Medium and Heavy Trucks

Have Truck Repair Questions? Ask an Expert

Ask an Expert,
Get an Answer ASAP!

Medium and Heavy Trucks

I have a 2002 gmc 6500 with a 3126. The truck starts hard in

Customer Question
the cold but if you...
I have a 2002 gmc 6500 with a 3126. The truck starts hard in the cold but if you plug it in, it fires right up. The wait to start light comes on for about two seconds then goes off. I have power at the connector for the solenoid. There is power at the big wire on the solenoid also. I do not get a ground from the computer. I ohmed out the wire to the computer it is is fine. If I unplug the air temp sensor the light will stay on in the truck for about 30 seconds but the power still doesn't go to the intake heater. I also cannot connect my scan tool to the truck to see what the intake and coolant sensors are reading, I'm not sure why it won't connect. The serial number of the motor is ckm38790
Submitted: 2 years ago.Category: Medium and Heavy Trucks
Show More
Show Less
Ask Your Own Medium and Heavy Trucks Question
Answered in 4 minutes by:
9/26/2015
Technician: Cat Man, Cat Engine Expert replied 2 years ago
Cat Man
Cat Man, Cat Engine Expert
Category: Medium and Heavy Trucks
Satisfied Customers: 9,006
Experience: I am ASE Master Truck Certified.
Verified

Thanks for asking your question. I will try and help you out.

What is the temperature where you are at?

When you say it starts hard, do you mean it's hard to start? Does it run rough at start up? Or does it not start?

Ask Your Own Medium and Heavy Trucks Question
Customer reply replied 2 years ago
the morning it wouldn't start it was About 40 degrees out. The truck would crank and puff a little White smoke but not start. I plugged it in for about 45 min and it fired right up
Technician: Cat Man, Cat Engine Expert replied 2 years ago

Thanks for the information.

If it's 40 degrees the inlet heater should stay on. The ECM will leave the heater on until the sum of the coolant temp and intake air temp exceed 120 degrees.

But to be honest. The engine should not have any trouble starting in 40 degrees. The inlet heater is not there to start the engine but to eliminate smoke at start up. It's an emissions thing.

I would suspect you have another problem.

The first is a low or no fuel pressure condition. The engine needs at least 25 psi to start. If it is low, the injectors will not get filled and it will not start. If the engine has a hand priming pump, and it gets stiff when operating it, the engine has enough pressure to start. If there is no hand priming pump, I would connect a psi gauge and measure the pressure. If the pressure is low, I would change the fuel filters first if you haven’t already. If it is still low, I would suspect a failed fuel pressure regulator on the back of the head or a weak fuel transfer pump. The pump is located on the back of the HEUI pump.

Second is a low injection actuation pressure. This is the high pressure oil system that activates the injectors. The engine needs at least 870 psi to start. If it is low, you have either a failed Injection actuation pressure control valve in the HEUI pump, a weak HEUI pump, a high pressure oil leak at an injector, or a faulty Injection actuation pressure sensor. To test the sensor, just unplug it. If the engine starts, the sensor is bad. It has 3 wires and is located on top of the engine near the front and screwed into the head.

Third is a failed engine speed timing sensor. Your engine has two. They are located on the driver’s side of the engine on the back of the engines front cover under the HEUI pump. The bottom sensor is the primary start sensor. If it has failed, the engine will be hard to start. The top one is the primary run sensor. They come as a pair.

Next is low battery voltage to the ECM while cranking. The ECM must have at least 7.5 volts DC to operate. I have seen weak batteries or a poor connection cause low voltage. You could have a poor connection at the batteries or starter.

Next is a faulty engine ECM. The ECM has an injector driver module inside. This is what powers the injectors. If it fails, the ECM will log injector codes for all the injectors.

Lastly are worn injectors. Over time the injectors can wear if they have a lot of hours on them. To verify, I like to check AC to the injectors while cranking. You should have between 20-40 AC while cranking. If you do, and you have good fuel pressure, the injectors are worn.

Most often when these things are happening there will be diagnostic codes in the ECM. If your engine has cruise control switches, you can pull the codes. If you have never done this, let me know. I can get you the procedure.

Please reply back if you need more help or have more questions. I am happy to assist.

