| Author | Message | ||
     Roderick |
I hope some of you more skilled and knowledgeable mechanics could help me. I have an '07 Grand Cherokee with a 4.7 at 144k miles. In April, I got an engine light and my very basic code reader said P0307, which mean cylinder 7 misfire. Checked the spark plug and found worn condition. Replaced plug. In May, same thing. Replaced the other 7 spark plugs, since I should have done that last time, and replaced no. 7 coil. Now, same thing. Only fuel injector left. At all time, no sputtering, no lurching, no engine revving up/down by itself, no unusual noises from engine and exhaust, no rough idle, no dying at stops, basically, the Jp runs as if no engine light at all. The worst case is cylinder 7 low compression. Digging into the engine is currently beyond my skills and tool sets. So if it comes down to this, how long and how much cost to repair ? If it is cylinder 7 low compression, the symptom should be persistent, meaning I should not be able to reset the code, correct ? Is the mileage any hint at the fuel injectors go bad or at least deteriorate performance ? Thnx much for any assist. Roderick (Message edited by Roderick on July 18, 2016) | ||
| Pikeben08 |
I'm not a Chrysler mechanic, but I am an engine controls calibrator so I've had to do my fair share of diagnosing car issues. If it isn't the injector it could also be an intermittent wiring issue for either the coil or injector. Any nicked wires? I would almost lean towards that rather than the injector if it is only happening once a month. Any other codes? Always number 7 cylinder? Does your tester let you check fuel trim? | ||
| Natexlh1000 |
If I were in your position, I would swap #7 with #8 and see if it follows the injector. My 2004 ram with hemi had a drooly injector. It was flooding itself after it was turned off. I was getting misfiring codes too but it was because I think I was the first monkey to change the plugs in the thing. My gaps were out to .060 to .075 Anyways, in my case, the injectors are pretty easy to pop out once I got the plastic intake stuff+airbox off. Happy hunting, I know these subtle things can take a while to figure out. | ||
| Hughlysses |
If it's running fine, you could always do this:  | ||
| Badlionsfan |
I really doubt it's a compression issue. Injector or wiring much more likely since you've already done plug wires and coil. What does the #7 spark plug look like compared to the others? That could give a hint too. | ||
| Ratbuell |
If the 4.7 is coil-on-plug, swap coils back and forth to see if it follows. Check harness connectors at the coil. Use dielectric grease to keep water out. Chances are you have a wonky coil and you'll see the code change cylinders when you move the coils. (I assume it's a c-o-p since you would otherwise have mentioned new plug wires...). | ||
| Ratbuell |
Saw you replaced the 7 coil. Make sure wiring isn't nicked and that the plug isn't corroded. | ||
| 86129squids |
   Hugh, that's kinda what I did after coming back from Glitchfest on the Triumph- the fuel level indicator failed, which killed the fuel gauge, and left the low fuel light on perpetually, arrrrgh... found a little weird sticker to cover the low fuel light, and cut a TWoS round sticker to cover the fuel level gauge. Now I just do it old-school, and watch the tripmeter to know when to hit the gas pump. And, now my Triumph's dash is kewler!!!  BTW, I'm selling the Triumph. CL ad posted, local to Knoxvegas. Blake, I'm in arrears to send you fundage as of this date, please know that when I'm not broke I'll catch up. And thanks. | ||
| Roderick |
Yes, the ignition type is coil-on-plug (COP), so no plug wires. No, there are no other codes, unless my basic code reader is that junky. Each time, only P0307 is flagged. Yes, all spark plugs changed in May. This is an '07 so there is one plug per cylinder. 2008+ is when there are dual plugs per cylinder. I will change the injector. Since the no. 7 coil is new, I will move it to no. 5 cylinder (next door) and see what happens. Will inspect all associated wiring at the same time. Am more worried about cylinder compression low than anything else. This would be a mechanical issue and I assume it will take at least $1k to fix ? Probably more depending on severity. But if it is compression low, I would think I would not be able to clear the code at all. Roderick | ||
| Badlionsfan |
I've never heard of low compression triggering a misfire light. I really doubt that's what it is. | ||
| Azxb9r |
Faulty injectors are common on the 4.7 but unfortunately so are valve train problems. Some one else mentioned swapping the #7 injector with another one to see if the misfire follows the injector. This is a very effective "low tech" diagnostic technique that is very effective and will only cost you time. Injector seals (the little oring where the injector goes into the manifold) can also cause a single cyl misfire, but they are usually accompanied by a P0171. The bad news is if it turns out to be a valve problem, the 4.7 is $$$to fix. | ||
| Thumper74 |
The 4.7 isn't terrible to work on. I would swap injectors with the cylinder next to it and see if the misfire follows that injector, but I would perform a leakdown test to ensure that it's not internal (valves,rings) | ||
| Akbuell |
If you haven't already, google Grand Cherokee fault code P0307. Should lead you to various Jeep forums, and someone(s) there will have dealt with it. Good way to find out what the issue and solution will be. Hope this helps, Dave |
