Do I have sticky valves?
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Do I have sticky valves?
Ok i have a 86 f250 with 351w ,holley 4180 carb, c6 tranny. Been working on for a while. I already rebuilt carb(mixture screws 1.5turns out), replaced intake manifold gasket. I think previous owner replaced spark plugs and wires. Also all vac ports capped off except pcv and distributor advance hooked up. I can put the vac guage on a manifold port and get 20-22psi. Although at idle the gauge is not steady is goes up and down 1-2ps, still staying around 20psi. Once i hit the throttle and rev it up it will drop to around 15psi then go back up to around 20psi. Is this normal or should the vac stay around 20psi with throttle response? Why is the gauge not steady at idle? Also i did a compression test all cylinder near 120psi or so. In addition the oil pressure is (20psi at idle ) due to sludge. I'm also planning on dropping oil pan and replacing oil pan gasket, oil pump and cleaning out any sludge. Should i check the valve lash and how do i know if they are sticking?
thanks
aric
thanks
aric
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From: The Big, Oregon
Is there a root issue you are trying to diagnose, or are you just checking the general health of the engine?
The measurement here is in/hg, not psi, if you had 20psi in your intake something is a bit off.
The idle vacuum sounds a bit high for a 4bbl, I'd expect more like 16-18in/hg but more isn't a bad thing. A higher lift cam or excessively low idle can cause erratic vacuum readings.
The vacuum will drop when you give it throttle since you are letting more air through.
If you have a sticking valve, it would have a definite misfire and shake to the engine. 20psi of oil pressure at idle isn't bad, especially if it's at hot idle.
The measurement here is in/hg, not psi, if you had 20psi in your intake something is a bit off.
The idle vacuum sounds a bit high for a 4bbl, I'd expect more like 16-18in/hg but more isn't a bad thing. A higher lift cam or excessively low idle can cause erratic vacuum readings.
The vacuum will drop when you give it throttle since you are letting more air through.
If you have a sticking valve, it would have a definite misfire and shake to the engine. 20psi of oil pressure at idle isn't bad, especially if it's at hot idle.
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From: Virginia
20 psi at idle is very good oil pressure. The vacuum guage will drop normally when the throttle is opened. The only way you get vacuum is when the throttle is shut or partially shut. If you open the carb wide open pulling a hill, you vacuum will drop to near zero.
Try messing with the idle screws more. The 1.5 turns is just a starting point. Get it warmed up and adjust the screws for best idle quality and highest rpm. Also they usually work better if you have the dist on the port that has no vacuum at idle.
Try messing with the idle screws more. The 1.5 turns is just a starting point. Get it warmed up and adjust the screws for best idle quality and highest rpm. Also they usually work better if you have the dist on the port that has no vacuum at idle.
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From: NoGa.
Ok i have a 86 f250 with 351w ,holley 4180 carb, c6 tranny. Been working on for a while. I already rebuilt carb(mixture screws 1.5turns out), replaced intake manifold gasket. I think previous owner replaced spark plugs and wires. Also all vac ports capped off except pcv and distributor advance hooked up.
I don't much like adjusting carbs by "how many turns in or out" ... if you you got all the other circuits correct ... you should be able to set the idle mixture with a gas analyzer ... I would even try adjusting the idle mixture to "best Idle" ... But that's me.
I can put the vac gauge on a manifold port and get 20-22hg. Although at idle the gauge is not steady is goes up and down 1-2hg, still staying around 20hg.
18 to 20 hg is pretty good ... and consistent with your compression test of 120 psi.
Once i hit the throttle and rev it up it will drop to around 15hg then go back up to around 20hg. Is this normal or should the vac stay around 20hg with throttle response?
Yep! Normal. Why? Because when you opened your throttle plates ... you sorta created a vacuum leak.
Why is the gauge not steady at idle?
Probably the intake pulse cause by the opening of the valves. Your reading is nothing to worry about.
Also i did a compression test all cylinder near 120psi or so.
I like to see them at "a buck and a quarter" ... but all is well and good here!
In addition the oil pressure is (20psi at idle ) due to sludge.
If you're thinking your O/P is low ... it AIN'T due to sludge. Oil Pressure ain't even ENTIRELY created by the pump. O/P is created by the clearances of the rod, main and cam bearings. Bad Bearings give low oil pressure.
Don't think so? Go out to your garden hose and take the nozzle off. Turn the water on. Running free ... you got "volume" of water ... and not much pressure.
Now put your thumb over the end of the hose.
NOW you got PRESSURE ... by relaxing or tightening your thumb you can increase or decrease pressure. That's how the bearing work regarding O/P.
OK...OK Because there are some guys that would lint pick ... I HAVE seen where debris from the nylon timing gears clogged up pump pickups and SEVERELY lowered O/P ... to the point engines got destroyed ... but THAT is in the extreme. (Also in old GM cars).
I'm also planning on dropping oil pan and replacing oil pan gasket, oil pump and cleaning out any sludge.
I'm not a "expert" on Fords ... my background is largely European automobiles ... but ... IF you think you got low O/P ... and IF you are gonna drop the pan ... it wouldn't hurt to pull the pump ... and check the clearances. Just remember ... a pump will only be as effective as the bearings will allow ... you could put a pump on there that was built to deliver 1,000 psi O/P ... but if you got bad bearings ... all that O/P POTENTIAL ain't gonna help a thing!
