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Car Misses - Changed Plugs Coils

New 11/23/204

Well, I did the rear coils and all the spark plugs. The car was starting to
miss bad for a while then suddenly after a while it started to hesitate, and
miss during acceleration and coasting on the highway. So I figured that it
was coils that were starting to go bad. So I replaced the coils on the rear
and I replaced the spark plugs. All the plugs looked the same, and in
pretty good shape (Changed less then 25k miles ago when being kirked) While
I was changing the plugs, I meant to check the compression. I forgot to
check it in the rear, and suddenly remembered about it after putting the
intake back together. So I only got to check the front. The first passenger
side read about 190, then the 2nd one in from the passenger side read 100
psi, and the other two read 200 psi on the dot. On the front row of spark
Anyways back to the miss, I replaced the rear coils and all spark plugs.
There is no more hesitation, but it still misses pretty bad when sitting and
idling in gear. Seems to only do it while in gear and usually but not always
only when warmed up. Tomorrow I was going to switch the front 4 coils out
with the rear coils I pulled out and see if that changes anything.

Is it possible this could be a bad TPS sensor? Or do you think I will need
to replace the front coils ? My car has almost 140k miles on it. And seems
like it is definitely been needing a lot of work. (Just spent near 1k in
parts, not including labor yet, is it ever going to stop?)
Thanks for any help..

Retest Cylinder 6, and compare it with say cylinder 7. Paul is right
that 25% is the most spread you want and I prefer to see it be under

If Cylinder 6 is confirmed as being lower again, Add about a teaspoon
of straight 30 weight oil into each of the cylinders your testing. If
they are much closer now, that suggests a ring or cylinder problem, as
the oil will make the ring to cylinder wall seal better. If #6 is
still below you comparison cylinder by 20% or more then that suggests
that the compression problem is in the head/valves.

Let me guess, you can still feel the miss? They say that with 50 PSI
or more of compression that the cylinder will still fire and not miss
rather it will just be weak, so until compression gets near zero the
PCM will not detect the cylinder at fault.

Good luck,

Testing and Inspection

Compression Gauge Check

Make sure oil in crankcase is of the correct viscosity and at proper level
and battery is properly charged. Operate vehicle until engine is at normal
operating temperature. Turn ignition switch to the OFF position and remove
all spark plugs.
Set throttle plate in wide-open position.
Install a compression gauge such as Rotunda Air Pressurization Kit 303-F011
(014-00707) or equivalent in No. 1 cylinder.
Install auxiliary starter switch in starting circuit. With ignition switch
OFF, using auxiliary starter switch, crank engine a minimum of five
compression strokes and record the highest reading. Note the approximate
number of compression strokes required to obtain the highest reading.
Repeat test on each cylinder, cranking the engine approximately the same
number of compression strokes.

Test Results
The indicated compression pressures are considered within specification if
the lowest reading cylinder is within 75 percent of the highest reading.

If one or more cylinders reads low, squirt approximately one tablespoon of
clean Motorcraft Super Premium SAE 5W-30 Motor Oil XO-5W30-QSP or equivalent
meeting Ford specification WSS-M2C153-G on top of the pistons in the
low-reading cylinders. Repeat compression pressure check on these cylinders.

Compression Readings-Interpreting

If compression improves considerably, piston rings are faulty.
If compression does not improve, valves are sticking or seating poorly.
If two adjacent cylinders indicate low compression pressures and squirting
oil on pistons does not increase compression, the head gasket may be leaking
between cylinders. Engine oil and/or coolant in cylinders could result.
Check the appropriate Compression Pressure Limit Chart when checking
cylinder compression.
Example Readings
If, after checking the compression pressures in all cylinders, the highest
reading was 1351 kPa (196 psi) and the lowest pressure reading was 1069 kPa
(155 psi), the engine is within specification and the compression is

Paul L Fisher
Ok, thanks for the help, I will check the compression again, and swap out
the front used coils with the other used coils. Yes the coils were swapped
at about 115k, so the rears were put in the front.

Well I rechecked the compression today and swapped out the coils. I was nervous that I was going to be in for expensive engine service, since I checked the compression about 5 times on that cylinder, and got 100 psi each time.. Well today I checked and I got 200 psi on all the cylinders. They were all exactly on 200 psi. I haven't checked the rear cylinders, Guess I will be assuming they are ok, hopefully.
As for the coils, I swapped them out with the old ones from the rear and the car drives awesome, and no problems. All those worries for nothing, and now put to rest.
Just figured I would give a note that I am running the denso IT-20ís, which are one step colder then Stock. And haven't seen anything out of the ordinary yet. Car still runs awesome.. I am working my way up to a chip from F.P.S. and Nitrous.
Thanks for all the suggestions.. Happy I didn't have to put any oil in the cylinder to find out what type of problem I was going to be facing.

I'm having the same problem with my 98..just hit 140K on it. Cams welded, I've been trying to diagnose this problem also with not much luck. No vacuum leaks I can detect. Compression is fine.. I've narrowed it down to a sensor or sensors. Threw 2 O2 sensor codes Bank 1 sensor 2 malfunction and Bank 1 Sensor 2 heater circuit malfunction. Now the car misfires bad but I've narrowed it down because its running rich as hell. At idle at a stop light or anything I can smell unburnt gas through the exhaust, so which tells me something is fubarred and telling the computer its at WOT when its at idle therefore the cylinders load up with fuel and wala you got the misfires. If I get on the gas hard it will usually stop after 4K RPM when its actually at WET and using all that fuel. Good 'ole computers!
Could the earlier reading of 100 psi indicated a chunk of something in the
secondary intake valve on that cylinder? How clean is your intake?

I'm just wondering if the reading was accurate, and you have since sucked the
crud through, so that the valve is seating again.

Brad Bender
Well I tried that pulled the vacuum hose off the regulator with the engine running and nothing changed. I'm not sure if that's good or bad.. TPS sensor reads 5 volts at idle on both the feed and return line from computer. So that's obviously bad.. I don't know if the egr valve can cause symptoms like this but its just too many different possibilities.

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