2005 Chevy Colorado 5cyl. Current Limited Fuel Injector

Hi everyone. It's been a long time since I've posted here.

Recently had to diagnose a 2005 Chevy Colorado for a severe misfire and crank no start which had nothing to do with the fuel injectors, it was water in the fuel. This condition happened 10 minutes after I replaced the alternator and the customer said that is what it did before and they thought they fixed it.

However I learned something about the control for the fuel injectors on this truck during the diagnosis. I was measuring the current for all the injectors at the fuse panel and saw what looked like square current ramps on every fuel injector. At a first glance, I thought that maybe they were shorted but thought that would be really odd for all of them to be shorted.

I took a closer look and found all the fuel injectors had exactly the same characteristics and pulled exactly the same current. I also looked at the control side voltage and that looked perfectly normal.

Balance test showed they all dropped 21 to 22 psi. GM spec is 10 psi but considering it was idling smooth when I first got there, not worried about it.

They all consumed a max of about .7 to .8 amps.

So this might be a variable for fuel injector waveform analysis. These are the first I have seen that do not ramp up.

Anyone else run into this?

Unless they all really are shorted but they engine did idle "decent" when I first got there. Some little skips to the engine once in awhile.

In the attached images, yellow trace is injector control side voltage and blue is injector current. These were captured during cranking.

I can't say I've ever ramped an injector on a 3.5L before? Not sure if that's normal or not. :huh:

There is a *little* bit of a ramp?



But it may not look like much of a ramp given the longer injection pulse width typically used during cranking.

FWIW, I did look at the injectors on an F-150 4.2L the other day. This was taken while idling:



Even at idle, there's still a bit of a flat top to it. Is this current limiting, or is that just the injector at full saturation? :silly:

That's a good observation. I didn't think about the real long pulse width during cranking compared to running. I never did check them with the engine running.

I couldn't tell you have those injectors you measured are full saturation or current limited. They look to be hitting 1.36A? I think most injector circuits would be limited to around 1A if they were limited. Something I'll have to pay more attention too. Interesting stuff!