89 cadillac deville, runs fine as long as I don’t accelerate too hard. But if I press too hard on the gas pedal the car seems to lose power like the engine isn’t running right. The car is too well insulated sound wise for me to hear what the engine is doing. We’re not talking about nascar type accelerations here either. There is a long hill on my ride home, about a mile long, with a 50 mph speed limit. The car goes 45 mph fine, but if I try to go any faster than that it slows down. Hard to tell, but it feels like the engine is losing power, not the transmission slipping.
The only thing I can think of is maybe the spark advance isn’t working, but this is a fancy shmancy computer controlled engine and I’m kinda lost on it. Any ideas on where to start looking?
My first thought is to check the exhaust system for restriction-blocked catalytic converter. I’m going to guess that the check engine light isn’t on, but does briefly glow so we know the lamp is good, yes? IIRC, poor performance can also be related to no power to the ECM/failed ECM. Most of the auto parts places will do a free scan tool check for you now that we have emissions inspections in central PA. Try the Auto Zone over on Carlisle Street across from North Hanover Mall.
Could be several things, but I’d look at ignition or fuel.
Check the computer codes, they may tell you something, especially if it’s a spark problem of some kind.
Look for bad spark plug wires, check the plugs, and the timing. It’s probably electronic ignition, so there aren’t any points or distributor cap, but a good mechanic or the dealer can probably check the output of the ignition module.
I had an 88 Pontiac Bonneville doing exactly the same thing, and it turned out to be a failing fuel pump. The pump capacity was down, and it was sucking air out of the tank. At low speeds it ran fine. But at higher speeds or under load, it would feel like it was running out of gas and wouldn’t respond. A few times it even pumped enough air into the fuel rail that the car stopped. Not enough gas to the injectors to keep it running. So I’d check the fuel pump early on.
I had a car with a dying catalytic converter that did exactly that. Under heavy acceleration or a steep hill, it acted like I was towing a huge trailer, yet for normal ops it was fine.
The problem got worse the longer the hill, as if that trailer just kept getting heavier.
The problem also got worse over time, slowly becoming more severe & also starting at ever lower loads. A new catalytic converter solved the problem instantly & completely.
I’ve never changed the spark plugs, but I’ve only had the car about a year. I haven’t done anything to it except change the oil.
The check engine light does not come on. I’ve never noticed it coming on, even briefly at startup, so it’s possible the light is dead. The “car is levelling” light comes on for a moment, but I don’t know if that is driven by the same computer system.
I thought you had to have a 95 or later car for the scan tools. I’ll check at the auto parts store.
Thanks for all of the replies. I’ll start checking into things this weekend, hopefully.
My car (4 cylinder GM) did exactly the same thing due to a bad spark plug (or two). The computer never generated a code since there was nothing wrong with the electronics.