Am I set up for failure?

[Holden]

*Update* It's alive! I ended up using the 2000 4.0 OHV engine and accessories with an intake, fuel rail, and wire harness/ecm from a 92 and it totally worked.

Quick Question!
After finishing the wiring on my swap I have a question about stock manual 4.0's from the early 90's. Regarding the deceleration mode from the ecm (cuts fuel because you are slowing down making you decelerate faster while in gear) do they flip in and out of this mode while rolling in neutral to a stop? If the clutch is pushed in it does not flip flop, but if it's out it does. Any input would help!

 

[Holden]

*Update* It's alive! I ended up using the 2000 4.0 OHV engine and accessories with an intake, fuel rail, and wire harness/ecm from a 92 and it totally worked.

Quick Question!
After finishing the wiring on my swap I have a question about stock manual 4.0's from the early 90's. Regarding the deceleration mode from the ecm (cuts fuel because you are slowing down making you decelerate faster while in gear) do they flip in and out of this mode while rolling in neutral to a stop? If the clutch is pushed in it does not flip flop, but if it's out it does. Any input would help!

By the way, it does this within the range of about 15mph-5mph when going faster or slower I don't think it does this

 

[lil_Blue_Ford]

Interesting. I have a high idle in my Choptop because I have an automatic trans computer on a manual trans truck. I live with it and hopefully eventually I’ll get the proper computer.

My 92 Ranger I had no issues but it’s also an automatic so I dunno.

 

[SenorNoob]

The only thing I can think of is that your TPS isn't dropping down far enough to keep it in at idle...

 

[Holden]

The only thing I can think of is that your TPS isn't dropping down far enough to keep it in at idle...

I actually did test that, the voltage coming out of it is smooth and within spec. ChatGPT claims that it's a normal thing, I just wanna know if anyone else experiences the same. Here's what the AI says:

Yes, what you're describing is normal behavior for a 1992 Ford 4.0L with a manual transmission and a working deceleration fuel shutoff (DFSO) system.

Here's what's happening:

When you're coasting in neutral without the clutch pressed, the engine and drivetrain are still connected via the input shaft, so the ECM can detect vehicle speed and engine speed together. In this case, the ECM might momentarily cut fuel (DFSO) as you decelerate, but it will kick fuel back in if RPM drops too low or if it thinks you're not truly decelerating anymore.

This can cause that in-and-out feeling—a slight RPM surge or flutter—especially if you're rolling in neutral and the ECM is toggling DFSO on/off.

But when the clutch is pressed:

The ECM knows the engine is decoupled from the drivetrain, so DFSO is disabled.

Fuel is delivered normally to keep idle smooth and stable.

No surging or in-and-out behavior occurs.

---

Signs it's behaving normally:

Happens only when coasting in neutral without the clutch in.

Goes away when you press the clutch or come to a stop.

No check engine light.

No aggressive RPM drops or stalls.


Signs of a possible issue:

Surging is very strong or leads to stalling.

Happens even when clutch is pressed.

Check Engine Light comes on.

Idle is unstable in general.


If you're not getting those negative symptoms, you're probably just feeling the ECM managing deceleration and idle. It's a quirk of early '90s EEC-IV engine management and is expected.

 

[Roert42]

Don’t trust AI chatbots. They’ll give you two different answers if you ask them the same question enough times.

Ask the chatbot to find documents and references, not to directly answer questions.