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Fuel delivery pressure. High reading

November 08, 2018, 07:27:57 pm

I had a check engine warning today on my 2003 U295. While going downhill in a lower gear, the rpm went over 2450, setting off the annunciator. Before reducing the rpm, I got a check engine light. VMSpc tells me it was a high reading on fuel delivery pressure, which soon returned to normal.

Is this anything to be concerned with, or just what happens with over rpms downhill?

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Re: Fuel delivery pressure. High reading

Reply #1 – November 08, 2018, 07:34:50 pm

I think you exceeded your high RPMs. Not sure if you hurt anything

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Re: Fuel delivery pressure. High reading

Reply #2 – November 08, 2018, 08:24:12 pm

I thought Brett told us (in some past thread) that our Allison transmissions would not allow the engine to exceed the max rev limit.  The trans is supposed to automatically upshift to protect the engine, regardless of what we have selected on the control panel.  What were you doing at the time that held the trans in a lower gear?

I think you are fine - pretty sure your engine will stand higher RPMs than that without any harm.  See page 4 of the file below (C8.3-325).  Under General Performance Data you'll see several max RPM numbers, all higher than what you describe.  Your ISL-400 should have similar limits.

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Reply #3 – November 08, 2018, 08:31:33 pm

Just a long downhill grade, manually in 4th gear. Went just over 2500rpm, enough for a bell, not enough for a forced up shift. Engine still runs fine.

I'm thinking the pid 94 might not be related. Just a spike in fuel pressure from the lift pump. Or a faulty pressure sensor. I looked over the engine, no leaks.

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Reply #4 – November 08, 2018, 09:28:38 pm

This info for a 2003 ISL-- yours could be different:

Engine ISL 400 w two stage Jake brake:
Serial number: 46210160. Engine family: 2CEXH0540LAC. CM: 5554 and CPL: 8106
Idle speed: 600-800. Peak Torque 1200 lb-ft @1300RPM. Peak HP 2100. Governed RPM 2330. Overspeed 2600.

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Re: Fuel delivery pressure. High reading

Reply #5 – November 08, 2018, 11:38:28 pm

No reason to every go over 2000 RPM going downhill. The Jake or retarder along with the service brakes will do the trick and keep speed where you want it. Over speeding the engine can bend pushrods and then they start rubbing on the cylinder head with lots of fine metal particles coming off.  This is what happened to a 8.3 owner several years ago on the forum. As I remember, the over rev ended up costing him $30K.

Never trust the Allison to do what it's supposed to do all the time. Most of the time it's fine but occasionally, I wonder what it was thinking.

Pierce

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Reply #6 – November 09, 2018, 12:36:31 am

ALL engines are different, consult your documents for max rpm. For my cat engine 2800 max rpm for hp, 3000 max rpm downgrade.THEY are ALL different!!!

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Reply #7 – November 09, 2018, 08:29:45 am

I use my m11 fairly hard downhill.  Revved it adds to the braking effect and retarder cooling.  Tested this many different ways.

I think my no load rpm is higher than 2,000 but I rarely exceed that.

8.3 is rated much higher and I would use it personally

3208 is 2600 for the 250 and 2900 for the 300hp. 

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Re: Fuel delivery pressure. High reading

Reply #8 – November 09, 2018, 09:35:40 am

Sorry, I had the Cummins 8.3 and M11 in mind as the RPM range is just about the same as our Detroit. Yes, all the engines are different. Detroit turned the fire service engines up to 2300 and 2400 RPM. Ours is 2130 RPM for max HP. I know it will go much higher but keep it to 2000 RPM downhill just to be on the conservative side.

Pierce

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