Chevy

Chevrolet Repair Questions? Ask a Chevy Mechanic for Answers ASAP

Ask an Expert,
Get an Answer ASAP!

Chevy

2006 Chevy Uplander 3.5 160k. I am trying to diagnose p0300

Customer Question
misfire. I have a...
2006 Chevy Uplander 3.5 160k. I am trying to diagnose p0300 misfire. I have a Snap-on Solus scanner and is picking up a hard misfire on cylinder 4, but also detects on 5 and 6 upon decel/throttle lift. Van has new plugs, wires, coil pack. I swapped #4& 6 injectors with no change to location of main misfire. #4cyl has 180lbs compression. Vacuum check at intake manifold shows 18.5 steady.
I did an injector balance test and found something puzzling. When injector #2 is tested, followed by #3 (or vise versa), the scan tool shows Error - injector has already been tested, when trying to test the second injector. I am hoping this is somehow causing the misfire, but I am not sure what to make of my ohm testings of the injector wiring harness - all the way back to the ECM. I am getting 28 m ohm from ground to each injector pin at the ecm (with connector disconnected at ecm).
Submitted: 2 years ago.Category: Chevy
Show More
Show Less
Ask Your Own Chevy Question
Customer reply replied 2 years ago
Front spark plugs (2,4,6) all looked the same when removed. No oil, coolant. I did a coolant pressure test at the radiator and it held 15lbs for over 15min.
Answered in 1 hour by:
12/4/2015
Chevy Mechanic: GM Tech (Cam), Chevy Technician replied 2 years ago
GM Tech (Cam)
GM Tech (Cam), Chevy Technician
Category: Chevy
Satisfied Customers: 29,652
Experience: GM Grand Master Technician 2007. 14 years experience.
Verified

Hi there, I am Cam. Your injector resistance, do you mean across the injector wiring from the ECM you are getting 28 ohms?

Ask Your Own Chevy Question
Customer reply replied 2 years ago
With the manifold harness disconnected I am measuring 11.2 to 11.8 ohm on each injector. From the common pink + wire to each - driver wire.
Chevy Mechanic: GM Tech (Cam), Chevy Technician replied 2 years ago

OK, are you able to see if you get a pulse with a noid light on each:

Ask Your Own Chevy Question
Customer reply replied 2 years ago
No access to injectors under plenum. I could probably backprobe the injector harness connector with some leads to noid light.
Customer reply replied 2 years ago
I used stethoscope to listen to each, and used solus to disable one injector at a time while listening. They are each making similar sounds and shut off when commanded.
Chevy Mechanic: GM Tech (Cam), Chevy Technician replied 2 years ago

OK, I see you have many new ignition wires and such, but did you check for spark on that one?

Ask Your Own Chevy Question
Customer reply replied 2 years ago
After I reconnect the injector harness to the main engine harness, then use meter at the ecm harness connector C2 - disconnected from ecm. I am measuring 14.2 ohms from each injector driver pin back to the #16 fuse
Customer reply replied 2 years ago
Checked for spark using inline spark tester.
Customer reply replied 2 years ago
I really thought that the error that my scanner was having with the combination of testing #2 injectors would lead me somewhere.
Chevy Mechanic: GM Tech (Cam), Chevy Technician replied 2 years ago

No IO don't think it will be causing this although we cannot rule out the ECM yet. Can you do a fuel injector flow test?

Ask Your Own Chevy Question
Customer reply replied 2 years ago
I used my scanner to do the injector balance test. Primes fuel pump, then pulses each injector for same time period. Each injector dropped the same. From 57lbs to 42 lbs.
Customer reply replied 2 years ago
Fuel pressure is like 57 running. Hold pressure for 20+ minutes when turned off.
Chevy Mechanic: GM Tech (Cam), Chevy Technician replied 2 years ago

So that means its not injectors, if you get spark and its the same and in proper time then we are looking at base engine. You did a compression test, but did you verify exhaust valve is opening? If its stuck closed it will still have great compression.

Ask Your Own Chevy Question
Customer reply replied 2 years ago
I did not remove valve cover but can reach both #4 rockers thru the oil fill hole. There is no rocker slack/noise/clearance, like there might,be with a bent pushrod or flat cam. But I am just speculating.
Customer reply replied 2 years ago
Sticking open/closed wouldnt there be fluctuating needle on vacuum gauge? This was steady.
Customer reply replied 2 years ago
What does it mean when the scanner is intermittently picking up misfiring on 5 and 6, but only when I let off the throttle. Bring up rpm to 18000 or so, then let off the throttle and it momentarily shows 5&6 misfiring. Not constant like #4 though.
Customer reply replied 2 years ago
18000 rpm! I meant 1800.
Chevy Mechanic: GM Tech (Cam), Chevy Technician replied 2 years ago

That is likely just due to the hard misfire on #4.

