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Ask GM Tech (Cam) Your Own Question
GM Tech (Cam)
GM Tech (Cam), Chevy Technician
Category: Chevy
Satisfied Customers: 29428
Experience:  GM Grand Master Technician 2007. 14 years experience.
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Having electrical issue with lb7

Customer Question

Having electrical issue with lb7
Submitted: 1 year ago.
Category: Chevy
Customer: replied 1 year ago.
03 lb7 has major intermittent electrical issue. p0202 0203 0205 0208 2149. Things I have done. Replaced whole top harness,ficm,pigtailes. Checked all wire nuts multiple times. I replaced injectors on my own and when I started Truck straight into limp mode. Pulled both valve covers twice checking nuts and wires finding nothing. Went through whole top harness and couldn't find any chaffing in wires. Still limp mode. Came out next day without doing anything else to it and it starts right up runs great for 2 weeks then problem again. Cleared codes and it runs again for few days. Sometimes it goes 1 day and it has went up to 6 months without doing it. Got tired of messing with it so I replaced top harness,ficm,pigtails,cleaned all electrical connectors and still same thing. I believe the only thing left is internal injector short. I ohmd out injector through pigtail and they are fine. As soon as I start it shuts down whole bank so I can't narrow it down
Expert:  GM Tech (Cam) replied 1 year ago.

Hi there, I am Cam. Can I ask if you had the orientation of the engine correct? On the druramax, Drivers side is even, 2-4-6-8 and passengers side os odd, 1-3-5-7. Is this what you expected and did you change all or just the effected ones?

Customer: replied 1 year ago.
I replaced all injectors bc of smoke at idle problem. After I changed all injectors truck started in limp mode with codes listed. But is extremely intermittent and have replaced ficm,top harness,pigtails and cleaned all wiring plugs
Expert:  GM Tech (Cam) replied 1 year ago.

OK, when you say the top harness and pigtails, you mean the top engine harness and the pigtails that go to the injectors under the valve covers?

Customer: replied 1 year ago.
Expert:  GM Tech (Cam) replied 1 year ago.

This only starter after replacing the injectors or did this start before replacing the injectors?

Customer: replied 1 year ago.
Only after
Expert:  GM Tech (Cam) replied 1 year ago.

Ok, so to make sure I understand completely, you replaced the injectors, this started, you replaced the rest and it remained?

Customer: replied 1 year ago.
exactly
Expert:  GM Tech (Cam) replied 1 year ago.

Ok, so one of the injectors, 2 3 5 or 8 is causing this. It has a fault inside and when it, the FICM detects one injector out or spec, it disables the group of injectors, in this case, 2 3 5 and 8. Unless it shows you a P020(2,3,5,8), its going to take testing each injector when the issue happens to know which to replace.

Customer: replied 1 year ago.
That's why I'm here ! Lol. I ohmed them all and they are all in spec from pigtail down to injector. How do I narrow down the bad one ? That's really the reason I contacted you but had to give the whole story
Expert:  GM Tech (Cam) replied 1 year ago.

Understood. IF all of these were the EXACT same resistance, and you were using a quality meter with the leads zeroed out, then you would have to do what I would, pick a bank, replace the 2 and see which is does. Beyond what you have done, there is nothing special about testing these. They run on 93 volts from the FICM so we cannot simply apply voltage to see. I know this is not what you want, but the fact of the matter is that your diagnosis is spot on so far.

Expert:  GM Tech (Cam) replied 1 year ago.

Were these GM injectors or aftermarket injectors?

Customer: replied 1 year ago.
Bosch reman
Expert:  GM Tech (Cam) replied 1 year ago.

Exactly what resistance did you get for each injector?

Customer: replied 1 year ago.
05
Expert:  GM Tech (Cam) replied 1 year ago.

And that is right in the middle of the spec. IT is 0.3 to 0.8 ohms. Did you zero the meter before testing?

Customer: replied 1 year ago.
I payed an arm and a leg for this multi meter. It self zeros it says. Is there not a way to unhook each of 4 trouble injectors one by one till it starts and doesn't throw those short codes
Expert:  GM Tech (Cam) replied 1 year ago.

Ok, self zeros, that must be a good one. Sorry no. The FICM is not that advanced. It works in groups. While it controls each injector individually, if one goes out of spec, it disables the group. Attached is the diagnostic chart for this.

Customer: replied 1 year ago.
I have to just start replacing injectors till it quits ?
Expert:  GM Tech (Cam) replied 1 year ago.

Unfortunately, yes. WE know its one of four, so myself I would Contact the supplier and explain to them what is happening. Then replace 2 as the time to get under each valve cover makes it harder to justify going in twice, unless you happen to get the bad injector straight away. However, I would get this engine really hot then test each injector again to see if you still only get 0.5 ohms.

Customer: replied 1 year ago.
Warmed up as good as possible on 4 cylinders then checked ohms. They all stayed between 4-5 accept cylinder number 2. It would go 34543 then stay at 3 for a sec then dropped to 2 for about a sec then started jumping between 2-5
Expert:  GM Tech (Cam) replied 1 year ago.

I think that is enough of a reason to replace it. Getting an inconsistent reading and one that does drop below spec points to it as being faulty. Replace that injector.

Customer: replied 1 year ago.
Is there any way the short could be between ecm and top harness plugs and cause injector short?
Expert:  GM Tech (Cam) replied 1 year ago.

The short and the wiring does not pass through those 2 large connectors, rather it goes straight from the FICM to the injectors. Everything you tested and the codes suggest it's a bad #2 injector.

Customer: replied 1 year ago.
Hey man. I got new solenoid for 2 injectors on driver side. 2and 8 replaced those and number 6 injector. Now I can't get it to start. Primed it for hours. Primer getting hard. I do notice that when it's cranking white smoke rolling out of exhaust. What could it be and how do I diagnose. Won't start to see if injector short codes are gone