Foretravel Owners' Forum For owners and Fans of Foretravel Motorcoaches September 07, 2025 ...

Check engine light - high fuel pressure

June 14, 2024, 08:58:40 pm

Strange thing happened a couple of days ago. Been parked in camp since.

Turned from one highway to another at about 5 mph. Immediately started down a 10% grade for about 600 yards. Pulled the retarder back to full and started down the hill. Transmission in normal drive mode. VMSpc showing 6th gear selected. As I neared the bottom, and was about to step on the throttle, a couple of things happened/were noticed almost simultaneously.

First, the transmission never up shifted. My VMSpc indicated I was in 2nd gear. I would have thought it would up shift if the rpm's were too high.

Second, the CEL came on for about 1-2 seconds and I got 2-3 dings on the alarm.

Third, about then, I stepped on the throttle, the transmission up shifted, the CEL went out and everything was normal.

Fourth, checking the VMSpc after we got to camp showed a high fuel pressure fault code associated with the CEL.

Not realizing the transmission had not up shifted, I may have hit the upper rpm limit. I did not notice what the tachometer was reading.

So a couple of questions:

Anything I should watch for as I head on down the road?

Is the CAPS fuel pump pressure related to engine rpm? 

Is the CAPS fuel pump direct drive off the engine?  Would high rpm's cause higher fuel pressure?

Any other thoughts on what happened?

Thanks

Rich

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Re: Check engine light - high fuel pressure

Reply #1 – June 14, 2024, 10:59:36 pm

The caps pump is driven directly off the engine timing gears. Under a full load the ECM wants to see 15k of high pressure injection pressure( produced inside the injection pump). I suppose at very high RPM it could produce pressure higher than called for. Just a guess. Just went through 2 weeks of CAPS injector pomp hell.

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Re: Check engine light - high fuel pressure

Reply #2 – June 15, 2024, 07:08:18 am

Thanks. That's my best guess on the high pressure reading. Hopefully it won't recur.

Still not sure why it didn't up shift but maybe it did automatically just before I stepped on the throttle.

I had about $3K of repairs done on the CAPS system about 5 years ago.

Rich

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Re: Check engine light - high fuel pressure

Reply #3 – June 15, 2024, 08:12:37 am

Might be a good idea to check for DIAGNOSTIC  CODES using the Allison shift pad.

Certainly worth the 2 minutes it takes.

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Re: Check engine light - high fuel pressure

Reply #4 – June 15, 2024, 11:29:55 am

Brett

Will do when we get to camp tonight.

Rich

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Re: Check engine light - high fuel pressure

Reply #5 – June 16, 2024, 02:39:42 pm

No transmission codes.  No problems while driving yesterday.

I'm going to claim a temporary CEL caused by high engine rpm's and hope it doesn't recur.

Thanks for the info/suggestions.

Rich

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Re: Check engine light - high fuel pressure

Reply #6 – September 07, 2024, 11:21:35 pm

Most engines have a higher no load rpm than the engines normal redline under load to allow overrev down grades

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Re: Check engine light - high fuel pressure

Reply #7 – September 08, 2024, 10:30:34 am

I'm just more conservative and don't let it get past 2000 rpm (2130 rpm fuel cutoff). The Jake usually keeps it in check but if not, I use a firm service brake application to drop the speed/rpm 300-400 rpm and then let it build again or downshift if it builds too fast.

Pierce

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