Weird Starting Issue After Truck Sits More Than A Few Hours

[TylerHagerdorn]

Key on engine off pressure was 54psi. It's not starving for fuel. I replaced the vent valve back at the tank and the purge valve under the hood. Now if I let the truck idle it'll throw p0172 and p0175, but only at idle. I don't have some fancy scan tool that will tell me flex sensor readings or any of that. On the cold starts after sitting for awhile and having to hold the pedal all th way down it dumps white smoke that smells like straight fuel and all you can smell is fuel. No it's not coolant smoke, it's pure fuel. When it's running it runs perfectly smooth and drives great. It's just the hard starts and the codes im trying to fix.

 

[TylerHagerdorn]

Alright well the coolant temp sensor connector was missing the locking tab on it and I pulled the connector out and it was busted inside so I replaced the connector and the sensor. On my scan tool it flashed the default negative cold setting for a second and then went back to normal temp. I had been running some fuel system cleaner in it and the truck was starting perfect no issues until the other day. It also wasn't throwing a single code until the other day where it popped the same two codes up again. I don't know if the fuel system cleaner was helping it or if the coolant temp sensor was bad since the connector was busted but I don't know why it's acting up again. Maybe it's the cold weather? I just don't know. Fuel pressure is perfect and the plugs look great they aren't soaked in fuel or anything. I also replaced the canister vent valve by the tank as well. The FPR isn't leaking. Everything is coming back fine so I don't get why i still need to floor the pedal to get it to start.

 

[TylerHagerdorn]

If you have a scanner, turn on your key while the engine is cold and before you have tried to start it, and check what the coolant sensor and air intake sensor are reporting for temperatures. I have seen before a coolant temp sensor that was reporting max cold and causing a huge amount of fuel to be dumped during cold start cranking.
Like yours, the only solution was holding it at wot clear flood to get it going.

What should the IAT read when the truck is cold? The CTS connector was missing the locking tab and when I pulled it out the connector was busted inside. It read max cold for a second on my scanner then went back to normal temps. I replaced both the connector and the sensor and had ran fuel system cleaner in it and drove it about 75 miles the next day and the CEL went away and no codes came up. It was perfect for a week or so and the other day it went right back to having this starting issue and I was getting low on fuel. So I don't know if it was because I was low on fuel or not. I just put some more fuel system cleaner in it and put gas in it yesterday and I haven't tried to start it today.

 

[TylerHagerdorn]

Alright so here's the readings-
Cold readings Not Running:
MAP-29(inHg)
ECT-32 degrees
IAT-32 degrees

With Truck Running:
MAP-10(inHg)
ECT-60 degrees
IAT-32 degrees
MAF-1.37(lb/min)

 

[hagar]

Alright so here's the readings-
Cold readings Not Running:
MAP-29(inHg)
ECT-32 degrees
IAT-32 degrees

With Truck Running:
MAP-10(inHg)
ECT-60 degrees
IAT-32 degrees
MAF-1.37(lb/min)

The ait is supposed to be what the temp is outside, so everything makes proper sense in your data provided for both key on and running. (Assuming it's 32 degrees out)

 

[TylerHagerdorn]

I mean what the hell else could it be? The flex sensor is working as it should and so is the purge valve. I've replaced every ground I can see and added some. Fuel pressure is solid both cold and warm. Regulator is not leaking gas out. Not getting any other codes. The other day I unplugged the maf sensor while it was running and it didn't die or change pitch or anything. I started the truck with it unplugged and it fired right up but I've had no MAF codes. Although everything im reading is saying it has to do with air because I have to hold my foot down for it to start. I always was told if the car dies when the MAF is unplugged it's good. And it's bad if it doesn't die. This issue is driving me insane.

 

[hagar]

I mean what the hell else could it be? The flex sensor is working as it should and so is the purge valve. I've replaced every ground I can see and added some. Fuel pressure is solid both cold and warm. Regulator is not leaking gas out. Not getting any other codes. The other day I unplugged the maf sensor while it was running and it didn't die or change pitch or anything. I started the truck with it unplugged and it fired right up but I've had no MAF codes. Although everything im reading is saying it has to do with air because I have to hold my foot down for it to start. I always was told if the car dies when the MAF is unplugged it's good. And it's bad if it doesn't die. This issue is driving me insane.

Not sure if it has been asked, but since you have a scanner, have you checked the fuel trims? I would be curious to see if the truck is pulling massive fuel once it is running.

 

[TylerHagerdorn]

Not sure if it has been asked, but since you have a scanner, have you checked the fuel trims? I would be curious to see if the truck is pulling massive fuel once it is running.

Fuel trims are absolutely perfect. They were a little messy until I replaced the Coolant temp sensor but they've been where they are supposed to be since. I've pulled all the plugs out they look great and are dry, no fuel in the oil or anything. Pressure is solid. I just don't get it. I've never had something like this happen before. After we replaced the CTS and drove the truck all day 75 plus miles the engine light went off by itself and I scanned it and no codes and it started so good until the other day when it was acting up again.

 

[hagar]

Fuel trims are absolutely perfect. They were a little messy until I replaced the Coolant temp sensor but they've been where they are supposed to be since. I've pulled all the plugs out they look great and are dry, no fuel in the oil or anything. Pressure is solid. I just don't get it. I've never had something like this happen before. After we replaced the CTS and drove the truck all day 75 plus miles the engine light went off by itself and I scanned it and no codes and it started so good until the other day when it was acting up again.

Pretty sure at this point, if a gm tech were working on it, the diagnostic waterfall they were following would say to replace ecm. You are getting too much fuel from your key on injector pulse and or cranking injection pulses, then you are shutting the injectors off by holding the throttle open while cranking, then the truck is firing and clearing all the excess fuel from the pre start/cranking fuel.
The only other way I can see causing this problem is if you have injectors leaking down and filling the cylinder with fuel while sitting.

Everything made perfect sense it was the cts, and you found the failed one, then it worked for a while.. maybe the circuit in the ecm that works the cts is faulty? Perhaps the damaged cts sensor caused a short in that circuit, the ecms are pretty easy to wreck with little shorts.

 

[TylerHagerdorn]

Pretty sure at this point, if a gm tech were working on it, the diagnostic waterfall they were following would say to replace ecm. You are getting too much fuel from your key on injector pulse and or cranking injection pulses, then you are shutting the injectors off by holding the throttle open while cranking, then the truck is firing and clearing all the excess fuel from the pre start/cranking fuel.
The only other way I can see causing this problem is if you have injectors leaking down and filling the cylinder with fuel while sitting.

Everything made perfect sense it was the cts, and you found the failed one, then it worked for a while.. maybe the circuit in the ecm that works the cts is faulty? Perhaps the damaged cts sensor caused a short in that circuit, the ecms are pretty easy to wreck with little shorts.

Cylinders have no fuel in them. Injectors are not leaking. Plugs are clean and dry. Even tested the injectors with noid lights. After the truck has warmed up it'll fire back up with no issues whatsoever. That is until it sits again for a few hours or more. Also, when the truck is running and you disconnect the MAF, it doesn't die or change or anything. I've owned tons of cars and fixed tons of cars and every car I've had if I've disconnected the maf while running it will die immediately. No I don't have any codes for the maf though. Today it also threw the P0172 and P0175 codes on top of the P0178 and P0443. Both purge valves were replaced with OEM. Didn't change a thing. I was considering it being an ecm because it has some other weird electrical things that have made me think it could be the ecm. I know it is a common thing on GM trucks and cars of the 00's.