94 4.0 Backfire through exhaust

[FoosballPaul]

Brief history and current diagnostics efforts:
Engine swap, original engine (94 Ranger 4.0) did not have EGR or Camshaft sensor. Swapped engine out with engine from 94 Explorer that has EGR and camshaft position sensor. Removed EGR and applicable ducting and plugged egr mount hole in exhaust manifold. Installed new plugs, plug wires, ignition coil pack, and oxygen sensors. Original wiring harness does not have plug for camshaft sensor so that is not hooked up.

Symptoms: When engine is accelerated at a gradual pace from idle to 4K rpms engine runs smooth with no hesitation, knock, or miss. If engine is accelerated at quick pace or if transmission (automatic trans) is engaged there is a very loud and intermittent backfire through exhaust system. I have checked for air leaks in exhaust system and vacuum leaks and can't find any. I believe the 94 Rangers had the older OBDI system so I have no way to read codes. I need to get this truck back on the road for my son to drive to work.
Any suggestions greatly appreciated.

 

[RonD]

I assume you are using original PCM(computer) that came in the truck.
Yes, 1994 was the last year of the EEC-IV PCM in Rangers, it used OBDI communications/codes

Check firing order on coil pack AND follow wires to each cylinder.

Because the Waste Spark system is used, 2 spark plugs fire at the same time, so engine can seem to run fine but exhibit odd behavior if firing order is off
Coil pack
3 4
2 6
1 5
Front

That 5 6 4 can get mixed up.
OK, that's the easy one to check.

Fuel pressure could also be an issue, revving engine in neutral doesn't use alot of fuel, revving engine quickly or under load does, if pressure is low then engine could be getting lean mix causing the back fires.

The TPS(throttle position sensor) is the "accelerator pump" on a fuel injection engine, in a carb the accelerator pump would give an extra squirt of fuel when you pressed down on gas pedal, the quicker or more you pressed down the more gas was squirted in, the computer needs a "heads up" to added extra fuel, the MAF(mass air flow) sensor is too slow to react, just like jets were in a carb .
If TPS wasn't working or not working right then engine would lean out when revved quickly or under load, causing back fires, same thing happened when accelerator pump was failing in a carb engine.

Harder one is fuel injector or spark plug, if a cylinder is running rich, or misfires, unburnt fuel mix can make to exhaust manifold and is ignited by heat from next cylinders exhaust valve opening, causing a back fire out the exhaust.
This could just be a weak spark plug or faulty injector.
Under load is when you say it happens the most, that is when the cylinder's temp goes up, PCM richens the fuel mix under load and weak spark plug will often misfire under load.

You can try a Clear Flooded Engine test
All fuel injection computers have this routine built-in
Turn key on, computer is on
Press gas pedal to the floor and hold it down, TPS(throttle position sensor) is sending computer above 4.5volts with throttle wide open, with engine at 0 RPMs and throttle wide open computer will turn off Fuel injector pulses but leave spark on, this is clear flooded engine routine, lots of air no fuel, as soon as TPS voltage drops below 4.5v then injectors will start working, even while cranking engine.

Now try to start engine, holding gas pedal down all the way
Engine should not start or even fire a little, there should be no fuel getting in

This test does two things, it tests TPS is working and if a fuel injector might be leaking.

This test/routine is also handy if an engine has been sitting awhile, you can get oil pumped thru the engine at cranking speed so no dry spots on startup

 

[FoosballPaul]

Thanks for the suggestions. I will give your suggestions a try and hopefully reply back with positive results.

 

[Spott]

OBD1 error codes can be read with a 12v test light by counting the flashes. I think there's an article in the tech library describing this and the resulting codes; if not, Google can help you find one of many pages out there with the information.

 

[FoosballPaul]

After further testing found following:
Strong spark at all plugs and plug wires routed properly.
Fuel pressure checks good, 37 psi while engine off/34 psi with engine off and holds pressure.
No cylinders firing on #1 bank. Can't check fuel injectors on that bank unless upper intake is removed. Is there any way to check for power to injectors upstream of injectors? Maybe check power at wiring harness or connection. I have Haynes repair for vehicle but it doesn't have very detailed wiring diagrams for fuel system.

 

[RonD]

The fuel injectors all get 12volts when key is on, computer Grounds an injector to open it.

There is a Red wire on each injector that is daisy chained from one injector to the next.
Red wire comes from EEC Relay, this relay closes when key is on, it also powers EEC(computer), fuel pump relay and Coil Pack.
It is in the engine fuse box.

Test battery voltage first, then with key on test Red wire voltage at as many injectors as you can, if you have a voltage drop of over 3volts you probably have a bad/corroded splice

Your '94 probably will be Batch Fire injection, on the V6 this means that computer will open 3 injectors at the same time, so from the computer there will only be 2 "ground" wires, each attached to 3 of the injectors.
Should be a Tan wire and a White wire used on '94.

If you see Red wire and then a different color wire at each injector then you have Sequential fuel injection, so 6 "ground" wires going back to computer on a V6.

I would disconnect Coil Pack wire and then crank engine a few times, a no start of course, then pull out spark plugs and see if any are dry, that would confirm injector not working on that cylinder(s)

Ford fuel injectors are low impedance, about 14ohms, with wire disconnected you can measure for that with OHM meter, 11 to 17ohms is fine

 

[FoosballPaul]

If I understand correctly, if I am getting power to the #2 bank of injectors I should be getting power to #1 bank of injectors but at different sequence. I will try turning engine over with coil pack disabled to check for fuel in cylinders. Still trying to locate wiring diagram to injectors to check for power in the harness/wire bundle to #1 bank without removing upper intake.
Thanks for the suggestion.

