I have a 2000 Jeep Grand Cherokee Laredo and recently had a check engine light come on stating misfires. Replaced spark plugs and it happened again. Cleared check engine light and then it drove for about a month with no problems. Now the check engine light is back but now it has started blinking and running really rough when at a light. It also seems to lack power when gas is pushed. This car has given us nothing but problems!! Anyone have any ideas as to what this could be? I am overwhelmed with diagnostic fees and we have already put so much money in this vehicle!
If the light is flashing it means you’re supposed to stop driving the vehicle and have it towed as there is a more serious malfunction occurring, as to what it could be, there are so many possibilities that i’m not going to begin to guess.
What brand spark plugs did you install? A RANDOM MISSFIRE code would not necessarily indicate spark plug failure. There are several possible causes for lack of power, also. For less than $150 a scanner is available which could help you avoid “overwhelming” diagnostic fees. It is not advisable to drive with the CEL flashing. If you get a scanner and run the basic test and post the results here you will get some relatively knowledgeable insight.
Many large auto parts store will allow you to plug in a scanner and read the codes for free. If you post the exact codes here, someone may be able to help. Whether you need to stop immediately when the CEL is flashing will be spelled out in your owner’s manual.
Is the code for random misfire or misfire on a specific cylinder? If the code is for a specific cylinder then the coil pack for that cylinder could be weak and failing. The problem could have been temporarily covered up by new plugs.
There was a tune up done in Feb 2010 and Delco spark plugs were put in. Then Firestone read codes off CEL in July and suggested a tune up again. Champion plugs were put in this time. Now the codes are P0300, P0303, P0305.
I would check out the spark plug wires, coils, sensors, and injectors. A 10-11 year old car will need maintenance, and you shouldn’t feel bad about that. Not that I enjoy paying bills, but it beats having no transportation.
Are the codes the same as the first time you had this issue?
The codes indicate misfire on cylinders 3 and 5. Problem could be wires since I don’t think both cylinders fire off of the same coil.
Were the old plugs fuel soaked when they were removed from the problem cylinders?
The plugs were not soaked. The codes do change, its always 5 but will randomly give 1,2,3 codes. It never gives 4 & 6 codes, oddly. There are also no wires as it is a coil pack.
Unless you have six coil packs, you have plug wires going to the other three cylinders.
Its one coil pack on an inline six motor, can you separate the spark plug wires from that coil pack?
Sorry. Thought you had a V6 engine.
So given the current codes that the CEL is giving, would any of you think a safe guess as to what is wrong would be that the engine coil rack is going bad and needs to be replaced?
No - its one guess.
Has anyone checked the compression? Has anyone checked the power supply to the coil rack? Has anyone checked out the fuel pressure and injector operation?
Misfires are often caused by problems with spark. But they also come from problems with fuel and compression.
Another side note, it seems to correct itself (for a short time) when you shut off and turn it back on. Don’t know if this makes a difference. Maybe making it something computerized?
If it works for a short while, it sounds like something is heating up and intermittently failing. A coil pack would be a prime candidate for this. People look at a computer controlled engine and see a mess of wires and sensors and freak out. But usually the computer is the most reliable part on the car and it’s the basics that fail–like ignition coils. Though I wouldn’t offer more than a guess that that’s your problem.