Engine sputtering, mechanic can't seem to permanently fix

#1

I have a 1989 Buick LeSabre with 219k miles. In August I took it to my mechanic because for a few weeks (possibly longer) the engine had been sputtering and lurching when trying to accelerate between 1000 and 1500 RPM?s. He replaced the ?coil pack? and the car seemed to be fixed.

Then 2 weeks later the problem gradually started to return and by 3 weeks the car was back to sputtering and lurching constantly while accelerating between 1000 and 1500 RPM?s. I took it back to my mechanic in October and he replaced all the spark plugs, fuel lines, and fuel pump. Viola, the problem seemed to be fixed.

A week later the problem gradually returned and I haven?t taken it back because I figured my mechanic doesn?t really know what?s wrong with it. Since the car seems to improve after he ?fix?s it? then returns back to sputtering, it would seem to me that he?s temporally abating the problem without actually fixing it.

Any ideas on what could actually be causing the sputtering, and how these ?fix?s? seem to have temporarily fixed it?

#2

He replaced fuel lines and fuel pump, but not the fuel filter? I hope you just forgot to include the filter.

Has your mechanic determined whether the problem is spark or fuel? Apparently not. It sounds like he, or she, is throwing parts at the car, hoping something will work. Testing is required. Perhaps another mechanic is required.

How’s the fuel pressure? With a new pump it should be OK, but you never know without testing it.

#3

I would think spark plug wires the next step, without a real mechanic able to diagnose the problem you are looking for guesses and that is mine.

#4

I had the same car “back when”. The problem you describe sounds like the ignition module under the coil pack. At least that is what fixed mine after the new coil pack didn’t.

#5

Just my humble opinion here but your mechanic appears to be guessing a bit and skipping a few steps.

The car has over 200k miles on it. On a performance problem the first step should be to pull the spark plugs and run a compression test. Undiagnosed low compression problems often lead to parts flinging.

I have no idea why he would replace the coil and not the plugs or wires. Low compression can affect the spark plug. Eventually the plug can start misfiring due to a weak cylinder and that in turn is rough on the plug wir. That in turn can kill a coil.
These things usually work like a string of dominos; the first one in line knocks the rest of them down.

I’m not saying that you have a mechanical engine problem here; only a possibility of one. The compression test will weed that out.
It’s entirely possible the whole problem started with a faulty plug and it simply weakened the plug wires and coil.

#6

Much can be learned from examining the spark plugs. They could have been examined the first time they were changed…and the second. The effects of oil burning, anti-freeze “burning”, excessive fuel usage, etc., will show on the spark plugs. Some of these photographs, of used spark plugs, will give you an idea of those effects: http://www.gnttype.org/techarea/engine/plugs.html

#7

A frequent problem that just goes away for a few days would make me suspicious of the engine computer. Sometimes they reboot themselves and work fine for a couple of days. I had a lot of that experience with an 85 Cadillac. It did just what your car is doing. Price a computer and you may find the price is good for the one for your car. ANY electronic thing under the hood that is not basic will cost you at least $100. Some people replace them one by one to avoid buying the computer and then end up buying it anyway. Your mechanic is just guessing, but not from any experience with your 80’s model GM car. This isn’t an every day problem and it will cost a lot of money to change everything under the hood. I recommend changing that thing that used to be right above the passenger’s right foot, on the firewall. I think you might find it there. On the 85 model, it looked like an aluminum box. Instructions come with the new one and pay no attention to the word “drivers”. You might have to remove the old one first so they can get a serial number to order the new one. The fixes worked because the battery was disconnected and caused the computer to reboot.

#8

you can likely test out pleasedodgevan’s idea w/out throwing the part at it first. the next time it is acting up disconnect the battery - I don’t know for how long - but I’d guess at least 30 min to make sure. hook it back up and see what happens. if a battery disconnect actually does the temporary “fixing” then you could be pretty confident in the computer as the problem.

#9

Thanks to everyone for your input. The problem turned out to be a bad sparkplug wire.