Cylinder 3 misfire.

1996
4.0l
150k miles
5 speed

Sorry to create another "misfire thread" but after reading all other search results and trying those fixes I am still getting a code. The misfire is barely noticeable at idle/driving.

Things replaced:
Cracked header with APN header and new gasket.
Crank shaft position sensor.
TPS
Sprak plugs, wires, cap and rotor.
Fuel filter
O-rings on injectors

Took care of original code which was misfire in cylinder 1, 3, 6, after 50 or so miles code came back with misfire cylinder 3. I am going to check the wiring to the injectors tonight as well as the spark plugs for fouls. I will post a pic of my findings.

Other issue that may help someone more knowledgeable then me:
Car has problem starting on first try take about 10 sec of me cranking the key to start it. I don't like doing this so I crank it once and the turn it off and crank it again and it starts right up.

Thanks for the help.

Derek

The long cranking time is probably the check valve in the fuel pump assembly. The 96 is a real oddball year, and if I remember right the fuel pump assembly is that single year specific and expensive. You might consider an in-line check valve. There was a BMW mod for adding the check valve in the tank at the fuel pump, don't have a link to it, you could probably Google the information.

As for the misfire--there was a TSB on multiple cylinder misfires related to carbon buildup. I don't think it was for your year, but you could run some MCCC--Mopar Combustion Chamber Cleaner, or Seafoam, through it to see if it improves.

joe_peters said:

The long cranking time is probably the check valve in the fuel pump assembly. The 96 is a real oddball year, and if I remember right the fuel pump assembly is that single year specific and expensive. You might consider an in-line check valve. There was a BMW mod for adding the check valve in the tank at the fuel pump, don't have a link to it, you could probably Google the information.

As for the misfire--there was a TSB on multiple cylinder misfires related to carbon buildup. I don't think it was for your year, but you could run some MCCC--Mopar Combustion Chamber Cleaner, or Seafoam, through it to see if it improves.

Click to expand...

Thanks I will try that tonight. And yes I have found this to be a wacky year. all sensors I have purchased for this jeep have been for different years some for 95 and some for 97 depending on the connectors.

First year of the OBDII, last year of the metal fuel tank, first year without a fuel pressure regulator in the fuel rail and other things for the 96.

Post up what you find.

Good luck.

Spark plug 1
Spark plug 2
Spark plug 3
Spark plug 3
Spark plug 4
Spark plug 5
Spark plug 6
Rotor
Rotor
Cap

Tested fuel injector's resistance, 12. Unplugged injector while Jeep was running and it started sputtering, did this with each injector and same results. Hope these pictures show someone something if not i guess it is time to take it to a mechanic and see how deep they want to stick it. Wires all looked good did full tune up about 1000 miles ago.

Thanks for looking.

Don't put an inline check valve between a fuel-tank mounted pressure regulator and fuel rail. If the regulator is on the rail it's OK.

I would lose the distributor cap, get one with brass contacts.

Plugs look good from what I can see (itsy, bitsy pictures).

Try the MCCC or Seafoam before you take it to a mechanic.

joe_peters said:

I would lose the distributor cap, get one with brass contacts.

Plugs look good from what I can see (itsy, bitsy pictures).

Try the MCCC or Seafoam before you take it to a mechanic.

Click to expand...

seafoam made the misfire worse? I also switched the plugs/injectors and it did nothing so wen home and seafoamed and now the motor shakes likes crazy and im sure all the sea foam is out because i drove it for a while after to see if it would stop even put some 91oct fuel and still misfires. One thing i did find while seafoaming is there is a small exhaust leak on where the header meets the exhaust. It looks like my long arm has crushed in the up pipe and made a small leak but didn't think that would cause the misfire?

A small leak in that area would tend to cause the o2 sensor to read LEAN, and the PCM would extend the duration of the injector pulse to enrich the fuel mixture so you would be wasting fuel in ALL cylinders, but I couldn't see a single cylinder misfire.

Ok, running rough. Pull each of the spark wires loose, then push them back on the spark plugs just enough to stay attached. Start the engine and while it is running pull one plug wire clear of its spark plug, one cylinder at a time, until you can identify the non-firing or weak firing cylinder.

Post up what you find.

Check your compression yet? I would expect low compression to cause worse problems than a single cylinder misfire but you might as well check it.

Yeah, 96 is a bastard year. I found that out the hard way. 95 and 97 are as well to some degree, that's what happens when a manufacturer is considering and making changes and some legislation comes along that they have to comply with halfway through. My bet is that without the OBD-II requirement starting in 96, the 96 model year would have been mostly a carbon copy of the 95 model year and the 96 to 97 break would have been much more complete. One of these months I intend to put together a big gantt type bar chart that shows what things changed in what years, but I haven't found the time to do it yet.

Compression dry test
120, 129, 129,120, 115, 120.

In order for 1 to 6. After doing the spark plug thing it seemed as if all the cylinders were making the same sort of problem. So I said F it Im going to buy spark plugs after putting new ones in the misfire was less and the code was then p3000 random misfire. I then fixed the exhaust leak the best I could and replaced the pre cat 02 sensor.Within this combination the problem has been fixed... Not sure exactly what it was but my guess was the 02 sensor. Either way no more misfire and no more CEL.. I drove it for about 45 min last night and nothing came back on or felt different. Also on another good note I am supposed to be getting a Dana 44 out of an 88 XJ tonight. Thanks again for all the help and quick responses. :wave1:

awesome, glad it's fixed!

The exhaust leak and upstream O2 sensor could easily cause this, especially if they leaned out the mixture enough that it actually was misfiring randomly. What plugs did you put in it? I usually go with Champion truck plugs or NGK V-fires, they're what the factory recommended and the snake-oil plugs don't do much for you in a 4.0.

kastein said:

awesome, glad it's fixed!

The exhaust leak and upstream O2 sensor could easily cause this, especially if they leaned out the mixture enough that it actually was misfiring randomly. What plugs did you put in it? I usually go with Champion truck plugs or NGK V-fires, they're what the factory recommended and the snake-oil plugs don't do much for you in a 4.0.

Click to expand...

I put champion truck plugs they have always done me well.. Minus this last time. :smsoap: