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Cat Man
Cat Man, Caterpillar Engine Expert
Category: Heavy Equipment
Satisfied Customers: 6145
Experience:  23 Years Caterpillar Engine experience.
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I have a 2000 chevy c 6500 witha cat 7.2 liter 3126 motor,

Customer Question

I have a 2000 chevy c 6500 witha cat 7.2 liter 3126 motor, stalled while rolling to a stop out
of gear, motor starts and runs for a few seconds with ether, has 30 pounds of oil pressure
when cranking, over 50 for the few seconds that it does start, fuel primer is pressurised, i do
know that the injector orings are leaking slightly, i do not know how to check for ignition
spark, have any suggestions, could this just be a fuse or relay problem?


dave
Submitted: 3 years ago.
Category: Heavy Equipment
Expert:  Cat Man replied 3 years ago.

Hi. Thanks for using JA! I will try and help you out.

 

I would like to ask you a few questions first, I hope that is OK.

 

Could you get me your engine serial number please?

 

When you say the fuel primer is pressurised, are you saying that when you activate it, it gets stiff and you can here the relief valve popping off?

 

Did the engines check engine light come when it shut down?

 

If it did, I would suggest pulling the flash codes from the ECM. Here is how to pull them.

 

 

Use the following procedure to retrieve the flash codes if the engine is equipped with a diagnostic lamp:

  1. Turn the ignition key to the ON position/Engine off.
  2. Turn the cruise control ON/OFF switch to the OFF position.
  3. Move the SET/RESUME switch to either position. Hold that position until the yellow lamp begins to flash.

The yellow lamp will flash in order to indicate a two digit flash code and the SET/RESUME switch may be released. The sequence of flashes represents the system diagnostic message. Count the first sequence of flashes in order to determine the first digit of the flash code. After a two second pause, the second sequence of flashes will identify the second digit of the flash code.

Customer: replied 3 years ago.
Cat Man,the engine serial number is XXXXX check engine light came on,as far as the fuel primer it has pressure when you unscrew the primer rod and push the rod down it is very difficult to push down,as far as hearing the pressure relief pop i havent heard that,i have changed the fuel filters in the past and have had to use the primer and it took several pumps to get it pressurised but still never heard a pressure releif pop,in this case it seems to already have pressure,is possible could you call me to speed up this process,this is a flatbed tow truck and my only source of income and i could stand to lose hundreds of dollars a day,thanks ,Dave XXX-XXX-XXXX
Expert:  Cat Man replied 3 years ago.

Thanks for the information.

 

Sorry. JA does not allow any other contact other than on here. Sorry.

 

Since you have pressure on the hand primer, I assume that the engine has enough pressure to crank. You may not here a popping on an 8YL engine.

 

There are only a few other things that can cause the engine not to crank and run.

 

First is power to the ECM. A good way to tell is the ECM is getting power is the check engine light. When you turn the key to the on position, the check engine light should come on then go off. If it does not come on, the ECM is not getting power. I would check the fuses.

 

Second is the engine speed timing signal. This signal comes from the 2 sensors that are located on the drivers side of the engine, behind the front cover.

 

Third I would be concerned with what is called the Injection Actuation Pressure Control valve. Or IAPCV. It is located on the HEUI pump and is a known problem on these engines. When these fail, it can keep the engine from starting and running. If the IAPCV has failed, the ECM normally has flash code 39 logged.
Customer: replied 3 years ago.
Cat Man,the check engine light is working properly,lighting and then going off,i am going to check for codes as you described and will get back to you shortly,as far as the sensors go could you be more descriptive on where they are,what they look like or what type of plug/wires are connected to them,as far as the IAPCV and HEUI pump goes i have no idea where these are located or what they look like,i did perform the code test as you described and no codes were left,thanks,Dave
Expert:  Cat Man replied 3 years ago.

