Bucking??? So was it like surging up and down in RPM's a bit or was it like stopping (misfiring??)? When was the last time the truck has been tuned up? I'd probably start at the spark plugs if its been more than a little bit since they were last changed.
The Stupid Engine Questions Thread
- Thread starter Mike
- Start date
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92silvy
Newbie
I bought it about 2 years ago and I've only out about 1,200 ok it since then. The rpms stayed the same as I was driving but the whole truck seemed to kinda lurch a little at a time. I didn't notice anything weird sounding with the engine but I'll listen to it a little more if it happens again
1990 Silverado
Swapped in 350 gmp crate motor with 30k
New oil pump and screen
New oil pressure switch
Fresh oil and filter
Replaced one quart with Lucus stabilizer
The oil pressure is way inconsistent.
First start up after the swap it sat and idled smooth with a gauge reading of 40 psi till warm then dropped to 20, still running smoothly.
Let it sit overnight cuz it was late.
Crunk up again this morning, same result. Oil pressure holding steady about 30, engine running smoothly....all appears well.
Everything seems fine, so off to the end of the road. My road is only about a mile to the end, and I got up to about 45. That had the gauge reading at about 35. Seemed good.
So I decided to drive a loop around the neighborhood. It's maybe a 3-5 mile round trip. About halfway through the round the oil pressure dropped to zero again. Then it jumped back up. I spent the next 2 miles of the trip watching the pressure float between zero and 25 on the gauge, and feeling the truck start run rougher.
Got it back home and let it (and me cuz i was pretty p*ssed....) chill. After an hour or so I went out and fired it up again. Pressure went to 30 for a few seconds then dropped to about 15. If I rev it a little I can bring the pressure up, but it's still running rough.
With a new pump, screen, switch, and fresh fluids... what's left?
checked the cam bearing while I had the pan off. no play in the rods to speak of.
I figure that because the oil pressure switch and the fuel pump run together, that when the pressure drops, the fuel pump starts to shut off. That somewhat accounts for the rough running, cuz it confuses the computer. But what could be causing the oil pressure fluctuations?
Swapped in 350 gmp crate motor with 30k
New oil pump and screen
New oil pressure switch
Fresh oil and filter
Replaced one quart with Lucus stabilizer
The oil pressure is way inconsistent.
First start up after the swap it sat and idled smooth with a gauge reading of 40 psi till warm then dropped to 20, still running smoothly.
Let it sit overnight cuz it was late.
Crunk up again this morning, same result. Oil pressure holding steady about 30, engine running smoothly....all appears well.
Everything seems fine, so off to the end of the road. My road is only about a mile to the end, and I got up to about 45. That had the gauge reading at about 35. Seemed good.
So I decided to drive a loop around the neighborhood. It's maybe a 3-5 mile round trip. About halfway through the round the oil pressure dropped to zero again. Then it jumped back up. I spent the next 2 miles of the trip watching the pressure float between zero and 25 on the gauge, and feeling the truck start run rougher.
Got it back home and let it (and me cuz i was pretty p*ssed....) chill. After an hour or so I went out and fired it up again. Pressure went to 30 for a few seconds then dropped to about 15. If I rev it a little I can bring the pressure up, but it's still running rough.
With a new pump, screen, switch, and fresh fluids... what's left?
checked the cam bearing while I had the pan off. no play in the rods to speak of.
I figure that because the oil pressure switch and the fuel pump run together, that when the pressure drops, the fuel pump starts to shut off. That somewhat accounts for the rough running, cuz it confuses the computer. But what could be causing the oil pressure fluctuations?
AK49BWL
GMT400 Forever!
You might check your grounds.. This sounds a bit like loose electrical contacts, especially with a new oil pressure sending unit and everything else having been replaced. It running rougher is a little strange tho, because the fuel pump should be powered by the fuel pump relay via ECM control in addition to the oil pressure switch. But definitely check grounds at any rate.
Last edited:
Thatfordguy
Because I can!!
So I had someone offer to trade me a 97 k1500 for my ford ranger. I don't really need another gmt400 but I'd rather have 2 of them than the ranger. Anywho it he just said it doesn't run right until 3k rpms then it runs perfect. Any ideas? Idk if it's throwing any codes or anything like that.
AK49BWL
GMT400 Forever!
Won't have much to go on until we find out if codes are involved.. My guess with nothing further is a bad sensor, possibly MAF, because above a certain RPM the computer switches to a non-MAF-centric algorithm to determine fueling.. Could be something as simple as needing a tuneup, or a vacuum leak though.
I'd definitely take another GMT400 over a Ranger
I'd definitely take another GMT400 over a Ranger
Big D
Atoadaso I f*kn Atoadaso
Wasup guys, trying to not clutter the forum with a stupid question, I need to order a fan clutch and its 10 dollars at least cheaper online, and im not gonna be around my truck for a day and I cant remember for the life of me if the the Mounting holes are 5/16 or 10mm or if the fan is standard or reverse rotation. grooved pulley on water pump is standard rotation and smooth is reverse.
Im almost Positive its Standard rotation, im hoping someone with a 454 TBI can give me A hard answer
1991 c3500 454 tbi Ac Gas 2wd
Im almost Positive its Standard rotation, im hoping someone with a 454 TBI can give me A hard answer
1991 c3500 454 tbi Ac Gas 2wd
I just did my K1500 and it was a reverse spin fan held with 10mm bolts from fan to clutch, and 13mm from clutch to water pump. Not sure if this translates over to a big block. I bought a "Car quest" brand one from Advance because it's really just a USA made Hayden.
Big D
Atoadaso I f*kn Atoadaso
what year is your truck
any part # with 2784 in it? thats Haydens number.
any part # with 2784 in it? thats Haydens number.
My truck is a 305 small block, year is 95. I'd go to your local Advance, look up the part, then have them pull it and verify it is in fact a USA Hayden before buying.
