How JustAnswer Works:

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

Ask Hal Your Own Question

Hal
Hal, Chevy Master Tech
Category: Chevy
Satisfied Customers: 1021
Experience:  ASE and Chevy Master , 31yr Dealership exp,
39646262
Type Your Chevy Question Here...
Hal is online now
A new question is answered every 9 seconds

99 suburban: under load..Fuel pressure..engine running..fuel filter

Resolved Question:

my 99 suburban idles rough, smells of gas, has a loss of power, bogs down under load and backfires. My codes are a P0300 (random misfire) and a P0174 (lean fuel). Fuel pressure tested: key on engine off 61psi engine running 55psi it has a new fuel filter. the lean fuel code and the gas smell make no sense at all. Any ideas what is going on? Where I can start to trouble shoot?
Submitted: 4 years ago.
Category: Chevy
Expert:  Hal replied 4 years ago.

Hi my name is XXXXX XXXXX to just answers.

 

When did this concern start?

 

What injector spider does it have? the poppet style , or the updated injectors style?

 

Can you read the miss fire indicators to determine the cylinders that have the highest misfires? Or do you just have a code reader?

Customer: replied 4 years ago.
I just have a code reader. my brother in law has a more detailed one and he hooked his up. it did not pull a specific cylinder misfire. it came out random misfire. Not sure what style injectors I have. I bought it with the build already done.

It just started last week thursday night.

It just seems odd that I have excess fuel. (the fuel smell and the backfiring indicate I am getting plenty of fuel) I tend to think it is not the injectors. Since you can't "time" these motors what would cause the injectors to "spit" at the wrong time? Does my logic make sense?
Expert:  Hal replied 4 years ago.

Here is what can cause the back fire. Condensation inside the distributor cap can cause a cross fire. If it backfires inside the intake, It can cause the injector tubes to melt and excessive fuel will flood the engine . (fuel smell)

The timing can be set and must be within 2 deg of 0tdc. it is set by reading the cam sensor offset, on a scan tool. But if it has been running fine and no check engine light up to this point, that is not you concern.

 

Check the distributor cap for moisture and corrosion on the terminals.

Use a small flash light to look through the throttle body opening to inspect for melted fuel line tubes.

If they are melted , install the updated design. It is cheaper than buying individual injectors, and runs better.

 

A scan tool that has the capability of reading live engine data is needed to see the cylinder misfire indicators. A P0300 is random misfire. that means more than one cylinder shows misfires. but there is usually one or two that show more than the others , and can be isolated with the proper tool.

 

Thanks

Hal

Customer: replied 4 years ago.
If I check all these things and they come out fine what is a good list of things to continue to check and rule out after this. backfiring is only one of my issues.

Expert:  Hal replied 4 years ago.
When does it backfire?
Customer: replied 4 years ago.
only when I jump on it
Expert:  Hal replied 4 years ago.
I know this might sound simple , but have you inspected for carbon tracks on the outside of the spark plug insulators? Or pin holes in the plug boots? coil wire corrosion on the terminal?
Customer: replied 4 years ago.
no but I will. That was my next step in all this was to check all the ignition pieces. Let's assume that all checks out fine though. Is there anything else this could be? I have had people still trying to tell me it is my fuel pump. you have not mentioned it once. I don't have the $$$ to just dump into this thing. I want to logically and methodically rule out one thing at a time until I fix it! If you could just give me a run down of all the possibles starting with the most likely going to least likely I would greatly appreciate it.
Expert:  Hal replied 4 years ago.

You said you had 56 psi fuel pressure. Are you saying that is not the case?

Ignition concerns like moisture in the cap, carbon tracks on spark plugs, distributor timing( cam offset). these things when under a loaded condition will cause a cylinder misfire, low power and a backfire, when the spark plug starts to fire again, and there is a rich fuel mixture in the cylinder.

 

Connect your fuel pressure gauge up and drive it under the conditions of the low power and back fire. If it holds 55-60 psi, fuel pump is good. Fuel filters that are restricted can cause low power , but i have not had them cause a backfire.

 

#1 Look for a black carbon track, or a cracked spark plug insulator.

#2 inspect the spark plug boots for small pinholes. A small white burn witness mark on plug boot may be present if there is a hole in boot.

#3 Coil wire terminal connections.

#4 burn through marks in distributor cap.( look where two terminal come close together) this cap has terminals that cross the cap, and can jump through the cap material.

