Every time I reach about 64 mph, the car begins to sputter spontaneously. As I give constant gas to keep it at that speed, the car hesitates, as if the gas isn’t combusting consistently. This sputter also happens sometimes when I’m simply accelerating for example from a stop sign, however, it is CONSISTENTLY doing it at about 64 mph. I can go faster and the sputtering seems to lessen (at 70+mph, as long as I’m accelerating). Took to mechanic, he couldn’t figure it out, although they suggest getting yet another computer.
I’ve replaced:
Distributor cap
Distributor
Spark plugs
Computer (from ebay, remanufactured)
The problem with this kind of a problem is that despite your unusually excellent symptom description the possibilities are still numerous. Personally, I’d consider the fuel pump at this point. Many things as they fail trip fault codes, but there’s nothing monitoring the pump. And the line pressure may appear fine in the shop, but drop under load. I wish I could provide a truly definitive test, but I cannot.
I suggest you find another mechanic
The fact that he suggests “getting yet another computer” leads me to believe he’s lacking in diagnostic skills and is grasping at straws
There are SO many tests that could still be performed, but apparently he hasn’t done much as of yet
The saying “You don’t know what you don’t know” seems to apply to this guy, at least in this particular situation
I second mountainbike’s suggestion regarding the fuel pump, as well as db4690’s suggestion about finding a mechanic who is more skilled at diagnosis.
Also consider a clogged fuel filter.
“Also consider a clogged fuel filter.”
…which, over time, could have damaged the fuel pump.
I think that the OP should anticipate the replacement of both the fuel pump and the fuel filter.
Truth is, the fuel filter on these cars is a part of the pump assembly. There’s two parts, a filtering “bag” through which the fuel is drawn and a filter that surrounds most of the pump. They all come out of the tank together. All should be changed IMHO at the same time. The pump “kit” contains everything but the main filter, which is ordered separately for about $50+. You should also order a new installation gasket, which also isn’t included in the kit. That’ll run you about $15.
Truth is, the fuel filter on these cars is a part of the pump assembly.
Not according to this:
" I can go faster and the sputtering seems to lessen (at 70+mph, as long as I’m accelerating)"
IMO this rules out lack of fuel pressure due to pump, filter etc.
It would get worse and worse as fuel demand goes up.
This is more like the “flat spot” carburetors could get.
I’d check for a problem with the MAF sensor (maybe just dirty) or throttle position sensor.
Another guess, you may have an egr valve that isn’t working correctly. That valve is supposed to be actuated during accelerations and high speed in proportion to the engine load, but if it gets over-actuated or opens and sticks open this symptom could result. The way I test the basic operation of my EGR on my own early 90’s Corolla, I hook a hand-held vacuum pump up to it and make sure it stalls the engine when vacuum is applied. That’s not a definitive test, but if it fails the EGR valve should be replaced. And be sure to check the diagnostic codes to see if the EGR code is on that list. Is the check engine light ever on?
As DB says above, replacing the engine computer should be at the very bottom of the list of possibilities, unless you have some other reason to believe it may be damaged. Following that suggestion your mechanic made is more likely to not solve this symptom and cause no end of grief.
Besides that, when going fast the parts of the car (engine related) that are exercised the most so are likely suspects are:
- distributor, cap, & rotor
- spark plugs
- ignition coil, ignition module
- crank and cam sensors
- fuel pump
- fuel filter
- cat
- valve clearances
Insightful, you’re correct. I didn’t realize this was a '97 when I posted.
I still suspect fuel supply, even more so considering the age, but this makes changing the filter a whole lot easier. In '97 they were still using a line filter.
Thanks for the correction.
TSM
I tend to lean towards a fuel delivery problem or even the possibility of an exhaust restriction; meaning a clogged converter.
I’m also not too enamored with the mechanic. A distributor cap is certainly not going to cause a problem like this and computer replacements are always suspect to me.
Recommending a second computer replacement just dims my view even more.
Fuel or exhaust. Clogged cat - a back pressure test could rule that out.
exactly
Those are relatively easy tests to perform, and don’t really take that long to do
fuel pressure tests would be the harder of the two, as this car does not have a fuel pressure test port. You’ll have to tee in, but that’s not really a problem if you have a fuel pressure “master” test kit, which isn’t really that expensive
2007 G6 same symptoms. Tested fuel pressure (normal), no MAF or MAP sensor, no codes at all… Starts around 55 or 60 mph, and gets better at 70 mph…considering spark plugs w/ fuel filter replacement. As suggested by a mechanic friend. Also low oil light has flickered but new oil and correct level, so also replacing oil sensor… Any suggestions welcome.
Did you get the problem solved?