sckootter
Forum Newbie
Posts: 38
Reg: 02-14-12
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 02-22-12 05:07 PM - Post#2193962
Hi guys I need some help please. I have a 93 k1500 4x4 with the 5.7 TBI. At cold start up the oil pressure is high above 40 psi. Now as the truck heatup to operation temp the pressure falls off. After cruising for about a half hour the engine is nice and warmed up to operating temp at a stop light the pressure will fall and check gauge light will come on. If I put the truck in nutreal the pressure will sit right above the red and the light will stay off. Also when cruisin down the road the pressure will be low and just make it to the first line in the oil gauge. I thought it was my pressure switch replaced that and still the same problem. The engine runs strong and has no noise at all. I have been researching the problem and alot of guys are leaning to the cam bearings. I dont have the money to do a total rebuild till I sell my other truck. I also have never replaced cam bearing before. Is it a hard task? I know you need a special tool and you have to line up the oil holes. I just dont know how far you install them and is there a stop to know when you have drove the bearing in far enough. PLease give me some input and let me know what you guys think.
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 stumppuller
"3rd Year" Gold Supporting Member
Posts: 437
Loc: Canada
Reg: 11-01-04
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02-22-12 05:23 PM - Post#2193965
In response to sckootter
That's a sign of age and wear, your bearing clearances have increased making the pressure drop. Most likely a combination of cam and crank bearings causing this.
There is no need to overhaul the motor yet, and cam bearing replacement is not an in vehicle job, the motor must be torn down. Change your oil to the next viscosity ie, 5w30-10w30-15w30-20w50-30 wt. A thicker oil will compensate for the bearing wear. I have run vehicles for many extra years by doing this.
-91 Sierra C2500, now K2500
-81 Chev K20 |
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355Cheyenne
Senior Member
Posts: 3743
Loc: Northern MN
Reg: 10-27-04
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02-22-12 05:37 PM - Post#2193969
In response to stumppuller
My 98 started to do the same thing as described after doing an intake gasket job. 0psi at idle and max 20 high high rpm. It was about 30~to 60 before. anyway pulled the motor and in dissasembly while there was some wear it wasn't terribly bad. Found the pressure regulator spring in the oil pump was gummed up and stuck open. I rebuilt with out any significant machine work, new bearings (mains, rods, cam) and I had everything cleaned and the heads done. After rebuilding I now get 20psi hot idle and 45ish max RPM; Cold it is 40psi idle and 60 max.
Point of the story is that it could be a bad oil pump. It would be worth pulling the pan and replacing it if not only to just inspect. even then with the pan off I would plasticgauge the rods and some mains to see how bad the wear was.
As stated, you could try thicker oil. I definitely see a difference from 5w30 to 20w30. I get a little more pressure with thicker oils but not likely a good idea in winter if you are up north.
| 98 Silverado k1500 4x4 350 |
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Allan In NE
Contributor
Posts: 897
Reg: 12-27-11
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02-22-12 05:39 PM - Post#2193970
In response to stumppuller
Not really; that's an old wives' tale.
Ever drain the 80W-90 out of a rear end fresh from a 10-mile run down the interstate? It has the consistency of water.
Allan
| Lifelong GM automatic transmission specialist |
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Allan In NE
Contributor
Posts: 897
Reg: 12-27-11
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02-22-12 05:40 PM - Post#2193971
In response to sckootter
Forget the cam bearings; get some inserts in that engine before you loose the crank.
Allan
| Lifelong GM automatic transmission specialist |
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sckootter
Forum Newbie
Posts: 38
Reg: 02-14-12
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02-22-12 06:33 PM - Post#2193996
In response to Allan In NE
what do you mean by inserts. New crank bearing or what please explain thanx.
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 Bad56Sedan
"6th Year" Gold Supporting Member
Posts: 528
Loc: Pasadena, Texas
Reg: 04-29-04
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02-22-12 08:21 PM - Post#2194049
In response to sckootter
I always changed the oil and filter in my truck about every 3-4500 miles.