Ask Your Own Chevy Question
Customer reply replied 2 years ago
What direction would you go with on this next? Any chance that it would be a lower intake manifold gasket leak? Or wouldthat show up as lean and fuel trim adding fuel.
Chevy Mechanic: GM Tech (Cam), Chevy Technician replied 2 years ago

It might be. Can you remove the vacuum lines to the crankcase, plug the ports then spray some carb cleaner or such in the oil filler and see if you get a reaction from the engine. If you do then it does confirm they are leaking internally.

Ask Your Own Chevy Question
Customer reply replied 2 years ago
I have not checked the carb spray trick yet. A few things on my scanner. First is injector pulse is 4.2, seems high. Downstream o2 is hanging at 840 mv. Seems rich. Charging voltage is 15.0 a little high. Spark advance at idle is 21-22.5
Customer reply replied 2 years ago
Maf 4.1 gm/sec, 2710 Hz
Chevy Mechanic: GM Tech (Cam), Chevy Technician replied 2 years ago

Is there a plugged catalytic converter?

Ask Your Own Chevy Question
Customer reply replied 2 years ago
Dont know. Has plenty of powr.
Chevy Mechanic: GM Tech (Cam), Chevy Technician replied 2 years ago

Ok, lets check that intake and see next.

Ask Your Own Chevy Question
Customer reply replied 2 years ago
Would I be able to tell by exhaust temp before and after.
Chevy Mechanic: GM Tech (Cam), Chevy Technician replied 2 years ago

For this it would be back pressure as measured from the pre converter sensor. Anything over 1 psi at any time is the limit.

Ask Your Own Chevy Question
Customer reply replied 2 years ago
Ok I will check intake. Will I see a difference in o2 sensor numbers or just watch/listen to the engine
Customer reply replied 2 years ago
No difference. Doesnt smooth out, speed up, slow down....
Customer reply replied 2 years ago
Is there a diagnostic "flowchart" that is followed for cylinder misfires? I don't have the capability to scope anything, though. Running out of ideas.
Customer reply replied 2 years ago
Van also has "service abs system" on cluster with no codes stored.
Customer reply replied 2 years ago
Any service bulletins for any of this?
Chevy Mechanic: GM Tech (Cam), Chevy Technician replied 2 years ago

Let me get one. NO bulletins.

Ask Your Own Chevy Question
Chevy Mechanic: GM Tech (Cam), Chevy Technician replied 2 years ago

Which engine, 3.5 or 3.9?

Ask Your Own Chevy Question
Customer reply replied 2 years ago
3.5
Chevy Mechanic: GM Tech (Cam), Chevy Technician replied 2 years ago

Here is the diagnose for P0300.

Ask Your Own Chevy Question
Customer reply replied 2 years ago
thanks. I will check the document. Done for today.
Chevy Mechanic: GM Tech (Cam), Chevy Technician replied 2 years ago

Sounds good

Ask Your Own Chevy Question
Ask GM Tech (Cam) Your Own Question
GM Tech (Cam)
GM Tech (Cam)
GM Tech (Cam), Chevy Technician
Category: Chevy
Satisfied Customers: 29,652
29,652 Satisfied Customers
Experience: GM Grand Master Technician 2007. 14 years experience.

GM Tech (Cam) is online now

A new question is answered every 9 seconds

How JustAnswer works:

  • Ask an ExpertExperts are full of valuable knowledge and are ready to help with any question. Credentials confirmed by a Fortune 500 verification firm.
  • Get a Professional AnswerVia email, text message, or notification as you wait on our site. Ask follow up questions if you need to.
  • 100% Satisfaction GuaranteeRate the answer you receive.

JustAnswer in the News:

Ask-a-doc Web sites: If you've got a quick question, you can try to get an answer from sites that say they have various specialists on hand to give quick answers... Justanswer.com.
JustAnswer.com...has seen a spike since October in legal questions from readers about layoffs, unemployment and severance.
Web sites like justanswer.com/legal
...leave nothing to chance.
Traffic on JustAnswer rose 14 percent...and had nearly 400,000 page views in 30 days...inquiries related to stress, high blood pressure, drinking and heart pain jumped 33 percent.
Tory Johnson, GMA Workplace Contributor, discusses work-from-home jobs, such as JustAnswer in which verified Experts answer people’s questions.
I will tell you that...the things you have to go through to be an Expert are quite rigorous.

