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Hey all. Got a 2017 Silverado with a 5.3 V8 with direct injection. Getting misfire on cylinder 2 ( can see on live data but only throwing p0300 code) Swapped coil and plug and lead with cylinder 4. No change. Still misfiring on 2 ( showing on live data)
Compression tested 210 psi ( same as cylinder 1)
Replaced the injector as when I applied 9v battery to it it didn’t sound right ( different to the others ) no difference still have rough idle and cyl 2 misfire on live data ( but no code)
When I connect a noid light to it it doesn’t flash as bright as I’d like but this is the only injector I can test with the vehicle running due to having to remove the manifold to access the rest.
Is there any way to check the voltage supplied to the injector
When going through online manuals I see this.
should I see 12v or 65v
The ECM controls each fuel injector with 65 V. This is controlled by a boost capacitor in the ECM. During the 65 V boost phase, the capacitor is discharged through an injector, allowing for initial injector opening. The injector is then held open with 12 V.
Any suggestions?
Just to update this. When driving it and watching live data I can see 0 misfires. When idle is misfires on cyl 2. When deceleration it misfires on cyl 2 mostly but some others also.
I have personally seen multiple GM 5.3 engines with similar symptoms (especially the fact that it’s an idle only misfire) that end up being a cam lobe warn off slightly. I’d pull the oil filter and cut it open to see if there’s metal shavings inside. I can’t say that I’ve seen this issue on one this new however
Why would if only be at idle is its a worn lobe? Surely it would do it under load too ?
Valve train related misfires typically are more noticeable at idle and less so under load. I have heard it is because at lower RPMs the cylinder can pull a greater volume of air giving the loss of compression greater impact on engine stability at idle.
Even if that's not exactly bulletproof theory, it's been good enough in practice for me over the years.
A relative compression test might point towards a mechanical problem, an in cylinder pressure transducer would also be beneficial.
Sometimes you can catch them with a running compression test as well when compared to the running compression of a good cylinder.
As far as checking the injector circuit, there may be a connector around the base of the intake manifold where the injector harness connects to the main engine harness, or you can measure at the engine computer connector itself.
When I connect a noid light to it it doesn’t flash as bright as I’d like but this is the only injector I can test with the vehicle running due to having to remove the manifold to access the rest.
I can't say I've ever tried using a noid light on a GDI injector circuit. But, I'm willing to bet that the noid light is probably dim because GDI injector pulse width tends to be pretty short. 1-2 ms, usually. That's barely any time for the bulb to start heating up.
You could watch both injector wires on a scope to check for the control circuits? But there's a lot of stuff going on there in a short amount of time, and it can get confusing quickly. Especially when you can't get to another injector for a known good. If you're gonna scope the injectors, I'd try to find a way to look at injector current ramps. Easier to decipher and compare to other cylinders.
I'd go for the running compression test like Noah suggested. That'll usually show a worn cam lobe/bent pushrod.
What are the total fuel trims during the idle misfire?
long term fuel trim bank 1 is 0
long term fuel trim bank 2 is -1
But the battery may of gone flat and reset it .
When doing a fuel injector balance test I get the following
1. 270 39psi
2. 353. 51psi
3. 270. 39 psi
4. 374 54 psi
5. 263. 38psi
6. 349. 51psi
7. 317. 45psi
8. 331. 48psi
When I did it again I got
1.180kpa
2.274
3.212
4.274
5.198
6.317
7.194
8.248
This all seems a little funky to me. Should I test wiring on cylinder 2 from ECM to injector or would the fact that I can feel the cylinder de activation when testing fuel injector balance imply that its working? It is not as noticeable as the rest of the cylinders tho
also pulled passenger valve cover to confirm no issues with push rods etc
Last edit: 9 months 1 week ago by jonny1. Reason: Update
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