#5 P0174 rt bank lean fuel mixture. swap o2 sensors bank to bank and see if the lean condition follows the o2 sensor. ( it will set p0171) , if so it could be a skewed sensor and should be replaced. A sensor that creates a false lean condition , will cause the computer to richen up the injectors on that side. This can cause converter to overheat, and melt down, resricting exhaust flow. a pressure test can be performed on the cat to make sure it is not restricted.

 

These are the most common causes that I have run into . Just by changing plugs can cause the boot not to seal properly around the plug, This opens up the opportunity for moisture to get in and cause the spark to jump. Once it starts jumping to ground, it starts building a carbon track. The longer it goes on the more frequently it occurs.

If this is what you find, replace the spark plug and the plug wire, at the same time.

 

If you need more information, Please Ask.

Thank You

Hal

 

 

Customer: replied 4 years ago.
This makes logical sense to me! my fuel pressure does stay steady, but people kept saying it sounded like I had a bad fuel pump. That did not make any sense. What you are saying does make sense.

Thank you very much!
Expert:  Hal replied 4 years ago.

Most people think they know what can cause a condition but never actually have repaired one. You were right for questioning that thought process. You sound like you have a very logical thought process, and I hope the information I provided you will be helpful.

Please if you need more help with this concern or another, Please Ask. I will be more than glad to help.

Thank You.

Hal

Hal, Chevy Master Tech
Category: Chevy
Satisfied Customers: 1021
Experience: ASE and Chevy Master , 31yr Dealership exp,
Hal and 7 other Chevy Specialists are ready to help you

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 L Rochester NY
< Last | Next >
  • 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 L Rochester 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!!!! Alex Los 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. GP Hesperia, CA
  • I couldn't be more satisfied! This is the site I will always come to when I need a second opinion. Justin Kernersville, 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. Esther Woodstock, 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. Robin Elkton, Maryland
 
 
 

Meet The Experts:

 
 
 
  • Tim's Auto Repair

    mechanic

    Satisfied Customers:

    7641
    Have owned a repair shop for 25 yrs.
< Last | Next >
  • http://ww2.justanswer.com/uploads/TI/tim37857/2011-10-28_23053_S6301814.64x64.JPG Tim's Auto Repair's Avatar

    Tim's Auto Repair

    mechanic

    Satisfied Customers:

    7641
    Have owned a repair shop for 25 yrs.
  • http://ww2.justanswer.com/uploads/DT/dt69nova/2012-6-15_234154_pic1.64x64.jpg Dave Nova's Avatar

    Dave Nova

    Chevrolet Technician

    Satisfied Customers:

    6870
    ASE Master Certification. GM World Class Certification
  • http://ww2.justanswer.com/uploads/ggrote1/2009-06-27_031011_me.jpg Gary's Avatar

    Gary

    Chevy Technician

    Satisfied Customers:

    5404
    15 years GM master tech
  • http://ww2.justanswer.com/uploads/testedtuff/2009-09-26_170108_pictures.jpg John's Avatar

    John

    Master A.S.E Automotive technician

    Satisfied Customers:

    4071
    A.S.E MasterTechnician A1-A8 w/L1,38 years experience General Motors Master Technician
  • http://ww2.justanswer.com/uploads/RO/rodcuda/2011-7-25_224114_Donhoff1.64x64.JPG Neal's Avatar

    Neal

    Chevy Mechanic

    Satisfied Customers:

    2306
    Shop Owner and Mechanic on multiple makes.
  • http://ww2.justanswer.com/uploads/goodwrench9124/2008-11-09_220838_dscf0007.jpg goodwrench9124's Avatar

    goodwrench9124

    ASE Certified Technician

    Satisfied Customers:

    2041
    Ase Master Certified, GM Master Certified Tech. Awarded GM Top performer, Hybrid certified
  • http://ww2.justanswer.com/uploads/DR/drivefast1971/2012-1-12_172422_0009051tQKh.64x64.jpg Ron Z.'s Avatar

    Ron Z.

    - Chevy Tech -

    Satisfied Customers:

    1912
    18+yrs experience. State Inspector and Chevy Diagnostics
 
 
 
Chat Now With A Chevy Mechanic
Hal
Hal
owner/service tech
858 Satisfied Customers
ASE and Chevy Master , 31yr Dealership exp,