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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 04-13-2015
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Black Smoke, Rough Idol

My 1993 ford ranger xlt 4.0 l v-6 was running fine, then started missing & Black smoke out of exhaust drove less than 100 miles used a tank of gas replaced plugs, wires, fuel filter. tps, maf, run high test, even tried a coil pack but didn't change idol so returned it. The smell of smoke is so bad after driving it for 2 days its making me sick. The engine has been rebuilt only with 1000 miles on it. I'm puzzled please help!!
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Old 04-13-2015
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I'm no expert but it sounds to me like you're trucks running VERY rich. Could be a result of a mistake in the rebuild process. Good luck, try searching the forum
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Old 04-13-2015
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Because of the black smoke(fuel), either your Fuel Pressure Regulator(FPR) is leaking or you have a stuck injector.

There is a quick test you can do, you use the Clear Flooded Engine routine found in all fuel injection computers.
Turn on the key
Press gas pedal to the floor and hold it down all the way
You are now in Clear Flooded Engine mode, and fuel injectors are shut off
(as soon as you release the gas pedal injectors will start working)

Try to start engine, it should NOT start, it should not even fire, keep that gas pedal down all the way

If it fires,(doesn't need to start just fire on 1 or 2 cylinders), then you have fuel leaking in, from FPR or injector

FPR is on the fuel rail it has the fuel return line and a Vacuum Hose connected to it, remove this vacuum hose and check it for fuel or fuel smell, if fuel is there replace FPR.
If FPR diaphragm leaks fuel is sucked into intake via that vacuum hose.

If FPR checks out OK then you will need to pull some spark plugs, all of them to be sure.
But first.............
Pull spark plug wires or unplug Coil Pack, we want no spark
Now do the Clear Flooded Engine test again, crank engine a few times, it won't fire now, no spark.
Now start pulling out spark plugs, if spark plug is wet with fuel then it's injector is leaking, you really should look at all the plugs to be sure, replace any injectors that had wet spark plugs.


If everything checks out as OK then you will probably have to replace the computer, but try unplugging the MAF sensor and starting the engine, with MAF unplugged computer uses factory air/fuel mix based on RPM, you should also see the CEL(check engine light) come on with MAF unplugged.
No CEL means computer is probably the issue.

Last edited by RonD; 04-13-2015 at 10:50 PM.
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Old 04-14-2015
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Thanks i sure hope not
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Old 04-14-2015
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Thanks so much, this ranger is my only transportation, being retired & disabled the cost of gas & parts are killing me. I put a lot of money in this truck when i retired but this issue is the first i've ever had. Thanks so so much Art
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Old 04-14-2015
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Icon9 1993 Ranger XLT 4.0L BLACK SMOKE, Rough idle??

Well i checked everything from fuel pressure regulator, maf, tsp, everything took plugs out after being in truck 3 days they were black, put new ones in still runs the same, un plugged maf sensor light came on so ecm is good. Fuel filter been replaced. This engine only has 1000 miles on it, LKQ rebuilt engine 3 years 110k mile warranty i'm lost still not running right and $80 in gas in 2-3 days less than 100 miles, stinks actually making me sick. please help!! Should i take it back to the people who put engine in? Art
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Old 04-14-2015
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It doesn't sound like you went through the diagnostic explained by RonD. That should help you understand more about what is going on. If that is more than you want to take on, you should take it back to the people that installed the engine.
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Old 04-14-2015
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well i printed it out and did it step by step turning the injectors off, hold gas pedal turn key on to turn injectors off, try to start with gas still head down didnt fire or even try to start. No fuel or smell on vacum side of pressure regulator. Took all plugs out they were black as coal, not wet just dry. Then he said unplug mass air flow if engine light comes on not computer. Could it be o2 sensors just asking, i have 2 upstream not sure contacted the company who messed it up, told them get me a rental car, take truck to ford. Thanks for reply just out of ideas
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Old 04-14-2015
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If your fuel system isn't leaking and MPG is in the toilet, and spark plugs are black then the fuel is getting burned.

Neither the MAF sensor or the O2 sensors can adjust the fuel trim enough to cause that.

So pretty simply from here.
Computer problem.

