Trying to fix up a 95 F-Superduty (bucket truck) with the 7.5L EFI that's got me chasing my tail around.


It runs fairly good off idle and gets about 200 kilometers to the 20 Gallon rear tank. However at idle is has a miss I cannot track down. I have had the truck for a while. When I got it, it had a blown head gasket. I replaced the headgaskets, decked the heads, waterpump, new plugs, wires, cap and rotor, set the timing to 10 degrese with the spout unplugged.


From there I drove it out to our acerage where it was used a little here and there to build our shop. Once the shop was built I started to rebuild the rusted out service body (body and paint). Now that the truck is functional, I am using it for work. Long story short......


Replaced front fuel pump ( crapped out ) and tank a few months back because the rubber gas line for the genset was punched through the tank in a strain relief connector and the hose degraded in the ethanol gas. New pump and sender with gen set port, as well as new tank.


Had a vac leak at the EGR valve solenoid - repaired with rubber vac hose. and now has no codes or check engine light anymore


However it has a bit of a miss at idle ( right from cold start and if its warm and running for hours) and smells rich when walking around the truck.
So affecting closed loop and open loop. Thinking its not a o2 sensor


Vaccume guage shows 18 in at idle


Checked fuel pressure as I was hoping for a bad regulator, runs around 32-35 ish dosent leak down when key off ( sits at 30)but guage needle was fluttering not staying constant. unplugging vaccume from FPR gives me 40 lbs. No fuel coming out when vac line is unplugged.


I rechecked the timing. still on at 10 and have not been able to locate anymore vac leaks using propane.


Dose anyone have any ideas to point me in the right direction to troubleshoot this further as I am really not one to throw parts at things.


Thank you in advance


95 F-Superduty
7.5L EFI, 5 Speed ZF

 

Miss; Steady Miss?
Did you do a compression check all around?

Any fluctuation from 18 inHg during Idle?

Excessive play in Dizzy?

Plug wires separated and off metal parts?

Rich; Black smoke?
Throttle Body and Air Bypass Valve Cleaned ?

O2 - Maybe

 

The miss is constant, however it is just bad enough to make the shifter vibrate on the ZF. I re-checked vaccume last night. was sitting at a solid 19 at idle. Distributor and Compression should be fine as was checked not long ago and Distributor was out and was fine when we changed head gaskets not even 3000 kilometers ago. Heads went to rebuild shop to be shaved as had .007 warp. Rebuilder checked heads over, decked and new valve seals. Plug wires are routed as from factory and appear to be far enough from sparking through. Not getting black smoke but you can smell unburnt fuel in it at idle. Still has the cat. I have a new fuel pressure regulator showing up today as the needle was dancing around a bit on the guage (fast swinging back and forth about 5psi either side of 32). I am also going to go out to my acerage and grab a MAP sensor off another 460 to try. When I unplug the vaccume to the map sensor the truck just about dies. I will also be cleaning the IAC today. I don't believe the o2 sensor is the culprit as it does this in open or closed loop. Will post back this evening on any new results. Also I left the fuel pressure guage on the rail overnight and it drained off pressure completely, although it holds constant pressure while I have a lunch break.

 

Does your truck have a Pulse Damper in the Fuel supply line ?

 

Where should I be looking?

 

and what would it look like?

 

Not sure if your config had one, but it was added to smooth out the pressure fluctuation from the Injectors switching off.

 

Just ran out and had a look. It dose not have anything like that on the fule line behind the block. Just 2 standard hoses, one to the FPR and one to the other side of the fuel rail.

 

Make sure you bleed the Fuel Pressure Gauge of air.

Usually removing the FP Regulator vacuum line will raise the pressure. Look for fuel being suck up the vacuum line from the regulator.

Your Key-On pressure range is usually higher than the engine running range due to no vacuum at the regulator.

 

You would think you would get an O2 Rich Code if you had un-burned fuel.

 

Maybe you have an injector/s not closing completely and dumping excess fuel.

 

Ok, so I replaced the FPR and it sits at 35 psi now. the needle on the fuel gauge barely moves now and the truck seems to have better throttle response and pings less than before. Changed the cap and rotor ( wanted brass instead of aluminum) and didn't seem to help any if at all. Still has slight miss at idle and poor mileage. ( atleast to me) 6.2MPG We had another E-350 van with same 7.5L and an E4OD and we were getting a solid 16 - up to 18, so I was atleast hopeing for 10.


IAC seems clean and functioning properly, vac still at 19


Was wondering about dropping off the smog pump, would that throw any check engine lights? / codes?. Should help clear up some engine bay space and mabey some parasitic drag.

 

If the fuel pressure holds constant for 2+ minutes with the key off would the injectors be leaking down? pressure dose bleed off completely overnight though.


Best way to look for a leaky injector would be?


pull the plugs and look for ?

 

Sometimes the Dampers are mounted right on the fuel rail.

 

Before; “The miss is constant”
After; “Still has slight miss”
Did it get better?

Pinging can be advanced timing, I usually like to run high-test while troubleshooting, to avoid low octane induced pinging.

Usually you don’t achieve anything from removing emissions system.

Although older EGR Valves are leaking by now, and folks block them of while troubleshooting, and never unblock them.

A leaky ERG Valve affects the Idle and deceleration negatively.

You do get a few codes from the missing emissions system components, an occasional CEL illumination, but they don’t affect much.

The only way I know to check Injectors is to pull them apply fuel pressure and pulse them. I imagine there are places that check them as well.

Worn or damaged fuel-injector filters can cause what is known as lean misfire, when there is too little gas in the air/fuel mixture.

I read somewhere that the fuel pressure can drop 5 pounds every 30 seconds. Sound like yours are doing better than that.

With the plugs, I would look for the obvious differences, color, etc., plenty of charts out there on plug characteristics. Just remember what plug comes from where.

Pull each Spark Plug Wire, check/listen for Spark & Change in Engine.

Spark Quality?

Sometimes an O2 sensor does not throw a code. You can monitor the O2 output to see if the voltage is low and causing a rich adjustment.

So folks remove all vacuum lines from the intake and cap them just to eliminate a vacuum line leak issue. But you would have to keep the FPR & Map/MAF connected if vacuum, using new temporary lines.

Some folks pull vacuum lines one at a time like you would spark plug wires

The there is always a possibility that your PCM is failing.