Diagnose engine misfire problem

This is a Town and Country 2003 van (3.8L). It ran fine then the next
day when I started it, it didn't run smoothly. The car shakes a lot.
Check engine line came on and I smelt gas. So, I shut down. I read
the code and it has 3 codes. 1 code is random engine misfire. The
2nd code is cylinder 3 misfire and 3rd code is cylinder 4 misfire.
So, I disconnect batter and replace all the spark plugs with a
platinum (2 prongs) spark plug. The service manual says platinum type
is the one, but the old spark plug from the car is coper type (I
believe, based on the look of it). Put everything back and starts.
The car no longer shakes, but the engine is not smooth. I plugin the
code reader and get a check engine light is on, but no code. So I
press clear on the code reader, which said it can't do that. But read
again, there is no code and check engine light is off.

I unplugged the wire to the spark plug of cylinder 4, and plugged it
into a test spark plug. Started the engine. Sparks came out of the
thing.

Plugged back and I drove around a couple block to see if the problem
goes away. Engine still rough, not smooth, and still no code when
read. I no longer smell gas.

How do I go from here for finding out what the problem is? What's the
most likely cause for this? Fuel system? What would a mechanic do
from here?

 

if you used bosch spark plughs get rid of them they foul out real easy

 

Unfortunately, I think that's what I got. However, I don't think I
can return it, because I already use it. Do you think I can do that?
Do you think that it's bad already that causes the current problem?

 

Take the vehicle out and get it hot, going about 40mph come to a coasting
roll for about 20sec and then check to see what the engine fault code says.
Chances are the plug wires are bad. The adaptive numerator may have to be
learned in order to detect what cylinder is misfiring. and coming to a
coasting stop will learn it

Glenn Beasley
Chrysler Tech

 

I took the car out this morning and drive it to hot. Also, I drove it
at different speed, including highway, 45mph, and slow with many
stops. I have tried to coast many times, but had to use the brake
eventually because I didn't have the distance, and morning traffic.
However, the engine light does not come on. I'll read the code
tonight. When the engine is hot, it seems to run more smoothly.
However, when comes to stop, it is still not smooth, but not as rough
as when started.

 

I got the check engine light on again. This time, the code is
cylinder 3 misfire. How would I go about to trouble shoot this? I am
thinking of measuring the resistance of the cord connecting to the
spark plug. Is this the way to do it?

 

By disconnecting the battery you erased the learned adaptive numerator
memory and all the rest your monitors. Therefore it would not show you
what cylinder was misfiring. That's why you should not do a battery
disconnect!! More then likely you have a plug wire that is causing the
problem. you can either go out and purchase a good set of wires to see if
that takes care of the problem or try switching number 3 wire with number 4
wire. If the misfire now shows number 4 cyl misfiring then you know for sure
the plug wires are at fault.

Glenn Beasley
Chrysler Tech

 

man i can't tell you how many people come to my shop and they say they just
did the plugs themselfs and 95 % of the time they are bosch
our first question to the customers is did u use bosch plugs!second is plug
wires that failed esp. on gm cars

 

or since you changed plugs you could swap plugs first

 

That's an excellent suggestion. I'll try that out. I was working for
the whole weekend. The cylinder 3 is inside, which means I have to
take the wiper rack out. I'll try to get that done as soon as
possible. Thanks.

 

You don't need to take the wiper module out to access plugs and wires on
this vehicle. Just swap the plug wires and you will more then likely see the
misfire went to the other cylinder. DO NOT disconnect the battery

Glenn

 

Thanks for the suggestion.

I have swapped the wire, same problem. The same thing happens when I
swap the spark plug. The cylinder 3 still misfire. I also put in a
brand new Mopar ignition coil. The problem still persist. I notice
that after running for a while, when the temperature stabilized for
awhile, the misfire appears to be gone.

I even brought to a local shop. They asked me to replace the ignition
coil, the spark plug, and the wires, and air filter, and gas filter.
I thought to myself, I can do all that. The point is that they must
know which is the bad one, and replace/fix that, not just replacing
everything. From the test, the wires appear to be good, same for the
spark plug. I can't imagine the ignition coil is bad, given it's
brand new. So, these mechanics doesn't know what they're doing, or
they're trying to fool me.

