2004 Jeep Grand Cherokee 4.7 problem
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- Mitchroberson
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- CalitechT.J.
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Travis T.J. Harrison
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On the crank it did sound uneven not really bad but it did make me wonder. I put a compression gauge in the cylinder that didn’t show the spike on the coil and the compression showed over 100 so I moved on.
I did hear some ticking pretty loud a few times under the valve cover. So that’s why I put a vacuum gauge on it and noticed the bouncing vacuum. Why would the coil not show the magnet Collapse only sometimes?
Turns out that all of this started when they put in a now radiator….. they finally told me it did get over heated. That made me wonder if the vacuum gauge was telling me head gasket.
But still thinking about the loud tapping some time under valve cover… At first I was told it was running rough so the put new spark plugs but it didn’t fix it.
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Without seeing the waveform, it's tough to say for sure. But I've taken secondary waveforms with several different Snap-On products, and none have had an issue. Can you take a screenshot with your Zeus and post it?I have another question it’s off topic kinda. My probe doesn’t do very good at watching the coils fire I have to unplug the ground some times for it to work. It might be my (homemade) cord but I don’t think so I’m scared it might be my Zeus I did purchase it used. Do you ever have issues with yours like that?
If you still can't make it work reliably, you might be better off scoping the coil primary voltage instead. The Zeus can handle the inductive kick without issue, and the primary still has tons to tell you about the spark and cylinder conditions.
You've got a tapping under a valve cover? AND it's been overheated? Red flag. Do a head gasket and relative compression before proceeding. There's no point in chasing anything else until you've done those, IMO.
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I plan on a compression test. Not a relative compression because I did a relative compression and didn’t see the problem. But I already did a compression test on one cylinder. The cylinder I unplugged the coil on as a cylinder drop test and it didn’t change the idle. So that’s why I’m leaning to amps on injectors.
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Sorry I missed you last night. If you're around for the next group chat, stop by! We'd have a good time doing some live diag.Okay I think I have bugged you enough for tonight tell me what the pictures tell you tomorrow. It's late I better stop thinking about this and get some sleep lol
I grabbed your first pic and inverted it for clarity:
Definitely a low cylinder. What were your scope settings for this capture? Which ignition coil were you connected to?
In your second shot, is this the missing spike you're referring to?
I think this comes down to your scope settings. Snap-On products will need Peak Detect turned on to catch detail on ignition events like that. It looks like you're on a two second screen? That should be just fine. But don't be afraid to make the Zoom function work for you, if you aren't already. Try one second or 500ms.
How would I test for a head gasket? I've started doing pressure pulse and manometer testing almost exclusively. I've got some examples posted here if you're interested in learning how:
www.scannerdanner.com/forum/diagnostic-t...s-blown.html?start=0
Blue water/block check is another option. Leak down testing each cylinder and looking for bubbles in the radiator would be another. Last would be to get the engine hot, shut it off and pull all the plugs, then put a pressure tester on the rad. Come back in the morning and look for coolant in the cylinders.
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I’m pretty sure it was the #2 cylinder I had marking on the relative compression test.
I didn’t think nothing about peak detention! I was going down the rabbit hole lol thinking it only don’t have compression sometimes that was why the spike was only missing sometimes. It’s really good to have this forum to be able to talk to others guys about scope testing! I haven’t heard about anyone else in town using a scope. I might be the only shop in town that uses one lol I know a few people that have them but don’t know how to us them lol I really appreciate your help!
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If your ignition trigger was on #2, then I think you've got enough evidence to revisit compression and leak down on that cylinder. Let us know what you find!
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I have found the main problem with this diagnostic! It was me thinking I could run thru these test real fast! If I would have took a little more time on the relative compression I would have seen it! And not had to do everything else I did. That was the first test I did LOL!!!! That is one way to get humbled! LOL worked probably 3 hours before I found it was probably a valve issue or head gasket when I could have known it in 15min and probably found the cylinder if I would have took the time to look at it better LOL well we live and learn. I will do my best to remember to update this and say what I find. Thanks a lot!
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- CalitechT.J.
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