THE NUTS AND BOLTS OF ELECTRICAL DIAGNOSIS
15 Minute
Misfire
Diagnosis
Quick Test
Examples
on the
Toyota
1ZZ-FE
by Mike Van Dyke
E
ngine misfire is one of the more
common problems we can be
presented with when diagnosing transmission operation on today’s
vehicles. Sending misfire problems
down the road can mean denying your
shop a quick, easy job, and the satisfaction of handing the keys to a smiling
customer.
An engine misfire can also have
potentially damaging effects on the
transmission. Think about the jolting
and shock load on the input shaft and
other splines when a misfire occurs with
the torque converter clutch applied.
After repairing a transmission with
spline or sun gear reaction shell failure,
it isn’t uncommon to find out during
the road test it has an engine misfire.
Recently I had the opportunity
to diagnose misfire problems on a
couple of Toyota Corollas with 1ZZ-FE
engines. The 1ZZ-FE and its variants
have been used in several Toyota platforms since its introduction in 1998 and
it shares many similar traits with modern engines being produced by other
automakers. The 1ZZ-FE is a 1.8 liter,
DOHC, 16-valve, 4-cylinder engine,
with variable intake valve timing, coilon-plug ignition, and port fuel injection.
Many diagnostic approaches taken with
this engine can be successfully applied
to other automakers’ engines.
The first situation was with a 2000
Corolla. The customer complained the
transmission was “bumping” or “shifting” when sitting at a stoplight after
the vehicle had been driven for a while
(engine fully warmed up).
32
32MvD-Misfire.indd 32
Figure 1: Scan data shows only cylinder #3 was misfiring.
Figure 2: Switching coils, spark plugs, or even fuel injectors from known
good cylinders can help narrow down the problem quickly.
GEARS August 2006
7/10/06 3:25:45 PM
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Failure 3
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15 Minute Misfire Diagnosis
A closer look
revealed the
culprit spark plug
was fouled with
deposits.
It so happens that when the customer arrived at the shop the symptom
was present. A road test with the customer verified the complaint. An initial
diagnostic fee was agreed upon and the
customer was given a ride home.
First I connected a scan tool to
check for Diagnostic Trouble Codes
(DTC) and to monitor any pertinent
scan data. The customer indicated a
possible transmission problem, but
“seat of the pants” intuition told me to
check for a misfire first. No DTCs were
present, but, as you can see in figure 1,
the misfire counter for cylinder number
3 was incrementing while the other cylinders remained at zero. There wasn’t
enough misfire activity to set a DTC,
but at least I knew the problem was
isolated to cylinder number 3.
Rounding Up the Usual
Suspects
Just for a quick heads up, I had
the service writer check prices on the
top three suspect components to cause
a misfire:
• OEM specified Iridium spark
plugs: $80 for a set ($20 each)
• Ignition coil: $160
• Fuel Injector: $240
Figure 3: A fouling spark plug ended up causing the intermittent misfire.
The age-old trick of spraying carburetor cleaner around the intake manifold gasket created no change in the
symptom, so I was fairly certain we
were dealing with one of our three main
suspects. But which part was at fault?
And how could I quickly diagnose and
be certain of the faulty part, without
wasting time and money by replacing
unnecessary parts? None of these parts
are particularly inexpensive; even the
spark plugs at $20 each aren’t cheap
when they may not fix the problem.
I wanted to make sure to keep the
diagnosis and repair process moving
smoothly in a positive direction.
Throwing Parts at the
Problem
Some options that ran through my
mind were:
1. Get out the COP (Coil-On-
What do you need to know?
UT-1 UNIT TESTERS
Compact, portable, affordable and vital for all transmission
shops. Cut unnecessary installation and removal,
by testing the hydraulic integrity of individual
transmission components.
SOLENOID TESTERS
A “must” for testing the “weakest link” in the transmission.
