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2004 Grand Cherokee Misfire #1 Cylinder


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Good evening everyone, I need your help on this one. 

 

I have a 2004 Grand Cherokee Laredo with 249 000km.  4 days ago after 20 mins of travel my engine started shaking and the engine light started flashing. I have a cyl #1 misfire code.

 

At idle the engine is running very well but when it is a litle bit warmer and i making it run at 2000 rpm or if i put it on drive with brake on, it's starting to shake. But if i give a fuel shot to 3000 rpm the misfire disappears.

 

Here's the tests that i have done:

 

I've tried a new coil pack because i assume that the spark plugs were ok ( i've change them 4 months ago,  approx 5000 km). It was worse 147 misfire cyl #1 in 3 mins, instead of 83 with the old coil pack.

I installed the old coil pack and changed the spark plug #1 by a new one, result: no change.

I've unplugged injector # 1 and i can see that the injection was cut on this cylinder so the injector was ok.

i've spray water on coil rack just to be sure that fire is not jumping and everything is ok

I've spray brake cleaner on all vaccum hoses and throttle body to see if i have vaccum leak and nothing happen, visual inspection of the hoses and look all good.

I've put a new ground because the one just beside the dipstick was in bad shape

I've tested compression on cyl #1 and i have 135 psi.

The engine is not burning oil or coolant.

 

I don't know if it's normal, i never paid attention to that before but the evap purge solenoid is clicking 2 shots / seconds

 

FYI i have done a lot of things on it in the last months. Here's the list

 

-Yesterday i'v change my water pump started leaking in the shop 3 days ago. At the same time i've change the timing chain and gears ( the timing is ok )

-2 weeks ago i've change my battery ( the old one  was 6 years old)  and i change both connectors and  cut 1 inch on all wires because there's corosion on it. I have cleaned wire on starter just to be sure to not have ground problem from there.

 

- Last august, i have change lifters and rocker arms, clean top of cylinders of carbon (not a lot on it), cleaned intake and exhaust manifold, cleaned throttle body, I've inspect all valves and they where good, i've cleaned them and i've change valve seals. Change oil and filter and 1000 km after i change it again. I'm running with 10w30

 

To be honest i'm a bite confuse about this problem

 

 

Thanks everyone for your help!

 

J-F

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J-F...Welcome to the forums!  I read your post closely.  Basic engine condition includes normal valve timing and lift (lobes and lifters opening valves uniformly and with enough valve lift), normal compression and normal oil pressure once running. 

 

Compression of 135 psi is okay, not great, but for the engine mileage, I would be looking for uniform compression in that range.  Check another cylinder's compression, or if you have access to a cylinder leakdown tester, check actual compression seal at #1 cylinder with the piston at exact TDC on the compression stroke.  Cylinder balance is important, if the other cylinders are 170-175 psi and #1 is 135 psi, that's not good.  Ideally, I like to see a variance between cylinders of 10% maximum.

 

Once past these four "basics" (confirm valve lift if suspicious, that's all that remains), the problem is fuel, ignition or vacuum.  You have been thorough and tested the #1 injector for rpm drop with the wires disconnected.  The spark plug is new, but is it clean burning like the other plugs? 

 

Since you have coil-on-plug, there is no risk of spark plug cable troubles.  The connection between the coil pack and spark plug(s) must be good with normal ohms resistance.  I would like to see the ignition performance on an oscilloscope, comparing the cylinders.

 

If you can eliminate spark to the #1 plug while the engine is idling roughly, see if it makes any difference to have the spark connected or not.  If the engine is idling roughly, and you disconnect #1 spark without a change in engine performance, the #1 cylinder is either not firing or not pulling its load.

 

Another good test is manifold vacuum with a simple vacuum gauge.  Hook the gauge to an intake manifold port and read idle vacuum and also the vacuum as the throttle opens to 2000-2500 rpm.  (Stay away from the engine cooling fan during this test!)  If vacuum is low overall, compression could be low or the ignition timing is off.  Make sure the coolant sensor is in good condition, check the ohms resistance of the coolant sensor.  Fuel mixture must be normal after engine warm up.

 

If the vacuum gauge shows a shaky needle at idle, you have valves that are either leaking or not seating properly, usually the result of worn valve guides.  I like the vacuum test for overall engine condition, and I want to see 18 in-hg of vacuum or higher at the manifold with the engine idling.  A "mystery" vacuum leak can be the vacuum reservoir or its vacuum hose, usually affecting the cruise control and heater controls.  The '04 Grand Cherokee also has a history of heater control issues.

 

Two items that often cause engine low-speed roughness and throw a misfire code on these Chrysler MPI/EFI engines: 1) the throttle position sensor (worn out) or 2) the crankshaft position sensor (dirty or defective).  I've solved symptoms like you describe by replacing the TPS switch or repairing the CPS.

 

Moses

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Good evening Moses, thanks for your reply. I didnt answer you before because i'm in my biggest period of the year at the shop. (I'm running a snowgroomer sale and service business). 

 

I have news on my 4L.  The  misfire code is not there anymore but the problem still there. Yesterday i've change cam sensor, tps and cps but nothing change. I make run the engine for 10 mins and i've wind it to 4000 rpm and at 3500 rpm i have the same reaction than the cutoff limit so i realise it was more serious than just sensor. After that i let the engine running 5 mins at idle and get back to front of the vehicle to make a video first one of 15 sec i can ear a little tick sound from front of the engine like cyl 1 or 2 .  I give a litle shot of acceleration (approx. 500 rpm) and pow!! i'v got a backfire in throttle body and after that the engine was knocking like someone is using an hammer on the block. That's it!  A piston is punching valves.

 

I've remove valve cover and the first valve on cylinder one is bended and i and lift the rocker arm near  0.5''.

 

 

Thank you for your help, Tomorow am , i'm gona receive another engine of 128000 km that i found and after lunch the vehicle is gonna run again!

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