Cold start hesitation

[mikez71]

Could it be weak ignition? Original plugs?

 

[Sparksalot]

I had a pinhole fuel leak between the tank and engine that caused similar behavior in thethirdtwin. It would lose pressure in the line after sitting several hours or overnight. Turned out the fuel line had abraided against the frame since new. Only took 8 years to manifest.

 

[dwinters14]

Could it be weak ignition? Original plugs?

Just changed plugs and wires, original coils though.

I had a pinhole fuel leak between the tank and engine that caused similar behavior in thethirdtwin. It would lose pressure in the line after sitting several hours or overnight. Turned out the fuel line had abraided against the frame since new. Only took 8 years to manifest.

I wonder if something like this could be the case. Next time I'm under her I'll track the lines back and look for any spray or leakage. It seems like little things like this tend to be common problems for me, seeing as a new MAF cleared a P0420/430...

 

[dwinters14]

oh well, with a try. in theory the leak also sucks in air and can make your o2 sensors read lean. so your long term trims adjust to richer than it actually is. I don't know that it would bother start up. but I did the external clamp on mine, it has worked well so far.

How did you get it behind the head? It looks like there's zero room. I'm gonna look at the stud on #7 and see if it's broken off in the head or the stud is sticking out so I can wiggle it out with vice grips with the manifold off. Definitely adding it to my to-do list, I just don't want to have to buy/learn to weld to get the studs out Not there yet lol

 

[j91z28d1]

it's not easy to get to, and a top side creeper helps a lot. but there is room. a flex head ratch wrench helped a lot if I remember right.

mine was the back bolt on the drivers side.

 

[donjetman]

How did you get it behind the head? It looks like there's zero room. I'm gonna look at the stud on #7 and see if it's broken off in the head or the stud is sticking out so I can wiggle it out with vice grips with the manifold off. Definitely adding it to my to-do list, I just don't want to have to buy/learn to weld to get the studs out Not there yet lol

Its doable. I put them on my engine in 2018. Its still going strong. Here's a post w/pics I did:

https://www.tahoeyukonforum.com/threads/exhaust-manifold-bolts-no-bueno.108605/page-3#post-1296439

 

[dwinters14]

Its doable. I put them on my engine in 2018. Its still going strong. Here's a post w/pics I did:

https://www.tahoeyukonforum.com/threads/exhaust-manifold-bolts-no-bueno.108605/page-3#post-1296439

Cool, thanks for this.

 

[dwinters14]

I tested the coolant temp sensor tonight and want to confirm everything before I potentially continue down that rabbit hole. I checked the sensor cold with the key in the on position and it read 30*C. Now keep in mind the temperature outside is 20*C, I'm not sure if that could potentially cause my cold start issue or not, but It's something to note. I also checked my resistance and it came in at about 2100 ohm's which is right in spec for 30*C.

Also I have to say for "check valves" being such common points of failure there's barely any concrete information on testing them which is frustrating. I'm going to cycle the key 3/4 times tomorrow before starting the truck to see if that changes anything. I'm gonna be p/o'd if it's bad considering I just bought this pump and have been chasing my tail for 6 months.

Morning Update:

Left the fuel pressure gauge on and primed the pump. Jumped to about 50psi, primed it 3 more times jumped up to about 58psi and I tried to fire her. Same long crank and struggle to turn over. Now I think it's safe to assume the fuel pump assembly is doing what it's supposed to and the problem is somewhere with the injectors.

I used a stethoscope on them when the truck was hot yesterday and they were all firing fine. I wonder if one is leaking or is clogged.

 

[ivin74]

I tested the coolant temp sensor tonight and want to confirm everything before I potentially continue down that rabbit hole. I checked the sensor cold with the key in the on position and it read 30*C. Now keep in mind the temperature outside is 20*C, I'm not sure if that could potentially cause my cold start issue or not, but It's something to note. I also checked my resistance and it came in at about 2100 ohm's which is right in spec for 30*C.

Also I have to say for "check valves" being such common points of failure there's barely any concrete information on testing them which is frustrating. I'm going to cycle the key 3/4 times tomorrow before starting the truck to see if that changes anything. I'm gonna be p/o'd if it's bad considering I just bought this pump and have been chasing my tail for 6 months.

Morning Update:

Left the fuel pressure gauge on and primed the pump. Jumped to about 50psi, primed it 3 more times jumped up to about 58psi and I tried to fire her. Same long crank and struggle to turn over. Now I think it's safe to assume the fuel pump assembly is doing what it's supposed to and the problem is somewhere with the injectors.

I used a stethoscope on them when the truck was hot yesterday and they were all firing fine. I wonder if one is leaking or is clogged.

Any updates? Just curious if you fixed the issue?

Have you verified the coils are good?
Look into the crank position sensor.