hi there ive got a 2000 gmc k2500 4x4 7.4l.I replaced the egr,iacv,cam position sensor,crank sensor,cap,rotor,plugs,all filters,front 02 sensors as my truck does not have the rear ones.the problem im having is its hard to start when its cold im at my wits end please help.I should also mention the motor was rebuilt around 20-25k ago

 

Could you better explain what is meant by "hard to start"? Does it crank full speed and not fire? does it fire and sputter? Will it fire right up and die when you put it in gear?

 

The 7.4's are notorious for the fuel pumps, fuel pressure regulators, and injectors going bad. Check your fuel pressure and do a leak down check. I bet your losing pressure. Does it start better if you cycle the key a few times before starting it?

 

yes it turns over full speed and doesnt fire takes roughly 2-3 trys before it fires up.As far as the fuel pump when the key is on you hear the pump loudly but i have not tested the pressure and what do you mean about cycling the key a few times?

 

K, so hook up a fuel pressure gauge to the tire-chuck at the right above the thermostat housing. Turn the key on, and let the fuel pump kick out (it runs automated, not on pressure cut-off). Check the fuel pressure reading and turn the key off. Watch the gauge, and if your injectors are leaking (a usual problem with the 454 ci), the pressure will drop to nothing within 5-10 seconds. The speed of drop is roughly related to the number of injectors that are shot, but I would guess your best bet is simply to change them out.

Other symptoms (at least, on mine...) include a too rich code (bank 1 and 2), rough idle, fuel mileage < 10 mpg, hard warm starting, smell of gas under hood.

If you check your pressure and it drops, as Shamrock said, it is probably your injectors. The 454's injectors are hidden under the intake manifold with no air movement whatsoever, so the one fellow I talked to told me that they cook every 50k. NOTE : You don't have to take off the distributor to extricate the fuel rail, and be careful with the metal injector clips on the plastic rail, they're secured by small tabs that break (i.e. 5 of 8) very easily. Having just done this job recently, I'm going to rig up a cold air return underneath the manifold in the hopes it keeps the injectors from baking.

 

Cycling the key means turning it to the on postion without starting the truck then turn the key off then back to the on position without starting etc etc. From my experience (and I currently have 3 vortec 454's) a long cold start is usually the pump leaking down pressure. So basically when you go to start the truck cold it has to reprime the whole system (fill the lines, filter,etc). That is why I asked if it helped when you cycle the key when cold. A hard or long warm start is usually the injectors - they leak the fuel into the manifold and when you go to start the truck it has to burn all that excess gas before cranking. It is only when warm because the gas will evaporate out of the manifold if it sits for a while. This is usually when you go to the store and run in for a few minutes and come back out it will turn over a few extra times and then will puff a little smoke as the extra fuel is burned off. Both are common on the Vortec 454's.

 

so i tested the pressure and found out the the pressure reg was bad changed it out and of course as my luck has it the new one was bad so after much cussing i replaced it again.worked great for about a week and now it seems to have the same problem.the truck runs so much better and fires first time in the morning and thats it.im to the point of saying eff it and keep it as is.will this ahrm me in the long run?