Should I check the valve lash and how do i know if they are sticking?
If you had a valve sticking ... it would show up as a bigger drop on the Vac Gauge at idle. Maybe as much as 8 to 10 psi. A BIG swing. You also would get a popping back ... through the carb if it was an intake valve ... the exhaust if otherwise. You ain't got that.
As for adjusting valve lash ... how many miles on the motor?
On an older motor with original lifters it might not be a REAL good idea. Unless you got a tapping somewheres ... I'd let it be.
thanks
aric
I don't much like adjusting carbs by "how many turns in or out" ... if you you got all the other circuits correct ... you should be able to set the idle mixture with a gas analyzer ... I would even try adjusting the idle mixture to "best Idle" ... But that's me.
I can put the vac gauge on a manifold port and get 20-22hg. Although at idle the gauge is not steady is goes up and down 1-2hg, still staying around 20hg.
18 to 20 hg is pretty good ... and consistent with your compression test of 120 psi.
Once i hit the throttle and rev it up it will drop to around 15hg then go back up to around 20hg. Is this normal or should the vac stay around 20hg with throttle response?
Yep! Normal. Why? Because when you opened your throttle plates ... you sorta created a vacuum leak.
Why is the gauge not steady at idle?
Probably the intake pulse cause by the opening of the valves. Your reading is nothing to worry about.
Also i did a compression test all cylinder near 120psi or so.
I like to see them at "a buck and a quarter" ... but all is well and good here!
In addition the oil pressure is (20psi at idle ) due to sludge.
If you're thinking your O/P is low ... it AIN'T due to sludge. Oil Pressure ain't even ENTIRELY created by the pump. O/P is created by the clearances of the rod, main and cam bearings. Bad Bearings give low oil pressure.
Don't think so? Go out to your garden hose and take the nozzle off. Turn the water on. Running free ... you got "volume" of water ... and not much pressure.
Now put your thumb over the end of the hose.
NOW you got PRESSURE ... by relaxing or tightening your thumb you can increase or decrease pressure. That's how the bearing work regarding O/P.
OK...OK Because there are some guys that would lint pick ... I HAVE seen where debris from the nylon timing gears clogged up pump pickups and SEVERELY lowered O/P ... to the point engines got destroyed ... but THAT is in the extreme. (Also in old GM cars).
I'm also planning on dropping oil pan and replacing oil pan gasket, oil pump and cleaning out any sludge.
I'm not a "expert" on Fords ... my background is largely European automobiles ... but ... IF you think you got low O/P ... and IF you are gonna drop the pan ... it wouldn't hurt to pull the pump ... and check the clearances. Just remember ... a pump will only be as effective as the bearings will allow ... you could put a pump on there that was built to deliver 1,000 psi O/P ... but if you got bad bearings ... all that O/P POTENTIAL ain't gonna help a thing!
Should I check the valve lash and how do i know if they are sticking?
If you had a valve sticking ... it would show up as a bigger drop on the Vac Gauge at idle. Maybe as much as 8 to 10 psi. A BIG swing. You also would get a popping back ... through the carb if it was an intake valve ... the exhaust if otherwise. You ain't got that.
As for adjusting valve lash ... how many miles on the motor?
On an older motor with original lifters it might not be a REAL good idea. Unless you got a tapping somewheres ... I'd let it be.
thanks
aric
WOW ... not many guys still use a Vac Gauge anymore ... not many know how.
That's a real shame because its a GREAT TOOL!
In the (VERY) old days ... my Dad used to have a "Motor Minder" vac gauge on his Buicks (My Dad had a bunch of Buicks that had Dynaflow Trnasmissions ... and three holes in each front fender!!!) ... he used to drive by this gauge ... If you held it at the HIGEST Vac reading you could get ... during CRUISE ... your mileage would go WAY up.
Or at least get "pretty good" ...
for a Buick straight 8!
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From: NoGa.
But you young kids wouldn't know anything about that.
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sorry i mean inches for the vac readings. I'm just wondering if my vac readings were normal. I'm tryin to diagnoise why the engine stall when put in gear sometimes or it will stall when coming to a stop. Its weird today we had it idling good in drive and I drove it back and forth and reverse it was somewhat ok although it did not upshift because the vac line to the modulator was capped off. So i connected the modulator then it shifted although i don't think that it downshift when i was slowing down since the engine stalled. I'll keep searching or start a new thread. if i don't figure it out soon i may just make a video of the engine running.
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From: Virginia
Make sure you do not have any vacuum at idle on the dist hose. If you run vacuum all the time on the dist, the idle will have a tendency to drop really low when putting a automatic in drive.
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i checked the vac advance and i think its working properly there is no vac at idle and vac increases as throttle response does. After reading others forums. I may check the ignition system one more time. Because when i was setting the timing it seems as though it was firing all the time. Now that i think about it there were two exposed wires on the ignition control module. I'll check to make sure its still getting good connection and if it is ill wrap the wires up in some rubber insulation or something.
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