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ajpurc
ajpurc, Auto Service Technician
Category: Chevy
Satisfied Customers: 68
Experience:  Head technician and diagnostic expert.
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Chevrolet sierra 2500 01 duramax goes into limp mode and

Customer Question

01' duramax goes into limp mode and p0093 shows up........i reset with my snap-on scanner and same thing happens just over half throttle. new filter and at an idle i'm getting 45lbs. of pressure from my pump.......no fuel in crank case! what do i check next?
Submitted: 2 years ago.
Category: Chevy
Expert:  ajpurc replied 2 years ago.

ajpurc :

Hey there my name is AJ and I can help you with this issue.

ajpurc :

The P0093 is a code for low fuel rail pressure. This can come from several things, 1. weak CP3 injection pump, 2. aerated fuel from bad fuel filter base or other fuel component, 3. Fuel injector returning too much fuel or 4. Bad fuel rail pressure sensor or fuel pressure regulator.

ajpurc :

I'm gonna copy up 3 charts and we will go over them.

ajpurc :

Do you have access to a scanner that can read data?

ajpurc :

If not, diagnosing this issue will be extremely difficult.

ajpurc :

Since we will not be able to look at rail pressure or fuel pressure regulator command %.

Customer :

yes..s however my truck and scanner are on the other side of the state right now.

ajpurc :

It will help tremendously to have a scanner so that you can command your fuel rail pressure up to verify a fix.

ajpurc :

One test you can do is to measure fuel return from the engine. You will have to disconnect a few fuel lines one being on the injection pump.

Customer :

some times the truck will cut out completely and not start unless hand primed.

ajpurc :

Does the primer get hard when you prime it up??

Customer :

first couple of tries it did.....but now it pumps easy even after start-up.

ajpurc :

The fuel filter base could be sucking air and causing this issue. We rebuild a lot of these filter bases. Alliant Power just came out with a seal kit for this housing that is around $50 and a dealer will make you buy the whole housing for $600!!

ajpurc :

If you want to measure return fuel flow you can remove the air intake pipe from filter to turbo and underneath the intake pipe will be a fuel junction block. There is a banjo bolt in the end that sends fuel in 3 directions. One rubber hose coming off it goes to the injection pump. You need to remove that line and plug it off at the banjo bolt. Then run a line from the rubber line on the injection pump into a bucket. You do not measure this fuel so just use a gallon bucket of some kind. Then you will remove the small return fuel line that is on the drivers side of the engine near the top back of the valve cover. There are 2 lines there. It is the smaller one. You will then run a hose from that fitting-engine side to a measuring container.

ajpurc :

Then remove the ignition 1 fuse.Crank the engine in 15 second intervals, with one minute cooling time between, until fuel starts to flow into the measurement container.

ajpurc :
  1. Elevate the hose to retain fuel in the hose, and empty the measurement container (2) into a suitable fuel container. Install the hose in the measurement container.

IMPORTANT: The engine cranking speed must be more than 150 RPM .

  1. Crank the engine for 15 seconds .

IMPORTANT: Do not include the fuel from the fuel injection pump return hose in the measurement procedure.

  1. Measure the quantity of fuel in the container.
    • If there is more than 35 ml (1.2 oz) in the measurement container, go to step 19.
    • If there is less than 35 ml (1.2 oz) in the measurement container, replace the fuel injection pump. Refer to Fuel Injection Pump Replacement. After the replacement, go to step 14.

ajpurc :

These tests however, DO NOT NEED to be run unless the charts above tell you to run them.

ajpurc :

The charts tell you how to test the fuel filter housing but you need a special pressure/vacuum gauge to do so

ajpurc :

And most of the time if the filter primer is not getting hard then that tells you that the filter base is not sealing off correctly and needs to be resealed.

Customer :

lets step back to first time i had problems...................i was doing 75mph and the motor died,caughed a little bit and i barely got it running enough to exit freeway....... i replaced the filter and it ran ok for a while then started the game of going into limp mode.........what is the availabilty on that seal kit?

ajpurc :

From the sound of it your fuel filter clogged, you replaced it go fuel pressure back, and then you developed another issue. How long did it run fine before it started going into limp mode?

Customer :

about an hour ......50 or 60 miles.

ajpurc :

The seal kit can be purchased from any Alliant Power dealers. Part # AP0029 or you can just go to google and type in that part # and there are some sites that have them.

Customer :

it was a small battle to get the pressure back after changing the filter.......at first...when hand priming the bottom fitting on the filter housing would loosen up and dump fuel? mystery to me! however i tightened it and the o-ring is not leaking.

ajpurc :

If you feel up to it you can remove the fuel filter base and bypass it in order to rule it out as the culprit. You just need to understand that unfiltered fuel will be going into your pump and injectors.

ajpurc :

Yeah that plastic sensor/drain is a PITA

Customer :

can i use the existing hoses and hardware or what do i need in order to bypass?

Customer :

out of curiosity....where is the fuel pressure sensor?

ajpurc :

You will have to find a piece of pipe that fits in the hoses that go to the filter base. It's really simple to bypass the hard part is finding a bent piece of tubing that is at the right angle to connect the 2 hoses together. You will probably have to crack an injector line or 2 to bled the air too.

ajpurc :

It is under the AC compressor threaded into the fuel junction block.

Customer :

in your opinion.....with my symptoms, does that rule out the sensor and regulator culprits?

ajpurc :

I've never had a bad fuel rail pressure sensor that only threw a P0093 but that doesn't mean it cant happen. The regulator could be the culprit but without a scanner that can read data it's hard to tell but most regulators I've replaced caused idle issues and other codes as well but scanner data will help pinpoint the culprit better.

ajpurc :

The last one I had doing this was caused by a weak injection pump but I've had several 01-02s that this issue was caused by injectors.

ajpurc :

Let me know if you need any more info and please accept my answer if you are satisfied to ensure I get paid for my work. Thanks

Customer :

my buddy has a scanner that reads data and he will be here shortly to read your advice..........

ajpurc :

Sounds good. Let me know what you find and I will get back with you tomorrow.

Customer :

thank you for the help!!

ajpurc :

No problem

Customer :

what does fuel juntion block do? what is technical name? (two banjo fittings and electical plug.....underneath air intake to turbo)

ajpurc :

Yep thats the fuel junction block. The banjo bolt sends out return fuel and the block part houses the rail sensor and sends fuel from the pump to the rails.

ajpurc :

Hey there. I was wondering if you had any luck with the truck. Please make sure to accept my answer if you are satisfied to ensure I get paid. Thanks

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