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Okay, just got the code read and it said that it was a “cylinder 3 misfire” I believe. They told me its probably the spark plug, but if its something else what’s the worst it could be? Also for verification I believe the code number was P303 or something along that numbering.
Did you know that the HEMI is not a hemi? Doesn’t have hemispherical combustion chambers. Real hemis became obsolete in the 1970s. The current HEMI has two spark plugs per cylinder. This suggests to me that, if one of the spark plugs is not firing, there would be only slightly reduced function. I have no hands-on experience with the Chrysler HEMI, so I could be wrong.
The sequence for diagnosis is the same in any event. Remove the covers that conceal the spark plugs. Get a look at the ignition wires running to the offending cylinder. Take the two plugs out and get a look at them. You can also take one or two plugs from another cylinder and look them for comparison.
If both plugs show evidence of misfire, the fault is probably not the plugs, but the circuitry responsible for firing them. Are the 2 plugs fired by a single coil? That could be the problem.
If one plug looks good and the other bad, check out the circuit for that plug, the ignition wire, the coil… I don’t know off hand if Eric has a video for checking out a coil, but maybe someone can suggest one for you.
(Chrysler came out with a pushrod hemi in the 1950s and a similar second pushrod hemi in the 1960s. The current HEMI uses capitol letters and it is a trademarked name. )Take alook at the plug n cylinder #3 and check the gap and see if its way out of spec.
If you suspect a coil issue, you would need to stress test it with an adjustable spark tester. Or, you could swap the suspect coil with another one on the engine and see if the misfire moves.
You can also buy or even loan out Noid Lights to check the integrity of the wiring going to the injector. The noid light should flash when the engine is running.
Some people will also ohm out the injector and check the resistance. However, this test is not always accurate. It is better to do a fuel pressure leak down test or have a tester to fire the injector will observing fuel pressure.
Another few tests would be a compression and leak down test of that suspect cylinder.
Worst case scenario would be a burnt exhaust valve or broken valve spring.
Start with the basics first.
Good luck.
Several quick questions. Not sure since its a newer vehicle but, I’ll have to delete the code after replacing or fixing whatever needs fixing correct? I mean I’m still in the process of checking the plugs but if I’m not mistakened doesn’t the computer deactivate the cylinder that misfired? Because initially there was some shaking like is typical with a misfire but it evened out and there’s none of that now. I’ll need to get my hands on some deep sockets and longer extensions to get to the plugs. Thanks for the input guys and I feel sheepish for asking this…(nervous laugh) what should i be looking for, how does it look when there is a misfire rather? I’ll assume that it will look either completely covered in carbon build-up or the tip will be damaged in some for or way in the mean time. Thanks again!
Yes I’m with keeping it simple. Plugs are a good start as that is an easy fix and required maintence anyway. Once you replace them you WILL have to reset the code because it sounds like it went into ‘limp in’ mode and the only way to get it out is to clear those codes. If you still have issue after replacing the plugs try a power balance to see if you can confirm cylinder #3 is at fault and if it still has an issue, I’ll provide a link for you. If you find that cylinder is not producing then check the spark and fuel for that cylinder as well as it’s compression to rule out a mechanical issue. If memory serves those trucks sometimes have issue with fuel injectors but lets not get ahead of ourselves, in fact you might try the power balance first as well as check for spark before you replace the plugs.
http://www.google.com/search?q=HEMI+combustion+chamber&hl=en&prmd=imvns&bav=on.2,or.r_gc.r_pw.,cf.osb&biw=1680&bih=949&um=1&ie=UTF-8&tbm=isch&source=og&sa=N&tab=wi#um=1&hl=en&tbm=isch&sa=1&q=spark+plug+chart&pbx=1&oq=spark+plug+chart&aq=f&aqi=g1g-m2g-S6g-mS1&aql=&gs_sm=s&gs_upl=10762l20623l0l23258l16l16l0l2l2l0l194l1877l3.11l14l0&bav=on.2,or.r_gc.r_pw.,cf.osb&fp=8cd9febe539bdb93&biw=1680&bih=949
Here’s some photos of faulty spark plugs to show you “what you’re looking for”. I still suggest you remove a couple of plugs from the functioning cylinders. That way you’ll learn what good plugs look like compared to “bad” ones. The photos usually show extreme conditions, so it’s helpfull to look at real plugs from from your engine.
