Rattle under high load
Asked by Colton Jan 28, 2018 at 02:12 PM about the 1995 GMC Sierra 1500 C1500 SLE Extended Cab SB
Question type: Maintenance & Repair
I’ve been experiencing a rattle coming from under
the hood of my 95 GMC Sierra C1500 with a 5.7 L
V8 350. It has 209k miles. When the engine is under
high load(65-70mph and giving more gas) I hear a
rattle coming from under the hood. Worst case
scenario it’s the piston bouncing down the
bore(FML) but I really need more suggestions
before tearing the engine apart or getting a new
one. ANYTHING HELPS!!!
4 Answers
I don’t think it’s going through oil. It has a leak in the rear main seal but I change the oil frequently and add when needed. But not burning oil.
It could be carbon buildup and detonation. Try running some premium fuel through it. If the noise stops it is detonation. Detonation can be caused by many things, so of which are, timing off (as Oldstorqnpower suggested), insufficient octane in fuel, carbon build up, EGR valve issues, etc. To get rid of carbon buildup you could do a Seafoam treatment. Do a Google search for more on that. Actually you can use water or transmission fluid instead of Seafoam for the intake treatment. Do NOT put water or transmission fluid in the fuel tank or the engine crankcase.
We did put GM top end cleaner in. It did its job but did not fix my problem. I alternate between regular and premium every other fill up. We also replaced my EGR gasket and plug wires. I’m gonna check the timing tomorrow.