When the truck had 150,000 miles, I noticed after making 2 hour trips on the freeway at 65mph
then getting off at the exit and stopping at the red light the pressure would drop down to about
3-5psi on a real gauge I had installed, the dash electric gauge would show basically zero.
I tried the heavier oil and it did keep the cold idle oil pressure up higher but not by much and the
2 hours trip pressure would end up being about the same when I got off the freeway.
I had heard somewhere and this may be incorrect but a rule of thumb was 10psi per 1K rpm, minimum.
But the pressure on my truck was dropping down further than that.
I was driving 6 days a week 130 miles in the morning and 130 miles back home in the evening.
So that low oil pressure when getting off the freeway 130 miles from home was bugging me.
So I decided to change the oil pump, naturally I got a high volume pump and
this brought the idle pressure up to about 25psi and about 50-60psi at 65mph. I’m thinking this is much better.
The next weekend I was off I was changing the valve cover gaskets due to the leaks from the high pressure.
Clearance between the rods was about 0.019 when I changed the oil pump, it made 240,000 miles before I sold it.
| VC56S 2 door Sedan, 33 Years |
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sgian
Valued Contributor
Posts: 4438
Loc: MO
Reg: 12-25-03
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02-23-12 12:50 PM - Post#2194278
In response to Bad56Sedan
I have a similar problem, and have also replaced the oil pressure sending unit. I'm going to buy a mechanical gauge to check the dash gauge before doing anything to the engine, and suggest you do the same.
| 04 Silverado Z71, 10 Cobalt |
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sckootter
Forum Newbie
Posts: 38
Reg: 02-14-12
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02-23-12 06:21 PM - Post#2194407
In response to sgian
I am getting a machanical gauge tomorrow and checking the pressure. I just bought the truck and I replaced the valve covers the oilsending unit and some odds and ends. What I did notice is when I change the vavle covers I have a sludge problem so I am fighting that also. If the pressure is low I think I am going to go with a high volume oil pump and cross my fringer till I sell my ford and can rebuild the engine. I will keep you all posted on this issue as I try to figure out the problem thanks for the help.
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sckootter
Forum Newbie
Posts: 38
Reg: 02-14-12
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02-23-12 07:22 PM - Post#2194435
In response to sckootter
I also wanted to add . If I do replace the oil pump should I stay with stock volume or HV?
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sckootter
Forum Newbie
Posts: 38
Reg: 02-14-12
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02-26-12 08:55 PM - Post#2195684
In response to sckootter
Well guys I got an update I put in a oil pressure gauge and a tach since the truck didnt have a tach. Anyway the presser is good running down the road and everything checks out. At idle in gear the rpms drop way down to like 300 to 450 rpms. I replace the IAC and still the same thing and when I sit at a light or sit with the truck idleing and take off feels like the engine loads up with fuel the clears out. Is there a way to adjust Idle speed or could there be another issue. Just need some info thanx.
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355Cheyenne
Senior Member
Posts: 3743
Loc: Northern MN
Reg: 10-27-04
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02-26-12 09:11 PM - Post#2195689
In response to sckootter
The idle speed isn't exactly adjustable on a TBI. It should idle around 700~900 rpm warm. What I would do first is pull the Idle air control valve and clean it with some electrical parts cleaner (NOT BRAKE/PARTS or CARB CLEANER IT WILL DAMAGE IT) and then clean the orifice that it screws into. Likely it is dirty / plugged.
| 98 Silverado k1500 4x4 350 |
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sckootter
Forum Newbie
Posts: 38
Reg: 02-14-12
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02-27-12 04:52 PM - Post#2195996
In response to 355Cheyenne
I already put in a new Idle air control valve and cleaned the orfic and the iac was clean due to it being new any other suggestions?
