1994 B4000 running rough

[Sagerific95]

Hey everyone, I’m a new member but I’ve been reading on this forum for years, I’m finally posting because I’ve run out of information to help me fix my truck…

So here’s the story. 3 years ago I purchased a 94’ B4000 SE, standard shift with high miles. The transmission was in the bed of the truck because 3rd gear was blown. I purchased a 1993 ranger 4.0 with a rotten frame from my buddy as a donor vehicle for my B4000, had less miles on it, ran fine and was a good candidate for an engine rebuild/ donor for my B4000.

The original engine had EGR,
The tube from the manifold to EGR valve was broken and the truck always ran terribly.
Fast forward to 2024, I rebuilt the 93’ engine completely with new bearings, and rings, with new aftermarket heads that are reinforced. As far as I can tell they are the older style larger chamber, however these heads were as cast and the chambers are pretty rough surfaces.
When I rebuilt the engine I used the 93’ intake manifold to get rid of the EGR as my truck does not need emissions where I live.
NOW HERES WHERE THE FUN BEGINS…
Every single sensor on the engine is new, including a Reman Dorman ECU for a 1993 from rock auto (capacitors were bad, I found out after reading about them on this forum), as well as injectors and here’s everything I know from trying to figure this out for 3 years:
- compression is fantastic in all cylinders, 185-190 psi across the board.
- tps setting is correct.
- fuel pressure is within spec, no fuel coming from FPR vacuum line.
- no vacuum leaks, smoke test confirmed.
- engine idle drops to +or- 550rpm when IAC is unplugged, engine does not stall.
- engine runs the same when MAF is unplugged.
- thermostat operates normal and is a 198F.

The only new but suspected to be bad components are the injectors, at the time of the rebuild I couldn’t afford the name brands and got a set for 80$ from Amazon.

Here’s what the problems are:

- the engine runs fine on choke mode.
- Once the engine is warm, the idle hunts and never stops hunting, sometimes it almost stalls as the rpm’s fall, but it always runs.
- Fuel mileage is about 11-13 mpg.
- No CEL ever.
- I HAVE to run 93oct fuel otherwise it detonates under load at highway speeds.
- On hot starts the engine misfires on 1 cylinder until I punch it and then it seems to go away.
- The engine always gets me where I need to go, but it always runs poorly. Gets bad Gas Mileage, and always idles like crap.

I know this was a long read, I appreciate anyone who has input. I’m an automotive mechanic, I’ve been out of the field for about 5 years, I work in aerospace now. I still have all my tools, a bit of knowledge and understanding. As we know there isn’t much communication from the ECU on these engines. I’m hoping somebody can help. It’s great to be here!

 

[gaz]

@Sagerific95
Which engine came with the EGR, the 94 or the 93. If it was the 94, then , than your truck has a California Emissions PCM:
• which series pistons are in the rebuild (if you do not know but have photos, post them)
• which series heads were used in the rebuild; the castings are marked in several areas, the bowl and exhaust ports will tell the story.

You replaced the PCM with a Rockauto rebuild, is it a California or a Federal programmed PCM?

Did you perform any valve work when you rebuilt the 93?

 

[Sagerific95]

@Sagerific95
Which engine came with the EGR, the 94 or the 93. If it was the 94, then , than your truck has a California Emissions PCM:
• which series pistons are in the rebuild (if you do not know but have photos, post them)
• which series heads were used in the rebuild; the castings are marked in several areas, the bowl and exhaust ports will tell the story.

You replaced the PCM with a Rockauto rebuild, is it a California or a Federal programmed PCM?

Did you perform any valve work when you rebuilt the 93?

Hey .
The original 94 engine had EGR.
All of the wiring harnesses are from the 93’ engine to go with the 93’.
The 93’ engine is obviously federal emissions due to no egr.
The 93’ dished pistons were used in the rebuild.
The website I bought them from state they are 95 and 98tm castings. From King cylinder heads.
The PCM is a federal emission to go with the 93 federal emission compliant engine.

 

[Sagerific95]

@Sagerific95
Which engine came with the EGR, the 94 or the 93. If it was the 94, then , than your truck has a California Emissions PCM:
• which series pistons are in the rebuild (if you do not know but have photos, post them)
• which series heads were used in the rebuild; the castings are marked in several areas, the bowl and exhaust ports will tell the story.

You replaced the PCM with a Rockauto rebuild, is it a California or a Federal programmed PCM?

Did you perform any valve work when you rebuilt the 93?

Sorry I missed your last question, I did not do anything to the heads, they were fully loaded, and bolt in ready. I still haven’t done a leak down yet, so it is possible I’m losing pressure through a valve. Although I would hope it’s unlikely.

 

[Sagerific95]

Hey .
The original 94 engine had EGR.
All of the wiring harnesses are from the 93’ engine to go with the 93’.
The 93’ engine is obviously federal emissions due to no egr.
The 93’ dished pistons were used in the rebuild.
The website I bought them from state they are 95 and 98tm castings. From King cylinder heads.
The PCM is a federal emission to go with the 93 federal emission compliant engine.

To clarify everything I used the engine and all the components from the 93’. The only parts used from the 94’ is the truck. I bought a federal Emission PCM for the 93.