What Customers are Saying:

I was having a terrible problem with the wheel bearings on my 98 Chevy Cavalier and I suspect that using this website saved me plenty of time and money.

Todd LRochester NY

Wonderful service, prompt, efficient, and accurate. Couldn't have asked for more. I cannot thank you enough for your help.

Mary C.Freshfield, Liverpool, UK

This expert is wonderful. They truly know what they are talking about, and they actually care about you. They really helped put my nerves at ease. Thank you so much!!!!

AlexLos Angeles, CA

Thank you for all your help. It is nice to know that this service is here for people like myself, who need answers fast and are not sure who to consult.

GPHesperia, CA

I couldn't be more satisfied! This is the site I will always come to when I need a second opinion.

JustinKernersville, NC

Just let me say that this encounter has been entirely professional and most helpful. I liked that I could ask additional questions and get answered in a very short turn around.

EstherWoodstock, NY

Thank you so much for taking your time and knowledge to support my concerns. Not only did you answer my questions, you even took it a step further with replying with more pertinent information I needed to know.

RobinElkton, Maryland

< Previous | Next >

Meet the Experts:

GM Tech (Cam)

GM Tech (Cam)

Chevy Technician

29,652 satisfied customers

GM Grand Master Technician 2007. 14 years experience.

Gary

Gary

Chevy Technician

9,357 satisfied customers

15 years GM master tech

Tim&#039;s Auto Repair

Tim's Auto Repair

mechanic

8,866 satisfied customers

Have owned a repair shop for 25 yrs.

Dave Nova

Dave Nova

Chevrolet Technician

7,092 satisfied customers

ASE Master Certification. GM World Class Certification

John

John

Master A.S.E Automotive technician

4,071 satisfied customers

A.S.E MasterTechnician A1-A8 w/L1,38 years experience General Motors Master Technician

Don - Mo Lurch

Don - Mo Lurch

Auto Mech / Electronics

2,918 satisfied customers

Chevrolet Cert., Heavy Line Mech, Race Shop Owner, Mobile Electronics.

Ron Z.

Ron Z.