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355Cheyenne
Senior Member
Posts: 3743
Loc: Northern MN
Reg: 10-27-04
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02-27-12 06:05 PM - Post#2196029
In response to sckootter
How are you verifying the idle speed? I wouldn't trust the dash and suggest connecting a proper tach before doing anything else.
| 98 Silverado k1500 4x4 350 |
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sckootter
Forum Newbie
Posts: 38
Reg: 02-14-12
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02-27-12 07:36 PM - Post#2196076
In response to 355Cheyenne
I purchased a sunpro tach yesterday and installed the gauge. I also installed a oil pressure gauge. The low rpm are only when the truck is warmed up if I keep the rpms up around 700 to 900 the oil pressure is good right arove 10 psi but if I am idling in gear the rpms drom between 300 and 450 and the pressure is low. I am lost at this idle problem and I also have a miss at that rpms also. Also when I leave the truck idle for about three to four minutes like at a green light the truck stumbles like it loads up with fuel then clears out and runs fine. 
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355Cheyenne
Senior Member
Posts: 3743
Loc: Northern MN
Reg: 10-27-04
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02-27-12 10:19 PM - Post#2196143
In response to sckootter
That could be a lot of things, I would hate to send you on a wild goose chase. For sure it could be the CTS, have you changed that out yet? If not just do it, cheap quick and easy. The other thing I would suspect is EGR, I would pop it out and clean it, could be propped open and leaking a little, but I would expect that at cold not just warm. So the when warm tells me it is when it goes into closed loop which indicates a sensor issue so the other thing I would be concerned about is your o2 sensor.
Have you done spark plugs wires cap distributor yet or recently?
| 98 Silverado k1500 4x4 350 |
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 someotherguy
Moderator
Posts: 23375
Age: 43
Loc: Texas
Reg: 08-01-03
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02-28-12 07:44 AM - Post#2196217
In response to 355Cheyenne
If the 300 RPM reading is real, the engine should be attempting (or succeeding) to stall. You have idle speed problems to cure before worrying about oil pressure; with idle speed falling down that low you WILL see oil pressure issues simply due to the engine speed with no other causes required.
Richard
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sckootter
Forum Newbie
Posts: 38
Reg: 02-14-12
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02-28-12 04:52 PM - Post#2196395
In response to someotherguy
thank you for the input. Not to sure what the CTS is (having brain fart). When I changed the IAC I did take off the egr and clean it worked fine when I put it back on and used a vaccum pump to make sure it didnt bleed pressure off and replace the egr gasket. havent messed with the 02 sensore yet. I Just dont know where to turn next. When it does run that low in rpms the engine does sputter and act like it is going to stall. I seen where you said about Idle problem I know that (not being a jerk just sayin) that is why I am trying to fix the idle problem. When I hold my foot on the pedal and keep the rpms around 800 the oil pressure stays at 10 psi. I know it is deffinatly a idle issue with the oil pressure. Keep the good info comeing and I will check what you recommend this weekend thanks. O I also have not changed the spark plugs or wires cap and rotor yetI pulled the cap off and it looked fine but I know look can be wrong. lol
Edited by sckootter on 02-28-12 04:54 PM. Reason for edit: No reason given.
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 CowboyTrukr
"2nd Year" Silver Supporting Member
Posts: 698
Loc: Salt Lake City
Reg: 06-20-09
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02-28-12 11:48 PM - Post#2196547
In response to sckootter
Skooter, the CTS is the coolant temperature sensor. It's the computer's input to measure the engine temp. Located right beside the water neck on top of the intake. There are supposed to be at least two grounds bonded to the water neck bolt, too. You can replace the CTS, if you plan and are quick about it without draining the radiator and without losing too much coolant.
Now, one thing to also check is the throttle position sensor. You need to have an analog ohmmeter to do this one. The digital ones are not fast enough to catch a broken winding in the position coil. The instructions in the FAQ section talk about how to check it. This little monster is notorious for appearing good ("it didn't throw a trouble code") and yet driving a guy nuts.
