I have been having starting issues on my 98 Blazer LT 4x4. So me & a friend that is a mechanic did a pressure test & leak down test & decided maybe we had a defective pump since it was installed two weeks ago & the starting issue was worse. The leak down test failed badly.
So we installed a new Delphi pump & checked all the lines etc. Installed another new fuel filter. The pressure & leak down passed. But the starting after sitting 10-15 minutes would still require 15-20 sec of cranking to start.
So Capt Hook was sending me a detailed check list to determine what was going on.
I had installed a locking gas cap awhile back & I wondered if it was OK. But if it was defective shouldn't a CEL code appear???? NO CODES at all. So I decided to remove the cap & just set it on the filler neck loose.
Well here is where I'm really scratching my bald head. I drove for 30+ miles stopped a few times & left it sit for 45 minutes when I came out the truck fired right up both times. I have gone out in the last two hours & started it a few times & it fires right up.
Now the kicker. NO CEL, It Drives great, the fuel mileage in town is improved by the on board computer.
Bottom line with a loose or no gas cap the Blazer starts & runs perfect.
Anyone have any thoughts on this??? I think I'm going crazy. I haven't called my buddy the mechanic helping me on this but will in the morning.
Thanks in advance.

 

I would think possibly a bad/leaking purge solenoid that is just venting all the time would cause poorer fuel economy and driveability but that would throw a code. I would get it scanned to check for pending codes. I don't really see any correlation between the evap system and hard starting except for the venting solenoid causing a rich condition.

 

Yea this whole deal has me crazy. I went out this AM & it fired right up. It has never started this good. & the gas cap is just sitting on the filler. I haven't tried to screw it back down yet. Could the wrong or a defective cap cause this???
This issues is driving me nuts. Not that I'm not already a little nuts.
Thanks for you response.

 

Well some caps will burp if the pressure gets to high but that is usually on older models. Modern vehicles are pretty good about purging the tank when pressure increases and they also have a reserve area in the tank to deal with expansion. I would get it checked for pending codes though.

 

I ran a code check. I just have a simple code reader. & No Codes, all systems checked OK, or at least the ones it would read.
There was not excessive pressure in the tank. One thing is this Blazer has been in 100-120 degree weather for 5 weeks now. As long as the tank filler is vented to outside air it starts & runs great. With the cap on it runs great but starting becomes an issue. Having to crank it 15-20 sec. before it fires.
I'm to a point that I think I will just run it as it is with the cap just sitting on the filler until I get back home. If it quits we have towing insurance. But so far with all the issues I have had with this Blazer it has not left me sitting on the side of the road YET. I'm so deep into to this vehicle it will have to run 300,000 miles to get my money out of it.

 

::::UPDATE::::
After the second new Delphi Pump a AC Delco cap & rotor, I ran the truck all one day with the gas cap removed. Only three times did I have a starting issue where it took 10-15 seconds of cranking to start.
I tightened up the cap yesterday filled it with gas & took a 400 mile trip today. I must of stopped & started the Blazer 25 times. It hit the first time every time. All I can do is think that after the second pump we had an air lock somewhere in the fuel system.
Anyway it ran great it started as it should & we had a great day.