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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  
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Misfire codes Coming Up

Hello all,
I have a 1999 Mazda B4000 4.0L v6 with the pushrod (OHV) engine. I'm new to this engine, so I'm really starting to learn about it now. I was driving home the other day, and I was a little over 2 hours from home when I got a flashing CEL and my engine started to sputter. I've had this issue before, I knew right away it was misfires. I pulled over, ran the codes, and got P0306 and P0302, misfires in cylinders 6 and 2. I knew I couldn't do anything at the time, so I cleared the codes and continued driving. A very short time later, flashing CEL comes back, only code was P0302. I carefully got home, kept the RPMs steady, only forced it up a gear to get up some hills. While I was driving, the flashing CEL would come on at seemingly random, and inconsistent times. I know that driving like this is not recommended, but I was low on options.

The next day I replaced my coil pack, wires, and checked the #2 spark plug, and it looked fine. No difference to how the engine runs, still super rough idle and misfiring. The CEL light has not come back on which is interesting, granted I haven't driven the truck father than a few hundred feet. I picked up a fuel injector for #2, I figured that that was the best next step? I'm going to be looking into that today.

I also discovered late how to move my damn fuel rail, which seems like it's built into the metal that runs between my upper and lower intake manifolds. Apparently I need an E-torx bit to loosen the bolts that hold the upper manifold on to raise up the fuel rail and pop out the fuel injector.

Does anyone have any input, if I'm headed in the right direction, or any tips on that else I could try. I know that after the injector, if that doesn't do the trick, then I could check the compression, but I don't know the first thing about doing that.

I also live in New England, and we're having a cold snap from the other side of hell so I have to spend my time wisely.
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On the 4.0l and 3.0l coil packs there are only 3 coils in there, not 6
So 2 spark plugs share a coil, both spark/fire at the same time
They are Match Pairs same as pistons are Match Pairs to balance an engine

In these V6s the match pairs are:
3 4
2 6
1 5

So 3 and 4 pistons are at TDC at the same time, as are 2 and 6, and 1 and 5
This balances the rotating mass in the engine

Ford uses a Waste Spark system, very first spark system invented, still used today, very simple and reliable.

If you look at above Matched Pairs you may have noticed the firing order on the coil pack matches it
[3 4]
[2 6]
[1 5]
Front

Those are the 3 coils in the pack, and why the one side is 5 6 4, not 4 5 6

So your diagnosis to swap coil pack was a good one since 2 and 6 share the one coil.
But there can be other issues within this shared wiring
The 2 spark plugs are wired in Series, so to compete a circuit both wires and spark plugs on that one coil must be good.

You can reverse the wires on the coil pack
4 3
6 2
5 1
front

It will still work fine that way
I do this every 5k miles or so because I use cheaper copper spark plugs, and because of series wiring the tips on one bank and the centers on the other bank wear out faster, by reversing the wires I get equal wear from side to side
Yes, I am cheap, lol.

But reversing a pair can tell you if problem might be in coil pack or wire and plug, see if misfire moves to opposite cylinder or stays put

And just as a heads up
The 4.0l OHV engine EATS spark plugs, motorcraft seem to last the longest, autolite next
Regular copper or DOUBLE platinum, never use single platinum on a Waste spark system, it is a "waste" of money, as one bank will wear out the same as regular copper
I have had new spark plugs fail early so don't assume new is OK, swap it to 1 or 3 and see if misfire moves

Last edited by RonD; 2 Weeks Ago at 01:03 PM.
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I'll do that swap to check the spark plugs. You mean move the actual spark plug itself, correct? If I look at the plug and it's burned out then clearly it's bad, could it be bad even if it looks okay?

Also, there is no CEL. It was flashing at various times on my ride home the other day, and I don't believe I cleared it between then and now, that would have been a poor decision. I just put it all back together and drove it down the road, same issues as before, but there is no CEL. That being said, I can't tell if the misfire moves. Does O'Reilly's have an OBDII tool that I can rent that shows the codes despite there being no CEL? I'm at a loss.
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Yes, to test spark plug itself swap it with another cylinder
Yes, looks can be deceiving, as men we should already know this, "she's not pretty she just looks that way", lol.

I have an old coil I use to test spark plugs, have had a few that "looked pretty" but were dead, weak or intermittent


Yes, OBDII reader can get History codes, codes that were set but not enough times to trigger CEL
Flashing CEL warns of possible engine damage, usually from misfires

You can buy a Bluetooth OBDII reader for under $30, they display on your smartphone or tablet via Bluetooth link so wireless.
APPS are free or $5 if you need more viewing options
These work on ANY vehicle sold in the US or Canada after 1996, required by law, so not a Ranger or Ford thing, not even a made in North America thing, so a good tool to invest in.
If you get one of these also get the Extension cable with it, usually $5-$8
OBD ports are often behind a door in the dash, the Bluetooth reader is small but may not fit inside the door, the extension cable is used then.
OBD port has power so no batteries involved.

