start up idle

[toothenator]

I have a 2000 gmc with the 4.8 in it around 150k. The motor has new plugs and wires and a new idle air control valve and a relatively new fuel filter yet sometimes on the start up, cold or not, it will die or have a difficult time at idle. Rev it a few times and it's good after that.

Any suggestions?

[Boog]

For about $20 a new coolant temp sensor might be in order, considering the age.

[toothenator]

maybe but isn't that usually associated with a high idle?

[Boog]

Nosir. Nothing to do with idle speed.
CTS reading is used to richen the fuel mixture on cold start up. Sometimes on cold start they will run so rich they'll die. Sometimes they start cold fine but run bad once warmed. Its' cheap at about $20. It's in the intake manifold next to the thermostat housing. Make sure the grounds there are also clean.

[toothenator]

thanks i'll give that a try

[67ChevyRedneck]

Check the fuel pressure. Mine did something similar at 120K. The check ball was bad in the fuel pump, allowing all the fuel to drain back to the tank after the truck was shut off. So it would either have trouble starting or running the first few seconds I started it. After that, it ran fine.

[toothenator]

Originally Posted by 67ChevyRedneck

Check the fuel pressure. Mine did something similar at 120K. The check ball was bad in the fuel pump, allowing all the fuel to drain back to the tank after the truck was shut off. So it would either have trouble starting or running the first few seconds I started it. After that, it ran fine.

Did you have to replace the whole fuel pump?

I changed the coolant temp sensor and problem is still there

[67ChevyRedneck]

Yes, the whole pump. The fuel gauge sending units also tend to get a little screwy with age (mine would to E to F every once in a while and bounce around) so the new pump/sending unit (it's all one piece) fixed both my issues. I know they're expensive BUT DO NOT CHEAP OUT. I have read over and over and over on the internet about aftermarket pump failure after failure after only being installed for 6 months to a year. When it comes to fuel pumps and converters never cheap out, buy GM.

I bought mine from GMpartsdirect.com. They're around $230 plus shipping but it's an all day job, not something you want to do again. There are two different pumps, something about special emissions (prob Cali vehicles) but if you send them your VIN they can tell you 100% what pump to get.

Again, this may not be your problem. You can buy a cheap fuel pressure gauge to make sure before spending $$$ on a new pump. I bought this one for $45 and it confirmed it for me, I've also used it a few times on other projects... they may even "rent" them out still???

http://shop.advanceautoparts.com/web...pressure+gauge


Here's my thread about it:

http://67-72chevytrucks.com/vboard/s...d.php?t=423012

It's been almost 3 years and 20K since I changed it.