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Cat Man
Cat Man, Cat Engine Expert
Category: Medium and Heavy Trucks
Satisfied Customers: 8822
Experience:  I am ASE Master Truck Certified.
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, I have a 2000 gmc 6500 with a cat 3126, no start,

Customer Question

Customer: Hi there
JA: Thanks. Can you give me any more details about your issue?
Customer: I have a 2000 gmc 6500 with a cat 3126 , no start , some white smoke coming out tail pipe smells like raw fuel , how can I pull codes , it does not have cruise control
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Submitted: 1 year ago.
Category: Medium and Heavy Trucks
Expert:  Cat Man replied 1 year ago.

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

Unfortunately without cruise control switches, the only way to pull codes is to have a service tool like Cat ET connected. I am sorry.

Did the engine just not start one day?

Or did it shut down on you while driving?

Customer: replied 1 year ago.
no it did not shut down while driving , in fact it happen one morning ,cranked but would not start , found the intake heater solenoid burned out , replaced and also replaced fuel filter . , also found a oil leak from the HEPU to cylinder head , replaced also it was working just fine for 10 days and this morning the same thing happen, So I change the fuel filter and removed the bleeder plug and cranked for 30 sec twice with no fuel coming out , removed fuel filter and and only found it quarter full . I just checked for restriction in the fuel system none found and also if I cap off the end of the supply line at the tank with a vaccum gauge fuel pump it pulls 25 inchs which should be more than enough.
Expert:  Cat Man replied 1 year ago.

Thanks for the information.

Does the yellow check engine light come on when the key is turned to the on position?

Customer: replied 1 year ago.
then goes out
Expert:  Cat Man replied 1 year ago.

Thanks for the information.

Since the yellow check engine light comes on, this indicates the engine ECM is receiving power and functioning. There are several things that can cause a crank no start on this engine.

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.

Customer: replied 1 year ago.
of coarse its starting up now but some white smoke coming out that you and can smell raw fuel, once running it will stay running
Expert:  Cat Man replied 1 year ago.

Thanks for the information.

Sounds like you have either a low fuel pressure problem. Or you have a injection actuation pressure problem. I would check the fuel pressure first. If it is OK. I would suspect an injection actuation pressure problem.

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

Customer: replied 1 year ago.
is there suppose to be a residual fuel pressure after shut down , if so how much for how long ?
Expert:  Cat Man replied 1 year ago.

No. The fuel pressure will fall down to 0 after shutdown. It should not hold pressure.

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

Customer: replied 1 year ago.
fuel pressure is 75-85psi at idle but it take about 8 sec to get there after a slugish start up
Expert:  Cat Man replied 1 year ago.

That is fine. It should maintain that pressure also while driving.

Customer: replied 1 year ago.
As you said yesterday are supecting a HEPU pump ? also to let know the engine has only 30 ,000 miles since a rebuilt by a cert cat tech
Customer: replied 1 year ago.
fuel system passes then on to the next
Expert:  Cat Man replied 1 year ago.

Thanks for the information. Yes I would next suspect the heui pump. I have seen them go out after a short time. A service tool like Cat ET will be needed to confirm. Sorry. I wish there was another way.

Customer: replied 1 year ago.
interesting there is box under the dash with a digital numbers that light up when turned on but just says 00, 2000 GMC c6500
could this be possibly a code reader?
Expert:  Cat Man replied 1 year ago.

I would not think so. I have not seen anything like that before. It would have to be connected to the engine data link to be able to read codes.

Customer: replied 1 year ago.
Hi there , Well I replaced the HEPU pump over the weekend , put it thru some drive cycles and even came up here yesterday morning and it started right up . This morning was another issue , cranks but no start and if it start it would stay running . So I pull off the PCM connectors found some oil in there , clean out connectors , check for good power and grounds but i did Find pin 70 with key on power was about .8 of a volt lower than the rest of the system. replaced 20 amp circut breaker now i have proper voltage. I bought a scanner today and found code 164-11-39 and 42-11-18 . when it does run now it run perfect
Expert:  Cat Man replied 1 year ago.

Me

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

Code 42-11-18 is defined as injection actuation pressure output fault. This is the two wire circuit that runs from the ECM to the heui pump. Since you have replaced the heui pump. The problem is either in the harness or the ECM is faulty. I would replace the two wire harness. Cat sells a two wire bypass harness. You do not have to replace the entire harness. If the harness is not the problem. It must be the ECM.

Code 164-11-39 is defined as an injection actuation pressure problem. This can be caused by the code 18, a bad heui pump, faulty IAP sensor, or a leaking injector.

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

Customer: replied 1 year ago.
what your saying is if 42-11-18 is cleared up then 164-11-39 should go away?
Expert:  Cat Man replied 1 year ago.

Yes that is correct. A 18 can cause a 39.

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

Expert:  Cat Man replied 1 year ago.

Hey. I just wanted to see how things were going. Please let me know if you need more help. I am happy to assist. If my information was helpful, please leave a good or higher rating so that I receive credit. Thanks.

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