As your HEMI has two plugs per cylinder, you will be able to compare the two against each other and if they look the same, you can compare them to plugs from an adjacent cylinder that that is known to be firing.
If they are simply not firing, you’ll see carbon fouling. If one is fouled and the other is OK the fault may be with the plug. If they’re both fouled, the fault is probably in the circuit and you’ll need to check the coil pack that fires them next.
If both are getting current from the coil pack and they’re carbon fouled, suspect the fuel injector as Eric suggests.
Eric’s suggestion to perform a balance test (disabling current to each cylinder, one a time, to find the the bad cylinder) is a good idea because the fellow at the parts store that scanned and read the code and told you it was number 3 cylinder, could easily be wrong.Its early morning, but did a power balance test to the cylinders I could reach which included the one that the code said it was. There was still a drop in rpms in the suspected cylinder but I didn’t notice a significant power drop in the first cylinder actually. so I’m a little stumped but I’ll be changing the spark plugs later today and get the codes reset and re-read because the MID light is now on solid even while running, but I assume its due to the power test at the moment. I’ll check back in later with the results. Thanks again, and I’ve seen most of your videos Eric but it surprised me that I hadn’t seen the power test video.
Only one of the plugs was fouled in cylinder 3 so should there be any further diagnostics? And if you or anyone else knows what the inside of one of these trucks hoods looks like, what would be the best way to get to the back plugs? I’m having a bit of trouble with that and removing the brake master cylinder or the air cover thing (completely forgot the proper name) seem like the best way to get to them but I don’t want to do any unecessary work.
Did you check out the free Chilton Online that another forum member posted in another thread to help with basic maintenance and repairs? If might have some info in there for you.
Sounds like you’re right on top of things. Not everyone can diagnose and find the shortest route between point A and B. In your place, I would still swap the the coil pack from number 3 with a known “good” coil pack. If there’s anything wrong #3 coil pack, you’ll know real soon.
If you’re working on ignition parts, this is standard operating procedure if the engine is yours. If you were working on a valve train, such as the pushrod valve train in your HEMI, you wouldn’t want to swap any components around because once they’re broken in, they’re no longer identical and interchageable.
I hope to hear that everything is working out for you after you have completed the repairs.In that you have 16 spark plugs and some are very difficult to replace, why not replace the bad one? Are the others you have looked at OK? If they’re original plugs, and not scheduled for replacement, keep ’em. 16 plugs will cost a fortune, but one will be cheap enough.
Do you need any further diagnosis? It may be the fault of the coil pack rather than the plug. If we were dealing with an older vehicle with a single coil, I would check the coil with my digital multimeter (Car guys call them DVOMs nowadays). On your HEMI, with coil packs and no ignition wires, I don’t know how to perform the test, but there’s a “shade tree” test that works fine and you don’t have to buy any new tools. Take the coil pack from number 3 cylinder and swap it with another cylinder. If your CEL (check engine light) comes on again, check the coil that came from number 3 cyl (look at the spark plugs under the suspect coil pack.) If you have a fouled plug again, you know the coil is bad.
I could be wrong, but I get the impression that you are a DIY and probably don’t want to buy a lot of expensive tools you will seldom use. If you can afford a code scanner (which you need to turn off the CEL and clear the stored codes) they’re a good investment and it’s nice to have your own. A decent digital multimeter will pay for itself too.The plugs don’t cost much actually since the oem are just copper plugs its about 2$ a plug but I don’t have a steady form of income right now, and yeah I’m a do it yourself kind of guy. Eventually I’ll invest in a code scanner but in the mean time I went and just had the autoparts store reset the codes. And I do need to change all the plugs, the gap on each one that I looked at was already a good amount larger than what it should be. Either way like many DIY people, I’ll find a way to get to the plugs I can’t reach easily. Thanks a ton guys, I’m really glad that as far as I can tell it was just the spark plugs.
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