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Engine Fault Code SPN 94 FMI 10

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I left E TN yesterday morning and with ~10 miles I saw a flicker of the warning light on the dash come on but went out immediately.  Then about an hour later I saw it again so I brought up the diagnostics page on the Silverleaf and it showed SPN 94  FMI 10 erratic fuel pressure. 

I had this once before in 2021, but it never showed up again.  In June/July I made a 2K trip and the rig ran flawlessly.   As far as I can tell the engine is performing as it should, still hitting 23-24 psi boost pressure, can climb grades as good or better then most of the trucks, temps all look good. 

So I cleared the fault code and continued my trip heading toward Utah.  But yesterday the fault code showed up several time and then this AM.  So I stopped at this AM and changed the fuel filters on the FASS transfer pump and the secondary filter in front of the injection pump.  I dumped the filter fuel into a small bucket and was surprised at how much trash there was in the FASS filters and even some in my secondary filter.  So I took off again and after a couple hours thought the problem was solved>>> NOPE

Had the fault code pop up again and it even derated the engine.  It was when I was slowing down to a stop light and when I started to accelerate it derated  but as soon as I picked up speed it took off.   

I just got on the Cummins Quickserve site and down loaded the troubleshooting guide, most of the stuff I can't do, no way to check fuel pressure.  But it does detail how to check the fuel pressure sensor.

So my plan tomorrow it to take a quick look at the pressure fuel sensor on the fuel pump.  I'll check the wiring and sensor. 


Anyone have any other suggestions. 

If it continues I'll try and find a shop to take a look at it.   Hate to do it but you gotta do what you gotta do.  I need to get this resolved before I go across the rockies. 

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@jacwjames I would definitely look at the sensor Jim.  A few months ago I got engine warning light and an engine derate.  I fortunately noticed that the Air Intake Manifold Temp was 185F.  Using a temp IR gun, I took the temp of the intake manifold and it was 130F.   So I replaced the Intake Temp Sensor and it worked.   Hopefully you can test the pressure and get a sensor if needed on the road.

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Going to see if I can easily get my eyes on the sensor this morning.  My air filter is mounted across the top of the air intake manifold passenger side of engine so it may have to be removed to even see it.

Just looked up the part number, unfortunately the OEM part is not available but Cummins has a TSB on a new one, they've changed the design which requires rewiring and some sort of bracket etc.  So my guess is that the original part had failures due to wires taking weight and failing.

If I can find the original sensor somewhere it would be an easy fix but I doubt there's one out there.  So it goes from a ~$200 to probably $750.   If I can find the original sensor I'll try and change myself, even if I have to pull into a campground and wait for parts, Amazon has one listed for ~$40.  If I can't I'll look for a shop. 

I'm in Junction City, Kansas right now, looking at options.   Anyone know of a good shop in Salina KS or Denver Co. 

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Had to remove the large elbow and crossover tube for the air filter.  But that gave me pretty good access, although a little bit of a reach and tight quarters.  To be able to get the sensor out I had to remove the smaller one next to it and then take another connector apart.  This allowed me room to move those pigtails to the side and get at the connector for the fuel pressure sensor.  Little bit of a bear to get the connector apart, had to use a long narrow screw driver to get it to release.

So I was able get the sensor out, couldn't see any damage to the wiring harness or at least the part I could see but from the connector to the sensor the wiring was good.

Took some pictures of the sensor and then put everything back together and started the rig.  Started and idled fine but the test will be on the road. 

Will start the hunt for a pressure sensor as I head toward Denver.  Coming up on the weekend doesn't help.

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Had this happen a couple of years ago on my Camelot with 400 ISL.  Engine would start to derate while driving down the road.  I would pull over, shut the engine off, restart and all would be well again for quite a few miles.  Finally ended up with the check engine light staying on continually.  Bought an inexpensive engine diagnostic tool and it showed this code.  It was also able to show me the fuel pressure which was way below normal.  Went to Cummins and bought a new fuel pressure regulator and installed.  Problem solved.   The fuel pressure regulator was much easier to get to than the sensor so I was glad it was the regulator and not the sensor.  Be careful with the regulator as it's under pressure when the engine is running and for a short time after shutdown.  Let the engine sit for a while before removing.  Also, there is a copper washer that creates the seal where the regulator is installed.  You would need to make sure you get the old one out and the new one in as part of the procedure to replace.

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Thanks Cal, I'll keep that in the back of my mind.

Not claiming a victory yet but drove 450 miles today and no warning light or fault code popped up.  Engine ran great, out paced most of the semis on the long grades into Denver. 

One thing I noticed is that the wiring harness hung straight down with the pressure sensor wiring taking most of the weight,  That is probably why the TSB with a new part includes some sort of support. 

I did check with a local truck shop on the sensor, they did not have and would take a couple days to get.  I am in Denver now and may check a couple here before I leave. 

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So I took a big leap of faith and continued headed west from Denver.   Left as soon as it started to get light, filled up with fuel ($4.18/gal) and headed west at which point you start climbing from the ~5300 ft elevation mark until you get to Eisenhower Tunnel.  Wish I had about 100 more hp to push my rig but it made it, at times dropping to 35 mph.    Engine performed about as good as can be expected, boost hitting ~23psi, transmission shifting down as it should but I did down shift into 3rd gear when it was struggling. 

Best part of all is that I did not have any fault codes pop up.   Still going to keep a close eye out but seems like pulling the sensor and cleaning the contacts and reseating the connector did the trick

Edited by jacwjames
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