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stumbles at 3000rpm


glenn123

glenn123

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I just recently did a 4.0l swap in my 89 ranger from the 2.9l.
everything seems to be working okay except when I rev the motor to 3000rpm it stumbles or stutters. like its not getting enough fuel or maybe getting too much. I can get past 3000rpms if a stay on it but its nearly impossible while driving. Im not sure if its a miss fire or problem with mas air flow. I tried another mas sensor I had laying around but still no change. I changed the fuel pump thinking it might be a difference in fuel pressures from 89 to 90 but no change. Also unplugged the mas sensor and tried it but still no change.
I am having problems with my neutral safety switch as it wont crank with the key so I start it by jumping the solenoid on the fender. I read on some threads where this could be an issue but not sure. I really need my truck asap its been almost a month with no truck!
 


RonD

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Well the computer could have a rev limiter, those are set for 3,000 RPM and only come into play when trans is in Park or Neutral, or if clutch switch was disconnected.

Automatics have an NSS(neutral safety switch) on the transmission
Manuals have a clutch pedal switch on the clutch pedal push rod
Both disable starter motor and both can set rev limiter.

Other thing that comes to mind is partially clogged exhaust
 
glenn123

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I have a manual trans. How can I jump the switch to the peddle? I have tried replacing the switch but no change.

And I'm positive my exhaust is clear.
 

RonD

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What year is the 4.0l computer, I would assume 1990-1994?

Rev limiter is above 6,000rpms in that case, EEC-V(1995 and up) have the 3,000rpm limiter when stopped.
My mistake.

Clutch switch by-pass here: http://www.explorerforum.com/forums/showthread.php?t=107698
But I recommend using/installing a working clutch switch if yours is bad or wiring is
 
glenn123

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The computer is from a 94 manual.
So is it possible my problem could be my NSS switch or wiring? Would that make the truck not wanna go over 3000rpm?
I mean its not like its completely stopping me from going beyond that point. If I stay in the peddle harder I can get past i . But at normal exceleration it doesn't want too.
 
enjr44

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IF the computer thinks you are in neutral or the clutch pedal is pressed it isn't going to go much over 3K rpm. That's the way it was built.
 
glenn123

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I gotcha. Well I've tried 3 different switches on the clutch peddle with no change. So I assume I have a wiring problem. I'm going to try and jump the switch when I get home and see if anything changes.
 

RonD

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If other switches didn't work then jumper wires at the switch won't work either, like you said "wiring problem".

This is the EEC-IV ('94 computer) pin diagram: http://www.auto-diagnostics.info/ford_eec_iv

Pin 30 is the Neutral or in gear input
The Ranger manuals didn't have a neutral sensor on the trans, the Explorers did, at the top of the trans on shifter plate.
So not sure how it would apply "neutral" to clutch pedal position?

Wiring diagram here which shows pin 30 being used on clutch pedal switch: http://www.therangerstation.com/tech_library/EDiagrams/files/Diagram_Enginecontrols4_0_3_0_3of3.JPG

EDIT:
Just thought of something, the '94 computer will want a speed sensor signal.
It is from the VSS(vehicle speed sensor) that is part of the speedo cable hook up on the trans.
If that didn't get hooked up then computer might limit RPMs
VSS seen here: http://www.therangerstation.com/tech_library/speedometer.shtml

Wiring diagram here:
 
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glenn123

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RonD said:
If other switches didn't work then jumper wires at the switch won't work either, like you said "wiring problem".

This is the EEC-IV ('94 computer) pin diagram: http://www.auto-diagnostics.info/ford_eec_iv

Pin 30 is the Neutral or in gear input
The Ranger manuals didn't have a neutral sensor on the trans, the Explorers did, at the top of the trans on shifter plate.
So not sure how it would apply "neutral" to clutch pedal position?

Wiring diagram here which shows pin 30 being used on clutch pedal switch: http://www.therangerstation.com/tech_library/EDiagrams/files/Diagram_Enginecontrols4_0_3_0_3of3.JPG

EDIT:
Just thought of something, the '94 computer will want a speed sensor signal.
It is from the VSS(vehicle speed sensor) that is part of the speedo cable hook up on the trans.
If that didn't get hooked up then computer might limit RPMs
VSS seen here: http://www.therangerstation.com/tech_library/speedometer.shtml

Wiring diagram here:
Click to expand...



So if my problem is that I don't have that number 30 pin. How can I go about fixing that?
 

RonD

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Not sure you need the pin 30 hook up, but you would give it 5volts from pin 26
And pin 30 is better suited for an automatic's NSS than a clutch switch, so probably not used on manuals


The VSS is better place to use REV limiter software, "if vehicle speed is 0mph, limit RPMs"
So if VSS sensor is not hooked up to computer then as far as it is concerned you are going 0MPH all the time, so RPMs are limited to 3,000
 
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