You can view LIVE data while driving with these so very good diagnostic tool, and easy to use once you get the hang of it

read reviews for your best choice
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I have an OBDII tool, it's wireless and uses the "Torque" app on my phone, super useful little thing. I have the live reading of RPMs running all the time whenever my engine acts up. I was tinkering with it, and I'm not sure how to get to the historic codes, but I'll do some digging into that. I remember one of my guys at O'Reilly's told me that they have a $600 or so diagnostics tool that shows way more detailed data, that's the one I was referring to.
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It would be the APP not the interface unit

Vehicle computers speak Machine Language, all 1's and 0's, but stored as hex bytes, 0-9 A to F for 16 total possibilities

Good look at whats available here: https://en.wikipedia.org/wiki/OBD-II_PIDs

So the user selects the information he wants using the APP/reader, it translates that and sends the Computer a Packet ID(PID) for the requested info, computer responds with data bytes for that PID, APP/reader translates that in to "english".

So APP/reader either has the PIDs needed or it doesn't, it is a straight "ask and you shall receive" system, no encryption or "limited access"
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Update: Spark plug in cylinder 5 had a lot of oil on it. Did a compression test, cylinder 5 had low compression. Took off intake and valve covers, the springs all look alright. I'm going to give them all another once over, then take off the heads and inspect the valve seats, heads, gasket, and block.
To have oil getting to the spark plug, it has to either be leaking through the valve openings or through the heads, correct?
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Usually only valve guide seals or rings
Valve guide seals won't effect compression, rings will

Can you do a WET compression test before disassembly, that will tell you if it is rings or valves that are causing lower compression in that cylinder
If you add a teaspoon of oil to a cylinder, compression test will always go up, but how much up tells you the tale.

i.e. if compression average on all cylinders was 155psi but one was 135 and you added oil to it and retested, if it came up to 145-150 then rings are the problem
If it was still under 145 then a valve issue

The oil provides a temporary seal for the rings but not the valves
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So you're saying that more often than not, the oil is coming down from above the valves versus up from the crankcase?

Valve ring and valve seat are the same thing, right? I'm not sure I understand that completely. So rings affect compression because beyond them is the intake/exhaust?
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There is only two ways oil can get into a cylinder, intake valve or piston rings

Intake valve can get oil from two places.
1. PCV system, pulls oily air from inside the crank case to intake manifold to be burned in the engine, if the cylinder with most oil is right below where PCV valve hose connects to intake then it is likely that is the source of the oil.
2. Valve stem seal, all valves have a rubber seal on their stem, this prevents oil from valve train area from being sucked into the cylinders, intake manifold runs with negative air pressure(vacuum) all the time, so a hardened or cracked seal will allow oil to be sucked down the stem and then sucked into the cylinder with new air/fuel mix.
Exhaust valve seals can also leak but that causes more problems with O2 sensor and Cat converters because it is not "sucked" into cylinder, it is pushed out with exhaust

No "valve rings"

Pistons have rings, they are really "C"s not full circle "rings"
The piston and cylinder wall gets sprayed with oil while engine is running this reduces friction and cools the piston and walls
There are 3 rings on a piston, 2 compression rings at the top and 1 Oil ring at the bottom

As said above the intake always has negative pressure when engine is running, well that negative pressure is CREATED BY the pistons/cylinders
As the piston goes down is sucks in the new air/fuel mix with that negative pressure.
If the pistons rings are failing then it can also suck oil up from cylinder walls past the rings
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I felt around the top of the intake valve(inside the intake, not in the valve cover area) and there didn't seem to be any oil in the area.

If the leak is the piston rings, how will I know that from a leak down test? I finally found the equipment for that test, but the adapter doesn't fit my spark plug hole and the hose doesn't fit the quick disconnect coupling on our air compressor, so I'm working on that at the moment.

To replace piston rings, I need to pull out the engine, right? That is something I don't have the space, time, nor resources to do. :/
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Compression test will tell you if it is valve or rings
Leak down is more for the state of the cylinders valves and ring seals

i.e. if you put 100psi air pressure into a cylinder at TDC and gauge shows 93psi then you have 7psi leak down, or 7% loss of pressure, which would be a new engine
15% leak down would be old high mile engine.

