2008 Chevy Impala 3.5 Hard Starting When Cold

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#1
Make
Chevrolet
Model
Impala
Year
2008
Miles
258000
Engine
3.5
All,
My very well maintained 258,000 mile 3.5 flex fuel 2008 Impala began to start hard as the temperatures dropped. After turning and releasing the key to initiate the starter to spin the motor, engine turns over and it struggles like it wants to run. The starter stays engaged as the engine struggles to pick up rpm’s. It it doesn’t start in the predetermined time frame, the starter shuts off. If the gas pedal is depressed halfway while the engine is turning over, it will start. When it is warm, it starts perfectly fine.
Solid 59psi at the fuel system test port. New plugs and wires. Cleaned and subsequently replaced the throttle plate and throttle position sensor assembly with a new Hitachi with no change.
Had the car in at the dealership for an alignment and asked the mechanic for his opinion. He replied with maybe the starter is sticking. I replaced it with a remanufactured one with no changes.
I’m stuck. Any ideas?
Nick in WI
 

billr

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#2
First guess is the IAC (Idle Air Control) system, next would be ECT (Engine Coolant Temperature) system. Note that I said "system" in both cases, it may be a single component or wiring/connectors or even physical blockage of fluid passages. And, "component" includes the PCM...

But why guess? Live-data will help avoid throwing more parts at this.
 

grcauto

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#3
You need a new mechanic. Starter is working. With engine cold I would use the scan tool to look at the IAT and ECT temperature sensors. They should read real close to each other.
 
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#4
I will plug into it and see what the scanner says, hopefully before I head to work this morning. I’ll be back. Thanks!
 
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#5
It started poorly, needing me to step on the throttle to get it running.
ECT was 73F and IAT was 50F. Within just a short time of running, the ECT jumped up to 82 and then 85. It would fluctuate up and down whereas the IAT would be real stable.
I ran it for just a minute or so before heading to work.
 
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#6
With 258K miles on it would do a compression check, engine could be worn out and pistons shrink.Get blowby, blows out the spark.

Chevy is doing a better job, for that famous 1957 283, needed a complete overhaul at 40K miles.
 

billr

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#7
After you get the ECT fixed (probably corroded/loose contacts at the harness connector), check the MAP. Is it reading reasonable? How far does it drop during a "crank but no fire" episode?
 

grcauto

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#8
It started poorly, needing me to step on the throttle to get it running.
ECT was 73F and IAT was 50F. Within just a short time of running, the ECT jumped up to 82 and then 85. It would fluctuate up and down whereas the IAT would be real stable.
I ran it for just a minute or so before heading to work.
If these are the readings when cold the ECT is off. If it reads higher than it should it'll cause the PCM to inject to little fuel. Put the scan tool on it and see what they read BEFORE you start it.
 

nickb2

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#9
Had the car in at the dealership for an alignment and asked the mechanic for his opinion. He replied with maybe the starter is sticking. I replaced it with a remanufactured one with no changes.

Useless. Throwing parts. I get so pissed offed when I read threads such as these.
You need a new mechanic.
I sadly, 100% agree with above.
 

nickb2

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#10
It would fluctuate up and down whereas the IAT would be real stable.

the ECT jumped up to 82 and then 85.


This is probably due to thermostat opening. I wouldn't worry in that, as long as the trims are good, we can nail this. I suspect low fuel pressure at start up, loss of fuel prime. No starter issue here.
 

nickb2

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#11
If I am reading this thread right, you are using a low latency scanner/code/live data thing.

Have you tried elm 327 simple devices, they communicate live data faster for a fraction of cost, but you need to learn how to navigate. I can help with that.
 

nickb2

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#12
@NickD, the 3.5l in this thing is the only gm engine that I have REALLY seen be corn feed gas and actually does 300 or so k km's.

Gm has some good designs, but somehow, never make it to mainstream market, to busy whoring to kia!!
 

nickb2

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#13
I currently reside in one of the most richest corn places in canada expect the prairies. These engines run fine up here. But they are fragile to cold because of the flex fuel algorythm. Certain ford engines also. You can see the flex fuel go by in live data, especially in mode six in hex form. That is where you get the values. But up here, we don't give a shyte cuz we have no such law.

So when summer hits, not a problem. Guys up here run a can of gdi cleaner or similar, works great also for flex, uses same sort of detergents to get job done, procedure is very similar, with normal injection, go through rail, with gdi, go through two system at once. Same product basically, but different system of administration.

Also, of note, these gm liked to spike amps in the fuel pump circuit, burning the relay AND pdc contacts. So that is essential to look at. The van that gm made had same drive train, so MANY tow trucks!!!!

FP and or burnt circuit/realy/pdc if it got that far!!
 

nickb2

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#14
Also focus on crank signal, if that is lost, you can also see that on a quick enough device. SO, if you wamt, ask me questions, I'll hook u up with a live dat recipe on the cheap if your willing to learn.