Easy-to-use. Tests up to six
solenoids at a time … each
separate from the valve body.
Infinitely variable duty cycle
control allows precise control
of the test. Also connects to
AXILINE Electronic Shift (AES).
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32MvD-Misfire.indd 34
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VALVE BODY TESTERS
Precise control! Easy to
operate. Quick set-up.
Simulates toughest driving
conditions while testing
electronic, hydraulic and
vacuum systems — valve
bodies, solenoids and
pressure transducers
— using actual transmission pressures and heated
oil. Computerized TDAC
System upgrade optional.
2.
3.
Plug) adapters to scope the
secondary coil waveform, or
probe the primary side of the
coil to get clues from firing
voltage, burn time, and burn
line slope.
Scope the injector voltage and
current waveforms to get more
clues from pintle humps, flyback voltage spike, current
ramp, etc.
Throw some known good parts
at it and see if it works.
A few high tech options to really
sink your teeth into with today’s test
equipment! Options 1 and 2 were very
tempting, but option 3 won out for me
because I had seen three other cylinders working perfectly, sitting right
there under the hood. That means three
known good coils, spark plugs, and
injectors.
AXILINE ELECTRONIC SHIFTERS (AES)
Isolate the transmission from the
ECU system, simulate and control
transmission, valve body, and
solenoids — with sequential and/or
adaptive process — and eliminate
the hassles, inconsistencies and
questions raised by cheaper, less
reliable hand-held systems using
older technology. Pre-programmed
software. Easy, instant on-screen
read … up to 16 solenoids at a
time … in any mix of DC or PWM.
When you
really need
to know…
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1
10:13:19
AM
GEARS 2/20/06
August
2006
7/10/06 3:26:12 PM
Figure 4: A burned exhaust valve was the final straw on this engine. The pistons
are clean around the edges, indicating oil consumption from bad rings.
Why not just swap coils with
neighborly cylinder #2, fire it up, and
watch the misfire counter? Or, if I have
to, roll up my sleeves and swap spark
plugs? I grabbed a 10 mm socket and a
speed handle. Two minutes later I had
the engine running after switching the
coils between cylinders 2 and 3 (figure
2). Number 3 cylinder was still showing misfires.
Then I dug in five minutes deeper
and switch the spark plugs between
cylinders 2 and 3. Ah ha! The misfire
moved to cylinder number 2. I installed
a set of spark plugs and the problem
was solved. The customer was anticipating an expensive transmission repair
and was very happy paying for the
diagnosis and spark plug replacement
instead.
A closer look revealed the culprit
spark plug was fouled with deposits
as shown in figure 3. The other spark
plugs were showing excess deposits
as well. The customer was informed
the deposits could be caused by fuel
additives or excessive oil consumption,
and the customer did acknowledge the
engine was using some oil between
changes.
A Not-So-Happy Story
Another Corolla came in with an
obvious misfire. This one had the MIL
lit, with DTC P0302 in memory: cylinGEARS August 2006
32MvD-Misfire.indd 35
der 2 misfire detected. Uneven cranking pointed toward a serious mechanical failure of the engine.
A compression test showed no
compression on cylinder 2. Removing
the cylinder head revealed a burned
exhaust valve and the pistons were all
very clean around the edges, indicating heavy oil consumption and poor
piston ring oil control (figure 4). The
engine had over 200,000 miles on it.
The customer agreed it wasn’t worth
doing a valve job and opted to install a
used engine.
A misfire can have many possible
causes: fuel delivery, spark/ignition,
and mechanical engine failure to name
the more common ones. Taking the
time and knowing how to connect and
use high tech test equipment is important when you need to verify the failure
of an expensive component or track
down an elusive problem in a circuit.
But on many occasions the basics can
be covered by applying some quick
tests or substitutions like the ones we
went over here.
Sometimes it helps to think simple
first before moving on to the more complicated or high tech approach.
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7/10/06 3:26:30 PM