Why wouldnt my truck start, Cat 3126??

[John White]

I run my truck out of the shop the other day, shut it off and had some other work to do. I got ready to bring it back in after about a hour. I forgot to wait till check engine light was out. (it was warm outside) It just cranked over and never would start. I waited about 30 min. went and tried it again, still no start, waited about a hour and still wouldn't start, just spin over. I finally had to do the No-No just to get it back inside for the night. I gave it a small shot of either. Fired right up. I checked the codes today and it has a 34 code which is a RPM fault sensor code. Where is this sensor located at and will it affect the way it runs. (having issues there too) Cat # CKM6522, 2003 KenworthT300.

 

[Mobiltech]

There are 2 speed timing sensors on the back of the front cover on the drivers side behind the air compressor if you have air brakes.
I have seen the wiring harness cause that fault too where it plugs into the sensors.
If you have access to Cat Et hook it up and view the engine speed on the status screen.
usually a sensor wont cause rough running. You may have an oil leak on the high pressure part of the heui system which would cause hard start too. Remove the valve cover and check for any leaks around the injector seals.

 

[John White]

There are 2 speed timing sensors on the back of the front cover on the drivers side behind the air compressor if you have air brakes.
I have seen the wiring harness cause that fault too where it plugs into the sensors.
If you have access to Cat Et hook it up and view the engine speed on the status screen.
usually a sensor wont cause rough running. You may have an oil leak on the high pressure part of the heui system which would cause hard start too. Remove the valve cover and check for any leaks around the injector seals.

It does have air brakes.

 

[John White]

It does have air brakes.

After valve cover is removed, can it be started and run to check it?

 

[Knepptune]

Those things are incredibly sensitive to bad oil. Are you close to needing an oil change. A cam sensor will make it hard to start as well. Ours would do the no start sometimes and it would either fire on starting fluid or you could add a half gallon of fresh oil and it would start right up. Changed the cam sensor and haven't had the problem since.

 

[John White]

It has a fresh oil change, all fuel filters. I took it to Cat dealer. ($250) just to check it out.) Have a feeling it is injector O rings or injectors. After they diagnosis if, I will probably have to drive it back to my shop and tear into myself. Again can you take the valve cover off and start the engine. Someone said if you see excessive oil leaking from one injector, that will be the one with bad O rings. Remember this has other issues also, such as no power. It doesn't smoke or anything.

 

[Mobiltech]

Yes you can start it and run it with the valve cover off.
Have you checked your fuel supply pressure yet?

 

[Joeyslushr]

I've had trouble with the wiring going to the timing sensors before.
Give the whole story...might help troubleshoot if we know everything

 

[John White]

It is at the Cat dealer being checked out. I only authorized them to check it out. After that I will have to try and fix it myself. After I get it back I will post back on here and let you know what they find as I am sure I will need some help. Wont it give you a code if there is a problem. The only code I got was 34. I did some research and some where I read that it wont start with a 34 code. I don't have a plug in scanner. In my area its hard to find any one that knows anything about the 3126.

 

[John White]

I just got a report from the Cat dealer. They said the RPM sensor is bad. I told them that in the first place $134. They said it would be around $800 for labor. $210 for parts. What is involved in replacing these sensors? Can they be installed without taking the Heui pump off?

 

[overworked]

One sensor, labor to change, and diag, $1010.00 . interesting.

 

[Mobiltech]

They must be allowing time to remove and install the air compressor. The sensors are behind it and very hard to get at with the compressor on. Still seems kinda high.

 

[John White]

They didn't say any thing about the compressor having to come off but said the the HEUI pump had to come off. Any thing I need to know before I tackle it myself?

 

[overworked]

They might be taking hueI pump off instead of compressor?

 

[faye]

I have a 3126 Cat hesitates on start up now and then, Will run sometimes for an hour or two then quit, let it sit for 1/2 hour and it will start back up but will cough and puke, I put an iap control valve on it and it didn't help as well as new fuel filters,Do you have any ideas what could cause this thank you

 

[Nige]

How anal are you about doing engine oil and filter changes on it as per the book and what oil/filters do you use..?

 

[faye]

3126 cat

How anal are you about doing engine oil and filter changes on it as per the book and what oil/filters do you use..?

It has had regular oil changes and cat filters used every time the cereal # is 8yl36898 if you hold the gas to the floor it will sometimes start backup but usually have to let it sit and cool down

 

[Nige]

From the sounds of it the hydraulic side of the injection system is starting to leak due to wear. Starting OK when the engine is cold but not starting when hot is the first clue. these engines are not tolerant of poor quality oil or missing the occasional oil change. Oil changes using a top-quality oil have to be done exactly by the book and using good filters if you want the engine to live, hance my question.

IMHO before you start throwing parts at it you really need to get a diagnosis of the injection system by a good technician who knows his way around the HEUI engine.

 

[faye]

3126 cat

From the sounds of it the hydraulic side of the injection system is starting to leak due to wear. Starting OK when the engine is cold but not starting when hot is the first clue. these engines are not tolerant of poor quality oil or missing the occasional oil change. Oil changes using a top-quality oil have to be done exactly by the book and using good filters if you want the engine to live, hance my question.

IMHO before you start throwing parts at it you really need to get a diagnosis of the injection system by a good technician who knows his way around the HEUI engine.

It's going in tomorrow for the test will let you know how I make out.... Sometimes it will run for 2 hours before it quits... I want to thank you for your help

 

[John White]

I have since replaced the engine in mine. Nige was a immense help in providing information. With the new engine, 95% of the time it will start right up. As soon as you turn the key. But once in awhile I have to let it cycle (with the key on for about 30 seconds) before it will start. Is this normal or a future problem I should be looking for?