Fuel Injector Troubleshooting

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Johnny O

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Before I go dumping cash into a set of Bosch injectors*, was curious if anyone had some troubleshooting suggestions.

Keep getting a random, intermittent P0300 in conjunction with P0306. It self clears just as randomly as it appears. Have had this since the day I replaced the plugs and COPs. (Which were replaced as it was #4 and #6 misbehaving before)

Plugs are the properly gapped NGKs yinze swear by and have less than 4k miles on them. COPs are all new ENA Blues (I know, I know....but I ain't spending MOPAR prices on a high mileage beat it up toy...LOL) with same mileage as plugs.
Shockingly, compression is a solid and relatively consistent 1400ish kPa (about 203PSI) across all cylinders with the usual, acceptable variations between tests.

While troubleshooting, I have gone as far as swapping plugs and coils to different locations. The codes remain the same (and random) indicating #6 is misbehaving...until it isn't. All plugs and COPS are uniform looking- no indications of arcing, sparking or the usual "bad" signs.

While on my trip I was "stuck" using any number of combinations of 85, 86 and 87 gas, some with ETOH and some without depending on where I could get fuel.
At home I run the 87 as the manual suggests and it is 10% ETOH.

Am I correct in my thinking that this original stock, OE injector is the source? I know very little about fuel injection systems admittedly.

Is it a viable plan I just buy one cheapo injector off Amazon first strictly for troubleshooting purposes before spending the chunk on the good Boschs?

Is there some other part of the system I should be looking at that my lack of experience with these engines in overlooking?

Any advice greatly appreciated!


*yes I am a hypocrite as I put cheaper 3rd Party COPs on, but insist on OE plugs and injectors...but only because my hook-ups at NAPA and O'Reilly couldn't get me a huge discount on a set COPs, but can get me the injectors at cost...also, like the old Monster cable scam and stuff dude...
 

Johnny O

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It also could be a carbon build up on the back side of the valves.
Chevron Techron Concentrate Plus is a very good cleaner for such issues.
Add two bottles to a full tank on your next highway run and see is that also helps with cleaning the injectors.
https://www.walmart.com/ip/Chevron-Techron-Concentrate-Plus-10-oz/16647989
Roger that. I’m gassing up Friday. I’ll stop and pick up a few bottles today in preparation.

Stupid me, I always forgot to check the valves on my VWs too.
 

LibertyTC

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Once the Techron Concentrate is in the gas, don't be afraid to toss the carbon out !
I try to mat it up a hill or two and try to see if the black carbon is visible in the rear view, or right side mirror too.
It's a very good scientifically engineered safe cleaner.
 

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lfhoward

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Techron is a good idea. I was going to suggest running a couple of tanks of Shell V Power gas for the extra detergents. Then go for a spirited drive. ;)
 

Johnny O

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Once the Techron Concentrate is in the gas, don't be afraid to toss the carbon out !
I try to mat it up a hill or two and try to see if the black carbon is visible in the rear view, or right side mirror too.
It's a very good scientifically engineered safe cleaner.
Sounds good.

Now to try and find a hill in Nebraska....
 

Johnny O

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So, I’ll throw the Techron in and then I realized I’m headed to the Sandhills on Friday. Ain’t a hill but 70-80 mph for six hours should do it.

ofcourse, as soon as we start discussing it, the MIL clears itself again ****
 

larryblevins

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I have a 2012 liberty with 146000 miles. For noise I think is fuel injectors I use Marvel Mystery Oil in every tank of fuel and 5 ozs in engine crankcase after every oil change. It is quiet and runs great. I also use platinum spark plugs for 40,000 miles so far with no issues.
 

Johnny O

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Marvel is a marvel for my VW. I’ve had nothing but bad experiences with the platinum plugs over the years.

good news is in this case there is no noises, just a random MIL that drives me insane lololol
 

Johnny O

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So two tanks and two treatments later, the #6 issue has actually gotten worse.

rechecked codes and such this morning- same faults. Difference is MIL doesn’t auto clear itself.

so, thinking at just a hair from 175k it’s time for injectors.

manny suggested brand? I hate to pay Mopar prices for stuff I know costs more only because it has a stamp on it.
 

Bikeflyer

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Ive tried the $36 set from china and they lasted a year(though it was probably pump grit), got some $180 bosch on the way. Honestly its about comparable to the mopars if you look on rockauto. I got my bosch set from amazon. You can flush them a little too.
 

Johnny O

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I’ll take a look at them!

Irony being right after I posted, ran to the hardware store and it reset…
<bangs head on wall repeatedly>
 

Ksat

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If you have a scanner with mode 6 capability, that may help you narrow down which cylinders are misfiring by accessing the misfire counter on each. To answer your original questions, a malfunctioning upstream O2 can be another cause of misfires. This happens because it cons the PCM into making the fuel/air mixture (typically) too lean by cutting injector on time to the corresponding bank. The PCM in turn spits out a P0300 and from there is left playing a guessing game as to which particular cylinder is causing the trouble when in fact they all are (to more of less of a degree) because the mixture on that bank is just too lean to support proper combustion. Since the PCM On your Lib had a misfire code for both cyl #4 and #6, it could be that bank 2 upstream O2 is faulty (both those cyls are on bank 2). Use a scanner with live data capability and check the short and long term fuel trims (stft & ltft) on that bank when engine is running and warmed up (closed loop) and see what it looks like. Also compare the values to those on bank 1.

A large vacuum leak on one or both banks could also be the cause of a misfire.
 
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Johnny O

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Thanks! This helps quite a bit! I do in fact have it narrowed down to #6 only. I’ll take a long look at bank 2 upstream and the trims. Things I were unaware of before.

a vac leak could be an issue too as when I bought it there was a hose disconnected, according to my notes. I reconnected it and basically forgot about it.

still learning my way around this system!
 

Ksat

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Try swapping an #6 injector with that from another cylinder and see if anything changes.
 

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