crank speed.
Note for custom-tuned or swapped cars:
If you’re running a tune (for gears, intake, or power adders), do not just “reflash back to stock” to pass inspection — it can throw fueling and timing way off and cause more issues. Work with a tuner who can build a clean emissions-compliant tune for your correct ECU and harness setup.
Symptoms:
Long crank (5–8 seconds) before the engine fires.
Intermittent — more common after a hot soak or sitting a short time.
No CEL or only EVAP-related codes (e.g., P0456 small leak, purge valve stuck open).
Some owners report this showing up after cooling system or intake work (thermostat, MAF cleaning, etc.).
Vehicle always starts, just delayed.
Ignore the “Dirty Key Fob” Myth
A dirty key fob does not cause long cranking.
If the car unlocks/starts normally, it’s not a PATS issue.
Don’t waste time or money here.
Battery & Starter Health
With engine off: Battery should read 12.4–12.6 V.
During crank: Voltage should not drop below 10 V.
With engine running: Charging system should hold 13.5–14.5 V.
A weak battery or dragging starter can cause long cranks, especially after the car is hot.
Fuel Pump Prime
Turn the key to ON (don’t start).
Listen at the rear of the car for a 1–2 second hum (fuel pump priming).
No sound? Possible fuel pump relay, fuse, or pump issue.
Fuel Pressure Test
Rail pressure should build to about 55–60 PSI at key-on prime.
After shutoff, pressure should hold for several minutes.
If it bleeds down quickly, possible bad pump check valve, leaky injector, or faulty fuel pressure regulator.
Shop can confirm with a fuel pressure gauge if you don’t have one.
Purge Valve (EVAP Canister Purge Solenoid)
A stuck-open purge valve allows raw vapors into the intake during startup, which causes a rich mix and long crank.
Quick test: unplug the purge valve’s electrical connector and try starting for a few days. If issue disappears, replace purge valve. (~$40–60 part, easy DIY swap).
Inspect purge lines for cracks, loose fittings, or disconnections (common after cooling system or MAF work).
Crankshaft Position Sensor
A weak or failing crank sensor can delay spark signal during crank.
Usually throws a CEL, but intermittent failure is possible.
Shop can scope/test the CKP signal during crank if basics check out.
Other Possible Causes
Leaky injector – check for fuel smell, rich exhaust, or fuel in oil.
PCM tune mismatch – if engine or ECU swap was done (for example 2001 vs 2002 ECU differences), confirm PCM, harness, and sensors match. The 2016 GT has MAF-integrated IAT; if wiring is wrong, sensor data may not reach PCM.
Most Common Fixes Reported
Replacing the purge valve solenoid.
Fixing fuel pressure bleed-down (bad check valve in pump or leaky injectors).
Addressing weak battery causing slow crank speed.
Note for custom-tuned or swapped cars:
If you’re running a tune (for gears, intake, or power adders), do not just “reflash back to stock” to pass inspection — it can throw fueling and timing way off and cause more issues. Work with a tuner who can build a clean emissions-compliant tune for your correct ECU and harness setup.
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