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If the intake valve doesn't open enough the amount of incoming air will be reduced, meaning low compression.
'94,

In a leakdown test air is provided by shop air, there is no intake or exhaust involved.
 

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2005 grand caravan 3.8L Lifter Valve Noise P0305 P0300
I'm experiencing a similar set of symptoms. But have not gone into the mechanicals yet.
Suspected spark. Changed coils plugs and wires. no help.
got a 0300 and 0305 code at one time early on.
with #5 plug out the engine runs smooth.
Suspect a hung valve or something because intake vacuum is terrible, almost no brake boost help.
At idle all plugs installed, after replacing the fuel injector for #5, still same symptoms.
Raising the idle one starts to hear a very nasty metal on metal sound. Sounds like a valve being hit, or a cam lobe smacking the lifter very harshly.
reminds me of the sound a v8 pushrod engine makes after the pushrod blasts straight through the rocker arm.

Seen any postings with pictures of the valve train?
Truant
 

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Best to start a new problem thread, because if the OP of this one comes back, there will be 2 unrelated discussions going on. Not very many valve-related problems on these engines posted here, but I do recall a number of months ago someone reporting a broken spring. You would likely get some helpful information by doing a compression or leak/down test to see where #5 is at compared to the others.
 

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found broken valve spring

Hi, yes, a new thread would be good.. next time :)

I found a broken valve spring, and that the valve stem had snapped off the retaining portion, the washer and half-moon clips had fallen off.
From the way the spring looks, its been broken for QUITE some time. I could have saved it if I'd acted when I heard the sound.
Symptomatically, thinking back I heard the beginnings of this about 9 months ago, but generally don't service the van. If your engine makes a "duke" sound or any abrupt or inconsistent metal sound, suspect a broken spring.

Removing front AND rear valve covers is EASY. Don't be worried about it.
You'll need a 10mm and a 5/16ths 6-point socket. the two screws on the inside center of the valve cover are harder to get to, but with a 1/4" drive flexible joint you should be able to get them off without issue. They are basically a little over finger tight. The valve cover bolts are retained by the valve cover gaskets, and you should NOT pull them out of the cover. There are two stud/bolts on the corners of the covers, and you'll need a 5/16ths open end or box wrench to get those off. if you are Slow and gentle prying up one corner of the valve cover you'll be able to reuse the gasket. don't touch the gasket, just put the cover down on some paper towels. Start with the front cover, without removing anything else. If that looks OK (you can even run the engine with cover off to check oil flow) then put that cover back and start on the rear.
To remove the rear cover when it's in the car, pull the intake plenum off, there are 8 bolts 10mm head. You'll need to remove the power steering pump reservoir (not the hoses, just the tank needs to be pushed away).. that's two 5/16'ths on top, and one 10mm in back and underneath the tank that doesn't come all the way out, just loosen and pull up on the tank.
You'll need to pull the EGR valve, I used a 10mm and knuckle on that. the lower bolt is tight clearance, but you can do with with normal sockets. If you have a beefy craftsman set, reach instead for your Chinese cheapo tools with a thinner wall.
The throttle cables come off, and there are a few connectors tied onto the throttle body. For the PCV hose on back, don't worry about the clamp, just gently pry upwards on the bottom of the hose with a screw driver and it'll slide off the intake. you can remove it from the valve cover later.
When the intake comes off, set it down on paper towels, and generally don't tip it over unless you have to. Soot doesn't matter, only sand is an issue.
Plug the intakes with papertowels (risk is sand and tools)
Blast away as much dirt as you can, being careful to keep it out of the intakes.
get dirt away from the rear valve cover if you can.
pull the 8, 5/16's bolts on the rear valve cover, and remove the PCV hose.
Push the power steering hose back (don't crack it off your tank!) and lift up the valve cover. it slides out without much trouble.. there is room, you're just bumping rubber hoses and such. If you cleaned it, there is little risk of dropping sand into your lifters.

search term to help others:
2005 dodge grand caravan valve noise misfire engine sound P0300 P0305 rocker rod camshaft cam
IMG_6445.jpg

if the spring fails, you might or might not see something like that. cell phone cameras make working on the back of the motor a snap. take pictures of what you can't see.

by the way, you probably do not need new intake gaskets (they're nice rubber), and the valve cover gaskets are also easily reused. Just check for rips or tears before putting things back together, but its very low risk in my opinion.
total time to check springs, 2 hours.
 

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Glad to hear you got it fixed up.

PS:
'94,

In a leakdown test air is provided by shop air, there is no intake or exhaust involved.
I was referring to the engines cranking compression would be low if the cam lobes were worn.
To your point yes a leak down test result would be unaffected by worn cam lobes.
Sorry for the slow reply, I total missed this a month ago.:blink:
 

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I would like to know how the engine managment system knows that its cylinder #1. Does that imply an injector issue, a spark issue...how would it know which cylinder is not always firing? I know this probably doesn't help, but it might be good to fully understand.

And by the way...I had a boat engine (inboard 4 cylinder) which suffered a bent valve in one cylinder due to minor water intrusion through the exhaust stream. After that happened, it idled with a "miss", but above idle it ran just fine. After I pulled the head and had a valve job done, it idled and ran fine afterwards. So a valve issue could be the problem. If its not spark, fuel mixture, injector issue...not much left.
 
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