Possible "lazy" Fuel Injector

[C5Steve]

Looking for a bit of advice based on others more extensive experience.

Over the weekend I had cause to remove and then refit the fuel rail. My first time doing this, the car had no issue with the fuel rail I just needed more space for another job. Once I refitted the rail, the car started straight away as normal however it had a clear misfire. Here's the process I went through:

• Shut off the engine and checked the codes - Car had a P0300 code. I know whilst this is for a misfire on multiple cylinders, it can also relate to just one cylinder if it exceeds the maximum number of events (I think that's right).
• Restarted the car and as I assumed this would be related to the injectors I went around and unplugged them one by one. Only one cylinder made no difference to the running of the car suggesting this was the cylinder with an issue.
• Removed the fuel rail again and checked all the seals etc. Injectors themselves appeared very clean (car is always run on V-power), no obvious issues. Refitted the rail ensuring everything seated correctly. Reconnected everything.
• Cleared the codes and restarted. Misfire still there, went around with a NOID tester and checked each plug to ensure the wiring wasn't the issue. All plugs showed they were receiving a signal, again only the same cylinder had no effect when being disconnected on the idle.
• Switched off and checked the codes again, still P0300 but also P0200 after the slightly longer run. Cleared the codes and restarted again.
• Still misfiring, allowed the car to run a bit and gave the car a little throttle to raise the revs. Idle almost immediately smoothed out. Let it run, few more revs, no issues or CELs or codes.

So, it appears to me that for some reason, one injector that was fine before removing but just didn't "wake up" properly after refitting. Is this a thing? Or should I be looking down the root of replacing one or all of them. Car has done around 75k miles, the injectors are the originals by the looks of them.

 

[teamzr1]

Not clear if after you raised the RPMs that the problem injector issue went away and now no DTCs tripped and idles correctly ?

P0300 is multi misfire, then P0301 to P0308 ( so P0301 is cylinder 1, etc) DTCs
Using an OBD-II scanner could monitor the 8 Current misfire (1 for each cylinder) and another 8 History counters to see which ones have misfire
The P0200 is saying an injector issue, including wiring problem, and there are P0201 to P0208 DTCs, one for each cylinder

Fuel injectors type for the C5 are EV1 which is the length and diameter
They are high impedance.
If feeling the coil of injector is bad with an OHM meter measure the 2 male pins of the injectors and they should all
measure the same amount of resistance, if any report different then internal coil has a problem

There are cheap fuel injector testers and cleaning products such as this one I had gotten from Amazon

 

[C5Steve]

Not clear if after you raised the RPMs that the problem injector issue went away and now no DTCs tripped and idles correctly ?

P0300 is multi misfire, then P0301 to P0308 ( so P0301 is cylinder 1, etc) DTCs
Using an OBD-II scanner could monitor the 8 Current misfire (1 for each cylinder) and another 8 History counters to see which ones have misfire
The P0200 is saying an injector issue, including wiring problem, and there are P0201 to P0208 DTCs, one for each cylinder

Fuel injectors type for the C5 are EV1 which is the length and diameter
They are high impedance.
If feeling the coil of injector is bad with an OHM meter measure the 2 male pins of the injectors and they should all
measure the same amount of resistance, if any report different then internal coil has a problem

There are cheap fuel injector testers and cleaning products such as this one I had gotten from Amazon



View attachment 25789

Thanks, to your first question yes, raised the RPMs and the issue has now disappeared. No CEL, no codes, idles fine.

It was just a P0200 code, no specific cylinder but there was only one cylinder that made no difference when unplugging the injectors. Wasn't aware you could get cheap testers, may look down that route if the issues recurs.