Misfire trobleshoting

beerdog

Registered
The '98 started misfiring Wed. The code reader brings up P0304 (cyclinder 4 misfire) and P0171. I changed the plugs. They definatly needed replacing but that was not the cause. The ectrodes were well used up, but the color was normal. I have also tried swapping coils between plugs, but the P0304 code always comes up. (Yes, i have cleared the code numeroruse times). I also changed the PCV, air filter, cleaned the throttle body, and cleaned the MAF. The P304 still comes up. The P171 code comes up sometimes.

I have not changed the 02 sensors yet.

Any other ideas what could becausing the misfire?

Also, the car runs fine for about 20 minutes after sits a llong time.
 
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Sounds like the 02 sensor on the right side.... but if you change one, ya might as well change 'em all.

If the plugs are platinum, the electrode is VERY short to start with.... how many miles on the plugs? Is this the same car with the oil in the plug valleys? I wouldn't change plugs yet....

Why do things like this always happen just before a big event????? SUCKS!
 
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Same car. Plugs are about a year old. The electrodes just looked worn out and bit burned up. The were no longer square. I just put the basic Autolites in.

Would bad O2's cause a misfire in only 1 cyclinder?
 
If they are reg plugs, not plats, they ARE burned up.....Have to wait till someone else that knows better about the O2's reads this......
 
I don't see how O2s would affect one cylinder unless the fuel injector is the real issue.

Are you saying you swapped coils, cleared the code and the same cylinder is indicated to be misfiring?
 
OBDII cars have 4 O2s, that means '96 and up. Each side has 2, one pre cat and one post cat.

It's a long distance guess but I think something is amiss in either that cylinder's injector or the primary wiring to the coil for that cylinder. I for one cannot see how an O2 would cause a miss in one particular cylinder.
 
I believe he has an old chip in the car, probably from LMS (in when he purchased it). Does that need to be removed? Can that be an issue in reading the codes or having problems?
 
My experience with chips is codes are not available with a chip. But yeah, if there is a chip, I'd pull it and then clear the codes and start with a fresh slate. If it's a true ignition miss, it will still be there.
 
The chip was not the cause. The P304 code is consistently produced. The P171 code no longer happens so lets focus on the misfire.

The positive side is that the gas milage goes up 20% without the chip so it is staying out. It was a Super Chip.

Are the injectors easily removed? Maybe I should try swapping with a different cylinder?
 
That's what I figured.

Before you go swapping injectors, there's a couple tests you can do.

Using a wooden dowel, long handle screwdriver or anything similar, hold it against the injector(s) and put your ear against the other end to listen to the solenoid tick. Listen for any differences.

Try unplugging the suspect injector and see if there is a difference.

Here's an excerpt from the manual...

Misfire Detection Monitor

The Misfire Detection Monitor is an on-board strategy designed to monitor engine misfire and identify the specific cylinder in which the misfire has occurred. Misfire is defined as lack of combustion in a cylinder due to absence of spark, poor fuel metering, poor compression, or any other cause. The Misfire Detection Monitor will be enabled only when certain base engine conditions are first satisfied. Input from the ECT, MAF and CKP sensors is required to enable the monitor. The Misfire Detection Monitor is also performed during on demand self-test.

The PCM synchronized ignition spark is based on information received from the CKP sensor. The CKP signal generated is also the main input used in determining cylinder misfire.

The input signal generated by the CKP sensor is derived by sensing the passage of teeth from the crankshaft position wheel mounted on the end of the crankshaft.

The input signal to the PCM is then used to calculate the time between CKP edges and also crankshaft rotational velocity and acceleration. By comparing the accelerations of each cylinder event, the power loss of each cylinder is determined. When the power loss of a particular cylinder is sufficiently less than a calibrated value and other criteria is met, then the suspect cylinder is determined to have misfired.
Misfire type A:

Upon detection of a Misfire type A (200 revolutions) which would cause catalyst damage, the MIL will blink once per second during the actual misfire, and a DTC will be stored.

Misfire type B:

Upon detection of a Misfire type B (1000 revolutions) which will exceed the emissions threshold or cause a vehicle to fail an inspection and maintenance tailpipe emissions test, the MIL will illuminate and a DTC will be stored.

The DTC associated with multiple cylinder misfire for a Type A or Type B misfire is DTC P0300.

The DTCs associated with an individual cylinder misfire for a Type A or Type B misfire are DTCs P0301, P0302, P0303, P0304, P0305, P0306, P0307, P0308, P0309 and P0310.

Continuous Memory Diagnostic Trouble Codes (DTCs) P0301, P0302, P0303, P0304, P0305, P0306, P0307, P0308, P0309 or P0310 indicate a cylinder has misfired in cylinders one through ten. Continuous Memory DTC P0300 indicates a random misfire has been detected.

Visually inspect the engine compartment to make sure all vacuum hoses and coils are properly routed and securely connected.

Examine all wiring harnesses and connectors for damaged, burned or overheated insulation and loose or broken conditions.

Be certain the battery is fully charged.

All accessories must be off during diagnosis.

There are many diagnostic tests involving special equipment but a quick scan of the diagnostic procedures all lead to a bad coil or faulty injector. Since swapping coils does not seem to get anywhere, I suppose swapping injectors would be the next logical attempt.

I'm not familiar with the Gen2s, but basically the process is the same with the Gen1s. Find the fuel schrader valve and release any residual fuel pressure. Remove the two (or more) hold down bolts on the fuel rail on the offending side of the engine. Unplug the injector wiring connectors. Slightly rock and twist the fuel rail while pulling up on the fuel rail to separate the fuel rail from the injectors. Injectors should pull out of the fuel rail but may pull out of the intake manifold as well. Pull the injectors you want to swap from the fuel rail and intake manifold. Inspect the end caps and o-rings before reassembly. Beware of loosing any o-rings or breaking the fragile plastic pintle caps on the end of the injectors.
 
Boy, we need a set of STICKY'S so that these procedures could be saved to for everyone when they need them instead of TRYING to use the search command! Search is so frustrating!!!

In the Ford Truck Enthusiasts forum they do that for each type of vehicle - (gas, diesel) and it saves SOOOOO much time involved in hunting for the correct search variable!
 
Well, the car has stopped throwing the misfire code. The only thing I did different was get some gas. Could it have been bad gas? Only time will tell


Bud....send a link to these stickys.
 
I'm not overly fond of too many stickies, but if people come up with valuable info that should be stickied, please let the mods know.

Or, for those of you with time and creativity, create some posts which have info or links to various info which can be stickied.
 
I'm not overly fond of too many stickies, but if people come up with valuable info that should be stickied, please let the mods know.

Or, for those of you with time and creativity, create some posts which have info or links to various info which can be stickied.

or just put it in the tech write up.
 
Beerdog, it might be a good idea to put a fuel injector cleaner/ dry gas fuel additive in your tank for now.
 
I'm not overly fond of too many stickies, but if people come up with valuable info that should be stickied, please let the mods know.

Or, for those of you with time and creativity, create some posts which have info or links to various info which can be stickied.

or just put it in the tech write up.

Another forum I visit has a Hall of Wisdom section which includes tech write ups and allows people to post replies. I regularly use that forum when fixing or looking for fixes. That may be something to emulate.
 
Purchased the most expensive fuel system cleaner "greased lightning". Personally, I thinkt he are all the same but i figure just buy the most expensive one to be sure. The car si running perfect.
 
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