mekantor

My motor has developed a misfire on cylinder 8 and I haven't been able to pinpoint the cause. Trying to rattle the braintrust here.

What I've done so far:
1. Swapped wires and coil packs to other cylinders to see if the problem would move.
2. Swapped spark plugs to see if the problem would move.
3. Tested resistance on all fuel injectors and also toggled them on/off with DAS. Resistance was good, 16-17 ohms for all. While toggled off, engine operated slightly worse.
4. Tested continuity of the coil pack wires back to the ECU, all good.
5. Tested compression on just the driver-side bank of cylinders 5-8, all good and matching at 10 bar.

I'm planning now to replace all spark plugs. I damaged a few in the process of pulling coil wires, was only able to replace them with close but slightly different models from the local store. I had 1 step colder so now there is a mismatch. Going back to normal plugs so they match all around in wear/type/gap.

My only other option will be to replace the fuel injectors, which are sitting on the workbench ready to go. I was hoping it was something electrical and I'd return them.
I've never seen an injector partially fail, usually completely bad or working, but I'm out of ideas.

SICAMG

If you have good compression ...that's very good to know ! You may have a sticking injector or a partially plugged injector. even though it will pass a continuity test, it could be defective.

bbirdwell

+1 ^
I've had fuel injectors cleaned and flow tested by both RC Engineering and diesel engine injector repair shops. Nice to get back a sheet showing the before and after flow rates and patterns.

Bay510E55

I second the injectors being the issue. I bet if you get new i injectors from fcp euro and swap them in you will eliminate your random misfire.

mekantor

It was injector! Running buttery-smooth now.

Took me approx 5h to do all injectors and all spark plugs, including cleanup around the engine. Hows does that compare with shop time ?

E55Greasemonkey

Spark plugs 45 minutes. Injectors 30 minutes.
Congrats on fixing it!

mekantor

Under 3 minutes per plug? Impressive!
I did some cleaning and extra compression tests along the way.

E55Greasemonkey

Yes, I've been working on these cars since 2003 😉and that's also with help from air tools 😎

mekantor

Cold start has been a bit rough, good otherwise.

I reset all the adaptations, hopefully that will help. Otherwise perhaps I'll try to get it re-tuned.

coobah

Well nobody would expect a perfect start from the engine with am empty fuel rail... Nice that its working again.

mekantor

No I'm saying its behaving this way still after a few days of driving.

equitiesguy

I fail to see how an air tool would help you remove 16 spark plugs at less than 3 minutes each --- unless you're an idiot and you put a power tool on them.

equitiesguy

How long did it run smooth? Are you getting misfire error codes on cylinder 8 from STAR? Did you scan the car for other codes with STAR?

mekantor

Because its an awkward spot, with little range of motion for a normal ratchet. And 8 per side of these, often not moving smoothly.

mekantor

Once it warms up its smooth at idle.

No misfire codes, but in Smooth Engine Running it is still which 8 is going out of bounds, but not enough to actually register codes. Rough, but not as rough when the failure was there prior to the repair.

No other errors on the ECU in Star.

E55Greasemonkey

It's called a 3/8" air ratchet, an impact swivel, and a USAG spark plug socket. Maybe you're an idiot?

SICAMG

Flat rate man !....got to love it !
I will swap my plugs out Monday or Tuesday and time it. I crack loose the plugs and then put the electric ratchet to it, never an issue and of course,manual ratchet to carefully tighten back up.

E55Greasemonkey

....

SICAMG

Yep as usual my yearly spark plug change took under an hour. Never really thought to see how long it takes LOL so it can be done.

E55Greasemonkey

Nice! The recommended interval is 60k miles or 5 years for the OEM plugs. If you go much beyond that, the plugs can be difficult to remove and may take longer.

SICAMG

Yea I blow a lot of Nitrous through this engine and run 104 Sunoco fuel so new plugs every year regardless plus I can see how the cylinders have been running. Cheap insurance to prevent miss fires.

Bay510E55

Check for vacuum leaks.

equitiesguy

If you put a power tool on a spark plug with an aluminum head, you're a stupid c u n t by any definition and anyone following your advice is a fool.

For reference USAG might as well be Harbor Freight. Garbage tools. You say it like you're proud.

E55Greasemonkey

Thanks for confirming your idiocy. 👍🏻
Now go watch some more YouTube oil change videos you shadetree hack! 😂

HLG600

As a general note, it is important to double-check the gaps as there is plenty of misinformation out there on trusting "pre-gapped" single prong plugs.

Case in point, when I changed my plugs last weekend, 15/16 of the NGKs were completely off the factory spec out of the box.

In terms of difficulty of removal, maybe 2-3 required a little extra effort. Plugs were original to the car (15 years, 55K miles on them).