Several of you have provided helpful diagnostic tips on my two previous
posts on this subject. Thanks.
'nother coupla questions.
While checking fuel pressure with KOEO, the pressure immediately came up
to 35 psi, then dropped back down toward zero. With KOER the fuel
pressure remains a steady 31 psi (engine cold). At shutdown, the
pressure drops to zero in about 3 to 4 seconds.
Is that indicative of one or more injectors stuck open? (All 8 injectors
Would a misfire between two spark plug wires likely damage the injectors
of those two cylinders when the injector of one was open during intake
stroke while the other was firing?
It's possible you have a suck or leaking injector. Mr. Moats pointed out
the other likelyhood for the drop in pressure you reported. I'd like to add
that, although the fuel pressure in my '93 Cougar (V6) acts just like the
manual describes, my '84 Bird (5L) with TB ingection acted like you
described from the day it was new. Ford wasn't worried and I drove it 180k,
then gave it away like that. I know it sounds obvious, but are you sure the
plug wires are on the right plugs? I swapped two when I put the new wires
on and had an awful time figuring out why the car ran badly. It set misfire
codes for one cyl but didn't set the other. Of course, that was on a '95
with EEC-V, I think yours is still EEC-IV. Have you tried the built-in
injector test using the EEC?
Let me reiterate from my previous posts. From the moment of ignition
there is heavy smell of gasoline. The tail pipes reek of gasoline and
there is much, much smoke. This condition did not exist prior to the
misfires between two cylinder plug wires.
I would concur with Moats if it were not for the gasoline pouring into
one or more cylinders. The fuel pressure is normal while the engine is
Since the excessive fuel problem evidenced itself at the same time as
the misfires, cause and effect thinking leads me to believe that the
misfiring cylinders (#3 & #6) damaged at least two injectors. That would
explain the heavy fuel smell at ignition. The injector fuel supply
manifold would have drained into one or more cylinders at last shut
down. Then, at key on, the fuel pump immediately shoves more gasoline
past defective injectors.
If remember correctly, did not this problem happen right after you replaced a
wire? So I'll say it again, go over your work. You might have with out knowing
it unplugged something, put the wrong wire to the wrong plug ect. There is no
way a misfire will damaged an injector.
No, I said that I temporarily repaired the misfire by insulating both
plug wires. Please assume that I have a modicum of mechanical aptitude.
I just do not work on autombile engines unless I am direly compelled.
I did say that two spark plug wires were shorting to each other. I
haven't checked the timing sequence of those two cylinders. However, I
easily can conceive where a fuel injector is open when, during a
misfire, the plug ignites the fuel that is being injected during the
intake stroke. That does not seem likely a healthy environment to parts
that are normally shielded from, and not designed for, combustion.
So I was partially correct, the problem happened after the repair. Still, the
advise is the same.
Unless you put the wrong plug wire on the wrong plug the "timing sequence of
those two cylinders" will not change.
Fuel is injected before the intake valve is open. A misfire will not damage the
injector. If by a very far chance you misrouted a wire enough to fire a plug
when a intake valve is open, you will know it by the constant back fire among
Like Thomas said, a misfire did not damage your injectors. If I had to take
a guess I would say it sounds like a typical ruptured fuel regulator
diaphragm. Pull the vacuum hose off the regulator and look for fuel....
there shouldn't be any. If you don't see fuel cycle the key a few times or
let it run while watching the regulator, sometimes it takes a while to show
up but I'm guessing you'll have a little fountain of gas squirting out. If
I'm correct the extra fuel is getting past the regulator and into the intake
manifold through that vac. hose and causing all your troubles. I'd like to
hear more about your shorted plug wires, I've never seen a 4.6 do what you
described. Usually they get a pinhole burned through the boot and just short
to the head.
Thanks for the reply, Bob.
I had previously checked the regulator and saw no fuel emission from the
vacuum inlet. But, then, there's no vacuum with the vacuum tube
I seem to have trouble communicating what I know occurred and what I
believe to have occurred. I know that #3 was shorting to #6. I had a DTC
indicating a #6 misfire. The engine ran rough. I followed the #6 wire
from the distributor for about four inches, where it laid across the #3
wire. I lifted it off the #3 wire and saw the familiar pinholes in both
wires where they made contact. I taped both wires. Subsequently, the
engine ran reasonably smooth. It also spewed considerable smoke and
reeked of fuel, which it had not done previously.
The normal firing order of this engine is 1-4-2-5-3-6. However, with the
two plug wires shorting, the effective firing order is 1-4-2-5-3&6-6.
The consequence, I believe, is that the #3 spark would ignite fuel in
the #6 cylinder while the fuel is being injected. That combustion on the
#6 injector's components which are not designed for that explosion would
likely damage those components. To the point that even after the misfire
is corrected, the injector is permanently open.
I understand why empiricism would lead you to suspect any of several
components. However, I had none, nada, zilch, zero fuel problems up to
the moment of misfire.
That doesn't matter, if it is leaking it will show up.....sometimes you have
to let them run for a while though. Let it idle with the vac hose off for
maybe 5 to 10 minutes, if it's leaking you will see it by then. Be careful
though, you don't want raw fuel leaking all over the top of your engine.
But you don't have a distributor, you have a coil pack on the front of each
The injector is located in the intake manifold and NOT in the combustion
chamber but it sounds like you have convinced yourself that injectors are
your problem so why not just replace them? No one here can say for sure what
is wrong, we can only guess based on the information you provide.