Ask Your Own Medium and Heavy Trucks Question
Customer reply replied 2 years ago
The truck has a new transfer pump and regulator that are about 2 months old. So I might have another problem but there is also one with the intake heater also correct?
Technician: Cat Man, Cat Engine Expert replied 2 years ago

Yeah I would think so. It should stay on for a minute or so at 40 degrees.

Please reply back if you need more help or have more questions. I am happy to assist.

Ask Your Own Medium and Heavy Trucks Question
Customer reply replied 2 years ago
why when I unplug the intake temp sensor the light in the truck stays on for 30 seconds but the intake heater doesn't have power. And also do you know what to check for when my scan tool won't communicate with the truck
Technician: Cat Man, Cat Engine Expert replied 2 years ago

The ECM will want to keep the light on when there is a fault with the inlet heater. Since it does not know the inlet temp. It will keep the light and heater on.

Most often when a scan tool will not communicate. There is a problem with the wiring from the connector to the ECM.

Ask Your Own Medium and Heavy Trucks Question
Customer reply replied 2 years ago
Also out of all those possible causes which one could it be if plugging the block heater in makes it start right up
Customer reply replied 2 years ago
Do you have a wiring diagram of the data link connector
Technician: Cat Man, Cat Engine Expert replied 2 years ago

I would suspect an engine speed timing sensor problem. I have seen them be the problem when cold but not when hot. I will see if I can find a diagram.

Ask Your Own Medium and Heavy Trucks Question
Customer reply replied 2 years ago
Thank you that would be great
Technician: Cat Man, Cat Engine Expert replied 2 years ago

All I have is the wiring connections for the ECM. It shows where the data wires connect to the ECM. I hope this helps.

http://www.dropbox.com/s/fhgnic1lfrmswsm/data.jpg?dl=0

Ask Your Own Medium and Heavy Trucks Question
Ask Cat Man Your Own Question
Cat Man
Cat Man
Cat Man, Cat Engine Expert
Category: Medium and Heavy Trucks
Satisfied Customers: 9,006
9,006 Satisfied Customers
Experience: I am ASE Master Truck Certified.

Cat Man 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:

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

He answered my question promptly and gave me accurate, detailed information. If all of your experts are half as good, you have a great thing going here.

DianeDallas, TX

< Previous | Next >

Meet the Experts:

Daniel Wilson

Daniel Wilson

2,139 satisfied customers

Owner at DJ Wilson

Cat Man

Cat Man

Cat Engine Expert

9,006 satisfied customers

I am ASE Master Truck Certified.

Wayne

Wayne

Journeyman

2,495 satisfied customers

worked on, Gmc, Macks, Freight liner,Mercedes Benz,,Ford, sterling

Jeremy

Jeremy

Certified Truck/Bus Technician

1,974 satisfied customers

ASE Med/HD Truck Technician, NATEF Diesel Engines and Electrical/Electronics Technician, EPA 608/609 HVAC Certified, Steering/Suspension and ABS/Brakes Technician

cumminsdr

cumminsdr

Mechanic

1,195 satisfied customers

All types of Cummins applications

Curtis B.

Curtis B.

Technician

770 satisfied customers

Technician turned service manager on multiple lines of trucks and engines, used in industry.

dieseldan55

dieseldan55

Contractor

74 satisfied customers

Road Service mechanic for Volvo Construction.

