Confusion
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New User
Joined: Aug 2003
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From: Byhalia, MS
Confusion
I have a rebuilt 390, and recently I've come up with some problems I can't explain or figure out.
First, and the most confusing, for some odd reason the motor sounds like it's got a slight case of vapor-lock. When driving down the road at an even speed, it stutters, no matter which gear I'm in, unless I'm on the highway.
Second, the oil pressure light comes on when the engine is at idle, even when driving if I happen to use the clutch (turning corners, etc.). The oil level is acceptable, reading full when I checked it earlier tonight.
Any clues?
Thanks so much.
First, and the most confusing, for some odd reason the motor sounds like it's got a slight case of vapor-lock. When driving down the road at an even speed, it stutters, no matter which gear I'm in, unless I'm on the highway.
Second, the oil pressure light comes on when the engine is at idle, even when driving if I happen to use the clutch (turning corners, etc.). The oil level is acceptable, reading full when I checked it earlier tonight.
Any clues?
Thanks so much.
FE "Freakin Expensive"
Joined: Dec 2003
Posts: 6,461
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From: Smith Mountain Lake, VA
It could be possible your getting a slight case of vapor lock..are you running a metal fuel line all the way up to the carb?Cause all metal lines will realy heat up in the summer heat/ if you are try taking about 12" of the line off..and replace it with a rubber fuel grade line...
And when the oil light comes on..does the motor start ticking? If not you might have a faulty sending unit going to the gauge?
Good Luck and keep us posted! Russ
And when the oil light comes on..does the motor start ticking? If not you might have a faulty sending unit going to the gauge?
Good Luck and keep us posted! Russ
Logistics Pro
Joined: Feb 2000
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From: Sun River St. George
stutters! I would look at the ignition system. Do you have points or electronic? The oil light issue sounds more serious! You need to determine how much oil pressure the engine is holding at idle. The most efficient way to do this is to install a calibrated direct reading pressure gage in the oil system usually at the sending unit. Post back with results.
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New User
Joined: Aug 2003
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From: Byhalia, MS
Originally Posted by RapidRuss
Ok..but hows your oil pressure..dont tell me that changed back too??
And to answer the question you asked earlier, it's got rubber lines rather than metal. That was changed when the engine was rebuilt about 2 years ago.
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FE "Freakin Expensive"
Joined: Dec 2003
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From: Smith Mountain Lake, VA
Well first of all try a new sending unit...and see if the light doesnt go out..thats the cheapest way you can go..and if that doesnt work..to really find out what you have..your going to need to put in a mechanical gauge..so you can find out right where you are! Russ
Postmaster
Joined: Apr 2002
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From: Coal country
My oil idiot light scared the living daylights out of me the other day. Turned out the sending unit wire had been rubbing along a rough casting edge on the intake manifold the last 40 years, and had finally worn through.
It simulated low oil pressure caused by a worn engine because it would come on only at idle That coincidence turned out to be caused by the fan and/or forward motion of the truck moving the wire just off the rough casting edge, but allowing the wire to drop back against the metal when stopped.
Total movement was less than 1/8 of an inch.
Discovered it by moving the wire, but I had to look close for the wear point.
It simulated low oil pressure caused by a worn engine because it would come on only at idle That coincidence turned out to be caused by the fan and/or forward motion of the truck moving the wire just off the rough casting edge, but allowing the wire to drop back against the metal when stopped.
Total movement was less than 1/8 of an inch.
Discovered it by moving the wire, but I had to look close for the wear point.
Fleet Mechanic
Joined: May 2004
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From: Montana
Ive had this problem on numerous fords.....Thats all ive ever owned, but I have come to the conclusion that most fords from the favtory have weak oil systems giving low oil pressure. Its a big pain in the @$$ but If you change out that guage and still get funky numbers like i always have, meaning I put the mechanical in and now it just shows low most of the time then goes up then goes so low its non existant....then i suggest an oil pump upgrade your pickup maybe malfunctioning or whatever.
Postmaster
Joined: Apr 2002
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From: Coal country
Egoman has also reaised a good point, in that FEs are notorious for scaring folks with their low oil pressure. 10 lbs per 1000 rpms is the figure for minimums I've heard. FE engines are tough.
I do NOT recommend a high volume oil pump, though for your FE. They tend to wash the bearings. I put in new rod and main bearings with a new high volume pump, and had to replace the bearings again 25K later.
I put a standard pump back in with the replacement rod and mains, and the problem hasn't returned 45K later.
I have seen this occur with several FEs, not sure why it doesn't occur with other engines.
I would like to hear other opinions on this.
I do NOT recommend a high volume oil pump, though for your FE. They tend to wash the bearings. I put in new rod and main bearings with a new high volume pump, and had to replace the bearings again 25K later.
I put a standard pump back in with the replacement rod and mains, and the problem hasn't returned 45K later.
I have seen this occur with several FEs, not sure why it doesn't occur with other engines.
I would like to hear other opinions on this.
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New User
Joined: Aug 2003
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From: Byhalia, MS
Thanks Russ, EgoMan, and banjopicker for the advice.
I'll start with the sending unit wire and see if there's any short along the way. I mean there shouldn't be, since the rebuild is so new, but you never know.
If not that, then I'll move to the next one, and so on, and so forth, until it gets fixed, or rebuilt again, or sold.
I'll start with the sending unit wire and see if there's any short along the way. I mean there shouldn't be, since the rebuild is so new, but you never know.
If not that, then I'll move to the next one, and so on, and so forth, until it gets fixed, or rebuilt again, or sold.