My car seems to accelerate normally for a 16 year old 1.6 but when i hit around 40mph (or what seems like 4th gear) the engine all of a sudden becomes very rough..like dieseling/vibrating. When I press the gas more seems to accelerate fine but as soon as i begin to lift off to a lower rpm the dieseling/vibrating returns. Timing is good & plugs are only a few months old. Air filter clean, fuel filter changed w/in last 6 months.
Any suggestions for me to check is greatly appreciated!
Sounds like it could possibly have something to do with the torque converter clutch. Try counting your shifts from a dead stop. You should feel 2nd, then 3rd, then overdrive, and then what feels like a subtle shift - which is the engagement of the torque converter. Try to find out exactly what gear you are in when you feel the vibration. If you can pinpoint a problem that seems to be related to a gear then drop the tranny pan and inspect for debris. Let us know what you find. Try to pinpoint the exact conditions when the problem begins.
additional info: the last couple days i've started having stalling issues & today my car died in 45mph traffic (car was at operating temps) and the only reason i didn't have an accident is i happened to be sliding into a center turn lane. could a bad fuel pump also explain my previous symptoms?
My car seems to accelerate normally for a 16 year old 1.6 but when i hit around 40mph (or what seems like 4th gear) the engine all of a sudden becomes very rough..like dieseling/vibrating. When I press the gas more seems to accelerate fine but as soon as i begin to lift off to a lower rpm the dieseling/vibrating returns. Timing is good & plugs are only a few months old. Air filter clean, fuel filter changed w/in last 6 months.
Any suggestions for me to check is greatly appreciated!
If you think it's got something to do with the tranny, then click the overdrive shutoff button (if this car has one) and try again. If it doesn't have the overdrive shut off button, leave it in 2nd gear and try again.
My bet is on a worn out distributor cap and/or rotor.
My thinking...
You let off the gas and it runs like crap. When you let off the gas, the manifold pressure drops off (manifold vacuum max's out), in which case, the timing goes to about as high as it can go. If your distributor cap has worn out towers and/or your distributor rotor's tips are worn out, the spark can't hit because it's trying to make the spark when the rotor and tower are both at their edges.
At lower speeds/rpms, less timing, higher speeds/rpms, more timing.
When you give it more gas, the manifold pressure increases (manifold vacuum decreases), the timing drops off a bit, and the spark is able to connect on a fairly good part of the tower/rotor.
For the heck of it, pull the dist cap and rotor, clean them up with a bit of sandpaper (don't go crazy, just brush them off a bit), and try again.
I've got an '88 Chevy Sprint (hey, gets 54MPG and I don't care!)...the above described scenario is how I know it's time to give the engine a tune-up. It'll start stumbling during decel and later will stumble during part-throttle cruise.
Distributor cap and rotor would be a good place to start.
My car had a very similar problem. It turned out to be the EGR valve. The car ran fine while accelerating, but once it shifted into 4th gear or overdrive, it would switch to "back massage mode" and misfire badly. The EGR engages at cruising speeds (40+ MPH), but if it gets stuck, it allows too much exhaust into the intake.
The car ran great after disconnecting it. All you have to do is remove the hose that attaches the EGR to the exhaust.
Another possibility is one of your fuel injectors is going bad. I had misfiring at specific speeds and never knew why. One day, one of the injectors died suddenly and I noticed that the car never misfired again after replacing it. Apparently the injector was "half dead" for a while, and wouldn't squirt fuel while under specific loads.
Could also be issues with EGR or IACV since its a part throttle issue. I have not been all the way through the ga16de yet so im not sure what the common vacuum issues are.
__________________
93 Sentra SE 1.6 manual
H/I/Soon to have full custom exhaust
Short Shifter, UDP, ES Motor mounts.
“If someone has a gun and is trying to kill you, it would be reasonable to shoot back with your own gun.” - Dalai Lama (Seattle Times, 05-15-2001).
I'd buy the EGR possibility, along with the 'half dead' fuel injector theory (although not as much)...
But I won't buy the IACV possibility since it's basically closed above 1600rpm according to the FSM (I forget what page it says that on, just something that stuck in the back of my head when I read it).
The car ran great after disconnecting it. All you have to do is remove the hose that attaches the EGR to the exhaust.
thanks all for the replies, definitely a couple things to look at.
When you say 'hose' are you talking about the pipe with flange nuts and do you mean just remove the end from the exhaust and plug it? I assume you are not referring to the vacuum hose on top that runs to the very-similar-looking thingy to the right of it which i think is called the bpt valve?
Yeah, it's the pipe that stems off of the exhaust manifold, near the O2 sensor. It's a little thicker than the width of a pencil. Follow it with your fingers and you'll find that it leads to the EGR. It's connected to the EGR with an "L" shaped rubber hose. You can either slip off one end or remove the hose altogether; I removed mine so it wouldn't be at risk of falling off or something. You can plug the exhaust hose if you want, but it doesn't make a difference either way; I didn't bother plugging mine. I didn't mess with any of the hoses that attached to the BPT valve or the other thingies.
wanted to report back...
i found the "L"-shaped rubber house coming from beneath the egr and going to the bpt (..i think). it was very brittle and i ripped it out. immediately the car is running smoother throughout the rpm range and in all gears (overdrive on/off) and no vibrating/rough idle or stalling. we just may make it thru another year, lol.
thanks 'thebrownrobert' for your help and to all for your suggestions.
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