First, my car is a 1994 cavalier, 2.2ohv, 5speed. The car will roll over to 180k tomorrow if I drive that one to work. Its in my profile if you want to know anything else, but I think the mods don't particularly matter in this case. The problem I have is, occasionally, but not always, when I reach the shift point for each gear, and randomly off and on when I'm cruising in 5th, It sort of "bogs". The feeling is similar to that of engine breaking, kind of like driving into a really strong wind, but I can feel a slight weight shift towards the front wheels, so it ain't that windy, though I've wondered the last couple days. Also, the car can still accelerate when this is going on, and if I pull my foot completely off the gas for a moment, the problem goes away. Now I've checked the brake system and wheel bearings to see if something could be binding, all seems ok. TPS, AIC, IAT, MAP sensors all test normal, and there is no check engine light. Also checked the spark, and Its firing strong on all 4 cylinders. My first thought was that for some reason I was not getting enough fuel when this was happening. But it seems to be the opposite, as my mileage has dropped off noticably, and my stainless tip now has a nice layer of soot on it. So, I'm burning too rich, I guess. I'm thinking o2 sensor, but if anyone knows anything or can think of anything, I would appreciate the input, Thanks.
When is the last time the fuel filter was changed? If the fuel pressure is too low, it will have an awful time trying to get the mixture right.
I was experiencing a similar sensation with my car (although more at low speeds), and after I changed the filter, it's running like new again, and I picked up about 5MPG. The filter wasn't plugged, but there was very noticeable restriction on the flow through it. It was a crappy one that came in an orange box, and after only 2 years the bottom of it looked like it was about to rust through. It had about 80,000km on it.
Other manufacturers put a maintenance interval on this - I wonder why GM doesn't anymore? I've changed mine twice now, and both times have made a noticeable difference, so I think the interval was too long. I think I'm going to use about 50,000km as a change interval from now on - the improvement in gas mileage more than pays for the cost of the filter.
Worth a shot anyway - and cheaper than most other things you could try. After that, I would check the air filter, and then maybe the O2 sensor. The sensor should set a code though, if it's not responding as expected. Hopefully your converter hasn't gotten damaged from the rich condition.
If things still don't seem right after that, I would try connecting a vacuum gage to see how it responds. It should get about 21+ inches at idle, and it should be fairly easy to accelerate keeping it up around 10. If it drops slowly at idle, it may be an exhaust restriction (plugged converter?). Hopefully you won't need to bother going this far.
Yeah, actually, my fuel filter is only about a week old, and the air filter element is perfectly clean too. I pulled my spark plugs and either they gave me the wrong heat range, or it was a mistake buying the autolite plugs at my last tune up. Either way, the plugs and wires showed serious signs that they weren't holding up. I had seriously doubted that the accel coilpacks would make a significant difference in spark, but apparently they do. so anyways, I got the accel wires, and bosch platinum +4 wires. Now this didn't solve my bogging problem, but it brought my mileage back up quite a bit. Now that i've been inspecting the car for possibilities, I have found there is some noise in the engine bay, and I believe it's enough to set off the knock sensor, Its like a loud ticking or tapping toward the passenger side of the engine. It sounds bad, like a valvetrain issue, but when I put the stethescope against any part of the valve cover, head, or block, I can't hear any ticking, it just sounds normal. So what could be making this noise? It seems to have a direct effect on the RPM of the engine, but it's a rapid noise, like a driven part, not like the noise the IAC makes when it goes wacky. also, when I first start the car, it is not there. after I let it run for a while, the noise comes, and when I hit the gas, it goes away, or it sounds like it does anyways.
Oh, I forgot to mention, I don't have A/C in this car, and I don't have a catalytic converter either.
Ok, update: the horrible noise, was a combination of a leak in the exhaust manifold gasket, and my alternator bearing. So I was wrong to say it had a direct effect on the RPM, rather, the RPM had a direct effect on the noise. So anyways, noise gone, but no improvement. I put the vacuum pump on my fuel pressure regulator. from 0 to whatever the max on the pump was, there was no change whatsoever. so I'm waiting on a new regulator now, and I hope that will be the end of this problem.