 

[Sagerific95]

Gaz, I actually can’t confirm if I got 94tm heads or 95tm heads. Where are the casting marks located? I’ll have to open the hood and confirm. Where are the casting markers located?

 

[Sagerific95]

Gaz, I just called king cylinder heads and I ordered 98tm heads. Their 95/98 castings are actually 98tm’s.

 

[Sagerific95]

 

[gaz]

@Sagerific95
Your response informs me that you did away with the camshaft position sensor, is this a fact?

YouR 93 was assembled with:
• 98 spec fast burn heads = +1 point compression
• from the pic, some milling was perform on your 93 block = plus some more compression
• pictured are original bore 91-94 shallow dish pistons

Running the compression ratio at 10:1 instead of 9:1 is going to cause extra heat, here are two actions that will help ease the heat:
• run one or two heat ranges lower spark plugs. To keep the cost down while determining which is better for your engine, try simple copper.
• using an engine oil cooler will also help to control engine heat

You state that it runs smooth while warming up but then has instability the 1 component that tell the PCM that the engine is up to temp is the engine temp sensor,I would look at that; if it is faulty (or intermittent), the PCM will go in and out of warm up cycle.

I would use either a 190 or 192.5 T -stat, to help control the heat; I've never seen a 198° used in these, why not let that water work to your advantage.

I recommend using the best known gas around, verses the cheapest.

The only other thoughts regarding this poor fuel economy are the gear ratio/tire size and or your driving habits, unless the age of your ignition system is begining to speak to you but definitely get it running smooth 1st.

 

[Sagerific95]

@Sagerific95
Your response informs me that you did away with the camshaft position sensor, is this a fact?

YouR 93 was assembled with:
• 98 spec fast burn heads = +1 point compression
• from the pic, some milling was perform on your 93 block = plus some more compression
• pictured are original bore 91-94 shallow dish pistons

Running the compression ratio at 10:1 instead of 9:1 is going to cause extra heat, here are two actions that will help ease the heat:
• run one or two heat ranges lower spark plugs. To keep the cost down while determining which is better for your engine, try simple copper.
• using an engine oil cooler will also help to control engine heat

You state that it runs smooth while warming up but then has instability the 1 component that tell the PCM that the engine is up to temp is the engine temp sensor,I would look at that; if it is faulty (or intermittent), the PCM will go in and out of warm up cycle.

I would use either a 190 or 192.5 T -stat, to help control the heat; I've never seen a 198° used in these, why not let that water work to your advantage.

I recommend using the best known gas around, verses the cheapest.

The only other thoughts regarding this poor fuel economy are the gear ratio/tire size and or your driving habits, unless the age of your ignition system is begining to speak to you but definitely get it running smooth 1st.

Yes camshaft position sensor is gone. I was aware that my compression has gone up with the 98 spec heads.
I can try a lower temp thermostat.
And I will pull and test ECT sensor. You should know I have a 3” aluminum fabricated radiator in it as well.
The block was not milled, just touched with a 24” sanding block to check for flatness. Those milling marks are factory. The ECT sensor was brand new at the time of assembling the engine, but that doesn’t mean it’s not bad now.
Ignition system is brand new as well from end to end. With double plat plugs.

I have a strong hunch that the cheap Chinese Amazon injectors I used are playing a huge part in this. I don’t have a noid light to test them so I’m just gonna bite the bullet and get a set of reman injectors from a reputable shop.
It’s funny that you mentioned an oil cooler, I purchased a sandwich adapter but just need to get the rest of the pieces to finish that.
I can pick up some colder plugs as well and see how that goes.
I exclusively use 93oct, the pinging is 99% gone when using 93oct, this is due to the higher compression. I’m fully aware of that.
For now I’ll try what you recommended. I’ll reply to this with any changes. Thank you

 

[Sagerific95]

Yes camshaft position sensor is gone. I was aware that my compression has gone up with the 98 spec heads.
I can try a lower temp thermostat.
And I will pull and test ECT sensor. You should know I have a 3” aluminum fabricated radiator in it as well.
The block was not milled, just touched with a 24” sanding block to check for flatness. Those milling marks are factory. The ECT sensor was brand new at the time of assembling the engine, but that doesn’t mean it’s not bad now.
Ignition system is brand new as well from end to end. With double plat plugs.

I have a strong hunch that the cheap Chinese Amazon injectors I used are playing a huge part in this. I don’t have a noid light to test them so I’m just gonna bite the bullet and get a set of reman injectors from a reputable shop.
It’s funny that you mentioned an oil cooler, I purchased a sandwich adapter but just need to get the rest of the pieces to finish that.
I can pick up some colder plugs as well and see how that goes.
I exclusively use 93oct, the pinging is 99% gone when using 93oct, this is due to the higher compression. I’m fully aware of that.
For now I’ll try what you recommended. I’ll reply to this with any changes. Thank you

I am running 31x10.50 tires and it has an explorer axle swapped with 3:73s. I understand these didn’t get great MPGs when new but 200miles out of a full tank seems exceptionally low.

 

[Sagerific95]

 

[gaz]

@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

 

[Sagerific95]

The engine does have a set of headers installed, made big improvements on the drive ability of the engine, also because the original manifolds were so rotten they weren’t usable.

 

[rumblecloud]

View attachment 109296

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