Rough Startup when warm.

[macamustang]

So when the car is warm SOMETIMES it has trouble starting up and makes a loud noise as it starts. Ive been chasing this for a long time and the dealer never seem to fix it. They have cleaned the whole fuel system, cleaned the Mass Airflow Sensor and now the Fuel Rail Pressure Sensor. All 3 times they have claimed they fixed the problem. 2020 GT 34k miles

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[slime_bullet]

wouldnt happen to have a dw400 fuel pump?

 

[macamustang]

Hmm Wouldn’t know, the car is completely Stock. What ever it had from the factory its what is has now.

 

[Shepard]

Did you ever figure this out? I have a warm start issue that can be similar. Most of the time it will crank a bit longer than usual or stumble/fail. If it fails and I try again, it starts. I've never been stranded by the car with this issue. I've had it happen regularly over the last year and never thought to fix it but my wife is getting annoyed by it. I just got my battery tested and voltage is normal, cold cranking amps look fine, alternator is fine.

I had my head unit die on me for a couple of days straight but it black-screened with the display still on. Makes me think there was a bad ground? On startup I see about 12v then it soars to 18v for a second before going back to 12. Could be related or unrelated to the warm start issue. I'm checking my evap purge valve and kick panel ground after work since I pulled a fuse down there and might have bumped the footwell ground.

Unsure if the voltage surge is conflated with these two different symptoms or if its just trying and failing to start on an overly rich mix with the evap purge stuck open.

(2018 GT)

 

[ORRadtech]

12V with a surge to 18V and back to 12V doesn’t sound right.
Start up (starter turning) should pull the voltage down to under 12V. I'd expect between 10V & 11V. I can't think of a good reason for a surge past about 14.5V. Good meaning not a fault of some sort. Normal operating voltage with the car running should be within a couple of tenths of 14.2V.
I'd recommend that you hook up a digital voltage meter to the battery and verify that the dash guage is giving you accurate information.
How old is your battery? A failing battery can give all sorts of seemingly unrelated symptoms.

 

[Shepard]

It's four months old, but it's lead acid not AGM. Not that it would or wouldn't contribute to something erratic like that.

I checked my purge valve for vacuum on startup and it seems to work at least partially, which is what I expected with no check engine codes for the evap system. There's still a few seconds of delay on startup between the valve moving from closed to open, which is normal behavior. There could still be a slight leak there which would make sense of there being no code and warm starts acting like they're too rich, especially since the second crank always succeeds if the first fails.

I wasn't thinking it was the battery but I can't rule it out at this point. The thing that puzzles me is the wild swing in volts that seems to relate to the startup issue. The head unit dying and coming back to life seems like it could be related, I'm not sure exactly how.

I'll probably go forward with just replacing the battery and seeing what happens.

 

[ORRadtech]

Four months shouldn't be bad unless it has a manufacturing fault.
If you have a battery charger try fully charging it with that. Then go by one of the chain auto parts stores and have them check the battery and charging system. The battery needs a good, full charge beforehand though.
While you're under the hood check that your battery connections are clean and tight. Also the starter connection and main ground.
I don't know if it has anything to do with your warm start issue but at least you can eliminate something.

 

[macamustang]

Hello!, no Im still having the same problem. I read that the injectors can cause this problem. So I will be replacing my injectors soon and see if it solves the issue.

 

[Shepard]

Just caught this but the voltage was read through a multimeter connected to the battery terminals when it was warm started.

 

[R6maddor]

Did you buy the vehicle new or pre-owned? If it was preowned there may be a possibility that it has an aftermarket tune. What octane gas do you run? I had a similar high pitch clunk noise happen sometimes, with vid attached, when I Sc’d my car and I originally thought it was the starter starting to fail due to the LTH. Ended up replacing the starter and the noise would still occur. What ended up fixing it was adding vp racing octanium to my crappy 91 octane fuel every fill up lol.

 

[macamustang]

Hello! I bought the car 0 miles. My brother did fuel with 87 one time. I dont know if that could've done that much damage

 

[R6maddor]

Afaik, the factory tune should adjust based on whatever octane 87 - 93 running, so hopefully there isnt any problem. Could be a bad tank of gas? You could try buying some octane booster, letting it mix up and see if it goes away.

 

[macamustang]

Yeah, ill try that VP octane booster.

 

[Shepard]

Hello!, no Im still having the same problem. I read that the injectors can cause this problem. So I will be replacing my injectors soon and see if it solves the issue.

I'll be following the post to see if this is it. I'm getting more suspicious that it's an injector/fueling issue since the EVAP at least appears to be ok. There may be a leak I don't know about. FORScan is able to show injector data per cylinder live so I will be doing that next. Your videos show what I'm experiencing almost exactly on my stock mustang.


So far

> Tried full tanks of different octanes (everything from 87 to 94, top tier ONLY, zero difference)
> Tried cold and warm starting in hot (80+) and cold (32-) temps
> Checked to see if EVAP sticks open on startup
> Full fuel induction system clean, less than 10k miles ago (including manifold)
> Tested battery, found that it is on the lower end of charge, health is fine

Still needed

> Trickle charge the battery to full (it's below 50%)
> Parasitic draw test to find possible electrical issue
> Log/test injector offsets/cutoff/cylinder balance in FORScan



- Dash voltage does show regular ~14v during operation

 

[macamustang]

Yes, once I change the injectors I will update here. To me a leaking injector makes sense but ill have to wait and see

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