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4.0L OHV & SOHC V6 Tech General discussion of 4.0L OHV and SOHC V6 Ford Ranger engines.

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  #1  
Old 12-03-2014
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Ford Ranger V6 4.0 5 Speed Engine Bogs down

1994 Ford Ranger V6 (X) code VIN. Engine bogs down after driving about a half mile. I have replaced MAF, TPS, IACV, PCV valve and line to manifold, plugs, wires, fuel filter and air filter. Have checked for a vacuum leak but have not found anything, idles fine.
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Old 12-03-2014
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Stop replacing stuff, you will make it harder to find the problem and waste your money.
50% of replaced sensors still worked fine, that's from Pro mechanic statistics
I would say DIYers would be closer to 90%

Plugs and wires, and Fuel and air filters are always good to change

Cleaning MAF sensor would have been the first thing to do as that is a common issue with Fords bogging down, but not usually on startup since computer is running preset fuel mixtures until it warms up.

I assume this is on cold start up since it only drives a mile?

It could be a collapsed cat converter or muffler.
These rust from the inside out since H2O(water) is one of the by-products of burning gasoline(H) with air(O).
If your exhaust gets clogged up then pressure at the exhaust ports won't allow new fuel/air mix to come in and power drops.
This is usually described as bogging, check exhaust pressure at tail pipe while some one revs engine, or use a vacuum meter.

Just to narrow it down the normal cold start should be like this
Turn on key
Fuel pump comes on for 2 seconds
Computer starts up
Crank engine
Computer opens IAC Valve all the way
Engine starts and RPMs are at 1,500+(because IAC Valve is open all the way)
Computer then closes IAC valve to pre-set idle target according to engine temp(ECT sensor data), 1,100 cold, 750 warm approx.

If idle is not staying high cold then ECT sensor could be reporting wrong data, these rarely fail but not never fail, they can be tested with OHM or Volt meter.
Failed or failing ECT sensor would usually cause poor cold start running or poor warmed up running, but not both.
ECT sensor has TWO wires, it is next to the ONE wire Sender for the dash board temp gauge, located just above thermostat housing.

Warm or cold computer doesn't use O2 sensor data for at least 2 minutes after startup, 02 sensors don't work until they are above 650degF.
If cold they are not used until engine temp is above 190degF so 5 to 8 minutes of driving
Computer is in Open Loop so really doesn't use many sensors it is running pre-set data programmed at the factory.


On a '94 there will be a Fuel Pressure Regulator(FPR) on the fuel rail(upper side of engine), the FPR will have fuel lines and a vacuum line attached to it, remove this vacuum line and smell it for gasoline, if there is gas in there then FPR diaphragm has failed, and when engine starts unmetered fuel is being sucked in to the engine causing it to bog down.
MPG would be very bad


What happens after the bogging down happens, does it recover at higher RPMs or just stay sluggish?
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Old 12-04-2014
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Thanks so much for the reply, I have stopped replacing stuff already as I am not sure which direction to go at this point. I drove the truck yesterday for about 20 miles and saw much improvement early on and then back to the same problem. I searched for a vacuum leak to no avail. Not sure how much more I can do as I do not have the special tools required to continue troubleshooting. I just want the truck to run well so that it will become dependable as a daily driver.

In answer to your questions I will start by saying that this is not just a cold condition, I did drive it for a while and did nor see the problem until about 5 miles into the drive, not to the same extent, but still definitely the same problem. IE While driving I was having to apply more throttle in order to keep the vehicle up to speed due to bog down. If I floored the pedal the vehicle would present slight hesitation and then would pick up speed like a bullet. So long as I kept my foot down it would work fine, if I let up off of the accelerator the vehicle wants to slow down and stall. I do not have the ability to read the codes and took it to my local Advance Auto and they do not have the ability either. I will try to use the light method later today and see if I can get it to display something useful. Also the fuel economy is terrible, so I will check the FPR and vacuum line attached and get back to you on that. Thanks for the help.
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Old 12-04-2014
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What about the cold start?

Does it follow the routine?

High idle at start up then idle slowly lowers as engine heats up.


Also, after engine is warmed up, leave it idling and unplug the connector on the IAC Valve, IAC Valve will close.
Idle should drop to around 500rpm or engine may even stall, either means no vacuum leak, or at least no leak that would effect performance much.

If idle stays high then there is a leak.

