Defueling issue

shortbusdriver

shortbusdriver

this guy
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May 17, 2009
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As you can see in my dyno graph, im having a defueling issue at about 2500rpm. I dynoed about 6 months ago and thats when I noticed it at first. Thing is is that it would never defuel on the street at all, so I didnt worry about it too much at first.

Now about a month ago I actually started noticing a loss of power on the street at that rpm, truck would literally fall on its face at about 2600 rpm and wouldnt come back till about 3000 rpm.

Im guessing that the rack is hanging or not moving smoothly for some reason ie. afc spring binding, GSK issue, or the rack hanging for some reason.

Has anyone else had this issue or know of what might be causing this. I would take the pump off and have a pump shop go through it but this is my only vehicle and cant have to much down time and I currently dont have the funds to do so either.

Im gonna take the AFC housing off tomorrow and check if the spring is binding for any reason, but other then doing that, im pretty much lost


scan0001.jpg
 
do you have a plate in it? i am thinking the governor arm is hanging on the plate, even if you slide stock plate you have to adjust arm...
 
running no plate

even if I did, Ive never heard of the govenor arm hanging under a plate at 2500 rpm
 
Last edited:
shortbusdriver said:
Im gonna take the AFC housing off tomorrow and check if the spring is binding for any reason, but other then doing that, im pretty much lost
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When you have the AFC off, look down in the governor area and with the shutoff lever up, cycle the throttle through its range of motion. You can watch the rack move forward. Maybe you'll see something there.
 
well pulled the afc housing off and checked that, spring isnt hanging up at all with what I can tell with putting shop air to it.

cycled the throttle all the way through and cant see any issues with it hanging there either

so now im stumped

and to make matters worse, I use to keep a lil baggy of parts and tools in my door and now they are no where to be found. Had a fuel plate, afc springs, extra metric nuts n bolts and allen wrenches to get my afc housing off when im not around my shop. things just keep gettin better
 
obvious stupid questions here, and before i ask i realize that your power wouldnt come back after the dip, but, what kind of fuel pump do you have and filter? i assume you have changed filters in last 6 months.

one idea i had was pull the fuel cap off and take it for a spin, suction on tank from pump could be causing this, its a long shot but free..
 
You have a Fuel PSI gauge? If you do, hows that looking? Im thinking it might be failing or have a leak and under load, it cant keep up. Possibly.
 
I have thought of that but was wondering why it would drop in the exact same spot every time and then come back afterwards. Thats why I was thinking it was more of a Govenor spring or rack issue.

I dont have a gauge yet, I am ordering one as soon as I get money, which may be a while. I have a pusher pump to throw on for now untill I get a real lift pump but want to wait till I get the fuel pressure gauge on first.
 
overflow valve... could be bypassing fuel at that rpm... how old is yours?
 
24vriviera said:
overflow valve... could be bypassing fuel at that rpm... how old is yours?
Click to expand...

no idea on how old it is, I have the spring stretched to .55" which is what weston recommend

Update, now when I really get on it the truck will totally defuel to idle and then will die on me. But all I have to do is restart it and it will run fine again. :bang
 
check your connections on your shutoff, sometimes all it takes is unplugging it and plugging it back in. try to clean the connections. hope this helps
 
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