(Yet another) 98 V70 GLT Misfire
 

I have searched a lot to avoid having to post what appears to be a fairly common problem, but cannot find a consistent solid answer.
Here are the current symptoms:
Under moderate to heavy acceleration, there is a power drain that I can only describe as a similar feeling to when you run out of gas. The more you get on the pedal, the worse the deceleration. If I back off, the missing/judder/power drain goes away. This problem started earlier this year. My car has a perpetual check engine light because of the stupid air pump/SAS valve thing that I refuse to fix (yeah, I know). I somewhat frequently check the codes and turn off the light. During this time, I had noticed once the misfire problem started, codes for the front o2 sensor showed up. Cleared them to see if it was a fluke, but they came back along with misfires on all 5 cylinders. Replaced the front o2 sensor at the same time I had (a proper Volvo tech) replace the timing belt and both CV joints. Since then, I had no issues until recently.
This may be a red herring, but I was driving down the freeway when a large hunk of concrete or metal fell off a truck--I could not avoid it and ran the f-ing thing over destroying a tire in the process. As I attempted to get off the freeway to change the tire, I got on the gas a little and the misfire came back. I turned on the hazards and then the "bulb out" light came on too. Basically, the car wasn't happy about the whole situation. At any rate, the misfire is pretty consistent now, but no codes beyond the air pump.
This is a GLT wagon with the low pressure turbo.
The plugs were replaced this winter, the wires are two years old. Have not attempted to check the injectors and I have not investigated the cap/rotor. I did pull the coil and attempted to check the resistance, but have only an analog multimeter and thin evidence that it's supposed to read .5 ohms--hard to tell on the analog.
Is there any solid process to weed out what may likely be the cause? I'm currently out of work and can't throw a lot of money at parts, but I do have plenty of time to troubleshoot.
Thanks!

It will set codes but ti start unplug the injectors one at a time to find out which cylinder is misfiring. Then start checking things from there.

Got no codes since the last clear except for the air pump; will just have to keep driving see if anything pops. Will probably try a cap & rotor as upon inspection, they appear to be originals.
Ran the car at night to see if there was any visible arcing from coil or anything else, but got nothing.

Thanks for the help

I would also replace the cap and rotor first; but if that doesn't do it, ck the fuel pressure...

Speaking of fuel pressure, is the fuel filter due?

More info:
I ended up replacing the cap & rotor. However, that has not entirely solved the problem. I did notice that when I took the air box apart, the filter had a big red rusty stain in the middle--near where the hose from the (now dead) air pump connects. So I've taken apart the dead air pump, damn thing is full of water. I heard that they usually drown after the SAS valve bites the dust, but I didn't think that the water would ever leave the pump, much less end up in the air box!
At any rate, car does run better with new cap & rotor, but still misses. I'm wrist deep in patching up the hose ends so I can test drive the car without the dumb air pump while I decide what I'm going to do with it. Seems like now I've gone to the trouble to get it out, I may try to do the VW air pump rebuild trick. It would be nice to get rid of that check engine light.
I'll also check the fuel filter if this doesn't go away as I'm sure it's not ever been changed.
Thanks everyone!

Got air pump out and missing has decreased, but still there under load at higher RPM. Will likely listen to Gdog and try a fuel filter this weekend.
Seems like finding a $40 Pierburg air pump is a bit of like finding a unicorn. Took it apart, cleaned and oiled it; spins freely, but is still dead. Oh well.
Thanks!

Ok, replaced fuel filter as prescribed, missing has lessened but is still present. Under about 3/4 throttle it is apparent and today it set off the blinking CEL.

Any suggestions?

Hmmmm...

Sounds like you still have diag work to do. Pull the codes to see if anything new there.

Assuming you find all 5 cyl misfire codes again..

I would sure like to know what the fuel pressure is when it's missing.. anyway you could hang a fuel pressure gauge on there and take it for a drive?

And it's interesting you said it got a bit better when you replaced the fuel filter. Possibly the fuel pump is on its last legs and its capacity to pump fuel is decreasing?? This could give you a lean-out condition that would show up under load that could cause all five cylinders to misfire..

You really need to determine if it's your ignition system or lack of fuel that's causing the misfire. You can ck the ignition by hooking up an inductive pick-up timing light to any one of the plugs wires (try each one at a time, or the coil wire) while running the light into the cab and driving to induce the misfire. Between monitoring the fuel pressure and the timing light you should see a problem with one or the other....

Also, please don't just throw parts at this; it's possible it's something else entirely. The parts you replaced already are different as they are regular maintenance items anyway.

Good luck!

Unfortunately, I do not have a fuel pressure gauge--but I did just get a new job so I may use the excuse to pick one up.
I did also put a bottle of Techron in the tank the day before yesterday to try and rule out dirty injector issues. I'll prolly stick another bottle in at the next fill up and maybe see where that goes.
At this point, I'm of the mind that there is some sort of fuel delivery problem; either weak fuel pump or clogged injectors-the rest of the ignition system has been largely replaced (plugs, wires, cap, rotor, etc). A local tech I take my Nissan to seemed pretty convinced that it's an injector problem (however he did not actually work on the Volvo).
Anyone have any thoughts on on-car vs. off-car injector cleaning?

Thanks!

what spark plugs do you have in it?