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fuel mileage sucks

K

khills

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So my truck (98 GMC 2500 HD 6.5 diesel, 302,000kms) wouldn't stay running and would throw a code for injector pump cam something or other. I pulled the optical sensor, put a splash of fuel conditioner in it and and put it back in and lined it up with the mark I made (or pretty close to it maybe slightly advanced literally by a hair) before I pulled it out. I dumped a little conditioner in the tank and I noticed either pressure or vacuum when I took the fuel cap off making me wonder if it was vacuum and starving the ip of fuel causing the code. So I left the cap loose the vent to tank. Since doing all of this I've noticed the fuel mileage is terrible. Does anyone have and ideas?
 
You're going to need a scanner to check the idle fuel rate to see if you got it close enough. Did your APP issue start at the same time?
 
So you're looking for an idle fuel rate of around 8mm IIRC. You adjust it by moving the optical sensor. Normally you would put as fine of scribe mark as you can and try to get it back EXACTLY the same. If it's off it can also affect the APP
 
To rule out vacuum in the tank leave the cap loose .....

You should also open the "T" valve bolted on the water crossover while at a idle and confirm you have good flow through the system...
 
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