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09 GT seems like not all cylinders working on cold start

716 views 8 replies 4 participants last post by  RSEOD 
#1 ·
Just like the subject says, when the car has sat overnight, the first start of the day isn't good.

There's no long crank, she starts right away, but for a few seconds she's quiet like a Prius! Like the engine started on just a couple cylinders. The engine is barely running, then it ramps up to a typical cold start idle, 1200rpm or so. During this process the engine is shaking and I usually hear it backfire a couple times, although not sure from where. Within 30 seconds everything is back to normal and she's running fine.

I was thinking maybe:

1- valve seals
2- leaking injectors
3- ???

No codes, no other symptoms. No blue, black, or white smoke.

Sometimes I smell a raw fuel odor under the hood when I first cold start the car, it's faint but it's there. No obvious leaks. Injector orings were replaced last year. Fuel pressure regulator isn't leaking, and according to my SCT X3, fuel pressure is pretty consistent at 40psi, whether idling or WOT.

Any ideas?
 
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#2 ·
I was thinking maybe:

2- leaking injectors

Sometimes I smell a raw fuel odor under the hood when I first cold start the car, it's faint but it's there.
This. You could have an injector that's sticking slightly open and allowing fuel to leak into the cylinder as it sits overnight.
 
#3 ·
I wonder if an external fuel pressure gauge would tell me anything, if it's just one injector, and it's a slow leak... I'll have to find out how long it's supposed to take for the fuel pressure to bleed down after the car is off.
 
#4 ·
When was the last spark plug change? That would be where I would go first.

Do you ever let the the key sit in the on position before starting or do you just turn it all the way when you get in it. I always turn the key to on, fasten my seat belt and then start the car. This insures fuel pressure on start up is where it's supposed to be when cranking it.

We have had some unusually cold mornings here the last few days, could just be it's not used to it and may need to learn how to idle in the cold. I have been driving my Mustang all week and it is a cold blooded beast. There has been the occasional morning this week where she seemed to struggle a little bit to settle into high idle. I don't think much about it.
 
#5 ·
Plugs are recent, about 4 months ago I changed them. It could be weather. But I want to take steps to check other areas of concern too. Just to be sure;)
 
#6 ·
Have you put a scanner on it and attempted to read codes? Just because the engine light is off doesn't mean something isn't floating in the computer.
 
#7 ·
Yep, no codes. I'm thinking its an injector or my valve seals are going bad. I just threw my back out yesterday, so I'm just laying around now... Haven't had a chance to trouble shoot it yet.
 
#8 ·
Boss, I've ruled out cold weather. It's 60 outside right now and on a cold start (engine cooled off from driving into work 8 hours ago) it did the same thing, started easily but ran like absolute garbage for about 5-7 seconds. Barely running, sounded like it was choking, engine shaking... Then it revs up to 1500rpm for about a minute, then drops slowly back to normal, and everything is fine again. Shut it off and start it up right away and it's fine.

So ruling out the weather, I'm looking at what?

Leaking injectors
Bad valve seals (that seal back up again as it warms up?)
Bad piston rings?

With no other noticeable symptoms this is a PITA!

Would a leak down/compression test tell me anything?

I have new injectors (for the blower I haven't installed yet, so if it's injectors that can easily be solved. However, I don't want to go through the hassle of installing my blower kit if I'm going to have to tear it all down to fix the heads or the engine.

Boss, id bring her by so you could look at her, but I'm working in New Mexico right now. Might be a couple weeks till I get back into town.
 
#9 ·
Bullitt95, I'd love to rule out leaking injectors, but don't really know how without pulling them out and seeing if any leak with the fuel rail attached... Im not sure if they'll stay in the fuel rail under pressure without anything other than their orings holding them in... Never tried that before.
 
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