Thanks for the information. Here are the locations of the components,

 

http://dl.dropbox.com/u/11922365/IAPCV%20ESTS.doc <<<<<<<<< click here

Customer: replied 3 years ago.
Cat Man,I did reply to you about the link you sent me not being able to load on my computer and you never replied,however I did call a Cat Dealer here in Ohio and they faxed me a photo copy that showed where the sensors were located,also you never explained to me where the IAPCV valve and HEUI pump was located,I also had a local diesel mechanic come out with a diagnostic machine but he claims that the VIN number isnt coming up properly in his machine,his machine was saying that my truck is a 2005 so he was of no help either,he also said that my truck should have two diagnostic ports,one rectangular and one round but he could not locate the round one,so I am kind of at my wits end here and losing my patience so I went ahead and ordered the two Engine Speed Timing Sensors at 123.00 a pop and will install them sometime Monday and if that takes care of the problem you will be paid for your time,I have used this site once before for a problem I was having with my 99 Ford Explorer that suddenly cut out,but before I found this sight I had it put on a diagnostic and it said that 6 sensors were bad,so thinking that sounded pretty crazy to me that 6 sensors suddenly went at the same time I used this site and asked a few mechanics what could be the cause,gave them the code that the diagnostic was giving but none of the answers seemed satisfactory to me due to the fact that the sensors they were referring to were in the transmission and this was a "no start" problem,then one mechanic simply said "check fuse number 13 under the hood" so I did and that was the problem,a simple fuse when all these other mechanics wanted me to replace sensors that arent cheap
Expert:  Cat Man replied 3 years ago.

I'm sorry, I did not receive a reply about the link not being able to load.

 

Let me know how you make out.

Customer: replied 3 years ago.
Cat Man,I just replaced both the engine speed timing sewnsors and the truck still will not fire,any suggestions on what to do next,could it be the injector o-rings?
Expert:  Cat Man replied 3 years ago.
It is possible that injector o rings could cause this but if they caused the engine to shutdown, you should have gotten a check engine light.

Were you able to pull any flash codes from the ECM?
Customer: replied 3 years ago.
no i havent had any luck with diagnostics,the cruise control doesnt work so i am not able to check the ecm that way,the engine light does come on when you turn the key to the on position and stays lits for a couple seconds then goes out,i had a deisel mechanic come out with a diagnostic machine but he said he could not make any sense of it because his machine was saying my truck is a 2005,he also said that my truck should have two diagnostic ports,one round and one rectangular but mine only has the rectangular,i did replace the starter last year and the first one they gave me going off the year was the wrong one,thestarter that worked was a 1999,so im going to call the dealer with my vin and try to find out whats going on there,also i was told that if i unplug the IAP sensor and the truck starts ( but will only rev to 1700 rpm) that the IAP sensor is bad,do you have any idea where that sensor is or what it looks like?
Expert:  Cat Man replied 3 years ago.
Yes. It is a 3 wire sensor and it is located on top of the cylinder head near the front.
Customer: replied 3 years ago.
Cat Man,i found the sensor and unplugged it and still no start,i did call the dealer and they say that 1999 and 2000 motors are the same,any suggestions?
Expert:  Cat Man replied 3 years ago.
They are the same. That is correct.

The only other thing I can think of is an Injection Actuation Pressure Control Valve. This valve is what creates the hydrualic pressure for the injectors. It is located on the HEUI pump and has a 2 wire connector hooked to it.


But like I said earlier, if this valve is bad, you will have a flash code 39.
Customer: replied 3 years ago.
Cat Man,first i want to thank you for your patience and time,i cannot seem to find anyone out here with the correct diagnostic machine for my truck,i have been on the phone with cat of ohio and they told me it could be the fuel pressure regulator valve or the IAPCV like you said but that sensor is 190.00,the regulator valve is 90.00,are these two things the most likely culprits left,seeing as i cannot find anyone with the correct diagnostic equipment i may just buy the sensor and or the regulator valve,any suggestions?
Expert:  Cat Man replied 3 years ago.
You are very welcome.



Since you can't find anyone with diagnostic tooling, I guess all you can do is try these parts.


But before you do, remove the valve cover from the engine and monitor the injectors while the engine is being cranked, it is possible that one of you injectors may be leaking high pressure oil and causing it not to crank. If there is a leak, it may be coming from the top o ring on an injector, or leaking from the injector itself.
Customer: replied 3 years ago.
Cat Man,my driver just told me that at the time this happened he heard a pop from under the hood,not the exhaust,could that have been one of the injector o-rings giving out,also i cant seem to find the pressure regulator i was told about by cat ohio,he said it was a 90 degree elbow located near the rear of the motor,any suggestions
Expert:  Cat Man replied 3 years ago.
The fuel pressure regulator is on the back of the head. The return fuel line is connected to it.



Yes. The pop he heard could have been an injector o ring or possibly the HEUI pump itself.
Customer: replied 3 years ago.