I am going back to the MAP/MAF sensor. I think your car has one. If it is
not sensing vacuum, it will cause the smoke and stink of gas you describe.
I'm a little confused, tho. We are talking about a 4.6L V8, aren't we? The
firing order looks like it's for a six...
By the way, we're just trying to help...
I initially suspected the MAF, but air-flow change can be read all the
way back to the PCM. Also, there was no fuel problem prior to the
misfire. I'm focusing on what a misfire could have affected.
As to your trying to help, I thank you all. You are a great aid in
helping dissipate some of my ignorance.
As to the firing order..... Jeez, I gotta get off this night shift!
[ 1-3-7-2-6-5-4-8 ]
First off, basics. It appears you have not replaced the wires and at least
looked at the plugs. Replace them, the tape will not stop an electrical leak,
only provide enough resistance in the wires shield to make the miss not so bad a
miss. Did you remove the wires to make your "repair"? In providing access to the
wires, did you remove any thing like unplug a injector or two? Did you remove
the intake air assembly and leave the MAF unplugged? Being it is a 4.6, the plug
wires are routed under the injector harness and many people unplug the injectors
to remove the plug wires. It is very easy to cross the injector connectors. Even
if that were to happen, you will NOT damage an injector. No if as you say that
fuel is dumping out the exhaust, you should have a check engine light on, and
have codes because if it. What are those codes?
Again, the injector fires BEFORE the intake valve opens. When the valve opens
the fuel has already been sprayed into the intake runner and the injector is not
CLOSED. So what you are thinking can not happen.
explosion. The burning mixture would be very low pressure and heat. There will
alos be a noticable noise coming out the throttle body.
To avoid confusion, there is a typo in this statement.
The injector IS closed when the valve is open, the word *not* should not be in
the sentence. This is how the sentance should read.
When the valve opens the fuel has already been sprayed into the intake runner
and the injector is CLOSED. So what you are thinking can not happen.
I have a 95 -Bird 4.6. I'm just an old backyard motor head. Not a
The 4.6 has two coil packs. According to the shop manual the ignition system
fires two plugs at the same time.
The one that you would normally expect to fire and the second plug on it's
exhaust stroke gets a weaker spark.
When I replaced my plug wires I had to remove the altenator because the plug
wires were run underneath the alternator.
The under hood electronics of the 4.6 built in 94 and 95 are slightly
different than the 96 and 97 models. The 94 and 95 models are touchy about
electro magnetic interferance. Using the wrong design plug wires like older
Crane designs will cause ignition misfires. Improper routing of the wires
will result in questionable misfirings at unusual rpm and speeds. In my case
it was fine until you got over 40 mph. The wires don;t have to be on the
wrong plug, just routed along the wrong path.
Get a set of new Ford plug wires for starters. Not cheap but worth the money
especially if you are still working with the original set.
You are using silicone grease on the boots right ?
The TCCOA web site, in the past has had long discussions about crank sensor
failures, plug wire failures around 40,000 miles, and coil pack failures.
You would probably be better off doing some data mining there than here
I replaced my plug wiring about 14 mo.s ago. Got them from NAPA. In
recent days I have been wondering if I should have gotten OEM. I was
rather amazed at how Ford had gone to great lengths at routing the wires
with numerous separating brackets. I tried to maintain the same routing,
but because of somewhat different lengths from the original I could not
maintain the same fastidious routes.
Per Moats' suggestion I looked at the plugs today. All were in the
initial stages of carbon build-up, except #6 (the original problem) that
appeared to be a bit wet (fuel, I presume). I could see carbon on top of
I also looked at the injectors. I had never seen one out-of-engine
before and they are different than I had supposed. I would not be able
to tell if one was defective by looking. But I am wondering if maybe #6
injector is stuck open. I put in a new plug with no change. I suppose I
should get a new injector just to rule that out. I haven't yet checked
the spark to #6. Will do that tomorrow, but I cannot imagine one unfired
cylinder pouring that much fuel into the exhaust.
I had noticed the dual firing on the schematic. I had presumed it was
meant to deplete the exhaust of any unburned fuel.
I had pondered over the crank sensor but didn't know what to make of it.
Not sure how to test it. I don't remember any discussions about it at
TCCOA. I've tested just about everything else within my capabilities and
have verified continuity back to the PCM. I'm still perplexed by the 20
BTDC timing. I checked it with an OBD-II scanner. I am disinclined to
believe it would be different read with a timing light (should be 10
BTDC per the manual). Maybe I'll put a timing light on it tomorrow, also.
I did read at some site where a fellow had a problem near-identical to
mine. He was complaining because a service shop had replaced just about
every sensor and gizmo possible and the problem was still unsolved.
Seems I remember they even changed the PCM.
Thanks for the response.
Steve Stone wrote:
On my 95 4.6 the manual (Chilton) shows that the plugs are in parallel after
the secondary coil. But the Chilton's is wrong, If you go over the coil with
an Ohm meter you will see that the secondary is not grounded to anything but
to the other plug.
Hello I have a 1997 Crown Vic. with 90 K on it when engine check light
comes mechanic read the code as 171 and 174 than replace the fuel filter
but next 50 miles it came back again and read the same codes instead of
start replacing everything I woud like to find out for sure what cose for
any help will be appreciated?
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