 

[RonD]

No, you will have 12v(battery voltage) at all 6 injectors when key is on.

But the injectors are not Grounded so won't open.

Electrical "Power" needs to flow from a higher voltage to a lower voltage for any electrical device to "work"(actually it is the other way around but that's another story )
If you connect a 12v light bulb to battery "+" nothing would happen, even if you connect both light bulb terminals to battery "+" nothing would happen.
No "power" is flowing thru light bulb.
If Battery "+"(12v) and battery "-"(0 volts) are hooked up to light bulb it will glow because power is passing thru the filament, from 12v to 0v

Same with fuel injector, it has the 12volts but no 0 volts(ground) so nothing happens.
Computer controls the Ground.

To test if fuel injector ground is working you need a Noid Light, this hooks up to and between Ford connector and fuel injector, when you crank the engine the Noid Light will pulse on and off as it is Grounded and unGrounded by computer, 12v test light usually won't work for this.

 

[enjr44]

Electrical "Power" needs to flow from a higher voltage to a lower voltage for any electrical device to "work"(actually it is the other way around but that's another story )

Depends on where you got your learning (training). Or it actually does go from high to low. When I was in school I was taught low to high; but, no one could factually tell for sure since you can't see (couldn't see) electrons or electron flow.

 

[RonD]

Depends on where you got your learning (training). Or it actually does go from high to low. When I was in school I was taught low to high; but, no one could factually tell for sure since you can't see (couldn't see) electrons or electron flow.

Yes, exactly, there is actually no "right" answer unless you are specific in what you are looking at.
Electrons have a negative charge so will flow towards positive charge
But electricity is not all about electrons, higher voltage will flow towards lower voltage, but even that has exceptions, lol.

And a bit pointless when talking car electrics, probably should not have even mentioned it, but have been called out for not mentioning it, so "right" answer still eludes us

 

[enjr44]

But electricity is not all about electrons, higher voltage will flow towards lower voltage, but even that has exceptions, lol.

Man, I hate to hijack this guy's thread cause he is trying to fix a problem and we are gassing.

But, 50 years ago, I was taught that voltage does not flow, period. It is like water pressure, you have it or you don't. It just creates the path for electron flow. Power (watts) is what makes things happen. Higher voltage just makes it happen with less wasted heat.

 

[RonD]

Man, I hate to hijack this guy's thread cause he is trying to fix a problem and we are gassing.

But, 50 years ago, I was taught that voltage does not flow, period. It is like water pressure, you have it or you don't. It just creates the path for electron flow. Power (watts) is what makes things happen. Higher voltage just makes it happen with less wasted heat.

Yes, it really comes down to what you call things, electricity and electrical energy are often used to mean the same thing.

Electricity does flow, it just does it very slowly, electrical ENERGY flows close to the speed of light.
Electricity is not lost in a circuit, the energy is.
Electricity is the "medium" used to transfer the electrical energy.

Like air is the medium for sound, the air doesn't move but is required for the sound waves to travel.
"In space no one can hear you scream", lol, no air

I like the billiard ball example for electrical circuits.
There are 40 billiard balls in a tube loop , all touching.
The balls are the "medium", the electricity.
I push 1st ball at the end of the loop, I am the Energy.
All the balls move slightly and slowly, but the energy moves fast thru each ball to the last ball, and is lost when last ball moves, but all the electricity(balls) are still there, electrical energy was lost/used not electricity

Clumsy example but that's what I learned in school so I like it

 

[Milton]

Electrical power measured in watts equals current measured in amps time electromotive force measured in volts.
An amp equals a large number of electrons (1 coulomb) flowing past a given point each second.
Each electron is carrying a given amount of energy/electromotive force as measured in volts.
So the power/wattage consumed by the circuit is the amount of voltage flowing past a given point each second.
My analogy is an electron is a bucket of energy. Voltage is how much energy is in each bucket. Current is how many buckets are flowing through the circuit. Power is how much energy is flowing through the circuit each second, or current times voltage. The formula is P=I*E

 

[RonD]

Couple of issues, electrons don't move down a wire very fast, 3ft an HOUR, would be typical, and they move in the opposite direction of energy flow, assuming DC system, because electrons are negatively charged they drift towards + and are repelled by -.
Electrons are moving fast, just not in a straight line, the energy is passed from one electron to the next by collision, so the energy travels very fast, like the billiard ball example and like the balls the electrons don't move very much.

Coulomb would be the measure of the energy, 1 amp = 1 coulomb/second, so not electron movement down the wire passing a point but bouncing around in the wire at that point.
And the more electron movement/collisions there are the warmer the wire will get, to reduce the heat you can reduce the energy(amps) or increase the available electrons, larger wire.

In an AC circuit electrons pretty much stay put in their location in the wire, because + and - alternate

 

[Milton]

By definition:
An ampere is a unit of measure of the rate of electron flow or current in an electrical conductor. One ampere of current represents one coulomb of electrical charge (6.24 x 10^18 charge carriers) moving past a specific point in one second.

A volt is the standard unit of potential difference andelectromotive force in the International System of Units (SI), formally defined to be the difference ofelectric potential between two points of aconductor carrying a constant current of one ampere, when the power dissipated between these points is equal to one watt.

Note the term "charge carriers". An electron is one type of charge carrier, so are protons and any ion. So yes it is the net movement of the charge carries that counts, not the simplified view of just electrons. Do electrons flow? Yes. Ever seen a high current vacuum tube diode in action? You can see the electron flow and it's faster than 3 ft/second, of course that's across a vacuum.

As for AC vs DC, if a charge carrier moves from left to right then right to left with in one second that counts as the flow of 2 charge carriers.

For most of our simple circuits viewing current as the flow of electrons with each electron carrying a specific amount of voltage works.