New guy comin' atcha with a cranky 240DL issue; bad hesitation at acceleration

[edvard]

Hi folks, I'm new here, hoping somebody can help. First off:
1990 Volvo 240DL 4-door Automatic. Over 250,000 miles (when I bought it the odometer didn't work and the previous owner bought it as a potential project car so he didn't really notice).

It was great when I first bought it about 3 years ago, but in the last year or two, it's started to get grumpy. The main symptom: hesitation and stumbling at acceleration. This is the biggie. Yes, there are other minor concerns, but when I have to wait for at least a quarter mile of "all clear" in both directions at an intersection just to escape the fear of getting creamed while pulling out of the gas station...

Work I've done over the past tow years that is relevant:
New fuel pumps (tank and main) and filter.
New fuel pressure regulator and hose.
New oxygen sensor.
New front oil seals.
New timing and other belts.
Cleaned throttle body.
New exhaust from header on down (long, painful story).
New head gasket and intake manifold gasket.
New MAF (remanufactured Bosch-style with the wire strung inside the wind tunnel).
New crank position sensor.
New speedo chip
New idle air control.
New water pump, hose, and thermostat.
New knock sensor.
New throttle position switch.
New intake hose (the big accordian-looking thing).
New throttle body shaft gasket watchamacallit.
New vacuum check valve.
New fuel injectors.

All symptoms:
- When I sit at a light or wait a little too long at a stop sign, I push the accelerator, and it spits and coughs and stumbles for 2-4 seconds before finally accelerating like normal. I don't pump the pedal, just press down normally.
- When starting cold in the morning, it will start up no problem, but after about 5-10 seconds, the idle suddenly goes very low; almost low enough for the car to die, but not quite, and it 'surges' a bit (not as bad as it was a year ago, but still). After driving a bit, the idle is fine.
-Sometimes when accelerating from a stop, it will backfire; not loudly, just a slightly louder *poof* and then it suddenly starts accelerating.
- When going at speed on the freeway, if I press the accelerator to pass a slow vehicle or speed up to change lanes or merge from an on-ramp, the car will actually slow down for a second or two, then speed up slowly.
- Some days it works better than others, but when it's having a bad day, I get a 2-3-2 code. Otherwise, no codes at all, but the hesitation is bad and refuses to get better.
- The main fuel pump has a very loud whine ever since I changed it. I didn't think it was a big deal after asking around about it, but I'm re-thinking (or is it re-panicking?) that situation.

I have checked and re-checked all hoses that I haven't already replaced because all symptoms point to an upstream air leak, but I just can't find it, and I've done everything else that I can find to do. This is my only car, I can't afford another (but somehow can afford to throw money at parts and pieces, right?), so I need to solve this before it simply dies completely, or I get in an accident because it wouldn't accelerate.

Some things I plan to do:
- Check the air filter and air filter box. Maybe I have a clog, I don't know. Seems unlikely, but who knows?
- Check rigid fuel line from pump to fuel rail. While changing the main fuel pump so long ago, the assembly that the pump and filter are attached to fell down from where I was un-bolting, and it seemed to bend the rigid fuel line where it's attached to the underneath of the car. The car otherwise runs fine, but in my imagination, there's a kink there that prevents fuel from traveling down the pipe as it shoud.

Thanks in advance!

[edvard]

No replies? Has the new guy stumped the MVS? Maybe more details are in order:

Air filter was fine. I blew it out with my shop vac blower, and hardly anything came out. I removed the pre-heater hose long ago.
Fuel line was fine. No leaks and no kinks. The next time I have to mess with the pump and filter, I'll take off the clip first just so this doesn't eventually become an issue; I don't imagine kinking a hose repeatedly will do it any further favors.

