Intermittent engine performance

Tiny
MATTHEW CHANCE
  • MEMBER
  • 1992 CHEVROLET 1500
  • 4.3L
  • V6
  • 4WD
  • MANUAL
  • 235,000 MILES
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.
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Monday, August 27th, 2018 AT 11:41 PM

28 Replies

Tiny
ASEMASTER6371
  • EXPERT
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
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Tuesday, August 28th, 2018 AT 1:33 AM
Tiny
MATTHEW CHANCE
  • MEMBER
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.
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Tuesday, August 28th, 2018 AT 2:11 AM
Tiny
ASEMASTER6371
  • EXPERT
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
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Tuesday, August 28th, 2018 AT 2:25 AM
Tiny
MATTHEW CHANCE
  • MEMBER
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.
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Tuesday, August 28th, 2018 AT 2:28 AM
Tiny
ASEMASTER6371
  • EXPERT
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
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Tuesday, August 28th, 2018 AT 2:47 AM
Tiny
MATTHEW CHANCE
  • MEMBER
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.
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Tuesday, August 28th, 2018 AT 3:04 AM
Tiny
MATTHEW CHANCE
  • MEMBER
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.
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Tuesday, August 28th, 2018 AT 3:09 AM
Tiny
ASEMASTER6371
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You are welcome.
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Tuesday, August 28th, 2018 AT 4:00 AM
Tiny
MATTHEW CHANCE
  • MEMBER
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.
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Tuesday, August 28th, 2018 AT 10:45 AM
Tiny
ASEMASTER6371
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No big deal. Sometimes a second opinion is good for your thoughts.

Get the test done.

Roy
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Tuesday, August 28th, 2018 AT 11:15 AM
Tiny
MATTHEW CHANCE
  • MEMBER
Compression test:
Cylinder 1=130
Cylinder 2=150
Cylinder 3=130
Cylinder 4=150
Cylinder 5=150
Cylinder 6=150
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Tuesday, August 28th, 2018 AT 2:35 PM
Tiny
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
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Tuesday, August 28th, 2018 AT 2:40 PM
Tiny
MATTHEW CHANCE
  • MEMBER
Yea, I understand that, figured I would do the compression test anyway.
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Tuesday, August 28th, 2018 AT 3:55 PM
Tiny
MATTHEW CHANCE
  • MEMBER
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.
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Tuesday, August 28th, 2018 AT 6:52 PM
Tiny
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
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Wednesday, August 29th, 2018 AT 1:34 AM
Tiny
MATTHEW CHANCE
  • MEMBER
Alright, good to know for future reference. Thanks
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Wednesday, August 29th, 2018 AT 9:59 AM
Tiny
ASEMASTER6371
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Yep, do that check and let me know what you find.

Roy
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Wednesday, August 29th, 2018 AT 10:04 AM
Tiny
MATTHEW CHANCE
  • MEMBER
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.
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Wednesday, August 29th, 2018 AT 2:18 PM
Tiny
MATTHEW CHANCE
  • MEMBER
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
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Wednesday, August 29th, 2018 AT 2:48 PM
Tiny
ASEMASTER6371
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Nothing from the radiator?
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Wednesday, August 29th, 2018 AT 2:51 PM

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