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Discussion Starter #1
Good day guys,

My buddy just purchased a 2007 F550, generally in great shape, 120,000 miles but it has several issues, likely due in part, to having been parked for about a year prior to the auction. I'm mainly a 7.3 guy so the 6.0 has features I'm not 100% familiar with so I'd like your thoughts on the following:

1. Overboost/limp at highway speeds - Boost seems to run awfully high just cruising down the highway, on the order of 22 PSI, spiking to 30+ on uphill pulls. This is triggering a CEL and limp mode until the truck is shut down. To me, not knowing anything else, this sounds like the VGT is not adjusting for different load conditions, nozzle staying too far closed. Does this sound reasonable? Is it possible to clean the turbo or maybe the control unit is fried?

2. Ride is awful - This particular truck is the smallest, lightest F550 and it rides like it has no suspension. Is there a way to "de-rate" the suspension since the owner doesn't need the full load carrying capacity?

3. High RPM's at highway speed - I'm assuming this has 4.88 or some other similar gearing. What are the options for something more reasonable like 4.11? Is 3.73 too low? Replacement ring/pinion? OD unit?

4. Dash gauges/lighting sometimes flashes or goes does - Is this a known problem on these trucks?

Thanks as always for your input!
 

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On the boost issue, check the EBP, MAP, and Baro sensors at KOEO and see if they are within 0.5 psi of each other. Make sure they are all in the same units (psi). Also, make sure that the EBP sensor tube is not plugged (I run a thick weedwhacker string down the tube). Same w/ MAP sensor nipple - make sure it isn't plugged.

Cleaning the turbo.
6.0L Power Stroke VGT Disassembly & Cleaning Procedures
 

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Discussion Starter #3
Great info Mark, thanks!
 

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Just wanted to post an update to this. I was able to actually drive the truck myself for a couple hours. In the time since we last spoke, the owner had the EGR valve replaced and the transmission flushed and filter changed.

The truck seemed to drive normally to me, aside from seeming to be low on power. Low power may be normal on this model if the engine is de-rated but I'm not sure it is. Boost acts normally and I noticed that the previous owner had replaced the turbo with another one from ebay. (markings on turbo housing)

The thing that's most annoying is the dash gauges and indicators going dead randomly. Battery light flashes, gauges go dead, more flashing, gauges come back. It does this over and over again as you drive down the Interstate. No poking around or pounding on the dash has any effect. Engine seems to run fine other than a small hesitation/missing at times followed by a small surge of power.
 

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The dash issues could very well be the power saver relay in the instrument cluster (not uncommon). Circuit Board Medics can address that if you send the instrument cluster in.

There are youtube videos on removing the cluster. It isn't hard.
 

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The rock hard ride is normal for a 550 that doesn't have 3500 pounds or more of bed, body, etc on it. You can make spacers and remove a lot of the rear leaf spring pack. I have a 450 with higher payload option and that makes it near to 550 payload. I took a lot of leaves out on the way to adding air bags....only after I took out a lot of leaves it still handled my 3000 pound pin weight 36 foot living quarter horse trailer just fine. I removed leaves that were about 3 inches of the leaf stack and replaced them with a block made of two pieces of heavy gauge channel of the proper weight (I think 4 inches) to keep the height near the same. Stock that trailer weight made it settle 1 inch. Leaves removed it drops 2 1/2 inches. It is no cushy ride empty in spite of all metal hauler bed but I no longer feel like I risk breaking my back on bad road unloaded. My truck is 60 inch cab to axle crew cab and weighs 9150 lbs empty I think that makes my bed 1500-1600 pounds as 2wd C&C are around 7500 lbs.
 

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Tire pressure has a lot to do with ride. If you are driving without a load consider dropping the rear tire pressure down to 45 psi and front to 65-70. You should be able to find a chart for your tires with a load/psi scale on it. Swapping overload springs for air bags is a great ideal also.
DENNY
 

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Discussion Starter #8
Thank you all for the great suggestions!

I really like the idea of removing some of the spring pack and swapping in air bags.

Also, regarding the crazy dash/gauge behavior, I went and removed/wiggled the lower connector on the alternator and it seems to have resolved this issue. Next time I have a chance and the engine isn't 700 degrees, I'll remove, check and clean the connector to make sure it's secure.
 
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