1988 Volvo 240 doesn't rev when gas pedal depressed
 

Hey guys

My 1988 Volvo 240 dl has been good, until the other day when it lost power while driving. The engine seems to start up and idle at normal revs, but when I apply the gas pedal, it doesn't rev up at all, and the revs seem to slow down. If I floor it, the revs drop and the engine almost seems to totally stop.

Any ideas what could be wrong? A mechanic friend of mine said the "choke might be stuck" but I have no idea what the means. The fuel pump is about 6 months old. I have some experience working on this car.

Thanks!

Based on your symptoms, I'd look at the MAFS first... the big sensor right after the air filter, multi plug. Unfortunately there is no good test for reliably checking it. You can try unplugging it and see if there is a change but with your symptoms, I don't know. Best is to try and swap it with a "known good" one but if you don't access to one, not so easy...

p.s. cars haven't had 'chokes' since carburetors. ignore your friend's mechanical advise.

re: swapping MAF, your 1988 uses LH2.2, so you have to find another LH2.2 car to swap it with, 1989+ used LH2.4 with a different MAF.

Thanks for the advice guys. I'll see about replacing the mass air flow sensor. I know another mechanic who specializes in old Volvos and may know where to get one. I'll post updates if I get this resolved.

Just unplugged the MAFS, and the symptoms didn't change (car would still stutter and almost die when the gas pedal pushed in at all), then I plugged it back in, and it revs like normal! ****ing weird, but I love old volvos. I haven't taken it for a drive yet, though. I'll let you know if it comes up again soon.

Thanks for the help guys! I called my local auto parts store and they had to order one for $160, so I hope mine doesn't need replacing.

hows your wiring harness?

Should be decent, I recently checked most of the electrical wiring, do you think that may have caused it?

the alternative is, the MAF connector wasn't making a solid connection due to corrosion or something.

did you inspect the MAF socket and plug when you unplugged and replugged it? were the contacts all shiny/clean, or was it grungy in there?

the 'biodegradable wiring' fiasco supposedly ended in 1987, but its always possible some older harnesses were used in 1988 (87 and 88 240's are identical). when these biodegradable harnesses fail, its often not visible externally, its the insulation inside hte black outer sheaths that fails. to inspect this, you have to slit the sheath and pull it back, and then you see cracked brittle insulation crumbling off the individual wires, and corroded wiring...

http://badmercedes.com/images/mercedes+wires_1.jpg

(yes, thats a mercedes harness, they had the same problem in the mid 90s, 5+ years after volvo fixed theirs).

If anything, plugging-unplugging the MAFS and the result you got confirms that the fault is in indeed the MAFS.

Be careful getting a MAFS from the local parts house for $160! May or may not work, and then it could be for a short time. These are questionably rebuilt units, or Chinese ones. Bottom line, if there is no positive results once you install it, you won't know for sure if the MAFS you got is bad, or the diagnosis was falty in the first place. One time I went through FOUR different MAFS before I found one that worked...

Car ran fine for a couple days, then had the same problem >.<
I'm assuming its a bad MAFS then.

I see FCPeuro.com has 3 MAF's for LH2.2 cars... the real genuine Volvo one is $340, the Bosch rebuilt one is $200 (plus a $75 core charge), and the never-heard-of-them one is $140 (+$100 core).


whaaa, from the photos, the VOLVO one is Made In China and while it says Volvo on the label, it also has a "GCP" logo I don't recognize.

note that LH2.2 MAF's must be tuned after installing, using an LED clipped to a test point and +12 (battery), when the engine is fully warmed up and idling in park/neutral, the LED should be blinking on/off, you adjust the screw on the MAF til its about 50-50 duty cycle. the test point is the pink wire on an empty 2-pin connector (the blue-white wire is for idle speed), this test point connector should be near/behind the power steering reservoir.

I finally bought a remanned MAFS and it wasn't cheap, but it seems to have fixed the problem. The car drives now.

I'm a little confused about tuning, could you explain it more or show a diagram?

Thanks

I don't have a diagram, and not sure what to draw to explain what I said. you need an LED test light, the + clip goes to the battery + terminal, the - clip of the LED goes to that test connector's pink wire. start the car and let it fully warm up, the led should be blinking. you adjust the little set screw on the MAF (it may be under a plug or cap) until the light ON time is about the same as the light OFF time...

Great, that helps a lot, thanks!

ok, how's this?

http://pierce.smugmug.com/photos/i-q.../i-q5vc5kF.jpg

I'm using my digital multi meter in '% duty cycle' mode.... this signal is very low frequency, like 1-2 per second, so the meter is bouncing all over the place. it doesn't need to be exactly 50%, just somewhere in the middle, eg, not all on or all off. that blue shell the black probe is stuck into is the test connector.

Just a side note... thats a marine fuse holder (with the orange leads) rather than the original white 25A fuel injection main fuse, as that fried 15 years ago... the other black fuse holder closer to the battery is for a trailer light adapter, never mind that.