I bit the bullet yesterday and got down to testing the connections at the ECU according to the Bentley manual to see if some wiring flaw was preventing a sensor from being read or something. Here's what I got:

"Fuel pump power supply from main relay"
Directions say to short terminals 20 and 21 to ground with ignition on, and both fuel pumps should operate. They didn't. I did some further testing of the relay, and I got some funky results, BUT both fuel pumps operate when I start the car (I know, because I can hear them!), so I'm not sure what to make of this result.
"Throttle switch full-throttle contacts"
Continuity test from terminal 3 to ground with the throttle fully open should have continuity, but mine doesn't. Hmm...
"Oxygen sensor wiring harness"
I'm supposed to get continuity from terminal 24 to ground with the oxygen sensor connected. Nope. OK, this one worries me, because no continuity means that there would be no or little signal from the sensor, but when the car is running, I get the voltage reading just fine - Bentley says it should be between 0.5 to 1 volt, and I get 0.7xxx volts pretty consistently, and it fluctuates up and down ±0.05 volts or so. So I guess the green wire has a break in it? But wouldn't I get a 2-1-2 code that says the signal from the oxygen sensor is missing, AND a 'Check Engine' light? I'll test it by grounding the connector and test for continuity at the ECU and report back. It may be that my O² sensor has too high a resistance from connector to ground; my multimeter tests anything above ~5KΩ as open.

[volvolugnut]

Have you checked your fuel pressure at the fuel manifold at the engine?
volvolugnut

[edvard]

I have tried, but the damn connector there is frozen completely; all attempts to separate the two halves are met with staunch opposition and the real possibility of damaged fuel pipes. I've tried with the best flare-nut wrenches I could get without losing a limb, vice grips (cringe), and even tried soaking the joint in Kroil. No luck.

I know the fuel pressure needs to be tested somehow, but not sure how without tearing it up. Do you have any suggestions? Both pumps and filter are only 2 years old or so.

P.S. Even when brand-new, the main fuel pump whines and buzzes like a hornet with road rage. The old one did also, and I think it was the original unit.

[edvard]

OK, no continuity from a grounded oxygen sensor to terminal 24, so I can safely assume the ECU is not getting a signal from the oxygen sensor, but that doesn't square with the fact that I don't get any "oxygen sensor signal missing" codes. I'm going to have to trace down the wiring diagram and find a convenient place to jumper a wire from the O² sensor to somewhere that directly leads to ECU terminal 24 to confirm, but I wonder if it's safe to assume that is the problem?

[volvolugnut]

As I recall, all of my 240 fuel pumps make noise.
I see you have replaced the fuel pressure regulator also. Still, you need to know if the fuel pressure is correct. Perhaps use some heat from a hot air blower (soldering iron?) on the fuel fitting and then try the wrenches again. Or, careful use of a small flame AFTER confirming you have no fuel leak.
Do you know if your fuel/air ratio is about correct? It is concerning that your O2 reading does not vary much. You might try removing the sensor and check if it is covered in soot. You could try burning the soot off with a torch and reinstall.
Have you tried unplugging the MAF to see if the problem improves?
volvolugnut

[edvard]

I'll try the heat trick for the fuel rail coupling, though I won't trust a torch, seems to me there's enough volatiles under the hood that aren't gasoline to warrant caution.

To tell the truth, I have no idea if the air/fuel ratio is correct, because of these problems I'm having. When I'm cruising down the freeway, it runs like a top, and I don't notice if the fuel consumption is excessive, but I write that off as most of the mileage I accumulate is on the 20-minute freeway drive to work and back. Stop-n-go traffic around town, not so much. When my wife takes the car for the day to do shopping and whatnot, she can use almost half of a tank in a day, and that's when it was running good. That doesn't happen so much lately because of how awful it's driving because she doesn't feel safe driving it in town, but worth noting.

I did take the oxygen sensor out to look at it, and it was indeed covered in soot. I couldn't find any info on whether this was bad or normal or what, so I wiped it off as best I could with a clean rag (I took advice not to get any grease/oil/dirt on it when installing) and put it back in. If I had some compressed air, I would have used that as well. I haven't driven it since, but the test I did was after that. Should I have not simply wiped it off? Like I said I couldn't find any info beyond replacing it if it's faulty.

I have tried running (not driving) it with the MAF unplugged, and sometimes it does idle better. Sometimes (less often) it's worse. I don't know anything beyond that, and I'm not daring enough to attempt driving it around the block like that. Same thing with the previous MAF, which was a genuine Volvo OEM, but it was different; that one had a little circuit board in the wind tunnel, and no wire, so I was constantly getting the 3-2-2 code, which annoyed me, so I got a remanufactured Bosch style with the wire in the wind tunnel. No more 3-2-2, but it didn't improve the performance.

[rice240]

Its been a few years, but did you ever resolve this issue? I have the same problem.