Mystery drag a$$ and vague miss in my non turbo 1988 f350 7.3 idi
 

I got the 3 g upgrade finished with brand new ground wires everywhere. Grounded to the block to the frame and of course the alternator to those places as well as the battery. Used 00 guage just in case lol. Now the other day i drove around from point a to b running errands for around 5 or 6 hours. Never drove above 65 the whole time, my driving not due to power loss, then started to get on the interstate and it felt like i was trying to pull a house. Didnt over heat but got warm. Shifts fine and nothing sounds wrong either except the vague, intermittent pauses in power. Just dragging a$$. Its 1988 f350 7.3 idi non turbo. New alternator, waterpump, ground wires, starter, batteries, reading is always 14 on mutimeter, new injectors, new fuel lines both to IP and in between injectors. Ran fine all day then the drag a$$. Tried topping off the tanks, cause they were low, just put a new fuel pump and tried both tanks so not a fuel pump issue. I have a new fuel switch module thing to put in but with both tanks acting the same i doubt its that either. Just looked at the IP and the pump side mark is to the passenger side mark meaning its slightly advanced? Oil is good and new and so is trans fluid, 5 speed manual. Air filter is decent and air flow is strong. Any ideas?



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That's a nice rig. I bet it WOULD tow a house! :-X06

You mentioned you installed new injectors, did you install a new fuel filter with the injectors? Just starting with the basics. :o

Overall the entire fuel system is new except the IP, the tank switch module on the frame, and the rear tank fuel pump. But like i had mentioned i doubt its anything from the fuel filter back since it does the same on both tanks. The gas guage moves when switching so im know the switch works at least.

Did it do this at idle as well or only when driving? A stumble or miss can be caused by air intrusion in the fuel lines. You can ID air intrusion with clear acrylic hose between the fuel pump and fuel filter and between the fuel filter and IP. If there are air bubbles in the fuel then that is BAD. :eek:

Well i dont have any signs of moisture or leaks on any injectors, collars, hoses that are on top. I would like to know where to get the 1/8th inch one way brass fitting that goes in the side of the fuel filter housing. Typically the hose goes from the no. 1 injector to the fuel filter as an air recycle point. I took the brass out a while back and its just an open hole. I was expecting some kind of bearing inside. I am going to slap that other tank switch module though. In my head i could see the switch working amd showing different fuel levels but possibly the module is stuck in between switching?

that fitting on the filter housing that goes to #1 injector was removed through a TSB from ford back in 89 or 90 to help with fuel filter drainback. if you removed the brass plug and left it open, that very well could be your source for air intrusion to the fuel system.
that fitting has been capped off on my 88 for around 400,000 miles without any issues at all.

Well yesterday i put the clear hoses on and ran it with zero bubbles or air coming in. Was hoping id see something but nope. Only furthers my mystery. I did see the thread about the fitting removal though. Im going to post a pic of something that has been a mystery to me though so eyes open please lol

S
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Zero air
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Far view
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A little closer
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There it is. What is that guy called/for???
o as you can see no air intrusions at all. In fact im just leaving the clear tubes on. This 2 pronged sensor has been unplugged the whole time ive owned it. Never seemed to make a difference. One time i did redo the wiring and put extra wire for length and added some heat shrint slip connectors for the ends. Plugged it in and started it and it ran terrible. Turned off the truck switched wire position, same thing, almost like a heavy miss fire. So ive left it alone. I think read somewhere it was an injector/temp sensor or a combination of the two.

that two wire sensor is a temp switch that controls the cold high idle/timing advance.
you really do not need it, i ran my 88 for 300,000 mile with it disconnected after knocking it off changing the alternator because it is a pain in the asterisk to hook up.
i finally hooked it back up when i put a new t-stat in the truck.

so when i plug it in and it runs bad what does that mean? The plunger under the throttle cable plate is bad? I dont think thats related to the power loss though?

there is a electric solenoid on the throttle sort of like a choke pull off. when cold this will kick out a bit for high idle. the other part is the cold timing advance. this is in the injector pump.
should be the rear connector on top of the pump. if you put power to that terminal it will change the timing to help warm up the engine faster.
that is all that sensor controls.
if it is not hooked up it will not go high idle or advance the timing when cold. ....


unless it was bypassed for some reason and hooked to 12 volts to be powered at all times.

So if i unplug the connector at the rear top of the ip nothing should change correct? And by rear do u mean grill side or firewall side?

firewall side. unplugged should do nothing unless it is cold, as in under 100 degrees engine temp.
the front connector(grill side) is the fuel shut off switch. put 12 volts to it and engine will run. remove power from it and engine shuts off.