1994 B4000 running rough

[Sagerific95]

Wow! You have carpeting in you shop....

Nice observation, unfortunately I don’t have a shop, I have a 12x14 shed with a gravel floor. I put thick rubber mats and carpet over the gravel. The other picture with the truck on the lift is at my buddies house… gotta make do with what you have, but I’m proud to say I can do great work with much less that your average shop.

 

[Sagerific95]

@Sagerific95
The 93-94 EGR 4.0l was rated at 23.8 mpg and the 93-94 FEDERAL at 22 and change.

Ford chose to go in an odd direction with the changes Incorporated in the OHV 4.0 vs their 2.9 exhaust manifold. The 2.9's exhaust manifold inlets are nearly matched to the heads exhaust port outlets while the 91-97 exhaust manifold inlets are very oversized when compared to the 91-97 head exhaust port.

If a set of 91-97 exhaust manifolds are used on a 98 spec head, the dynamics are further exaggerated. This is not helping your exhaust flow/velocity. While I am not absolutely certain how much fuel economy this is costing your engine, it is another component in your equation.

Using a set of 98+ OHV 4.0l exhaust manifolds (or headers) may help you recover some lost efficiency; ironically, even stock 2.9l manifolds, with your build (or headers), will also offer improved performance but will require a minor adjustment to the EGR tube boss

Hey I have an update as of 4/29/24…
Just took a 1,000 mile round trip from CT to PA. I bought a 1qt bottle of Lucas upper cylinder lubricant and fuel injector cleaner, used most of the bottle on the trip, filled the tank about 4 times. I’m now truly convinced the majority of my running issues are from those cheap Chinese injectors and the high compression heads (I’m going to ask my machine shop if they can machine a head spacer). The engine runs far smoother and the idle is almost perfect when the Lucas product is in the fuel. The engine had more power down low and the MPGs went way up, before I was getting 200mpg per tank, and on the last leg of the trip I got almost 280 miles out of a tank. I filled it again with plain 93oct and no product, idle went back to its erratic nature and MPGs dropped back down.

 

[gaz]

@Sagerific95
Hello,
The Ford OHV 4.0l is considered to already have an intake manifold spacer because of the fuel rail design. If you wanted a super cheap intake manifold spacer you could use 2 fuel rails with the injectors on the lower rail, the upper rail solely as a spacer (this, of course would require 3 gaskets).

 

[Sagerific95]

@Sagerific95
Hello,
The Ford OHV 4.0l is considered to already have an intake manifold spacer because of the fuel rail design. If you wanted a super cheap intake manifold spacer you could use 2 fuel rails with the injectors on the lower rail, the upper rail solely as a spacer (this, of course would require 3 gaskets).

That’s good to know, what would be the benefits of a manifold spacer? I’ve used throttle body spacers in the past, but all those do is improve throttle response.
I was talking about a CYLINDER head spacer to lower the compression.

 

[gaz]

@Sagerific95
First off you are getting a free bump in power, tq a fuel economy by having the increased compression, reversing that would be an error.

Raising the cylinder heads to lower compression is more than generally accepted no-no. However, it has been my experience that there are one or two companies that will offer a thicker than stock gasket for extra durability...the other end of this is we are talking about negligibly thicker; in other words, not thick enough to lower the compression back to stock level and...it is not a desired move as it will have a direct affect on lower intake manifold alignment.

My bust on misreading your post regarding raising the cylinder head. To answer your question about an intake manifold spacer:
• the idea is that increasing the distance traveled will increase the velocity, yielding more, possibly cooler air into the mix; cooler because the upper manifold is further (insulated by distance and potential cooling...more metal in the air higher to disipate more heat).

 

[gaz]

@Sagerific95
If you had a 3-D printer and made the fuel rail for this engine, I would be the FIRST CUSTOMER INLINE!! No injector pockets necessary...RIGHT