390 Issues after drunken doughnuts.
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Senior User
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From: Port Angeles WA
390 Issues after drunken doughnuts.
Ok I know what everyone is thinking here but hindsight is 20/20. A few days ago after about 10 beers I ended up doing a bunch of doughnuts in a mud field at my buddy's house and now my 390 sounds like the top end is hurtin pretty badly. Its a 76 F250 4x4 with a C-6.
When it starts up my oil pressure goes WAY up to about 100lbs (which is not normal) and then right back down to the standard 40 like it always does. Also after it warms up it sounds like I have a hole in one of the header tubes. And under a somewhat heavy acceleration, I sounds and feels like it missing VERY badly.
One of my buddys was thinking that I may have floated a valve? Any ideas?
Thanks,
When it starts up my oil pressure goes WAY up to about 100lbs (which is not normal) and then right back down to the standard 40 like it always does. Also after it warms up it sounds like I have a hole in one of the header tubes. And under a somewhat heavy acceleration, I sounds and feels like it missing VERY badly.
One of my buddys was thinking that I may have floated a valve? Any ideas?
Thanks,
Cargo Master
Joined: Apr 2004
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From: Golden, CO
Originally Posted by bchitwood73
Ok I know what everyone is thinking here
I agree with fordraceboy, do the basic diagnostic stuff. It's easier to make real decisions with real info. I've had a lifter get stuck; older engine, some deposits, working engine hard (hot) and wind it up a little higher. Only difference is that it missed at all RPMs, and I had it resolved before the engine cooled.
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From: Port Angeles WA
Ok, the plot thickens. Did a compression test this weekend and I have a high of 170, and a low of about 115 HOWEVER this compression tester is junk, the hose was leaking and the release valve was messed up so I am not investing too much concern on that just yet. I also took the rocker shaft off the drivers side and inspected all the rockers and pushrods and everything looks fine.
After reading some other posts I am starting to think I may have a sticky, or bad lifter? I would rather not pull the heads off just yet but I will if its looking like I have to.
After reading some other posts I am starting to think I may have a sticky, or bad lifter? I would rather not pull the heads off just yet but I will if its looking like I have to.
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From: Port Angeles WA
I didn't put a straight edge across the stems but thats a good idea, I will do that. As far at the pushrods go, I did check them all out and they are all strait. Something tells me the problem is with a lifter. Has anyone ever heard of damaging a lifter and having strange results like this? A guy I work with thinks I may just have a week valve spring but this all happened at once so I don't think thats it. I may just eat the $300 for a new cam and lifter set.
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Post Fiend
Joined: Dec 2003
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From: "Islander"
With the rockers off, stem height correct do a bleed down compression check, this would be a good time to check you spring pressures. If all comes up good just replace lifters. How many miles on the timing chain set and cam?
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From: Port Angeles WA
This motor was professionally rebuilt right before I bought the truck about 3 years ago. It has about 50K on it. I have all the paperwork from the rebuild. While I am doing this I was thinking about sticking in a high volume oil pump, Once this motor gets up to operating temp it only shows about 10lbs of oil pressure at an idle which I have heard is normal for all FEs. At 2500 rpm its running about 25lbs.
Post Fiend
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From: "Islander"
Being your a 4 x 4 it should be easy to pull the pan, check rod and main bearing, replace if needed as well the pump. This would only be done after a blow down check comes up good.
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From: Port Angeles WA
Sorry, I did put the rocker shaft back on and its running now. I am going to borrow my friends vac gauge tonight. So I am looking for a jump, or spike in vacume pressure at an idle correct? What kind of range is acecaptable for manifold vac pressure? I have a mild RV style cam which does not seem to effect the idle much at all.
Thanks for your help guys I don't know what I would do without this forum
Thanks for your help guys I don't know what I would do without this forum
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17-22 and steady would be good vacuum reading.
drifting vac needle ind. improper carb adj or minor vac leak
gauge reading steady, but drops regularly equals burnt or leaking valves.
low reading ind incorrect valve timing
gauge fluctualtes as engine speed increases could be ign miss,blown cyl head gasket, leaking valve or weak spring.
this was taken from an older chilton book
drifting vac needle ind. improper carb adj or minor vac leak
gauge reading steady, but drops regularly equals burnt or leaking valves.
low reading ind incorrect valve timing
gauge fluctualtes as engine speed increases could be ign miss,blown cyl head gasket, leaking valve or weak spring.
this was taken from an older chilton book