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'86 Pontiac engine knock/rattle/clatter

My 1986 Grand Am, 4-cyl, has a problem groing up hills. It runs normally on flat road, and I get about 27 mpg on highway; which is more than I got in 1986 (about 23). But there is a long prominent hill on the freeway here where I seem to lose horsepower and the engine begins a fast "knock" (more like a rattle or clatter), I am forced to downshift to preserve speed and decrease the rattle (but still can't get over 50 mph on the uphill side); once I reach the top of the hill, the rattle stops and feels like I have power back. I've run some Redline Fuel System Cleaner thru it without much effect; it seems to run normally on flat road. I haven't tried 93 octane in this little engine. Do you think that would be worth trying? Thanks for any suggestions.

GS

Reply to
GarySport
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Have you ever replaced the oxygen sensor?

Reply to
TOLYN9

No, so maybe I need to do that. Is that something an amateur like me can do? Maybe I can find some instructions on the Web. About how much does one cost? Thanks.

GS

Reply to
GarySport

$25-30 and up depending on model and brand, try here for an idea:

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Installation requires a special socket with a slot up one side to lay the wire in. Instead of paying big bucks for the special socket, go to the pawn shop and find a deep socket that fits the sensor, get a grinder or dremel tool and grind your own slot for wire clearance. Total cost? $2-3 at most, and it will last you the rest of your life.

O2 sensors of that era tend to need replacing every 30-50k miles, so if your has much more than that it's probably due.

JazzMan

Reply to
JazzMan

I would suggest checking the EGR in addition to the o2 sensor. If the egr doesn't open, it could cause ping/detonation. The computer would then retard timing to try and prevent the ping. Easy to check on this model. Lean fuel mixture caused by dirty fuel filter,weak pump should also be considered. Have you tried to pull any codes? Has your check engine come on?

Reply to
CURLY

I put some 93 octane in today, and it did perform a little better on the big hill; I realize that doesn't fix the problem, however. I can't pull any codes myself, and not sure how much they can get off this '86. I'll have to get my mechanic to check those things out. No, the check engine light doesn't come on for the most part. It has come on at very rare intervals if I'm stuck in traffic idling for a long time, but it goes off when I feed some gas to increase the RPM. The surprising thing with all this is that I continue to get almost 30 mpg. When it was new, it only got about 24. Thanks.

GS

Reply to
GarySport

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