Catman,is the regulator accesssible from under the hood or from underneath the truck,also what actually is the pumps function and do you have any idea what the pump costs?

Expert:  Cat Man replied 3 years ago.
The regulator is accessable under the hood. If your truck has a doghouse, it is easier to get too.

The HEUI pump make the high pressure oil to activate the injectors. The injectors need a minimum of 870 psi to crank. If there is a leak at an injector, a failed IAPCV, or HEUI pump, the engine may not run.
Customer: replied 3 years ago.
Cat Man,what is the process of finding out if the HEUI pump is bad?
Expert:  Cat Man replied 3 years ago.

You will need a 5000 psi gauge. You hook it to the metal output line of the pump that connects to the head. Once it is installed, you crank the engine. Of course the engine will not start. But you must have 4000 psi steady (no fluctuation) while cranking. If the gauge fluctuates or does not make 4000 psi, either the valve is bad or the pump. If it fails the test, I would replace the Injection Actuation Pressure control valve first then retest.

 

Please be careful. This high pressure oil can be very dangerous.

Customer: replied 3 years ago.
CatMan,so its not something that could be diagnosed with codes,or engine oil pressure while cranking,or by taking the valve cover off and if an o-ring is shooting oil past the injector,the pressure test is the only way of determining that the pump is bad
Expert:  Cat Man replied 3 years ago.

Basically, if te engine has a problem with the High pressure oil, it could be caused by the HEUI pump or an injector.

 

Pressure testing the pump, or deadhead testing it as it is sometimes called, is just the procedure to diagnois the HEUI pump.

 

If there is an injector leaking oil, you do not need to test the pump.

Customer: replied 3 years ago.
CatMan,out of everything we`ve talked about how likely is it that the problem is the pump,is it a common problem with my particular cat motor,we already know the the o-rings are leaking so if i pull off the valve cover and crank the motor and see oil spraying from around the injectors that means the pump is good,correct?
Expert:  Cat Man replied 3 years ago.
HEUI pumps are not a common problem on these engines. They are pretty relyable. The most common problem is the injection actuation pressure control valve on the pump.


Yes. If you see an injector leaking, your HEUI pump and valve are OK.
Cat Man, Caterpillar Engine Expert
Category: Heavy Equipment
Satisfied Customers: 6145
Experience: 23 Years Caterpillar Engine experience.
Cat Man and other Heavy Equipment Specialists are ready to help you
Customer: replied 3 years ago.
Cat Man,Thanks for your time and I will accept your answer so you can be paid,also if I want to talk to you again how do i do that?
Expert:  Cat Man replied 3 years ago.
You are very welcome.



All you have to do in the future is ask for Catman is your original question. I will be sure to get it.
Customer: replied 3 years ago.
OK Cat Man,again I appreciate everything you`ve done and will be sure to ask for you in the future,and I apologize about the difficulties and how much of your time this has taken,Dave
Expert:  Cat Man replied 3 years ago.
No problem. Glad I could help.
Customer: replied 3 years ago.
Cat Man,I wanted to leave you a tip,after i accepted your answer it went to another page where i could enter my tip for you but there was no where to submit it,Dave
Expert:  Cat Man replied 3 years ago.
That is OK. Thanks for the accept.
Customer: replied 3 years ago.
Catman,I just put 27.00 dollars into my account,it was meant to go to you,how do i get it to you?
Expert:  Cat Man replied 3 years ago.
When you clicked on accept, I got paid. All is good.
Customer: replied 3 years ago.
Cat Man are you online now?
Expert:  Cat Man replied 3 years ago.
Yes.
Customer: replied 3 years ago.
ok this is dave,the one that has the 7.2 cat 3126b,i have had several diagnostics tests done and still will not start,i replaced both timing sensors,the iap sensor that goes on top of the cylinder head and have replaced the solenoid on the heui pump,had the pump tested and it rated at 4200 psi,this was done by a cat mechanic with the correct software,he claims that i am ot getting any voltage or high pressure to my injectors,so now he is saying that i may havea crack in my head which is leading to the loss of pressure,im not buying it due to the auto shutdown my truck has and the fact that the motor was running fine and was not running hot,in fact it has never run hot enough to shut it down,any suggestions,also do you know what the voltage should be at the injectors,dave
Expert:  Cat Man replied 3 years ago.
I have never seen a cracked head cause low injection actuation pressure. However I have seen a leaking injector cause this. If you have 4200 on the pump that is good. By chance did the cat tech put the gauge in the head and measure the pressure there? The engine needs 870 psi to start.

