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Elusive Acceleration/Reving Up Problem 200 1988

posted by nockenwellenrad on Mon Dec 20 12:50 CST 2010
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last visit: Mon Nov 11 11:00 CST 2013

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Hello Merry Volvo People

I've got a weird one for you. My friend's '88 240 all of a sudden started exhibiting a very profound hesitation upon acceleration. Under load or not, when you rev up it hesitates like crazy- seeming almost certainly like a lack of fuel. No lean pop, just boggggggg… It does it almost right off the bat. If the engine is fairly cool it seems to rev fine for one or two minutes but then starts bogging again. The car IS drivable- if you are very gentle on the throttle and go like granny.

We've tested just about everything under the sun. Newish (but not known good) Air Mass Meter swapped in, coolant sensor and TPS checks at the ECU (good), most if not all of the other checks at the ECU a la Bentley Bible (good!), different fuel pump swapped in, new pressure regulator (it was leaking anyway but no dice). If you unplug the AMM it makes little difference. Do we have two bum AMMs? The one we swapped in was quite new from FCP Groton.

We haven't put a new in-tank pump in yet, but it acts the same regardless of how much gas is in the tank and it seems to be running if you listen in the filler opening.

Any ideas? Still a bad AMM? Is it possessed?

Many thanks in advance…

Jim
--
'58 PV444
'66 1800S
'67 122S Estate
'70 142S
'72 142E
'78 242GT
All are pretty and run except the '78 The irony!
http://www.olddeadvolvos.com

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Elusive Acceleration/Reving Up Problem 200 1988

posted by nockenwellenrad on Sun Dec 26 02:41 CST 2010
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last visit: Mon Nov 11 11:00 CST 2013

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Hi Folks

Update: we did indeed have two bad AMMs on our hands. We located a known-good unit and it runs fine now.

The disturbing thing is that one of the originals we tried was a rebuilt unit from FCP Groton with very few miles on it. The car it was in didn't have the intake air setup installed so it wasn't a case of premature fry-out. I suspect the rebuilder they use is leaving some key components un-replaced? I'd be interested in knowing whether others have had similar troubles with FCP units.

Thanks to all for help and happy Boxing Day!

Jim
--
'58 PV444
'66 1800S
'67 122S Estate
'70 142S
'72 142E
'78 242GT
All are pretty and run except the '78 The irony!
http://www.olddeadvolvos.com

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Elusive Acceleration/Reving Up Problem 200 1988

posted by Goatman on Mon Dec 20 16:15 CST 2010
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last visit: Sat Jul 26 20:30 CST 2014

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Hallo,

Check that the fuel pressure is correct. Easier said then done, I know, but still it would be a good idea.

Another idea is to warm the engine until symptoms appear, then pull the injector rail and observe the spray and quantity. A real neat trick would be to measure the injector pulse width and compare it to before, and to after the start of symptoms.

Yes, two air meters can be bad. As far as rebuilt ones, I have heard that they are inferior.

mit den besten Glückwünschen,
Goatman

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Elusive Acceleration/Reving Up Problem 200 1988

posted by nockenwellenrad on Mon Dec 20 21:43 CST 2010
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last visit: Mon Nov 11 11:00 CST 2013

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Greetings Goatman

Easier said than done is right. I pulled out my pressure gauge but need to scrounge around for fittings. It would be nice to have a tee that I could install before the rail. Does anyone make such a thing? There has to be a decent fitting source here in the City. We have a killer bearing & seal outlet and a fantastic fastener shop within a mile of my place.

I do suspect that the newish AMM is kaput. That would be just our luck.

Thanks for your help!

Jim

/this is why I prefer the vintage that have only one or two wires that make the motor run!
--
'58 PV444
'66 1800S
'67 122S Estate
'70 142S
'72 142E
'78 242GT
All are pretty and run except the '78 The irony!
http://www.olddeadvolvos.com

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Elusive Acceleration/Reving Up Problem 200 1988

posted by ricko on Mon Dec 20 13:52 CST 2010
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last visit: Thu Aug 21 08:31 CST 2014

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Could you swap in an known good AMM from a running car?

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Elusive Acceleration/Reving Up Problem 200 1988

posted by nockenwellenrad on Mon Dec 20 21:31 CST 2010
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last visit: Mon Nov 11 11:00 CST 2013

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I was thinking of that but I don't have one right on hand to try. It sure seems like an AMM problem, doesn't it?

Thanks,

Jim
--
'58 PV444
'66 1800S
'67 122S Estate
'70 142S
'72 142E
'78 242GT
All are pretty and run except the '78 The irony!
http://www.olddeadvolvos.com

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Elusive Acceleration/Reving Up Problem 200 1988

posted by dinomartino on Mon Dec 20 13:15 CST 2010
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last visit: Fri Oct 24 04:43 CST 2014

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Has it had recent cylinder head work, or had the valves adjusted recently? You are describing to a T the symptoms I had when a mechanic adjusted my valves too tightly.

john

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Elusive Acceleration/Reving Up Problem 200 1988

posted by nockenwellenrad on Mon Dec 20 13:26 CST 2010
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last visit: Mon Nov 11 11:00 CST 2013

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Hi John

Thanks for your response. Nope- no precipitating events at all. The car had been running like a charm for a while. We haven't taken a compression test yet because one of the plugs is pretty seized in there (no can o'worms for me, thank you), but it doesn't act at all like a miss. It's more of a uniform fuel starvation.

I neglected to mention before but we also unplugged the O2 sensor to try and spot any measurable difference- nothing. Also swapped an ECU in from a parts car (again, not known-good but different and what are the chances?) Seems to be running in limp-home mode. Odd.

Thanks,

Jim

--
'58 PV444
'66 1800S
'67 122S Estate
'70 142S
'72 142E
'78 242GT
All are pretty and run except the '78 The irony!
http://www.olddeadvolvos.com

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Elusive Acceleration/Reving Up Problem 200 1988

posted by butch on Mon Dec 20 21:53 CST 2010
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last visit: Wed Nov 20 06:46 CST 2013

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Re: "we also unplugged the O2 sensor to try and spot any measurable difference- nothing."

Are you certain the catalytic converter media is not broken or melted and clogging the exhaust?

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Elusive Acceleration/Reving Up Problem 200 1988

posted by nockenwellenrad on Mon Dec 20 22:15 CST 2010
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last visit: Mon Nov 11 11:00 CST 2013

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Hi Butch

The converter was replaced last year so it wasn't the first thing on my list, but checking that out is a good idea. I'll try the vacuum gauge method and see if the reading drops off steadily at constant elevated rpm.

Once the car is up to speed it's fine. It is only when you accelerate that it balks. Not sure if a plugged converter can cause that (I figure that plugging would cause it to be powerless on the highway as well), but who knows what's going on.

Thanks!

Jim

--
'58 PV444
'66 1800S
'67 122S Estate
'70 142S
'72 142E
'78 242GT
All are pretty and run except the '78 The irony!
http://www.olddeadvolvos.com

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