I took the car back. Now, I want to give it a last shot before
bringing it to another autoshop. I want to go by the book. I have
the diagnostics book from the manufacturer.

It appears that other problems could be gas related. Some of the
steps (about 18) asks me to check the pressure of gas, which means I
have to access to the fuel rail (do I?).

The diagnostic book doesn't say this, but I imagine that swapping the
fuel injectors would give me some indication too, is that a correct
assumption?

I already bought the pressure gauge.

The question is do I have to to take out the upper manifold to do
this? How about the lower manifold? Taking out the lower manifold is
very tedious. I have to drain coolant. It (the book) asks me to
replace the gasket everytime I do this. Sure, I can replace it, but
for diagnostics?

Also, if the fuel injector is the culprit, then do I have to take out
both manifolds?

Please help.

 

First of all, are you the same person I replied to a month ago or are you
just replying to this thread? what engine? Fuel pressure wont cause a cyl
misfire on one cylinder!! Go back to basics......you have to have fuel
pressure, I assume you do because the vehicle runs and you aren't getting a
multiple cylinder misfire. assuming that you have spark on all cylinders
because you aren't getting a primary ign fault code. the next step before
throwing any other parts at this would be to check compression on the
effected cylinder. If I were to bet I would say you have low compression.

Glenn

 

I have a 98 caravan with the 2.4l 4cyl. I was getting a random misfire
and I put di-electric grease in both ends of the sparkplug wires and
that stopped the misfire.

 

Thank you for the reply. Please see inline comment below.

Yes, it's the same me.

The first time I got the problem, use the OBD to read, I got multiple
engine misfired, cylinder 3 misfire, cylinder 4 misfire. Now, I got
cylinder 3 misfire.

I'll check the compression on the cylinder 3. But first, I have to
learn how to do that.
Below is for your reference of the steps the diagnostic book said. It
applies to all P030x misfire problems.

1) Visual check: worn serpentine belt, binding A/C compressor, P/S
pump (I just replaced this a while back, wonder if the rebuilt part is
bad, not problem with steering power though), water pump.
Misalignment water pump, P/S pump, A/C compressor pulleys. Corroded
PCM power and circuits. Improper CKP, CMP, MAP and TP Sensor
mounting. Poor connector for CKP sensor, fuel injector, ignition
coil, etc. Vacuum leaks. Restricted Air induction system or exhaust
system.

2) Ign off, disc ign coil connector, disc the fuel injector connector,
ignition on, engine not running, use test light probe A142 ASD relay
output circuit at the ign coil connector and fuel injector connector.

I can see the ign coil connector and probe that. I think with just
cylinder 3 problem, it can't be this. I don't know how to probe the
injector connector as yet. I wonder if I have to take out the
manifold(s) to get to that.

3) Ign off, disc. ign wire from spark plug. Disc fuel injector
connector of the cylinder being tested. Install a spark tester on the
ign wire. Crank engine, observe the tester.

4) Ign off, remove spark plug, visual check spark plugs.

5) Release the fuel system pressure. Install fuel gauge to fuel rail,
start engine and observe the gauge reading. (334 KPa +/- 34 KPa)

6) Release the fuel system pressure. Install fuel pressure gauge,
start engine until max pressure. Ign off, use clamp to pinch the
rubber fuel line between the fuel pressure gauge and the engine.
Monitor the pressure gauge for > 5 minutes. Replace the leaking fuel
injector(s) if pressure is below spec (400KPa +/- 34 KPa)

7) Release the fuel system pressure. Ign off, connect fuel pressure
gauge to fuel rail. Start engine until max pressure. Ign on, engine
off, use DRBIII actuate the fuel injector for cylinder misfired.
Check for drop in pressure.

8) Check: engine vacuum, engine valve timing, engine compression,
engine exhaust system, engine PCV system, torque converter stall
speed, power brake booster, fuel contamination, cam lobes, cylinder
leakage test, valve springs.

These are a lot of checks. I don't know how to do most of them.