Here is how system works:

MAF sensor reports volume(pounds) of air coming in to intake
Computer uses 14:1 air:fuel ratio to calculate the amount of fuel that should be added to that air.
Air:fuel is burned in cylinder
O2 sensor reports the Oxygen content of the exhaust, too little oxygen = Rich, too much oxygen = Lean

If O2 reports Rich then computer opens each on that bank injector for less time, if O2 reports Lean then computer opens injector longer, this is called injectors "pulse width".

But here's the thing, the computer has limits for how long or how short the injectors should be open at specific RPMs, if this range is exceeded for Rich or Lean then CEL comes on to warn driver of a problem, your CEL didn't come on.

Your injectors are obviously open to long, and not stuck open.
O2 sensors failed to report Low Oxygen, could they be bad, but both failing at the same time would be very very odd.
(O2 sensors and Catalytic converter maybe be bad now because of this through, and I am surprised CEL isn't on for that.)

If MAF sensor is under or over reporting air volume(pounds) that would cause CEL to come on because O2 sensors would have shown Rich/Lean being out of range, i.e. doesn't match air volume.

Computer isn't reporting anything is wrong, computer is the problem.
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Old 04-14-2015
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Ron D if i replace the computer can i just buy a reman from autozone, advance or even ebay. Disconnect battery pos terminal, install computer thats behind drivers seat rear the back small seat i found it there. Can I RonD just plug it in, leave terminal off for 10-15 mins, put terminal on & gor from there for do i have to have it programmed or what, thanks for all the info. Art
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Old 04-15-2015
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That's the 4x4 module in that location, behind jump seat.

In '93 the computer, PCM, should be in the engine compartment, drivers side on the firewall, it has a large 60-pin connector, follow the large group of wires.

Yes, unhook the battery and remove the PCM, it can be a pain to get to the bolts.
Open the top of the PCM and see what it looks like inside.
It should look like this: ford eec iv

If you see black or corroded spots then yes, replace it, these don't fail very often so even used they are a good bet.
If PCM looks good inside then check the 60-pin connector, it could be the problem, if it gets water inside pins corrode and feed computer wrong data or voltage.
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Old 04-15-2015
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Thanks RonD for that info, i will keep u updated thanks Art
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Old 04-16-2015
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RonD Well today i took a reading on the fuel pressure in which was just like you said, pressure was good never dropped, run it was 30-35psi Took compute out, such a pain but got it out in 2 hours. Looked at it, is there any way i can get it checked out of the truck? Thanks RonD
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Old 04-17-2015
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Fuel pressure looks good, and if it doesn't keep dropping after engine is off then no leaking injectors or FPR

No, as far as I know not even a Ford Dealer can test a computer, in or out of the vehicle.

What does it look like inside?
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Old 04-17-2015
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Well RonD, I took it apart looks clean, im checking all of it with a magnifying glass to see if everything is complete & nothing broken. One resistor looks brown tint but not sure. I want to try to get something fixed on this u are awesome, heck im retired i should be fishing lol!! Anyways let my look real good & i will let you know. The service center who messed my truck up finally got me a rental so this gives me time to get things checked out. RonD when done checking it i will let u know asap thanks Art
P.S. They have had my truck for 6 months i drove it a week & nothing but problems, im not getting repairs dont there i'm trying to figure it out with your help before i take it to ford at there cost thanks Art
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Old 04-17-2015
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RonD, CAREFULLY LOOKING at this i found i guess a resistor blue oval i can make out A9315 its burnt on one side, i barely touch all of them this one looked brown so i took a tooth pick a scraped brown stuff from it and it was burnt so i guess it needs a computer. Gezz it was hard to find but thank god with your help i found it. Thanks RonD, Waiting for the response from the service centers ins to send me a check for a new one, i will keep u posted thanks again RonD
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Old 04-17-2015
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Your welcome............I hope.

Because of your past tests and the symptoms it really came down to a computer problem but.............from my end it is still just a guess.

Some Ford service dept techs are really good, others........well they are "trained".