But with leak down test you can also listen at the tail pipe and intake, you would hear if a valve was not sealing all the way by the hiss of air
Also in some case the oil filler tube and you might hear the hiss of air from bad rings.
You can also add oil to a cylinder AFTER doing the test, then rotate engine and retest with oil helping to seal the rings, it will seal better but how much better tells you if Rings are the main loss of pressure

Metal valves against metal seats and metal rings against metal cylinder walls CAN NOT make an air tight seal, so all will leak air, its the amount of air that matters

Compression test DRY and then WET(oil added) can tell you the same thing as far as Rings or Valves and loss of compression(leak)
Leak down can tell you which valve, intake or exhaust, or rings
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The exhaust valve in cylinder 5 was destroyed. I'm going to inspect all of the springs, valves, guides, rockers, and pushrods, but more than likely just replace most of them while I'm in here.

I've done some digging into valve seats, and the only way to remove/install that I've found is to cut or grind them out and then press the new ones in, is that the general way of going about that?
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Yes, thats the only way

Research new head prices as well

Good read here on the 4.0l OHV engine/heads: Rebuilding The Ford 4.0L Pushrod V6 : The Ranger Station

1998-2000 had the smaller exhaust ports for higher velocity

A burnt exhaust valve usually has a cause, Lean condition in a cylinder makes whole cylinder hotter, exhaust valves get the hottest since they are not cooled by incoming air/fuel mix

All valves rotate as they open and close to prevent "hot spots", if valve stops rotating then it will burn
Valve seats are cooled by coolant, and thats how valves are cooled, by good contact with the valve seats when they are closed, valves are closed 3 out of the 4 strokes in each cycle so they are closed and cooled 75% of the time.
So valves and seats are ground at opposite angles to make the best/largest surface area contact to dissipate the most heat possible, also best seal during compression stoke and firing.

So check rocker on that valve and its stem to see if there is something that shows that it stopped rotating
And injector for that cylinder might be suspect

Last edited by RonD; 1 Week Ago at 01:37 PM.
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I'm looking at Rockauto for all of the parts to rebuild the heads, and they add up. It looks like replacing the whole heads altogether might be cheaper, especially since they come with the valves assembled. I would just hang onto the rockers, rocker shafts, and pushrods, unless some of them need to be replaced. I'm worried about the valve seat under the burnt exhaust valve too, I got a quote from a machine shop nearby of just under $500 to grind down and install all new valve seats. Sooooo I'm thinking new heads. Or just one new head, since the issue was just under the drivers side one. Other than being down this deep into the engine and might as well changing out both, do you have any input or warnings against just replacing one head?
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4.0l OHV was known for cracked heads if overheated, so people often replaced just one head, the cracked one, so not an issue with that.

But I would have other head pressure tested and surfaced, also the valve guide seals changed unless you have a spring compressor.
You might want to do this first, just in case, might get a better deal if you do need 2 heads, set

You need to match the casting if only replacing the one head, so '99 engine would need the 98TM casting, used from 1998 thru 2000 model year
And with the 1998-2000 you would still need 98TM casting if swapping both heads unless you changed exhaust manifolds as well

Last edited by RonD; 1 Week Ago at 09:39 AM.
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The broken valve is on the drivers side head, and the crack is on the passenger side. I'm considering getting used heads from the local junkyard, I know they have an engine for $650, but with the chance of it having similar problems, I don't want to risk it, plus the money and time spent swapping it out. Would you recommend using used heads? Should I bring them to a machine shop to be inspected? I'm going to clean up the burnt head and see if it's alright, and then see if I need both.

Based on our war with those bolts, the exhaust manifolds are never leaving that truck lol
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The heads have to be 98TM castings

Call the machine shop and find out how much to clean, pressure test and surface the heads
Add that to the cost of the used heads to get "your" cost
Assuming these are money back if one is cracked, if sold "as is" then could be risky with used 4.0l OHV heads.

And then find out price for rebuilt/new heads with valves and shipping to your location, to get "your" cost

Compare the two prices and go with your gut

Also ask machine shop how much for them to get you rebuilt 98TM heads, they often source parts and can get some better deals than you can, and they can get bare heads install valves and seat for less than on-line heads and shipping, heads are heavy, lol.
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I've been searching a bunch of different places for heads. And most quotes to clean and test heads run up to $450 for a pair.

Last edited by Fastcubesolver; 1 Week Ago at 04:16 PM.
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Clean, pressure test and surfacing ONE V6 head should run $60-$70
Cleaning is $20
Surfacing is $35
Crack test $25

So $120-$140 a pair
But for sure under $100/head, it is all labor

Not sure you could even spend $225 labor per head
Valve grind on V6 should be $120 per head, $20 per valve
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Got everything back together, then we took off the coolant hose that runs into the front of the lower intake manifold, with intentions of taking out the thermostat to flush the system. The LAST bolt we put back in strips the threads out of it's hole in the manifold. We're waiting for a close quarters drill and a set of helicoils.
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