I have a Chevy K1500 sierra with a 350 that is not EFI. That’s a long story from when my project began. OK, I bought someone Else’s problem. Replaced the engine and it starts and runs fine, until you drive it under load. I’ve checked the timing and it’s set at +2 degrees. I rebuilt the carb (not the problem) Replaced fuel filter which was not plugged. Vacuum advance seems to be working fine. As long as I don’t push the accelerator hard it drives fine. It just has no power for passing or pulling a load. Any help would be appreciated.
If it’s stock the 350 should have throttle body fuel injection. Is the current engine the original? Could be a fuel starvation issue, have you checked the fuel pump?
It’s not the stock 350. It’s a carburated 1986 350 from a C20 van. I bought it from a wrecking yard. I couldn’t find a 5.7 EFI engine. I wish I could have found one locally. I also had to replace the fuel tank due to rust problem and the electric fuel pump which was not working. I had to re-run new fuel lines and install a new sending unit. The mechanical fuel pump was replaced from the original C20 due to space restrictions (4 x 4) with a new fuel pump. Not sure, maybe it doesn’t have enough volume than the previous one. The fuel pump works fine while revving the engine at idle. I’m guessing it’s fine if it’s just based on a specific fuel pressure. If you might think that’s the problem I might have to replace with an electrical external fuel pump.
Your timing should be set around 8 degrees BTDC at idle with the vacuum advance disconnected and plugged. This may help your lack of power issue. If it doesn’t, and you find no other issues such as fuel starvation or exhaust restrictions, your camshaft could be excessively worn. Many older, higher mileage smallblock Chevys develop flattened cam lobes over time, resulting in lack of power and, sometimes, backfiring and the like. Lack of power is the most common symptom of flattened cam lobes. A vacuum test will reveal whether this is the problem or not.
I’ll look into those tomorrow. What type of vacuum test? I’m guessing Carb. Do you know what psi the fuel pump should be delivering? Pulling the cams out isn’t a quick job I’m sure.
Is it a QuadraJet carb? Is the truck equipped with a catalytic converter?? The '86 carb will be a “feedback” type controlled by an ECM…How about the EGR valve, working or not??
Clogged converter or slipping automatic transmission; or clutch as the case may be?
Other than that, there’s always the possibility of a tired old engine with low compression.
Vacuum test and compression check will definitely rule out mechanical problems, and they are easy to do. A flattened camshaft, a possibility I mentioned earlier, will show up in the form of fluctuation on the vacuum gauge. A manifold port is the best place to hook up a vacuum gauge. A Haynes manual will tell you more about how to use and read a vacuum gauge. A flattened camshaft often accompanies a tired engine, as it is most frequently found in high mileage or workhorse engines that led a hard life. Another good indicator of the condition of the engine is to listen to it run with the air cleaner off. This is best evaluated by someone who is familiar with engines, but a healthy engine should have a good, strong “sucking air” sound from the air horn of the carburetor which intensifies rather dramatically when you crack the throttle. Compression and vacuum tests will verify the condition of the engine.
It is a quadra jet carb. But it had an electronic solenoid of some type on the front of the carb that I had no connection for. I replaced the whole carb for another one which is all manual. I think the EGR is working fine. I’m not getting any fluctuation in idle control.
I initially thought it might be the tranny since the truck had a 5th wheel attachment in the bed from what I can tell. The engine compression I tested was good, don’t remember the numbers but they were close. It ended up being that I set the timing too low at 2 with the vacuum advance still hooked up. It’s been a long time since I worked on a non fuel injected vehicle. After I reset the timing according to mark9207 it ran fine and had good pickup. Thanks for all your guys input. I appreciate it very much.
Compression readings that are close do not mean the engine is good. Maybe all 8 are equally bad.
A rule of thumb on compression is multiply 20 X the compression ratio. Knock a shade off for altitude, barometric pressure, etc. (Thinner air affects it and so on.)
If you think the transmission could be slipping you might try a stall test. Set the park brake, hold the foot brake, and try to quickly rev the engine while the transmission is in DRIVE. (NOT Overdrive)
The engine should stall out at around 2000 RPM give or take.
Do this test quickly and don’t beat it to death. If the RPMs go up to 3000 or whatever odds the transmission is on the way out due to slipping.
You can repeat this test in LOW and SECOND but allow a few minutes between each test.
You can bump the timing up a little more, as high as 12 degrees, as long as you don’t get any spark knock…