Another test you can do is to use the "Clear Flooded engine" routine that is part of all fuel injected engine computers.
Turn key on
Press gas pedal all the way to the floor and hold it there(turns OFF fuel injectors)
Try starting engine

Engine should not start and should not even fire, try to start.
Key on + gas pedal to floor(TPS above 4.6volts) tells computer to turn off fuel injectors but leave spark on, so.....clears flooded engine.

As soon as you release the gas pedal injectors will start, so leave it down all the way.

If engine fires during this test it means it is getting fuel from somewhere, could be leaking FPR, or could be from leaking fuel injector.




Only tool needed now a days is a volt/ohm meter
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Old 12-04-2014
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I will run the cold start and the "clear flooded engine" and see if I can make some headway. I di unplug all of the sensors that I replaced one at a time and received the indication that it was unplugged and the idle of the truck slowed. It seems that all of the sensors that I replaced are all working properly. I will try to read the codes later today when I get home from work. I will let you know the answer to your specific questions, later today. Thanks again for the help.
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Old 12-04-2014
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When you do read the codes the unplugging of the sensors should show in History codes, just a heads up of why those code may be there.
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Old 12-04-2014
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Just performed a normal cold start and received al the correct indications. Will try reading codes next.
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Old 12-04-2014
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Here are the codes:
Key on engine off
111
15
12
512

Key on engine on

99
81
57

Hope this helps to narrow some things down. Thanks again for the help. I did look up the codes and there is one that seems like it could be the answer, (12) Idle speed control motor, but I am not sure with this many codes displayed what to chase. I also need to do the ISC learn procedure so I will go and do that now.

At higher RPMs the engine recovers and runs fine so long as I keep my foot to the floor.

Last edited by dskkri1; 12-04-2014 at 05:37 PM. Reason: Forgot an answer to a previous question
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Old 12-04-2014
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Codes are not making alot of sense
Ford computers were changing to 3 digit codes in '91 so by '94 you should be getting only 3 digit codes, BUT there are some Fords of that vintage still using 2 digit codes, so not unheard of.

But you wouldn't get 2 and 3 digit codes, it would be one or the other

11 system OK
11 system OK
51 ECT sensor out of range
25 Knock sensor
12 IAC valve not controlling idle correctly

99 IAC Valve needs to learn correct warm idle setting
81 boost control solenoid
57 intermittent park/neutral switch

There is no knock sensor or boost sensor on your engine
Park/neutral switch could be referencing clutch switch, but never seen this code come up before.

ECT sensor can be tested with volt meter, and could cause a rich mix, bad MPG.

IAC Valve codes make no sense at all

What I don't see are any performance related codes, like running Rich(42) for your bad MPG.

Your computer could be what is going bad.

Disconnect negative battery cable for 10 minutes, this should reset computer, then drive it as best as you can for a day and get the codes again.

Last edited by RonD; 12-05-2014 at 09:35 AM.
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Old 12-05-2014
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OK will do, thanks again for the help. I will look into a computer for this truck I am sure that will cost me an arm and a leg. Just want to get to the bottom of this one.
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Old 12-11-2014
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Here is the new set of codes after disconnecting the battery and reconnect with running after. Still all the same symptoms. No power after start-up and vehicle will only accelerate if you floor the accelerator.

111, 157 KOEO
99,81,57 KOER

Looks like 157 is referring to the MAF which is hard to believe seeing that it is brand new. Let me know what you think. Thanks again.
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Old 12-11-2014
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Assuming all 3 digit codes you have
111 157
998 157

998 = Did not pass Key On Engine Off test yet (Get 111 in KOEO first)

157 = Mass Air Flow signal is/was low or grounded
So you could just have a bad(grounded) wire.

get a volt meter and read here for voltages you should see at MAF wiring: Ford Ranger Mass Air Flow Cleaning, Removal and Installation
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Old 01-12-2015
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Computer fixed the problems

Good afternoon,

I just wanted to get back to you and let you know that this was a computer problem for the most part. Replacing the computer fixed the bogging down problem and all of the other symptoms that were present. I am now getting a check engine light after warm up but no other symptoms what so ever. The truck is actually running great. Thanks so much for your help and patience. I will report the codes again as soon as I read them. By the way the computer was 194.00 55.00 core plus tax not too bad and it was brand new with a 1yr warranty.

Thanks

Dave

Last edited by dskkri1; 01-12-2015 at 12:37 PM. Reason: Forgot to add info about computer
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