< Previous | Next >

Related Medium and Heavy Trucks Questions
I'm a new operator. How do you turn on a liebherr tower
I'm a new operator. How do you turn on a liebherr tower crane and also weathervane it ? … read more
Daniel Wilson
Daniel Wilson
Auto Mechanics 1&2/diesel mech
2,139 satisfied customers
How many hours on my D6R cat can i expect to run without
how many hours on my D6R cat can i expect to run without engine transmission and undercarriage overhaul … read more
catmastertech
catmastertech
Field service technician
Vocational, Technical or Trade Scho
1,287 satisfied customers
My E350 van has a lot of heat and unwanted air coming in
Hello, my E350 van has a lot of heat and unwanted air coming in around the passenger feet area. Even when the vent is off lots of air, sometimes smelling slighlty of exhaust is coming in. The origin s… read more
Pete
Pete
Independent Auto Technician
Vocational, Technical or Trade Scho
138 satisfied customers
Dertoit 14 frighliner 2005. I changed ecu fuse, restart with
I changed ecu fuse , restart with take off negative from battery … read more
spankyjr1
spankyjr1
Retired
Vocational, Technical or Trade Scho
19 satisfied customers
2009 freightliner Detroit 60 14L. Throwing fault code ECU
2009 freightliner Detroit 60 14L. Throwing fault code ECU 128 SID 154 Fail 00. I cant figure out what code this is.… read more
Wayne
Wayne
Journeyman
Vocational, Technical or Trade Scho
2,495 satisfied customers
I HAVE A 2015 Freightliner cascadia DD15 with a headache
I HAVE A 2015 Freightliner cascadia DD15 with a headache code 5246 FMI 15 … read more
roy
roy
Associate Degree
3 satisfied customers
I have frightlinet detroit series 60 chck engin light on eng
I have frightlinet detroit series 60 chck engin light on cod eng sht hi 128 351 00 and eng sh hi 128 351 03 … read more
Daniel Wilson
Daniel Wilson
Auto Mechanics 1&2/diesel mech
2,139 satisfied customers
09 Isuzu F Series Medium Duty A/C compressor will not
09 Isuzu F Series Medium Duty A/C compressor will not engage. … read more
Andy3221
Andy3221
truck /coach technician
Vocational, Technical or Trade Scho
222 satisfied customers
Need to set injector pump timing while pump is installed.
Need to set injector pump timing while pump is installed … read more
FIX-IT
FIX-IT
Comercial transport technician
Vocational, Technical or Trade Scho
784 satisfied customers
Getting a 12 8 code. Seemed to Have lack of power. Smoke,
Getting a 12 8 code. Seemed to Have lack of power. Smoke, maybe coolant burning coming out of ac vents, Stop Engine light comes on if a wait a few minutes any try to drive away. Water temp seems to be… read more
Daniel Wilson
Daniel Wilson
Auto Mechanics 1&2/diesel mech
2,139 satisfied customers
I HAVE COOLANT GETTING INTO OIL ENGINE REBUILT 50,000. MILES
I HAVE COOLANT GETTING INTO OIL ENGINE REBUILT 50,000. MILES AGO WHAT IS CAUSE? … read more
Curtis B.
Curtis B.
Technician
Associate Degree
770 satisfied customers
We have a 2004 freightliner schoolbus. something is going on
we have a 2004 thomas freightliner schoolbus. something is going on with our tail lights. they suddenly stopped working... … read more
Daniel Wilson
Daniel Wilson
Auto Mechanics 1&2/diesel mech
2,139 satisfied customers
2009 Peterbilt with isx Cummins on insite trying to do a
2009 Peterbilt with isx Cummins on insite trying to do a stationary regen says clutch pedal is depressed just put in new clutch switch still says depressed try to bypass with jumper wire still says de… read more
FIX-IT
FIX-IT
Comercial transport technician
Vocational, Technical or Trade Scho
784 satisfied customers
Will turn but will not fire. 2006 Mack Granite with AMI_370
will turn but will not fire. 2006 Mack Granite with AMI_370 engine. … read more
Daniel Wilson
Daniel Wilson
Auto Mechanics 1&2/diesel mech
2,139 satisfied customers
It turns over but doesn't crank warn engine light flashing
It turns over but doesn't crank warn engine light flashing very fast … read more
Wayne
Wayne
Journeyman
Vocational, Technical or Trade Scho
2,495 satisfied customers
2009 freightliner century with Detroit 60 series. I have a
2009 freightliner century with Detroit 60 series. I have a basic scanner and scanned what the check engine light was and the code came up (003662 14 spn). What can this be?… read more
Wayne
Wayne
Journeyman
Vocational, Technical or Trade Scho
2,495 satisfied customers
My Rv shut down codes are SPN627 and FN12. I am not sure I
I have not tried anything except trying to start engine just trying to determine where to take it for repairs … read more
cumminsdr
cumminsdr
Mechanic
High School or GED
1,195 satisfied customers
I am getting DPF fuel pressure voltage and EGR delta
I am getting DPF fuel pressure voltage and EGR delta pressure and fuel delivery pressure codes on a 2012 pack at motor … read more
Daniel Wilson
Daniel Wilson
Auto Mechanics 1&2/diesel mech
2,139 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