Dies At Startup Idle

dukesrebelyell · June 24, 2011

so i have the 5.7 350 it just turned over 200k. lately its been struggling to start. when it fires up it gets through about 2 seconds and then it chugs out. the only thing i have figured out is that if i give it a little gas when it initially fires up it will not die. then after it actually starts running it will vary the idle by a few hundred rpm at idle until it has 10 or so minutes to warm up. it also has a bit of a lag when you press the gas, you can tell that something is happening in the engine but it sounds like the rpms are not rising as rapidly as they should. so when you hit the gas to move you hear a delay and also feel it as well. my initial thought was the idle air control, but that didnt fix anything. i dont want to keep throwing parts at it. any help would be great.

GMstrong · June 24, 2011

Check fuel pressure.

GMstrong · June 24, 2011

Just noticed that its a 90 how does the injector spray look?when was the last time you did a full tune up?could be your iac valve too alot of things it could be.

rodram · June 25, 2011

I have to agree with Keith's first reaction here... check the fuel pressure and check the spray pattern of the fuel at the throttle body ...

I think the TBI engines have a spec fuel pressure of 13 to 15 psi ... and there is not a lot of leeway on that because if you have only 9 or 10 psi, your truck may start to act up just like you are describing ...

.. it could be other things too, but check out the fuel pressure and injector spray first

dukesrebelyell · June 27, 2011

i have changed the IAC and TPS. still no change. as for the fuel pressure, is it supposed to read 13-15 at idle? i changed the fuel filter about 2 months ago so i doubt its that. but if the pressure is reading below 13 will it be the fuel pump more than likely?

thanks for the help.

GMstrong · June 27, 2011

anything lower then 12 is probably a weak fuel pump

dukesrebelyell · June 28, 2011

so when its at idle and finally runs ok, after about 5-10 minutes, i can give it some throttle and it will rev up in an ok fashion. when i put it in gear and give it gas, just enough to get it rolling, it chugs out and wants to die. i barely made it back home after it died on the road a couple of times but fortunately i was able to get it restarted and baby it home. i dont have a way to check the fuel pressure but with the intake off i can see a spray coming from both injectors and the quantity increases with an increase in throttle. i did notice that there was a drop or two of fuel running down the middle of the injector bracket. not sure if its getting too much fuel and dying or if its not getting enough.

rodram · June 29, 2011

... well .... sometimes you just have to find someone, and pay if you have to, to get the diagnostic work done.

you need to know your fuel pressure before making the decision if you need a new fuel pump ... they aren't cheap (don't buy a cheap one, get a Delphi or ACDelco) and the labour is kind of a pain in the ass .. so you don't want to do that if it is not necessary