Suddenly stalling on warm/hot starts

[pmor4243]

I'm hoping someone could give me some ideas on what to check for here. My 19 GT A10 has suddenly developed an issue where it is stalling on startup when warm.

The car has had a Procharger tuned by Wengerd for the last 8k miles and all has been good until about 2 days ago. I noticed it started to have some very weak starts when the car was already warmed up or hot, but it would recover. Now, just a day or two later, it will stall about 95% of the time when starting up after it is warm. It then seems to fire up and run 100% normal after a second try. Its as if the car isn't getting any fuel on the first start but does on the second.

I'm not really sure what to look for here and would appreciate any thoughts.

I did add a water/methanol nozzle to the car about a month back purely to help with knock prevention. You can see in the picture below, the nozzle is over 12" upstream from the MAF sensor which is in the intercooler. Is it possible that the methanol injection has found a way to mess of the MAF sensor? I would assume this would also result in fuel trims being off across the board or a code coming up which has not happened.

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[ypena02]

Do you have an aftermarket fuel system?

 

[pmor4243]

Do you have an aftermarket fuel system?

Stock fuel system, with upgraded injectors. All of which has been working well so it's weird that it would all of the sudden start having start issues.

Wengerd did send over a revised tune to try but I have not had a chance to really test it out yet.

 

[pmor4243]

So I got an updated tune from Wengerd that did resolve the issue for about 3 days worth of driving then it started doing the same thing.

Would I be crazy to suspect that my fuel pump may be on its way out? Im not sure if this starting issue could be a symptom of that. Has anyone run into that or have any ideas on things I can check to narrow down what the issue is here?

 

[ice445]

It's very possible the low pressure pump in the tank is the culprit, if it struggles to stay running after a hot restart. Do you have any way to monitor the fuel pressure? Most decent scan tools can pull it up for display, you'll want to hit the button but without your foot on the clutch/brake so that it's in full power but not starting and see what the fuel pressure reads cold, and then again after a good drive.

 

[EmCel]

Not sure if it would be the fuel pump but possible. Everyone has diff experiences with it. I didn’t have any problems before my fuel pump went out. It happened suddenly. The morning that it did, started the car hesitated for a couple of seconds, it shut off twice, started again and drove it about 8 miles, it kept jerking and finally DEAD once I got to the mechanic lucky me.

My mechanic called me and said it’s the fuel pump and replaced it. Done.

 

[pmor4243]

Thanks guys. Ya once it starts up all seems normal, which has me less convinced it’s the pump.

I actively drive with and SCT hooked up so I can monitor knock, fuel trims, pump pressure etc and I’ve also hooked up my hp tuners device to watch the same things.

So far, everything seems normal, fuel pressure looks good and is consistent regardless of hot or cold.

I’m going to pop the bumper off in the next few days and recheck all of the intercooler hoses. If that doesn’t check out, I may throw my stock injectors back in and see how those behave.

 

[pmor4243]

Well, I *may* have found the culprit, it turns out that last time I checked/adjust my intercooler pipes and clamps (about 2 weeks ago) the MAF harness extension got between one of the hose clamps and pipes and was effectively crushed when tightening everything back down.

The wires all looked ok other than being a little flatter than normal, but I have to imagine that this could be a big part of the problem.

From what I understand, the maf sensor reading are pretty precise so flattening all of the wires in the clamp like that could have an impact on how the maf reads right? I still dont know how this would create starting issues on the first crank but then otherwise operate just fine...

Either way, I have ordered a new harness and am hoping that fixes the issue, but Im not overly optimistic.

 

[Bluelightning]

Are you running 93 or e85?

 

[pmor4243]

91 actually. Highest we have in Utah.

 

[pmor4243]

Well, to test my theory, I cut the maf extension harness and soldered the wires back together to eliminate any possible damaged sections from causing reading issues (while I wait for the new harness)


Unfortunately no change. Still wont fire on the first try when warm.

 

[Cobra Jet]

If the issue is only occurring after the car has been run to normal operating temps, then check the threads below that may offer some help.

I will ask though - with your posted setup and this happening, have you pulled plugs to read them yet?


Check these threads for starter failing due heat soak or it overheating:
https://www.mustang6g.com/forums/threads/starter-woes-2-0.166411/

https://www.mustang6g.com/forums/threads/part-number-for-just-the-starter-solenoid.166114/

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How old is your battery? The battery could have issues with heat soak and cause sporadic starting issues as well. Even if testing the battery without a load, the test result may look ok, but the battery could still have 1 or more bad cells.

 

[pmor4243]

If the issue is only occurring after the car has been run to normal operating temps, then check the threads below that may offer some help.

I will ask though - with your posted setup and this happening, have you pulled plugs to read them yet?


Check these threads for starter failing due heat soak or it overheating:
https://www.mustang6g.com/forums/threads/starter-woes-2-0.166411/

https://www.mustang6g.com/forums/threads/part-number-for-just-the-starter-solenoid.166114/

---

How old is your battery? The battery could have issues with heat soak and cause sporadic starting issues as well. Even if testing the battery without a load, the test result may look ok, but the battery could still have 1 or more bad cells.

Thanks for the links, I'll definitely read through those. At first glance it looks like they had the starter actually fail. In my case, the car fires up very fast, no extended cranking or failure to crank, it just also dies immediately after firing up. Then start again, and all good. I have tried hooking up a jumper to the car when starting just to rule out the battery and unfortunately still run into the issue.

I did pull the plugs about 1,000 miles ago and they looked good, but I have not pulled them since this started happening, that is next on the list. They only have about 3k miles on them so far but Ill have to see what they look like. I have been using boostane since the procharger install and just got a methanol kit set up but am still dialing it in as its not giving me the knock prevention I was hoping for.

I have ordered a new MAF sensor to try as well. If all of that doesn't do the trick the only other things I can think of would be injectors or possibly a fuel rail pressure sensor.

The only thing that I can see in the logs that looks off (and I just noticed this) is the the fuel rail pressure looks like it is way high. With the car warm and engine off, it was reading at 2,591 psi. When the car starts, it seems to stay north of 2kpsi even though the tune is only commanding around 400psi. I was always looking for low fuel pressure but is it normal for the fuel pressure to stay that high?

 

[pmor4243]

And to add another very weird thing to this. I went to pull the injectors to see if anything was going on there and when I disconnected the fuel pump relay under the seat like I have done in the past, the car started and idled like normal, but it never died, it just kept idling for several minutes without a single hiccup.

How can the fuel pump still be feeding fuel with the plug being disconnected?

 

[pmor4243]

Well, I got a new MAF sensor in, new fuel pump control module, checked the plugs, checked the injectors for leaks, pressure tested the system up to 10 psi with no leaks, have had 2 tune revisions from Wengerd with no change am now completely out of ideas.

Before I take this to a shop and pay more money for troubleshooting, does anyone have any other thoughts as to what might contribute to the car firing up immediately when hot, but then immediately stalling? This is very repeatable and it will always fire up and run great on the second try.

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