If you haven't already, I would remove the valve cover and see if you can see a leak why cranking the engine.

As far as the injectors, you may see around 30 AC while cranking but could get up to 90 AC while running.


Customer: replied 3 years ago.
no he checked the pressure at the back of heui pump by disconnecting the line
Expert:  Cat Man replied 3 years ago.
It sounds to me like you may have a high pressure oil leak under the valve cover. I would remove the valve cover and crank the engine and look for a leak. If you have a leak, it should be easy to see. BE CAREFUL. High pressure oil is dangerous.
Customer: replied 3 years ago.
yeah i did that before when you and i were working on this and i didnt see any oil activity anywhere
Expert:  Cat Man replied 3 years ago.
I see. Well if the head is cracked, the oil should be going somewhere.

You may want to disconnect the injector harness just outside the valve cover and connect an AC meter to one of the injector wires, then crank the engine. If you are getting AC, the ECM is trying to start the engine. If you are not getting any AC, there is an electrical problem.
Customer: replied 3 years ago.
the injector test was performed and it came back no voltage,how is the engine oil that feeds the injectors returned to sump,is there an oil regulator somewhere,scanner said zero oil pressure but when test was done manually by deadheading at the outpurt port of the heui pump it read 4200psi,
Expert:  Cat Man replied 3 years ago.
The oil is returned to the engine from the injector. It spills the oil out onto the top of the engine.

There is no oil regulator.
Customer: replied 3 years ago.
Catman,seeing that the pressure we are talking about ,if the head was cracked would i still see some oil activity under the valve cover or would a crack be enough to drop the pressure so low that you wouldnt see any activity at all,also seeing that the motor wasnt running hot what do you think is the most likely,a crack or bad injector seals?
Expert:  Cat Man replied 3 years ago.
I would lean more towards injector o rings.
Customer: replied 3 years ago.
so if there was a crack in the head you likely would see some oil activity even though the head is cracked?
Expert:  Cat Man replied 3 years ago.
Yes you would. If the crack was on top oil would be going everywhere.


The crack could also be into the fuel or cooling system as well.
Customer: replied 3 years ago.
ok so if there was a crack we would most likely see activity unless its going into the cooling system and if an o-ring was bad we wouldnt see any activity at all?
Expert:  Cat Man replied 3 years ago.
Yes. That is correct.
Customer: replied 3 years ago.
ok one more question referring to the pop i heard right before this happened,if the head cracked would i hear it,or if an o-ring went would i hear that?
Expert:  Cat Man replied 3 years ago.
I would think you would not hear a head crack. I would think you would possibly hear an o ring.
Customer: replied 3 years ago.
ok,i have another question,i just went out to the truck and checked the water pump belt,it is somewhat loose but still tight enough to turn the water pump,if the water pump was not turning like it should and allowing the motor to get hot wouldnt that show up on the temp gauge,because the temp gauge was reading normal as always
Expert:  Cat Man replied 3 years ago.
Yes. If the water pump belt was slipping the engine would have ran hot.
Customer: replied 3 years ago.
and that would have showed up on the gauge,correct,and if the belt was slipping to the point of overheating my auto shutdown would have occurred before any damage was done,correct?
Expert:  Cat Man replied 3 years ago.
Yes. If the engine would have overheated the check engine light would have come on and the engine would have shutdown.
Customer: replied 3 years ago.
ok now back to the o-rings,if an o-ring was bad it would show no pressure and no voltage to the injectors,correct?
Expert:  Cat Man replied 3 years ago.
Yes that is correct. If there is a leak it will cause the pressure to drop and because the pressure dropped, the ECM will not power the injectors.
Customer: replied 3 years ago.
ok now if the head was cracked would it show the same,no pressure and no voltage,or just no pressure?
Expert:  Cat Man replied 3 years ago.
Yes. If the head was cracked and causing low actuation pressure, the ECM would not fire the injecters. That is correct.
Customer: replied 3 years ago.
ok so if you were me what would you do seeing as i have already purchased the o-rings and have the valve cover off,this may be a no brainer but i have to ask,replace the o-rings and see what happens?
Expert:  Cat Man replied 3 years ago.
I would. If there is an o ring broken, you will see it when you remove the injector.

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