Ford 460 Engine Misfire Problem
drinkm...@my-deja.com
Stats: 1982 Ford Econoline E-350
7.5 liter (460) , Holley 4180C 4bbl carb (vacuum secondary)
Non-computer controlled, non-catalyst.
Duraspark II ignition (consists of ignition module, coil,
no points distributor)
All parts are stock. No mods or aftermarket kits.*
*-Vehicle has about 100k mi, block was replaced by previous owner about
10k mi ago. It appears that every bolt-on part was reused, and that only
the block itself, including the heads were replaced with a stock unit.
Generally the engine runs fine, except that emissions have always been
a problem. I had a mechanic friend of a friend do a tune up about 2
years ago, at which time he told me he rebuilt the carb. The truck
passed inspection, and did run better, but was used very little since
then.
Recently, upon getting it inspected again, the HC reading was very
high, and the tech pointed out that an engine misfire was likely to be
the cause. It was indeed misfiring, and in the little that I do know,
unburned fuel = HC. Since my friend's friend had moved on to another
place, I decided to try to tackle it alone. I have dabbled in engine
work on and off, but am by no means an expert. So I get a set of
original Ford service manuals (by luck) and begin reading.
The first thing I notice is that the carb could never have been rebuilt
like I was told, based on the age and condition of the gaskets. Also,
after it was worked on, the vacuum secondary no longer worked. This
wasn't really a problem because of the engine size and vehice purpose,
so I ignored it as long as the thing kept passing inspections.
I picked up a Holley rebuild kit, and kept checking.
The misfire seems to occur at all engine speeds, so I figured it must
be spark related. I changed the rotor, cap, wires and plugs - and
voila! - a significant improvement. Engine vacuum is now solid and
reads a healthy 21 in Hg at idle. However - the engine still misses
once in a while. It's very subtle if I'm watching and listening to the
engine run, but when I listen to the exhaust, I can hear it "cough"
every 3 or 4 seconds. If I put the truck in gear, the miss goes away
almost completely. I followed the procedure for setting idle mixture
with no real change in smoothness. I Wish I had access to a full blown
emissions tester, to track my progress, but all I have is a one-gas
(CO) device. Using it confirms that the CO reading does vary with
mixture setting. I check all the obvious stuff - vacuum hoses, EGR
valve, choke sticking - all ok.
There is a problem with the Thermactor valve. It is always open
allowing air to be pumped into the exhaust manifold at all times.
The service manual indicates that this should close after 100 secs at
idle, to prevent exhaust system overheating. The problem is in the
valve itself, but since it doesn't leak vacuum, and is actually serving
to improve emissions at idle, I've decided to leave this alone for now.
When I check the timing - it's WAY off, by like 30 degrees. The books I
have conflict as to which cylinder is #1, but whichever one I use for
the timing reference, #1 or #5, the timing is either 30 deg retarded or
40 degrees advanced. (I did remove and plug the vacuum advance hose)
If I swing the distributor in either direction, the engine RPMs go
down, and as I approach the listed spec, will barely run at all.
I'm beginning to suspect that the joker who assembled the rebuilt
engine didn't follow the proper procedures for engine timing.
(While I sometimes think I must be doing it wrong, I also think I can't
be. I went ahead and tried EVERY cylinder as the timing light trigger,
and none of them gets the timing mark even close to the reference.)
I have some new info (tonight) regarding cylinder numbering and plan to
re-check the timing again tomorrow to be sure my findings are correct.
I will also confirm that plug wiring is correct, just to be safe.
I would eventually like to have everything set to factory spec,
hopefully with no misfires, before going back for emissions testing.
I'll probably replace the Thermactor Valve after getting it inspected,
unless someone can tell me why that would be a bad idea.
In the meantime, I've decided I need all the help I can get, so:
Has anyone seen this before?
Could this simply be distributor alignment?
Am I missing something? (pardon the pun)
Should I ignore it and move on to rebuilding the carb?
Any info and ideas would be greatlty appreciated.
Sent via Deja.com http://www.deja.com/
Before you buy.
Dean Dardwin
You have done a great job of problem determination.
Standing in front of the engine, facing the water pump, the plug to your
right is #1. Usually we call it the "first plug on the driver's side".
If I had a dollar for every engine that had an incorrect timing mark
indicator I would be rich. Even brand new ones right from the factory have
them installed way off.
Here's an idea from an old-timer. Hook up a vacuum gauge to manifold vacuum.
Remove any vacuum line at the distributor and plug the end of the line.
Start the engine. Let it warm to operating temperature. Retard the timing
(turn the distributor in the direction that slows the engine down a little).
Then advance the timing with an eye on the vacuum gauge. When you get the
HIGHEST, STEADIEST vacuum reading, again retard the timing about 1/2 of an
inch of mercury on the vacuum gauge, then tighten the hold-down clamp. This
will be the optimal timing for that engine.
Good luck!
Dean
Thomas Tornblom
> A couple of thoughts:
>
> You have done a great job of problem determination.
>
> Standing in front of the engine, facing the water pump, the plug to your
> right is #1. Usually we call it the "first plug on the driver's side".
This I seriously doubt...
Every Ford engine I've seen has the passenger side cylinders numbered 1
through 4 and the driver side cylinders 5 through 8.
--
Thomas
Thomas Tornblom
> Dean Dardwin <d...@dxd.com> writes:
>
> > A couple of thoughts:
> >
> > You have done a great job of problem determination.
> >
> > Standing in front of the engine, facing the water pump, the plug to your
> > right is #1. Usually we call it the "first plug on the driver's side".
>
> This I seriously doubt...
>
> Every Ford engine I've seen has the passenger side cylinders numbered 1
> through 4 and the driver side cylinders 5 through 8.
Left hand drive of course.
--
Thomas
Dean Dardwin
An apology from an old Chevy man!
Dean
Thomas Tornblom wrote:
> Dean Dardwin <d...@dxd.com> writes:
>
> > A couple of thoughts:
> >
> > You have done a great job of problem determination.
> >
> > Standing in front of the engine, facing the water pump, the plug to your
> > right is #1. Usually we call it the "first plug on the driver's side".
>
> This I seriously doubt...
>
> Every Ford engine I've seen has the passenger side cylinders numbered 1
> through 4 and the driver side cylinders 5 through 8.
>
> --
>
> Thomas