3800 rpm wall/ hesitation

[Apex944]

So, I have been trying to hunt down the reason for why I get an early fuel cut between 3500-4000 rpms. If I go just partial throttle, not even 1/4 throttle, it'll continue on up to 4k rpms and on. But if I give it 1/4 or more throttle it hits fuel cut around 3500-4000 rpms and falls on its face until I let off the gas.


It idle's perfect, rev's perfect sitting still all the way to redline, drives perfect under 3500 rpms.

I have a few idea's and have been doing tests with my DMM and other things but I just can not figure it out.

I figured it was the MAP sensor so I tested it.
The Black/White wire reads 12.2 volts
Brown/Red wire 2v at 3.9 in Hg
Brown/White wire 4.99v
Black wire is ground

I think I may have been doing the test incorrectly but it says to check pin D on the connecter with KOEO and the 3.9 inHg on the sensor.

I even hooked up an RB FCD to my map sensor just in case it was faulty, that way it would be bypassed. But it still has the same issue.


My TPS seems to be good as well. I hooked it up to my O-scope and it doesnt have any drop offs or spikes anywhere and I set it to 1k ohms at rest and it hits 4.4k ohms max/WOT.

My fuel injectors were just cleaned.
My fuel pump, fuel sock, fuel filter are all brand new.
New spark plugs, wires, coils are all good.
Timing is close but I have the wrong pulley so I cant set timing just yet.
Grounded the MAP sensor ground and pin 2C on the ECU which is the sensor ground.

I gutted the main cat converter and checked out the resistor pack.
The car does run better with the gutted cat, and the resistor pack is good but the 3800 rpm wall is still there.


My AFM had 2.5 k ohms of resistance on one of the tests for the pins. Should have only been 200-600. Pins E2 and Vs.
I put another AFM on it, the correct one I need of course, and made sure it was to specs.

Still has the hesitation.

I pulled the vacuum to the map sensor and capped it off to simulate a load on the engine and to see if the 3800 rpm problem is secondary injector related, and of course it is.

At exactly 3800 rpms sitting in the driveway the car bounces off of it like a rev limiter and it leans out everytime it hits, although the misfire could be causing the lean condition.

I checked for voltage coming out of the resistor pack- a little over 12v

So I removed the UIM and checked out the wire colors to the injectors.
So far so good, everything is plugged in correctly according to the haynes wiring diagram. The FSM doesnt specify the colors all that well....

I tested for voltage, yep they all have a little over 12v.

Tested for continuity from the injector plug to the computer plug, yep they all have continuity and are the correct wires for the correct pins and only have .3 ohms of resistance on them.

I re-checked the resistance of the injectors and they are all the correct low impedence injectors.

I hooked up an LED to 12v and grounded it to one of the secondary ground wires off of the ECU. It lit up just like it should when it hits 3800 rpms and it bounces off of it until I let go of the gas.
Which means the computer is telling them to fire so they should be working.

I put a needle into each ground wire off of the ECU for the injectors and grounded it out intermittently with the ignition on and I heard clicking come from each injector which means theyre working fine for the most part.

Anybody have any idea's?
I havent gotten any replies to my thread from "the other forum" for a few days now....

I was thinking possibly too much fuel when the secondaries kick on due to my walbro 255 pump?

Thanks for any help

[Apex944]

So, I have been trying to hunt down the reason for why I get an early fuel cut between 3500-4000 rpms. If I go just partial throttle, not even 1/4 throttle, it'll continue on up to 4k rpms and on. But if I give it 1/4 or more throttle it hits fuel cut around 3500-4000 rpms and falls on its face until I let off the gas.


It idle's perfect, rev's perfect sitting still all the way to redline, drives perfect under 3500 rpms.

I have a few idea's and have been doing tests with my DMM and other things but I just can not figure it out.

I figured it was the MAP sensor so I tested it.
The Black/White wire reads 12.2 volts
Brown/Red wire 2v at 3.9 in Hg
Brown/White wire 4.99v
Black wire is ground

I think I may have been doing the test incorrectly but it says to check pin D on the connecter with KOEO and the 3.9 inHg on the sensor.

I even hooked up an RB FCD to my map sensor just in case it was faulty, that way it would be bypassed. But it still has the same issue.


My TPS seems to be good as well. I hooked it up to my O-scope and it doesnt have any drop offs or spikes anywhere and I set it to 1k ohms at rest and it hits 4.4k ohms max/WOT.

My fuel injectors were just cleaned.
My fuel pump, fuel sock, fuel filter are all brand new.
New spark plugs, wires, coils are all good.
Timing is close but I have the wrong pulley so I cant set timing just yet.
Grounded the MAP sensor ground and pin 2C on the ECU which is the sensor ground.

I gutted the main cat converter and checked out the resistor pack.
The car does run better with the gutted cat, and the resistor pack is good but the 3800 rpm wall is still there.


My AFM had 2.5 k ohms of resistance on one of the tests for the pins. Should have only been 200-600. Pins E2 and Vs.
I put another AFM on it, the correct one I need of course, and made sure it was to specs.

Still has the hesitation.

I pulled the vacuum to the map sensor and capped it off to simulate a load on the engine and to see if the 3800 rpm problem is secondary injector related, and of course it is.

At exactly 3800 rpms sitting in the driveway the car bounces off of it like a rev limiter and it leans out everytime it hits, although the misfire could be causing the lean condition.

I checked for voltage coming out of the resistor pack- a little over 12v

So I removed the UIM and checked out the wire colors to the injectors.
So far so good, everything is plugged in correctly according to the haynes wiring diagram. The FSM doesnt specify the colors all that well....

I tested for voltage, yep they all have a little over 12v.

Tested for continuity from the injector plug to the computer plug, yep they all have continuity and are the correct wires for the correct pins and only have .3 ohms of resistance on them.

I re-checked the resistance of the injectors and they are all the correct low impedence injectors.

I hooked up an LED to 12v and grounded it to one of the secondary ground wires off of the ECU. It lit up just like it should when it hits 3800 rpms and it bounces off of it until I let go of the gas.
Which means the computer is telling them to fire so they should be working.

I put a needle into each ground wire off of the ECU for the injectors and grounded it out intermittently with the ignition on and I heard clicking come from each injector which means theyre working fine for the most part.

Anybody have any idea's?
I havent gotten any replies to my thread from "the other forum" for a few days now....

I was thinking possibly too much fuel when the secondaries kick on due to my walbro 255 pump?

Thanks for any help