Ok fuel pressure on the new pump is the same as the old one so I guess I changed it for no reason... BUT I did figure out what the miss was. I actually got a bad NGK spark plugs from the factory that had the porselain cracked on the inside. That took me awhile to find. BUT the cranking when cold is still there.
So I decided to do a compression check. My results were not so good. All the cylinders were within the 15% but the numbers were very low. ranging from 100-125 throughout the 8cly. After doing this I did realize that I didnt do the compression check quite right. 1 I did it on a cold motor instead of a hot motor which is suppose to give you more because the pistons and rings etc expand and give you better numbers. 2 I was not opening the throttle blade when cranking for the test. Im not sure how much those 2 things effect the numbers. The truck has no blow by and doesnt smoke.

So another question, is it hard to crank when cold because of the compression? How much do you need to crank a 5.3? Thoughts...still not sure why im only 48-50psi on fuel pressure.

 

If your engine is a VIN #Z (Flex Fuel) then 48-54PSI is normal.

Engine Compression Test (Mechanical Throttle)

1. Charge the battery if the battery is not fully charged.
2. Disable the ignition system.
3. Disable the fuel injection system.
4. Remove all the spark plugs.
5. Block the throttle plate wide open.
6. Start with the compression gauge at zero and crank the engine through four compression strokes, four puffs.
7. Make the compression check for each cylinder. Record the reading.
8. If a cylinder has low compression, inject approximately 15 ml. (1 tablespoon) of engine oil into the combustion chamber through the spark plug hole. Recheck the compression and record the reading.
9. The minimum compression in any one cylinder should not be less than 70 percent of the highest cylinder. No cylinder should read less than 690 kPa (100 psi) . For example, if the highest pressure in any one cylinder is 1035 kPa (150 psi) , the lowest allowable pressure for any other cylinder would be 725 kPa (105 psi) . (1035 x 70% = 725) (150 x 70% = 105).

•  
  • Normal-Compression builds up quickly and evenly to the specified compression for each cylinder.
  • Piston Rings Leaking-Compression is low on the first stroke. Compression then builds up with the following strokes but does not reach normal. Compression improves considerably when you add oil.
  • Valves Leaking-Compression is low on the first stroke. Compression usually does not build up on the following strokes. Compression does not improve much when you add oil.
  • If two adjacent cylinders have lower than normal compression and injecting oil into the cylinders does not increase the compression, the cause may be a head gasket leaking between the cylinders.

 

Compression is good. Took the valve cover off to see if I had a broken valve spring or bent pushrod. They all looked good. Tahoe runs great now except for on startup when cold and on high RPMs on the 2nd-3rd shift. Im gonna try another MAF sensor before I give up

 

I'd be curious if the injector baskets weren't full of crud. It kinda does sound like a fueling issue.

Also, what spark plugs are you currently using?

 

Yeah I'm pretty sure it is too, we hooked back up to HPtuners to see what was going on and for some reason the fuel trims keep spiking high. It had ngk tr5ixs when I got it and I put tr6ixs in it. Thought maybe it was the plugs so I swapped back but no difference. I ran seafoam through the gas when I first got it to try and clean the injectors so idk

 

When it finally starts does it surge real hard and move the whole vehicle? I'm having the same problems with mine. I keep getting random missfire codes. When it's cold you can crank on it for 45 seconds at a time and it won't start. But when it does I jumps like it's in gear.

 

Yes once it does crank up it runs ruff as crap like it has a cam in it. Loaded up bad with fuel and smokes for about 30 secs and then smooths out.

 

Well I've replaced crank and cam sensors. Fuel pump. Clean maf sensor. And it still does it. It acts like it floods it's self.

 

I'm gonna try coolant temp sensor tomorrow

 

Where is the IAT sensor at on theses?