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Old 12-11-2007, 03:07 PM   #1
paulofvf
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Default 940....stumbles,misfires, hesitates...jerky acceleration

Iīve been having a problem on my 93 940 b200ft ...

the car runs fine on LPG , but it runs badly when on petrol, under load


symptoms are:when on petrol, i hit the gas and it will hesitate ....as if the mixture is too rich or sometimes he will just stop revving ....and feel as if i had hit an invisible wall

if i keep pressing the accelerator it will continu to hesitate and make some bump noise somewhere in the front .....then around 2500rpm it will return to normal, and later between 3500/4500rpm will feel again like hesitating


under acceleration sometimes it misfires a lot , sometimes it misfires less........i hear some kind of backfire in the air filter box when this happens..or so it seems


what do you think it could be??
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Last edited by paulofvf; 12-11-2007 at 03:12 PM..
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Old 12-12-2007, 07:01 AM   #2
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today it was worst, but after a few acellerations it became better, then worst again


do you think it could be the fuel pump relay?

Last edited by paulofvf; 12-12-2007 at 07:15 AM..
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Old 12-12-2007, 07:57 AM   #3
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my symptoms are the same as your
http://forums.turbobricks.com/showth...y+acceleration

inside my opinion
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Old 12-12-2007, 08:05 AM   #4
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Quote:
Originally Posted by NitroX5 View Post
my symptoms are the same as your
http://forums.turbobricks.com/showth...y+acceleration

inside my opinion
yep!!! kinda like it, in mine it takes longer to rev again, and car becomes more hesitating....


here in Portugal, a friend of mine from a portuguese volvo forum told me it could be the fuel pump relay, have you checked it? i have to check mine!!


i run my 940 on LPG and it runs fine!! only does that when on petrol , iīve changed spark plugs,
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Old 12-12-2007, 08:33 AM   #5
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I can do more hesitate, but i get off the throttle for a while(usually), but if i keep forced-pushing henceforward the car jerk all the time.
I didn't check the relay since 3 month:D . I think is good or possible the coil surface burned, and not support enough volts to pump??
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Old 12-18-2007, 09:42 PM   #6
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been noticing that the problem is getting worse......it only revvīs if i go gently on the throttle......., that means that i canīt go uphill


by the other hand, once the RPM are above 4000 or so, it revs a lot better....




do you think it could be bad mixture????
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Old 12-18-2007, 09:45 PM   #7
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I think that's just vac leaks somewhere. Mine behaves very much the same when there's a leak.

Does the LPG system use the AMM? Could be that too.
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Old 12-18-2007, 09:52 PM   #8
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Quote:
Originally Posted by slowmotion View Post
I think that's just vac leaks somewhere. Mine behaves very much the same when there's a leak.

Does the LPG system use the AMM? Could be that too.

but if it was a vac leak then it would do the same when on LPG? or not?

i really donīt know if the LPG uses the AMM....but i think it doesnīt! it flushes the LPG directly through the ....intake (i think it is called that way)
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Old 12-18-2007, 09:56 PM   #9
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Try unplugging the AMM and see if the problem is the same or worse (when using petrol).

i.e. If the AMM is good, it should run a LOT worse unplugged.
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Old 12-18-2007, 09:58 PM   #10
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Quote:
Originally Posted by slowmotion View Post
Try unplugging the AMM and see if the problem is the same or worse (when using petrol).

i.e. If the AMM is good, it should run a LOT worse unplugged.

will try that tomorrow (itīs already 3a.m here in portugal)!

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Old 12-19-2007, 10:14 AM   #11
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have you tried changing plugs?
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Old 12-19-2007, 10:26 AM   #12
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Quote:
Originally Posted by sweetswede View Post
have you tried changing plugs?
theyīre new!
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Old 12-19-2007, 11:39 PM   #13
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today i removed the fuse from the LPG system......and it started running fine on petrol!



so i believe the problem is due to the LPG........WTF?!
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Old 12-20-2007, 12:10 AM   #14
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maybe both fuel systems are running at the same time?
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Old 12-20-2007, 12:41 AM   #15
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Quote:
Originally Posted by HonestJhon View Post
maybe both fuel systems are running at the same time?
that is what i think itīs happening when running on petrol!

but when i run LPG everything is fine!



by the other hand, if i take the fuse, it runs fine on petrol, but i canīt run on LPG
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Old 12-21-2007, 04:19 AM   #16
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yo-

spray some water or carb cleaner on the injectors when your car is idling... listen for change in rpm.. i was having real similar problems as you and it turned out to be a leaky injector seal. Also, wiggle some wires and see if anything odd happens.


good luck.
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Old 12-23-2007, 01:55 PM   #17
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My car had some stuttering problems etc. I replaced the ignition coil. and it worked
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