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94 ranger 4.0 losing power.

RangerFabWorks

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I’ll try to keep this short and sweet. On the 94 ranger 4.0 I got. I’m having an issue. It will run perfect cold. Idle. Rev out. After about 10 mins of running. It will lose power more and more. And start popping through the throttle body. Unless you put it to the wood. Then it wakes up. Also has a farting sound at idle through the exhaust.
I kinda threw the parts cannon at it. But also diagnosing it along the way. New parts include.

Ecu
Tps
Maf
Coil
Wires
Plugs
FPR
ICM
Intake gaskets
Injectors
Fuel pump and filter
Replaced all the vacuum lines
Temp sensor
Intake air temp sensor
O2 sensors
Intake tube and filter

fuel pressure idling is 32. Fpr unplugged is 40. Holds pressure for 45 mins off.
Was getting code 121 for tps out of range. Swapped the tps for a motorcraft one. Got rid of that code. But I’m getting codes 172/177.

today while driving home. When it was running the worst and not revving at all. I unplugged the maf. Truck instantly idled better. And drove much better. Down on power. But atleast drove.

I’m thinking faulty MAF. (it’s a cheap cardone replacement. I have a hitachi one on order)

Thoughts please?
 


RonD

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Too bad you replaced all those things
New parts are a PAIN, can't trust them

This is odd, right
lean on one side, rich on the other
172 (R,M) Oxygen sensor not switching - system was lean - Right
177 (M) Oxygen sensor not switching - system was rich - Left

But I had this before on my 1994 4.0l, it was just after I had new clutch put in, so I had that info
The shop had REVERSED the O2 sensor plugs
The plugs are both near each other so easy to do
So benefit of hind sight, swap the plugs around

There is only 1 wire color difference in the 4 wires on each O2 plug in
Drivers side O2 has a red/black wire on the truck plug
Passenger side has a grey/light blue wire on the truck plug
That's on a 1994 4.0l, don't have a 1990 diagram

And it also fits the "gets better at WOT(wide open throttle), the computer ignores O2 sensors at WOT, this was one of my clues to fix mine

O2 sensors are also not used with cold engine, they need to be warmed up to 650degF, also another clue for mine

Engine ran great when I left the shop with the new clutch, cold engine, after a few minutes CEL came on and engine started running poorly
Had a steep uphill on the way home, so had to floor it, BINGO, ran great with lots of power, then ran like crap when I let off the gas again
Codes were lean and rich
 
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RangerFabWorks

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So I unplugged the sensors 1 at a time to make sure I didn’t cross the plugs. Maybe someone before me messed it up?
 

RonD

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Just look at the wire colors
 

RangerFabWorks

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Ron. Pm me your address. I owe you a bottle of scotch. I swapped the plugs. Running amazing now. Thank you so much.
 

RonD

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Good stuff (y)

Thanks for the offer
keeping our older 4.0ls running is enough for me, lol
 

Splash 4Ltr

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You may have solved my problem too RonD, I have the same engine & tranny that you have & the same symptom's that RangerFabWorks had. A shop put in a new clutch system in my truck, did they switch the O2 wires? I am going to check today, will let you know.
 

RonD

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Symptoms
CEL comes on
Engine runs OK on cold start then starts to act up once warmed up(O2s being used once they are above 650degF)
Engine runs OK at WOT(wide open throttle) after warm up(O2s are ignored when at WOT)
 

Splash 4Ltr

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Symptoms
CEL comes on
Engine runs OK on cold start then starts to act up once warmed up(O2s being used once they are above 650degF)
Engine runs OK at WOT(wide open throttle) after warm up(O2s are ignored when at WOT)
Hello RonD,Re O2 sensors I know you said that the Dr side should have red & black wires, the pass side should have grey & blue wires. I checked & I have grey & black wires on both sides plus 2 white wires on both sides. I changed those sensors some years ago and that's what the auto parts store gave me. The truck was running fine until
just a couple of weeks ago. Maybe the auto store sold me the wrong sensors?
 

RonD

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You are looking at the O2 side of the round plug connection, those have same colors on both sides, O2s come with a Lead wire(4 wires) and connector attached, and have standard wiring so can be used on either side

Color codes for O2 brands seen here: https://i.pinimg.com/originals/0a/42/62/0a426277744731981e8389f87d9d5523.jpg


The wire colors I posted are on the vehicle side of the round connector, they will have 3 wires that match on both sides, but drivers side and passenger side will have 1 different wire each
In 1994
red/black wire on drivers side
grey/blue wire on passenger side
 

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