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940....stumbles,misfires, hesitates...jerky acceleration

paulofvf

New member
Joined
Nov 21, 2007
Location
Lisbon, Portugal
I?ve 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??:roll:
 
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today it was worst, but after a few acellerations it became better, then worst again :grrr:


do you think it could be the fuel pump relay?
 
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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 , i?ve changed spark plugs,
 
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??
 
been noticing that the problem is getting worse......it only revv?s if i go gently on the throttle......., that means that i can?t go uphill :grrr:


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????:roll:
 
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.
 
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 don?t know if the LPG uses the AMM....but i think it doesn?t! it flushes the LPG directly through the ....intake (i think it is called that way)
 
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.
 
today i removed the fuse from the LPG system......and it started running fine on petrol!:roll:



so i believe the problem is due to the LPG........WTF?!:grrr:
 
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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