FG Has Problem at High Elevation

[bobar]

I need help with a Fuso problem.

The problem is erratic operation at high elevations.

We recently took our Earthcruiser, built on a 2007 Fuso FG chassis, up Pikes Peak which tops out at 14,115 feet. All was fine until we got somewhere within a mile or so from the top at maybe 13,000 feet plus. We were running fine typically in 3rd gear at about 20 to 25 mph for most of the trip, then in 2nd at about 15 mph near the top when it got steeper. With increasing frequency as we ascended, the engine reduced power in cycles. It was at normal power for 5 seconds then power was cut by maybe 30 to 50% for 5 seconds or so. We could maintain forward movement but we were slowing down from 15 mph. Then power was automatically returned to normal, and the cycle repeated again and again all the way to the top.

High stress indeed with a steep slope, a 22 ft vehicle on a 24 ft wide roadbed and no shoulders to speak of, cars following, cars coming down, and all you can see ahead is blue sky, cliff to your left and space to your right.

We maintained around 2400 rpm with normal power. I did not notice the rpm when power dropped as my eyes were glued to the road. Engine coolant temp stayed below 195, and I have no gauge for exhaust gas temperature, boost pressure, or any other parameter that might help diagnose the issue.

We subsequently came down with no further issue and later crossed a couple passes at 12,000 ft with no issues.

Here’s my speculation on possible causes. The engine has no oxygen sensor but there is an atmospheric pressure sensor integral to the ECU. Perhaps the ECU is programmed to cut power by decreasing fuel flow or rail pressure when it senses low atmospheric pressure or a high EGT, which could be caused by a rich mixture due to the low density air at that elevation. Perhaps the wastegate is releasing boost pressure, but it does not appear to be connected to the ECU, only to the intake manifold through a rubber hose.

Admittedly the circumstances of this problem would be rare, but there are several roads between 12,500 and 13,500 ft in Colorado that we would like to tackle.

What could be causing this? Any help would be appreciated

 

[pugslyyy]

Is it possible that this could be a low fuel pressure issue due simply to the long steep climb?

 

[bobar]

Thanks for the input Jon. And thanks for showing us Robinson Fuso at Expo this year. Very generous with your time and information.

There is a fuel rail pressure sensor that sends an input signal to the ECU. But I'm not sure why the pressure would be low given that we were able to maintain a steady comfortable rpm, until the engine started cutting power on its own of course. The fuel feed pump, which is part of the Bosch CP3.3 supply/injection pump, pulls fuel out of the tank (there is no separate lift pump like many other diesels) and is driven off the camshaft. So since rpm was steady I would think the CP3.3 pump would continue to supply normal fuel pressure. But I could be overlooking something.

 

[gait]

FG649 2004, I experienced engine warning light on intermittently above 4,000m (13,000 ft), and almost permanently above 5,000m (16,400 ft). The diagnostics (read with blink codes) said low turbo boost pressure. Consistent with low atmospheric pressure at higher altitude.

I'd have to look at my notes again but recollection is that lower gear / higher revs / comfortable speed helped increase the altitude at which the light came on. I also have two tanks, one has longer fuel lines than the other and engine is occasionally sensitive to the lower fuel pressure. Switching to the better tank seemed to help but I didn't switch enough to confirm.

 

[pugslyyy]

Thanks for the input Jon. And thanks for showing us Robinson Fuso at Expo this year. Very generous with your time and information.

There is a fuel rail pressure sensor that sends an input signal to the ECU. But I'm not sure why the pressure would be low given that we were able to maintain a steady comfortable rpm, until the engine started cutting power on its own of course. The fuel feed pump, which is part of the Bosch CP3.3 supply/injection pump, pulls fuel out of the tank (there is no separate lift pump like many other diesels) and is driven off the camshaft. So since rpm was steady I would think the CP3.3 pump would continue to supply normal fuel pressure. But I could be overlooking something.

Surging can be an indication of a clogging fuel filter.

I was just wondering because I've not had issues with hesitation due to altitude, but I have had loss of power due to fuel contamination and clogged fuel filters - and for me it was always worst slogging up a long grade (because fuel consumption was highest then). Cutting in my (aftermarket) auxiliary fuel pump would boost the fuel pressure back up to a level where the surging went away.

 

[Raker]

Just a thought Bobar, when I drove semi trailers up long steep grades it was important to keep an eye on the pyrometer, if it reached 600 degrees then a down shift would get things cooled. I wonder if the ecu is trying to compensate?

 

[gait]

PS. I knew there was something I forgot to mention.

Black smoke from exhaust. The higher we went the more black smoke.

Its possible to retune a bit to match the locals, but I decided not to as we would be back to sea level a few thousand km later.

 

[bobar]

Thanks Raker. That is certainly a possibility. I wish I had a pyrometer; I should install one. I installed one on my Dodge 2500 with the Cummins 6.7l engine and it was certainly eye-opening to see the range of temperatures depending on how much you were on the "gas". It's a little unnerving to install one because you have to drill and tap a hole in your exhaust manifold. A good trick is to glob up the drill bit and the tap with grease, and to put a small rare earth magnet on the drill bit and tap, both of which serve to capture those bits of metal you don't want in your manifold and going through your turbo.

 

[bobar]

Thanks Gait. As far as I know we didn't get black smoke, but then again my eyes were glued to the road ahead. Black smoke would mean rich mixture (due to low oxygen levels) and that, I understand causes high EGT. The ECU could be reacting to that. It's strange that I didn't get any engine warning lights.

 

[bobar]

I'm looking at improving the fuel filtration system, getting something down to 2-3 microns, like a FASS or Air Dog system, but that's a topic for another day.

 

[dlh62c]

I'm looking at improving the fuel filtration system, getting something down to 2-3 microns, like a FASS or Air Dog system, but that's a topic for another day.

Do your homework on this. Adding additional filtration sounds like a good idea, just make it doesn't cause your fuel pumps to work harder and thus shorting their life.

 

[bobar]

Thanks dlh62c. You've nailed what my main concern is. The 2007 FG uses the Bosch CP3.3 pump which has a fuel feed pump integral to it. It pulls fuel from the tank; there is no separate lift pump. It's hard to get solid information on this issue. Some Chevy diesels have the same pump, with no lift pump, and FASS and Air Dog systems have been apparently successfully applied. These systems incorporate their own pump so you would be adding a pump where there was not one, giving you two low pressure pumps. One thing I do know, water, air and dirt in the fuel are the WORST things possible for our HPCR systems.

 

[dlh62c]

You missed one!

Dirt, air and water are easily taken care of. Its the cross contamination with other fluids such as gasoline that can really do a number on modern common rail diesel engines. Know thy fuel source. A locking fuel cap isn't a bad idea.

Something else to consider is how the pump's performance is measured via the vehicles diagnostic firmware. It could be via current sensing. Adding additional filters might cause the pumps to work harder thus pulling more current thus causing an inadvertent fault.

In the end, its your rig, you can add all the mods you want.