9) Ign off, disc the fuel injector connector, ign on, engine not
running. Use DRBIII erase DTC. Use 12 V test light connected to 12
volts, probe the injector control circuit. Use DRBIII actuate the
fuel injector. If test light blink/flicker, replace the fuel
injector.

10) Ign off, disc fuel injector connector, disc PCM harness
connectors. Check injector control circuit for open, short.

11) Ign off, release fuel pressure, raise vehicle, disconnect the fuel
pressure line at the fuel pump module, install fuel line adapter fuel
pressure gauge between fuel supply line and the fuel pump module. Ign
on, engine not running, use DRBIII actuate the ASD fuel system test,
observer pressure gauge. Is within 400KPa +/- 34 KPa? Repair fuel
supply as needed.

12) Ign off, release fuel press., remove fuel pump module, check fuel
inlet strainer for plugged. Replaced if so.

13) Ign off, measure resistance of ign wire. Is it below 10K ohms?
Replace if above

14) Ign off, disc ign coil harness connector. Remove the fuel pump
relay or ASD relay. Use 12 v test light connected to 12 volts. Probe
the ignition coil control circuit. Crank the engine for 5 seconds
while observing th test light. If light brightly blink, replace the
ignition coil.

15) Ign off, disc ign coil narness connector. Disc the PCM harness
connectors. Check the coil control circuit for open, short to ground,
short to voltage. Repair as needed.

16) Inspect wire, repair as needed. Replace and program the PCM.

 

You have pulled this test from a Chrysler Diagnostic Manual and without the
DRB it is useless. Perform a compression test on the effected cylinder(s)
The only way fuel pressure would affect one cylinder would be a stopped
up/inop injector.

Glenn

 

Compression test will be my 1st priority this evening. Just to think
ahead, what would I do next if the compression test fails? Succeeds?

 

The passed weekend was hectic for me. I had to work in the weekend.
A few errands turned up. A loss of a family member. I couldn't get
this done, other than got my self a real compression test kit (I
thought I had one, but it's a fuel pressure meter).

If I have time tonight, I'll do that (besides changing the oil on the
other car). I have a few questions though. The factory service
manual said to test while hot. This means, I probably needs to take
the wiper module off, right? Because I'll get burnt taking out the
spark plugs with little space. Is there a better way to do this?

The more important question is that every guide I read, it says if the
pressure is low, "squirt" a tea spoon of engine oil into the spark
plug and test again. What does "squirt" mean? Like spray with some
kind of pressurized bottle, or with a hand lever? I called advance
auto parts, and they don't know what I am talking about. I don't
think "squirt" means just pour the liquid in. What do DIYers use for
this and where do I get it? Thanks.

 

I would do the test on a cold engine just so I didn't burn myself.
While you might be a more accurate number on a warm engine in the big
picture you are more concerned about differences between the cylinders
than the actual number.

Make sure you disable the ignition system and block the throttle open
to run the test. Keep the battery charged up so that the engine is
spinning at the same speed for each cylinders test.

Just get the oil in there. You can squirt it in using an oil can if
you have one available and are able to get it in there. I usually use
a piece of clear hose and a funnel... Stick the end of the hose in
the sparkplug hole then pour a little oil in the funnel. You want to
give it a little crank to distribute the oil before you test again.
Basically you have a big empty hole and you just need to get some oil
in there.

In case you aren't aware...
You put the oil in and test again if you have low compression to test
the rings. Oil will help seal worn leaky rings so the numbers go up.
If the numbers don't go up with the oil then you have a valve problem
or a really big problem with the rings.

Steve B.

 

Thank you Steve. That was helpful. Reading your post, I feel like
listening to my older brother in a good way.

The results are in. The compression test passed. Here they are:

Cylinderressure (PSI)

1 : 192
3 : 195
5 : 200
2 : 190
4 : 190
6 : 180

The trouble cylinder 3 has 195, which is within 2.5% of the highest
cylinder 5 of 200, and the cylinder 6, with the lowest pressure has
180, which is within 10% of the highest.

This is cold engine test.

So, what could be the culprit here? Is it the bad fuel injector? If
that is the case, do I just remove the upper manifold (not the lower
manifold) to replace this?

Thanks all.