Intermittent engine performance

1992 CHEVROLET 1500
235,000 MILES • 4.3L • V6 • 4WD • MANUAL
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WALKINGTOOLBOX
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VIN Z TBI.
Five speed transmission 12'' 10 bolt rear end.

The mileage is accurate to frame, the engine was replaced before I bought the truck. Possibly rebuilt and was told it rumored to have 350 guts in it. Owned for three or four years now. When I first got it it had blown head gaskets. Replaced them, plugs and wires, and it ran fine, no rattles, no tics, no smoke, smooth. Then it starting having overheating issues, got close to red twice, replaced bad water pump with one off a 350 v8, swapped radiator to the big ones attached to the 350 v8 and put in a 185° thermostat. Performance wires, new distributor, new ICM. Replaced all those because it ate ICMs, new distributor fixed that.

Truck is not a hot rod by any means but it definitely surprises you, I fooled a lot thinking it had a v8 but over time it has lost power, oil pressure at first start is little under 60, after it has warmed up at idle pressure is 30 or lower sometimes hitting a low of 10. 50 during a decent acceleration. It does smoke some have to really look to see, on occasion it will create a small cloud after idling at stop light then accelerating, rarely will it create a small cloud on start up. It absolutely does not like it when I turn the AC pump on.

I will admit oil and filter has not been changed completely in awhile, what I mean by that is when I did my clutch I replaced rear main, oil and filter (year and half ago) but it still leaks so it gets a quart once a week. I did however remove the oil cooler lines, could never get them to stop leaking! Maybe that was a bad idea. This bad performance does not happen every day, but every other day which I do not really understand.

Is this engine toast?
Should I try some things before a rebuild/replace?

Anything is appreciated.
Thanks.
Aug 27, 2018 at 11:41 PM
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ASEMASTER6371
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Good morning.

The low oil pressure is the key. That is an indication of worn main and rod bearings. That is what will push you to rebuild or replace the motor.

As far as the overheating, did you have the head planed when you did the gaskets? A warped head will cause this issue and the smoke as well, if it is white.

Roy
Aug 28, 2018 at 1:33 AM
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WALKINGTOOLBOX
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Yea, the heads got looked over, and it does smoke white, some days it is worse some days it does not smoke at all. The smoke is small no clouds by any means, only time it leaves a cloud is after driving for a bit and taken off at a stop.
Aug 28, 2018 at 2:11 AM
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ASEMASTER6371
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Yep, you are burning coolant.

You need to have a leak down test done on the cylinders to find out where the leak is from with the head gasket.

Roy
Aug 28, 2018 at 2:25 AM
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WALKINGTOOLBOX
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Not sure if it is burning oil or not, I do have a small leak either rear main or oil pan. As far as the leak down test, is that a somewhat simple test to do? I have actually never done one, I will check my radiator level and see if it has gone down any.
Aug 28, 2018 at 2:28 AM
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ASEMASTER6371
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It is a test where you remove the plugs and insert shop air into the cylinders one at a time. Then you watch the coolant level in the radiator. If a head gasket is leaking you will see movement in the coolant in the radiator.

Roy
Aug 28, 2018 at 2:47 AM
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WALKINGTOOLBOX
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I will will get that done. I also just remembered I changed my spark plugs less then a month ago, they did not look like they where burning oil now that I think of it.
Aug 28, 2018 at 3:04 AM
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WALKINGTOOLBOX
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I still have the old plugs, I will take a picture of them and get a opinion on them. Thanks so far for the help.
Aug 28, 2018 at 3:09 AM
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ASEMASTER6371
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You are welcome.
Aug 28, 2018 at 4:00 AM
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WALKINGTOOLBOX
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So found my old plugs, checked coolant level in radiator and well it is way low. So I guess you are right I m burning coolant, cannot believe my brain did not come to that conclusion.
Aug 28, 2018 at 10:45 AM
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ASEMASTER6371
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No big deal. Sometimes a second opinion is good for your thoughts.

