2005 Jeep WK 4.7 P0300 Misfire - JeepForum.com
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post #1 of 73 Old 11-27-2018, 04:15 PM Thread Starter
Jeepwk999
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2005 Jeep WK 4.7 P0300 Misfire

Starting up a new forum that is fresh and not cluttered.

I have had a misfire on my 05 Grand Cherokee for about 2 months now. The code is P0300. So it is a random misfire.
What i have replaced/done so far:
O2 Sensors (Mopar)
Spark Plugs ( Gapped correctly and used Champion which are the OEM ones)
Fuel Pump (Mopar) Fuel pressure is now at 60 +-2
Camshaft Position Sensor (Mopar)
Compression Test 175-180 in all cylinders

Car is stock besides:
K&N CAI
MBRP Catback
Previously had Superchips 93 tune but changed back to stock tune. As well as running 87 octane.

I do hear some sort of air leak currently and it sounds exactly in the area that is shown in the picture. I believe the hoses connect to the air cleaner, crank case, and intake.
Part No would be 53013757AA

https://i.imgur.com/ecqMbZP.png

Thanks all

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post #2 of 73 Old 11-28-2018, 07:34 PM Thread Starter
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post #3 of 73 Old 11-29-2018, 07:07 AM
90grandoneer
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Exhaust leak(s), broken exhaust log studs/bolts. What's the fuel economy like? What did the old spark plug electrodes look like.....color? How many miles on the vehicle?

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post #4 of 73 Old 11-29-2018, 07:20 AM
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Fuel Filter? Vacuum Leak somewhere? Just throwing those out there.
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post #5 of 73 Old 11-29-2018, 07:46 AM
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post #6 of 73 Old 11-29-2018, 08:10 AM Thread Starter
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Quote:
Originally Posted by 90grandoneer View Post
Exhaust leak(s), broken exhaust log studs/bolts. What's the fuel economy like? What did the old spark plug electrodes look like.....color? How many miles on the vehicle?
Fuel economy is crap haha. Has been around 8-11 MPG. When I did the plugs I pulled them twice. The second time, some had black tips others looked normal. 96K miles. I know my Catback might be a little loose but that’s it.
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post #7 of 73 Old 11-29-2018, 08:11 AM Thread Starter
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Originally Posted by ZEN357 View Post
Fuel Filter? Vacuum Leak somewhere? Just throwing those out there.
Fuel filter is built into fuel pump, which was replaced. I think it also may be a vacuum as I do hear the air sound coming from the area pictured. Was wondering if that could cause the misfire/ has anyone replaced that area.
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post #8 of 73 Old 11-29-2018, 08:25 AM
jtec
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TSEJEEPERS - the photo above IDK what are you trying to bring to my attention?

Why have we NOT put a scanner on this vehicle? At least ck for codes...

for vacuum leaks try the old school trick using carb or brake cleaner, if unsure google carb cleaner vacuum leak test

When I see the price of OEM I think aftermarket.
When I see the quality of aftermarket I think OEM.
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post #9 of 73 Old 11-29-2018, 09:01 AM
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If you're hearing a vacuum leak I'd definitely start with the vacuum leak, but to throw out other easy-to-check options that you haven't mentioned yet:

Does the belt look good? Is the tensioner gauge in spec and does the tensioner hold steady? If you clear the codes and don't use the HVAC system, does the code come back?

The misfire system on these vehicles (like most modern vehicles) is stupid simple: it's not "detecting" anything beyond a change in the crank sensor output. Anything that affects the speed the crank turns will set a P0300. A worn belt can cause a random misfire. A bad pulley can cause a random misfire. A bad tensioner can cause a random misfire. A dying compressor will absolutely eventually cause a random misfire.

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post #10 of 73 Old 11-29-2018, 10:20 AM Thread Starter
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Quote:
Originally Posted by jtec View Post
TSEJEEPERS - the photo above IDK what are you trying to bring to my attention?

Why have we NOT put a scanner on this vehicle? At least ck for codes...

for vacuum leaks try the old school trick using carb or brake cleaner, if unsure google carb cleaner vacuum leak test
When I do check the code it is always P0300. I did have some codes before relating fuel being rich. But have fixed since then. Will try the carb/brake cleaner test today.
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post #11 of 73 Old 11-29-2018, 10:23 AM Thread Starter
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Quote:
Originally Posted by colinzj View Post
If you're hearing a vacuum leak I'd definitely start with the vacuum leak, but to throw out other easy-to-check options that you haven't mentioned yet:

Does the belt look good? Is the tensioner gauge in spec and does the tensioner hold steady? If you clear the codes and don't use the HVAC system, does the code come back?