Greg
'94 Silverado K2500 4X4 5.7 5spd Xcab LB
RV cam, Pace Setter Headers, TBI spacer, Flow Tech air cleaner adapter, Hypertech street chip
"The only thing necessary for evil to triumph is for good men to do nothing" Sir Edmund Burke |
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cdmhenry
Very Senior Member
Posts: 2248
Loc: Minden, NV.
Reg: 09-14-00
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02-28-12 11:51 PM - Post#2196548
In response to sckootter
Sounds like the O2 sensor is bad to me.
If you shut it off at very low idle does the exhaust pipe smell like unburned fuel?
Get a scan tool on it and find out if the sensor reads correctly.
MAP sensor might be bad or have a leaky line.
| Every Government Interference In The Economy Consists Of Giving Unearned Benefit, Extorted By Force, To Some People At The Expense Of Others - Ayn Rand |
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sckootter
Forum Newbie
Posts: 38
Reg: 02-14-12
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02-29-12 05:19 PM - Post#2196844
In response to cdmhenry
alright thank you guys for the input. this weekend I will have to check out those posabilities. My friend is a certified electrician so he should have a anilog meter. I have not tried the smell the exhaust trick but will also try that . Come to think of it when I got the truck it was idling for a little bite and my brother stepped out of the truck and said he smelled a gas smell standing beside the truck. The gas tank dont leak because I have not smelled gas at all while I go to start the truck in the morning. So it might be the 02 or the map sensor. I will let you guys no what I find out as soon as I find something thanks agian.I also have a new CTS that I have not put on yet is there only one up by the thermastat houseing. I did notice one on the left head by the plugs what is that sensor? I am thinking it is a CTS also.
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markss
Forum Newbie
Posts: 67
Age: 59
Loc: Palm Beach County, Fl
Reg: 12-02-11
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02-29-12 05:58 PM - Post#2196859
In response to sckootter
The other sensor is for the gauge. Mark
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sckootter
Forum Newbie
Posts: 38
Reg: 02-14-12
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02-29-12 07:12 PM - Post#2196887
In response to markss
So are the two sensoes the same or are they diffrent?
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CowboyTrukr
"2nd Year" Silver Supporting Member
Posts: 698
Loc: Salt Lake City
Reg: 06-20-09
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02-29-12 07:39 PM - Post#2196904
In response to sckootter
They are different. The one on the side is a single wire one.
'94 Silverado K2500 4X4 5.7 5spd Xcab LB
RV cam, Pace Setter Headers, TBI spacer, Flow Tech air cleaner adapter, Hypertech street chip
"The only thing necessary for evil to triumph is for good men to do nothing" Sir Edmund Burke |
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sckootter
Forum Newbie
Posts: 38
Reg: 02-14-12
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03-13-12 04:32 PM - Post#2202159
In response to CowboyTrukr
Well guys I changed my cts this weekend and the rpms are still low. Good news is my pressure is higher now since I think my sludge problem is beginning to go away. I am still stumpt on the low Idle sutuation.
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CowboyTrukr
"2nd Year" Silver Supporting Member
Posts: 698
Loc: Salt Lake City
Reg: 06-20-09
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03-13-12 10:26 PM - Post#2202309
In response to sckootter
Skootter, have you checked the throttle position sensor?
'94 Silverado K2500 4X4 5.7 5spd Xcab LB
RV cam, Pace Setter Headers, TBI spacer, Flow Tech air cleaner adapter, Hypertech street chip
"The only thing necessary for evil to triumph is for good men to do nothing" Sir Edmund Burke |
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sckootter
Forum Newbie
Posts: 38
Reg: 02-14-12
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03-14-12 04:58 PM - Post#2202631
In response to CowboyTrukr
no not yet I am going to check that this weekend or maybe just change it. I figure soon enough I will have changed all the sensors under the hood then it will be good to go.lol 
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