- Chevy Tech -

2,734 satisfied customers

18+yrs experience. State Inspector and Chevy Diagnostics

< Previous | Next >

Related Chevy Questions
My water from the radiator is mixing in with my engine oil.
My water from the radiator is mixing in with my engine oil … read more
kwiggins29059
kwiggins29059
Associate Degree
219 satisfied customers
I already change the spark plugs and wires on a Malibu 2003
I already change the spark plugs and wires on a Malibu 2003 Chevy it won't start … read more
kalamykid
kalamykid
Pactor automotive
Vocational, Technical or Trade Scho
97 satisfied customers
I need my engine rebuilt. Cracked the radiator and
I need my engine rebuilt. Cracked the radiator and overheated the engine. Lost power and won't run now. … read more
rpmdiag
rpmdiag
High school
7,267 satisfied customers
New engine, new starter, radiator, distributer ,coil, map
new engine, new starter, radiator, distributer ,coil, map sensor in '1993 Chevy Silverado K2500 7.4L 4L80E trans, setting code 42.. Also new ignition module … read more
Cesar Jimenez
Cesar Jimenez
Owner/CEO
Vocational, Technical or Trade School
84 satisfied customers
Engine light on" clean exhaust filter continue to dric. Ve
engine light on " clean exhaust filter continue to dric … read more
BOBBYSS
BOBBYSS
TECHNICIAN/ADVISOR
Associate Degree
8,343 satisfied customers
Won't start, get spark from the spark plugs, have put gas in
won't start, get spark from the spark plugs, have put gas in the intact still won't start. Starter is turning all the belts … read more
heavy_chevy_396
heavy_chevy_396
Vocational, Technical or Trade Scho
2,518 satisfied customers
2014 Chevy Silverado 4.3 cylinder two misfire a spark plug
2014 Chevy Silverado 4.3 cylinder two misfire a spark plug is looks like it's wet with gasolineAlso engine code P0106… read more
fordguy4u
fordguy4u
Automotive Tech
Vocational, Technical or Trade Scho
70 satisfied customers
Pulled spark plug out and fuel came out with the plug.
pulled spark plug out and fuel came out with the plug. … read more
Dan
Dan
Automotive Technician
Vocational, Technical or Trade Scho
25 satisfied customers
Misfire code p0306 I️ changer distributor cap spark plug and
Misfire code p0306 I️ changer distributor cap spark plug and wires new fuel pump don't understand why code is appearing … read more
Gary
Gary
Senior Technician
Vocational, Technical or Trade School
58 satisfied customers
My catalytic converter went on my 2008 Impala I think
My catalytic converter went on my 2008 Impala I think because I had a wiring problem that made the fuse blow that controlled the circuit for the O2 sensors. Also I had a AIR valve that was stuck in th… read more
Chris (aka - Moose)
Chris (aka - Moose)
Vocational, Technical or Trade Scho
108 satisfied customers
My catalytic converter failed a couple of years ago. I think
My catalytic converter failed a couple of years ago. I think it was a combination of a stuck AIR valve and a wiring problem that kept causing the fuse that controls both O2 sensors and the EVAP soleno… read more
fordguy4u
fordguy4u
Automotive Tech
Vocational, Technical or Trade Scho
70 satisfied customers
Misfire in cylinder #1 replaced coil and spark plugs, engine
misfire in cylinder #1 replaced coil and spark plugs, engine light on and flashing. Put in injector cleaner also. … read more
eauto
eauto
self employed
High School or GED
74 satisfied customers
Crank, no start. fuel pump is working. spark plugs (I think)
crank, no start. fuel pump is working. spark plugs (I think) are firing. … read more
eric remington
eric remington
FORMER SHOP OWNER/TECHNICIAN/INSPECTOR
associates degree
293 satisfied customers
I Want To Take Out The CATALYTIC CONVERTERS on my 2005 chevy
I Want To Take Out The CATALYTIC CONVERTERS on my 2005 chevy malibu can i disconect the stabilyzer ends and tist it to remove the cat … read more
AMEDEE
AMEDEE
AUTOMOTIVE TECHNICIAN
Vocational, Technical or Trade Scho
9,105 satisfied customers
Pete again, lack of power like a catalytic converter is
Hey Pete again, lack of power like a catalytic converter is stopped up or air filter stopped up, no codes, checked back pressure on pre-cat 02 sensors and after cats, doesnt appear to have stopped up … read more
Pete
Pete
Independent Auto Technician
Vocational, Technical or Trade Scho
138 satisfied customers
The check engine is on. I have changed all the spark plugs
Hi the check engine is on. I have changed all the spark plugs and core and ignition core. … read more
GM Tech (Cam)
GM Tech (Cam)
Chevy Technician
29,652 satisfied customers
Knock sensor on bank 2, catalytic converter on bank 2 codes
knock sensor on bank 2, catalytic converter on bank 2 codes on 4.3 liter 2011express van … read more
Ron Z.
Ron Z.
- Chevy Tech -
Vocational, Technical or Trade Scho
2,734 satisfied customers
The catalytic converter. Is it worth the cost to replace it?
the catalytic converter. Is it worth the cost to replace it? … read more
Ron Z.
Ron Z.
- Chevy Tech -
Vocational, Technical or Trade Scho
2,734 satisfied customers
Disclaimer: Information in questions, answers, and other posts on this site ("Posts") comes from individual users, not JustAnswer; JustAnswer is not responsible for Posts. Posts are for general information, are not intended to substitute for informed professional advice (medical, legal, veterinary, financial, etc.), or to establish a professional-client relationship. The site and services are provided "as is" with no warranty or representations by JustAnswer regarding the qualifications of Experts. To see what credentials have been verified by a third-party service, please click on the "Verified" symbol in some Experts' profiles. JustAnswer is not intended or designed for EMERGENCY questions which should be directed immediately by telephone or in-person to qualified professionals.

Disclaimer: Information in questions, answers, and other posts on this site ("Posts") comes from individual users, not JustAnswer; JustAnswer is not responsible for Posts. Posts are for general information, are not intended to substitute for informed professional advice (medical, legal, veterinary, financial, etc.), or to establish a professional-client relationship. The site and services are provided "as is" with no warranty or representations by JustAnswer regarding the qualifications of Experts. To see what credentials have been verified by a third-party service, please click on the "Verified" symbol in some Experts' profiles. JustAnswer is not intended or designed for EMERGENCY questions which should be directed immediately by telephone or in-person to qualified professionals.

Show MoreShow Less

Ask Your Question

x