The misfire system on these vehicles (like most modern vehicles) is stupid simple: it's not "detecting" anything beyond a change in the crank sensor output. Anything that affects the speed the crank turns will set a P0300. A worn belt can cause a random misfire. A bad pulley can cause a random misfire. A bad tensioner can cause a random misfire. A dying compressor will absolutely eventually cause a random misfire.
Not sure what the HVAC system is but, the code has to do with gas/ air I believe. I get a strong stutter when trying to accelerate almost as the car doesn’t have enough air or fuel. But after replacing the fuel pump, I think that should be out of the question. The belts seems fine as well as the pulleys. I don’t think those can affect my driving to the point where I do get a flashing CEL and a really bad stutter when trying to accelerate at a high rpm of around 2-3K, while driving on the highway.
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post #12 of 73 Old 11-29-2018, 10:58 AM
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what does the scanner say?
codes?
ECT, o2 sensor voltages, Fuel Trims Long and short, MAP, TPS, ?

How did you get code p0300 - key trick?

Plugs have black tips, a code for rich, 8-10 mpg, vacuum leak, flashing CEL - there are still some parts to replace -

When I see the price of OEM I think aftermarket.
When I see the quality of aftermarket I think OEM.
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post #13 of 73 Old 11-29-2018, 01:33 PM Thread Starter
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I think the head gasket may be blown. Can anyone here confirm? That’s the oil cap. It was low on oil and coolant. So I decided to check oil and fill it. Also have black goop coming out of the back of the exhaust...
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post #14 of 73 Old 11-29-2018, 01:45 PM Thread Starter
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Quote:
Originally Posted by jtec View Post
what does the scanner say?
codes?
ECT, o2 sensor voltages, Fuel Trims Long and short, MAP, TPS, ?

How did you get code p0300 - key trick?

Plugs have black tips, a code for rich, 8-10 mpg, vacuum leak, flashing CEL - there are still some parts to replace -
Codes I have right now are P0300, P0302, and P0335. I used to only only get P0300.
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post #15 of 73 Old 11-29-2018, 02:10 PM
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Quote:
Originally Posted by colinzj View Post
If you're hearing a vacuum leak I'd definitely start with the vacuum leak, but to throw out other easy-to-check options that you haven't mentioned yet:

Does the belt look good? Is the tensioner gauge in spec and does the tensioner hold steady? If you clear the codes and don't use the HVAC system, does the code come back?

The misfire system on these vehicles (like most modern vehicles) is stupid simple: it's not "detecting" anything beyond a change in the crank sensor output. Anything that affects the speed the crank turns will set a P0300. A worn belt can cause a random misfire. A bad pulley can cause a random misfire. A bad tensioner can cause a random misfire. A dying compressor will absolutely eventually cause a random misfire.
Yes and no... to clarify, these things will cause a ghost misfire. If the belt or tensioner is causing this code it will never cause a full on misfire. When these cause a P0300 the engine will appear to be running just fine but you will have this pesky flashing MIL occasionally and the P0300 and/or P030X.

Quote:
Originally Posted by Jeepwk999 View Post
I think the head gasket may be blown. Can anyone here confirm? Thatís the oil cap. It was low on oil and coolant. So I decided to check oil and fill it. Also have black goop coming out of the back of the exhaust...
It is not uncommon for the cap to look like that and is mostly normal on the 4.7l engine. You may be looking at a head gasket, but that picture is not an immediate cause for concern.

Quote:
Originally Posted by Jeepwk999 View Post
Codes I have right now are P0300, P0302, and P0335. I used to only only get P0300.
Multiple, cylinder 2 and crankshaft position sensor. The 4.7l is dependent on the crank position sensor to run, so if you don't have a stalling issue or almost stalling issue, it has me wonder if you ever unplugged the sensor? I know you said you were after the camshaft position sensor in your last post.

Were you ever able to measure your vacuum?

2005 Jeep Grand Cherokee - Work in progress...
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