Fuel Injector Troubleshooting

Johnny O

Turning dirt roads and dead-ends to dust.
KJ Supporting Member
Joined
Apr 29, 2021
Messages
1,793
Reaction score
1,849
Location
Bellevue NE
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

Turning dirt roads and dead-ends to dust.
KJ Supporting Member
Joined
Apr 29, 2021
Messages
1,793
Reaction score
1,849
Location
Bellevue NE
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

Well-Known Member
Staff member
Moderator
Joined
Oct 24, 2008
Messages
8,730
Reaction score
1,326
Location
B.C. Canada
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.
 

Attachments

  • Chevron Techron.jpg
    Chevron Techron.jpg
    273.6 KB · Views: 7

lfhoward

Well-Known Member
KJ Supporting Member
Joined
Dec 9, 2012
Messages
1,481
Reaction score
1,338
Location
Philadelphia, PA
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

Turning dirt roads and dead-ends to dust.
KJ Supporting Member
Joined
Apr 29, 2021
Messages
1,793
Reaction score
1,849
Location
Bellevue NE
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

Turning dirt roads and dead-ends to dust.
KJ Supporting Member
Joined
Apr 29, 2021
Messages
1,793
Reaction score
1,849
Location
Bellevue NE
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

New Member
Joined
Mar 14, 2018
Messages
6
Reaction score
3
Location
VA
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

Turning dirt roads and dead-ends to dust.
KJ Supporting Member
Joined
Apr 29, 2021
Messages
1,793
Reaction score
1,849
Location
Bellevue NE
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

Turning dirt roads and dead-ends to dust.
KJ Supporting Member
Joined
Apr 29, 2021
Messages
1,793
Reaction score
1,849
Location
Bellevue NE
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

Full Access Member
Joined
Jul 7, 2009
Messages
126
Reaction score
17
Location
Strasburg, PA
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

Turning dirt roads and dead-ends to dust.
KJ Supporting Member
Joined
Apr 29, 2021
Messages
1,793
Reaction score
1,849
Location
Bellevue NE
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

Full Access Member
Joined
Nov 11, 2018
Messages
157
Reaction score
67
Location
ny
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.
 
Last edited:

Johnny O

Turning dirt roads and dead-ends to dust.
KJ Supporting Member
Joined
Apr 29, 2021
Messages
1,793
Reaction score
1,849
Location
Bellevue NE
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

Full Access Member
Joined
Nov 11, 2018
Messages
157
Reaction score
67
Location
ny
Try swapping an #6 injector with that from another cylinder and see if anything changes.
 

Johnny O

Turning dirt roads and dead-ends to dust.
KJ Supporting Member
Joined
Apr 29, 2021
Messages
1,793
Reaction score
1,849
Location
Bellevue NE
Installed new Boschs all around, et viola! Problem solved.
 

Johnny O

Turning dirt roads and dead-ends to dust.
KJ Supporting Member
Joined
Apr 29, 2021
Messages
1,793
Reaction score
1,849
Location
Bellevue NE
Installed new Boschs all around, et viola! Problem solved
 
Top