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Old 07-16-2019, 03:09 PM   #1
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diminished power

This thread prompted me to create my own thread and see if folks can offer advice.

I just returned from a two-week road trip from Portland and throughout northern California. We drove a little over 2,000 miles and camped all over, from the eastern Sierras to the coast. We had a great trip (report to come soon) but I did notice some mechanical issues.

The van is a 2001 E250 5.4L V8 (gas) with a GTRV conversion. I am the original owner. I think this issue has been occurring for a while, but I noticed it more since I was doing a lot more driving on this trip.

What I notice is that the van loses power climbing and seems to accelerate more slowly than in the past. Even getting up to highway speeds takes longer, though it seems OJK once I reach speed. The other thing I notice is that it downshifts frequently when I use cruise control. For example, cruising along on a fairly level grade and a slight incline will cause a downshift and a larger incline will cause it to downshift more/again.

I haven't had it in to a mechanic yet, but I thought I'd seek the wisdom of the forum. Thanks for any assistance you can provide.

I replaced the air filter mid-trip and thought it was a little better, but now think I either imagined that, or it was only temporary.
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Old 07-16-2019, 03:13 PM   #2
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How many miles on it? What has been replaced? I would check all the air intake stuff like the filter and make sure nothing is clogged. Then I would do the same on the fuel side: fuel pump and filter etc.

Have you added significant weight? Are you at altitude where you weren't before?
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Old 07-16-2019, 03:28 PM   #3
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It has around 87,000 miles. Virtually nothing has been replaced. The fuel pump was replaced several years back.

I don't think I've added much weight beyond the original camperization. I do have a Yakima storage box up top now, but am hauling about the same gear I always did, just relocated to the top.

I'm basically at sea-level in Portland, but this trip took us up to over 6,500' a few times.
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Old 07-16-2019, 03:31 PM   #4
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I noticed very diminished power when driving my van home to CA from CO while I was at altitude. So it might be that.

If not, remember that everything on your van is now 18 years old. So most filters and rubber parts will need to be replaced. Even though the mileage is low, lots of parts have hardened or worn out. Start with the easy stuff and replace it yourself and work toward the more involved stuff. That way you can cheaply figure out if anything makes a difference.

Good luck!
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Old 07-16-2019, 03:50 PM   #5
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Non-turbo motors lose 3% per 1,000 feet. So when you were in the Sierras, you were already down 25% just from elevation. Then add in grades that are steeper than they look.

So... your experience might actually be expected. Of course, always check air and fuel filers if you think might be low on power.

The "shifty" nature especially using cruise control just means you are heavy and would benefit from either lower rear-end gears, and/or a 5-star tuner.
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Old 07-16-2019, 04:27 PM   #6
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Could be catalytic converter starting to get plugged but your mileage is low; any issue there would likely throw an OBD2 code. There are ways to test for that. On the other side, you could pull a spark plug to read it - don't necessarily need to pull all 8. But a rich or lean mixture and/or failing spark plugs or wires or distributor cap could cause some issues.

With all the white lightning (alcohol) in fuel today - it may just be that current fuel is horrible and you're feeling the effects of that. It may be that at elevation the vehicle is retarding the timing for some reason - maybe an unperceived knock? Might try a dose of the next octane up.

But a mechanic who can check the catalytic and how the engine is running under load would be ideal.

Please report back on findings!
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Old 07-16-2019, 05:09 PM   #7
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Quote:
Originally Posted by SMB123 View Post
Please report back on findings!
Will do, may be a bit, lot's of irons in the fire right now, but thanks.
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Old 07-17-2019, 09:44 PM   #8
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Originally Posted by carringb View Post
Non-turbo motors lose 3% per 1,000 feet. So when you were in the Sierras, you were already down 25% just from elevation. Then add in grades that are steeper than they look.

So... your experience might actually be expected. Of course, always check air and fuel filers if you think might be low on power.

The "shifty" nature especially using cruise control just means you are heavy and would benefit from either lower rear-end gears, and/or a 5-star tuner.
There is a distinct loss of power whenever our van gets into higher elevation, such as the Sierras, and its disconcerting. I've wondered if a custom tune from 5-Star to compensate for the thinner air would be a fix. I used to switch out the carburetor jets in the VW to accomplish the same thing.
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Old 07-18-2019, 07:14 AM   #9
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There is a distinct loss of power whenever our van gets into higher elevation, such as the Sierras, and its disconcerting. I've wondered if a custom tune from 5-Star to compensate for the thinner air would be a fix. I used to switch out the carburetor jets in the VW to accomplish the same thing.
Why is it disconcerting? It's simply physics. All natural-aspirated motor will do this. Your PCM is already adjusting the mix so it won't run rich like a old carb'd motor.

The 5-star tune will add a little more power, all the time, but since it only adds about 15 hp, you'll still notice the elevation affects above 5,000'. Besides the slight extra power, it will help drivability through better transmission programming, which honestly is a greater benefit than the slight power gain.

There other ways to add more power, across all elevations, to help ensure you still have a power reserve at high elevations, such as cat-back exhausts. Or you can go all out and add forced-induction.

But do you really need more power? Are you at WOT and losing speed? Or are you just afraid to let the engine rev? The Triton motors are relatively high-revving motors, so you have to spin it win it.
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Old 07-18-2019, 08:11 AM   #10
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The disconcerting aspect is a very sluggish response when, say, I turn onto a curvy mountain road out of a campground and need to accelerate in order to get up to traffic speed. Punch on the skinny pedal, wide open throttle, nothing happens for a bit, then a s-l-o-w acceleration. The revs don't happen. I just didn't expect that kind of performance from a V10. Our passenger car doesn't exhibit that kind of large change in response at altitude, so I'm wondering why does the van. At sea level, it's great, got the 5-Star perf tune, a noticeable improvement over stock. Thanks for your knowledge.
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