Get the test done.

Roy
Aug 28, 2018 at 11:15 AM
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WALKINGTOOLBOX
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Compression test:
Cylinder 1=130
Cylinder 2=150
Cylinder 3=130
Cylinder 4=150
Cylinder 5=150
Cylinder 6=150
Aug 28, 2018 at 2:35 PM
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ASEMASTER6371
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Okay, compression good, but that is not the test. You need to do the leak down test as I described.

Roy
Aug 28, 2018 at 2:40 PM
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WALKINGTOOLBOX
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Yea, I understand that, figured I would do the compression test anyway.
Aug 28, 2018 at 3:55 PM
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WALKINGTOOLBOX
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Having trouble getting a hold of a proper leak down tool, might have to go the poor man route and just use a hose. For the results are these correct?

Air leak through valve cover or dipstick tube= rings
Air leak through TBI= intake Valve
Air leak through exhaust= exhaust valve
Air leak through radiator= head gasket or cracked head

For a little confirmation, well a leaking intake gasket cause burnt coolant? Or is that just a head gasket area issue

It does not over heat anymore after I did the water pump, I added a picture of oil pressure and temperature after a thirty minutes highway drive then at idle for some reference I suppose.
Aug 28, 2018 at 6:52 PM
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ASEMASTER6371
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Results are correct.

If it was an intake, you would have coolant in the oil but not burning it at all.

Roy
Aug 29, 2018 at 1:34 AM
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WALKINGTOOLBOX
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Alright, good to know for future reference. Thanks
Aug 29, 2018 at 9:59 AM
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ASEMASTER6371
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Yep, do that check and let me know what you find.

Roy
Aug 29, 2018 at 10:04 AM
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WALKINGTOOLBOX
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Well, so far I have done cylinder 1 and 3, both leaked out threw TBI 1 was a lot 3 was some, but not out the radiator. Should I continue? I know these two cylinders were the lowest compression.
Aug 29, 2018 at 2:18 PM
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WALKINGTOOLBOX
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Well I completed it
Leak down test results:

Cylinder 1=air through TBI, A lot
Cylinder 2=air through TBI, a lot
Cylinder 3=air through TBI, some
Cylinder 4=nothing
Cylinder 5=air through TBI, a lot
Cylinder 6=air through exhaust, noticeable
Aug 29, 2018 at 2:48 PM
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ASEMASTER6371
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Nothing from the radiator?
Aug 29, 2018 at 2:51 PM
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WALKINGTOOLBOX
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Zero.
Aug 29, 2018 at 2:52 PM
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WALKINGTOOLBOX
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Now, as I stated it does not smoke all the time, so maybe it is not in burn mode?

Ugh, my brain.
Aug 29, 2018 at 3:02 PM
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WALKINGTOOLBOX
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White-ish, blue? I do not know.
Aug 29, 2018 at 4:43 PM
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ASEMASTER6371
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That is blue smoke. Most likely from the valve seals on the valves. The oil leaks down the valve guides and goes into the cylinder and burns off when you start the car.

Roy
Aug 30, 2018 at 1:17 AM
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WALKINGTOOLBOX
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This a simple fix or do the heads need to come off and be rebuilt?
Aug 30, 2018 at 1:19 AM
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ASEMASTER6371
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The valve covers have to come off and the rocker arms removed.

Then remove the spark plug and add air to the cylinder to support the valve when you remove the springs.

Then you need to use a valve spring removal spring and remove the valve springs. Then the seal can be accessed and replaced.

Roy
Aug 30, 2018 at 1:25 AM
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WALKINGTOOLBOX
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Okay yea, I was not to sure that could be done without taking heads off, do both intake and exhaust seals all around? Is there anything else I should probably do while I am there?
Aug 30, 2018 at 1:29 AM
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ASEMASTER6371
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Yes, they both have seals.

Make sure you clean out all dirt and debris from the head and the return holes to the oil pan.

Roy
Aug 30, 2018 at 1:38 AM