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Discussion Starter #1
I have posted this same thing just about everywhere. As well as had my van in a couple of high end diesel shops that just don’t know where to go either.

My 1998 E350 7.3 is a beautiful pristine condition Van. It got roughly 18.5-19 mpg driving 70-75 mph on the highway. All day, everyday. For me and for the original owner I bought it from. It’s a camper van and all it does basically highway drive.

I’m super meticulous about hand tracking my mpg. Randomly about 8 months ago I noticed the fuel gauge start to drop from full only a few miles after fill up. Normally it won’t move until atleast 50-70 miles. Sure enough I get about 15.5 mpg. And that’s where I’m at. It won’t change. Just happened “overnight”.

No it’s not winter fuel. Cleaning the EBP tube has to be a myth. No it’s not a 5 inch lift with 37s that I forgot to mention, and no 15-16 mpg is not “good for a 7.3 van”. Atleast not mine.

Ive heard IPR, ICP and all sorts of other things. Any ideas?
Please help me I’m losing my mind.
 

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-How long have you had the van?

-did you reflash the ecm for the larger tires? Flash tuners and chips don’t do it even if they claim you need to change the abs model sensor input number via only three software suites. I ask because if the odometer is reading distance of stock tires you are driving quite a bit further aka your odometer is telling you, you drive less miles than you did.

Whoever is telling You the IPR or ICP is the cause needs to take a step back and learn what those sensors actually do and what their readings actually mean. Aka a faulty IPR is very complicated and coul involve the but backing off, valve sticking open, wire failure from getting all the dropping oil/fuel being below the HPOP and fuel bowl abd more likely to cause random no starts and rough running than a 2-4mpg drop etc.

-gotta be honest getting 18-19mpg at that speed in a van is NOT COMON at all.
 

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Discussion Starter #3
I’ll edit the original post. I probably wasn’t clear. I did not put a lift or tires on the van. Everything has remained exactly the same. I just hear a lot of people asking questions like that one for example: “ did you put bigger tires on?” No, none of that. Everything thing is all the same. Just go on a trip one day and after fill up, the gauge starts making its way down after only a few miles. Normally these trucks stay at the full line for quite a while before moving. Providing they are healthy.
And yes 18-19 mpg would be not common at all in a van with 37s haha.
 

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Considering how meticulous you seem to be, I would start with ruling out the rotating parts, bearings, sticking calipers, service the rear, 4wd parts, ect.

Also how worn are the tires? are they even?
 

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Have you eliminated the gauge being the problem? I had a similar issue. Gauge started dropping real fast after running for miles after fill up. I filled up again and drove for 200 miles then filled up and drove another 200 miles and filled up again and found my MPG hadn't changed which indicated to me my gauge was going. I changed it out and have had no problem since.
 

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Does this van have the mechanical fuel pump or does it have an electric pump? If it runs the mechanical pump, the fuel pressure can drop and sometimes cause mileage to drop. The screens on the regulator for the mechanical pump can also get dirty. What's the fuel pressure at when idling? Just other stuff to look at. Cheers!
 
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