Hi, i have a 2008 Tahoe its having a little bit of rough idle and starting issue. When i try to start it up it like misses and starts up it but only does it occasionally and when heat soaked. It almost sounds like spark knock. I took it to a local mechanic and they diagnosed a bad fuel regulator/pump. The fuel pressure jumps to 60 then tappers off to 47-47psi but on heat soak with the fuel off it would climb to 75-80psi. So i dropped the fuel tank and put a brand new ac delco whole fuel pump assembly. It seemed to fix it for a about a week and a half no starting issues or rough idle. Its not doing it as as frequent as it was but im assuming it will start back to doing it more often again. Is there anything else that it could be? Also forgot to mention everything runs fine other than that. Thanks for the help.

 

Should be a minimum of 55-57 PSI with 60-62 PSI normal.

 

I haven’t got to check it again yet but I knew it was out of spec. So I changed the fuel pump and didn’t have any issues for about a week and half but now I am. I’m going to try and check the fuel pressure this weekend and see where it’s at. I’m just trying to see what else could cause this? Thanks for the help.

 

Hard or rough start on a hot engine could be a sign of a leaky injector when engine is off. Try running a heavy dose of a good injector cleaner like Techron through a couple tanks of gas.
When it's hard starting when hot give it some throttle and see if it starts easier.
A slightly leaking injector will not affect a cold motor, they like extra fuel when cold, not when hot.

 

I’ll try that, thanks for the info. What kind of Techron should i use? Full system cleaner or injector cleaner?

 

I would go with the injector cleaner. They may both be the same stuff in different bottles though.

 

Either one will work fine. They both contain PEA. It's also what is used to clean the valves on Direct Injection engines, but it works only if you spray it in the intake side with DI motors. Chevron first used it in the early 1970's, when it was called F-310 (Formula 310). I've seen carburetors as clean as a whistle, that used Chevron gasolines.

 

Thank you guys for the help and the info I’ll try that and see how it does!

 

I got some Techron fuel injector cleaner it’s now working it’s way through the system now. I’m as wondering how I can test for a leaking injector?