One thing I remember reading a while ago was that 90% of all sensors(like MAF, TPS, ect) and controls(like IAC Valves, computers) that were swapped out by DIYers were actually good.
Well you kind of expect a high number there because they are just swapping out stuff until engine works again, lol.
BUT(big but), 50% of all sensors or controls swapped out by PROFESSIONAL mechanics were good and working fine.............that is way too high IMO, it could just be padding the bill, that would be the best reason, lol, because the only other reason would be too much training and not enough KNOWLEDGE.
Gasoline engines haven't changed at all in over 100years, they all still used the big 3 to operate correctly, spark, fuel, compression, I think "they" skip over that part in mechanic school in some cases.
You are getting too much fuel, so fuel pressure, fuel leak, or computer

Last edited by RonD; 04-17-2015 at 10:56 AM.
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Old 04-17-2015
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The question remains, what caused the PCM to fail? Was it old age, somebody shorting something, something not right in the electrical system, etc.? If it failed from old age then replacing it is should work well. What are the chances that something in the electrical system caused it and could eventually cause the PCM to fail again? I don't know enough about these systems to answer that question.
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Old 04-29-2015
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Hello RonD NOW I REPLACED COMPUTER u wont believe whats going on im so upset have spine surgery & back surgery next month im about to call ford bill monro let them deal with it. I put the computer in, keep in mind my battery terminals been off. I turn the key on a few times to ensure lubercation on motor without starting it. i go to start in the motor runs fulll throttle i turn key off its done this even after leave battery terminal off 5 mins then hook it back up still runs like i have my foot all the way down. im lost thinking i tried i just dont know what to do. the old computer resister was burnt but im thinking its caused alot of other problems im not aware of please help im loosing my mind , i think im going to send the computer back have them send me another if this dont take care of it , im sending the truck to ford RonD thanks Art

Last edited by bigblue93; 04-29-2015 at 08:21 PM. Reason: sending bad part back
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Old 04-29-2015
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I far as I can tell you have tested everything there is to test, Ford '90-'94 4.0l systems are just not that complicated.

When you first start the engine cold the computer uses it's own, in memory, fuel mix.
It does use MAF sensor to calculate air but also RPM to check sanity of MAF data, 4.0l engine uses 4 LITERS of air every 2 RPMs, if MAF sensor isn't reading that way then computer will turn on the CEL.

TPS sensor is just to get quicker throttle response, without it engine will still run fine but you would notice a lag/delay when you push gas pedal down because computer would wait until MAF sensors air flow increased before adding more fuel, which happens fast but you would notice.
TPS is like the accelerator pump on a carb, engine will run fine without it but you would notice if it wasn't working.

O2 sensors are not used on cold engine so they are off the table if symptoms happen when cold.

IAT(intake air temp) sensor doesn't have enough "pull" to run over rich, it can cause slight changes rich or lean but only slight.

ECT sensor can cause rich running but not for long, computer would question it's sanity if it didn't show engine warming up, and it is a slightly rich mix, more than IAT but not Black Smoke rich

That's about if for sensors

Engine racing when starting reads like IAC valve is fully open and not closing.
Or throttle plate is loose, pull off plenum(big air tube) and see if throttle plate is flopping around.
If TPS was showing computer Wide Open Throttle(WOT) there would be no fuel injectors running.
Fuel injection computers have a Clear flooded engine routine
Key on
Gas pedal to the floor, hold it down(TPS sends computer 4.6volts, WOT)
Crank engine
It won't start because it has no fuel.

I can't even see shorted wires causing this, it seems to just come back to computer
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Old 04-30-2015
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Thanks RonD IM taking computer off this morning sending it back for another and see what happens from there but first im going to see if that throttle plate is loose but i cant see that happen ive not touch the truck since i used $10 worth of gas to go less than 5 miles. I will keep you posted thanks again RonD
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Old 04-30-2015
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Well RonD if i had a lot of money i would give u some but im retired, disabled & loosing my mind. Once this is figured out i will try to donate something to you. Well the throttle plate is not loose, took computer out at 5am, going to return it. I will keep you posted thanks again RonD art
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Old 04-30-2015
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Just wanted to say that yes, Ron is fantastic, he is helping me with a problem with my Ranger.
My wife and I are also retired so I have to be careful with money also.

So good luck with your problem, sounds like Ron is correct with the computer being the
problem.

Mike

Last edited by mmisk; 05-04-2015 at 09:09 AM.
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Old 04-30-2015
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Thanks Mike he is awesome
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Old 05-03-2015
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Take the computer out and check it for corroded or broken wires to the diodes look for black circles on the board itself under the diode's.
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