I just picked my truck up from the tuner. They said on the dyno everything was fine. But during the street tune the injectors maxed out in the top of third gear. But not on the dyno. It is a 03 Sierra with a .030 over 5.3, tsp low lift 2 truck cam, tsp long tubes, 3.73 gear. It has a frame mounted fuel filter. Looks original. They said I need bigger injectors. But to me I would think they would have seen that on the dyno. They said if you punch on it from a stop at 5000 and up the injectors 115%. I'm no expert. But seems more like a fuel delivery issue then an injectors size issue. I am going to change the fuel filter and see. What do y'all think. Truck put down 309hp and 305 tq at the wheels. The po said he was told it had a roll race button. When you hit the tow haul mode button let's say at about 30 the motor drops to an idle if your not on the gas. Then when you floor it the rom shoots up and slams into gear. They could not find anything in the tune. They compared it to a stock tune and didn't see anything that could cause it to do that. Any thought?

 

What size injectors do you currently have in there now? have you plumbed up a gauge on the fuel line to see what your fuel pressure is actually doing? copy of the log/tune?

 

Roll race button sounds like magic fairy dust, nothing in the tune would show anything like that.

I agree with the guy above, what size injectors and the tune file and log would be handy.

 

Factory injectors. No log file of the tune. I don't have any software for it. I have not put a gauge on it and didn't sound like they did.

 

Stock injectors are only like 25lb/hr, it's time to upgrade for sure.

They can barely support just over stock horsepower and if you are making 300whp, that's already 60-70 more than factory.

Jump up to some 31lb/hr 8.1 injectors if you don't plan to go much further.

 

Where can I get 31lb injectors that are plug and play? It has been a while since I have looked for some but last time I did I never found any that are a direct replacement.

 

Anywhere that sell the Vortec 8.1 fuel injectors. I'm sure some vendor does or even ebay. They are direct fit and injector information could be pulled from a 8.1 tune file from like a easrly 200's silverado/sierra/avalanche.

Think 17114503x2 is a delphi part number. I search ebay for 8.1 vortec injectors and found the 31lbs and 42lbs/hr marine injectors too.

 

So I changed the fuel filter and hooked a fuel pressure gauge up and went for a drive. I also had my cheap scanner on watching stft and ltft. First off the truck felt much better. A lot smoother. Full throttle the fuel pressure stayed 58psi untell it shifts the back to 58psi. I didn't top it out in 3rd maybe 4500 or so almost 100phm and fuel pressure was solid 58psi and both fuel trims were dead on 0.0. I'm not against buying injectors but they said they will have to retune the truck and it will cost me about 150 to retune. I will be getting hp tuner software anyways. So with my tiny bit of new info is there any way of telling if I need bigger injectors?

 

No, because you can't actually see what the injectors are doing with out the proper software.

The duty cycle is like how hard the injectors are working to maintain the fuel needed.

When they tell you that you're at 115% when they peak that means they have to work really hard to maintain the correct amount of fuel needed. You really don't want to max them out or you risk burning them up.

When you're cruising around you will see something like 30%

So let me put it to you like this. Let's say your truck takes 2500 rpm to drive around and the max recomended safe RPM is 6000. Let's say you pull a normal load and it takes 5000 rpm and Now let's say you want to pull 2x the load and it takes 7000RPM.

The truck may do it, but was only intended to go to 6000RPM max. By taking it above that it could fail at any time.

The injectors are the same way. You have to over power the coils to deliver the fuel needed. It will work, but for how long?

 

Well I'll just not run it hard in 3rd then. Thanks. Does the whole tune really need to be redone with an injector swap?