I just bought this car from a family member, it hadn’t been used for about a year except for a monthly drive around the block to keep things from seizing up. The first time I drove the car was this past weekend and it had a horrible bog, I could hardly accelerate away from a stop. Anyway, I got it home and went about checking for simple things like a clogged air filter/ rodent nest in the air intake etc. but everything looked good. Later in the day, I took the car to the hardware store and it ran perfectly like it was miraculously cured, I shut it off, went into the store and when I came back out and started it, it was bogging again. I shut it off then started it up again and back to running perfectly! I drove the car on the highway today and put 250 kms on it without incident then it started to develop a subtle bucking feel. I stopped for gas, filled it with 91 octane and it ran poorly the rest of the way to my destination.
not sure if it’s related but I thought I’d mention that on occasion when I start the car, the exhaust sounds loud near the front down pipe but it almost goes away after 10 seconds of running.
Any ideas?

 

One of the first steps should be to scan the car with a compatible scan tool. Then take that info and see if it relates to the problems you are having.

 

As to the noise, on some Volvos there's a flex pipe in front of the cat, plus there may be an EGR tube. Either of those can create an exhaust leak that you can hear - and when the engine warms up, the leak gets closed. You'd need to have a shop put the car on a lift and then give a listen with the engine running. You may be able to do a simple visible inspection for broken exhaust mounts, cracks etc in the downpipe or header.

Also, to add to hoonk's suggestion, many scan tools can also record run time data that can report things like fuel trim while the engine is behaving badly. You can buy your own or check with Autozone etc to see if your local store lends them out.

 

Thank you both for the replies to my post. I have a Bosch OBD1200 CodeConnect scan tool that I just bought so I’ll have to play with it and use the data stream feature and see what I find. I didn’t mention in my initial post that there are no stored or pending codes which in itself is a potential clue to the problem. As for the exhaust, I’ll see what’s leaking and go from there, I do all my own repairs and have welders and other necessary tools to fix it.
I promise to report back with the cause of the bog once I figure it out.

 

I'd be suspicious of fuel pressure - ie the FPR relay gets warm and sticks, the pump may be overheating and starting to fail etc (can draw too much current which will heat up the relay) or an air leak (torn boot/ torn diaphram in a component like the oil separator etc). or possibly a engine coolant temp sensor (I've seen these throw a code other than a misfire and the temp guage may act up / read incorrectly.

 

Interesting that you mentioned a sticking relay, it reminded me that on the weekend with engine off and key out of ignition, there was a buzzing sound under the hood that stopped after a minute or so. Something to look into.

 

I’ve got a bit of an update… I was suspecting a fuel pressure problem so I performed a fuel pressure monitor with my code reader and had a very consistent 55 lbs throughout the throttle range. Next I thought I’d check the MAF, the wire was quite dirty so I cleaned it with the appropriate MAF solvent then reinstalled but bogging was still present. I then ran a monitor on the MAF to see how it was reacting and found that the LB/M reading was erratic, sometimes jumping around between 2.7 to 10 .3 with throttle at the same approximate position. After that, the intermittent problem went away so that was the end of the diagnostics until it acts up again. I’m curious to know if anyone else has had MAF issues and what their symptoms were.

 

Hi all.
the car experienced the bog again today when I accelerated away from a stop. I had my diagnostic tool in the car so I pulled to the shoulder and hooked it up and captured a recording of throttle command and ignition advance. As you can see, at 19.8 seconds into the recording, the ignition advance suddenly drops to -30 degrees and then jumps to +25.5 approximately two seconds later. I’m not an expert in interpreting this kind of data but to me, it doesn’t seem normal. I’m hoping someone with technical experience can give me a clue as to what’s going on.
thanks!

 

Update: In the process of removing the throttle body in order to clean it, I discovered that the resonator on the intake tube was very loose and not completely seated into the tube, in fact, it was so loose it was bouncing around and I’m surprised that it didn’t fall off. Apparently, someone had it apart at some point and didn’t reinstall it properly. The resulting effect was unmetered air entering the engine which caused the bogging condition. The item I’m referring to is a black plastic triangular shaped part directly below the A/C hose in the picture.