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S70 2.5t misfire

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radek93
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Joined: Sat Dec 07, 2019 2:43 pm
Year and Model: S70 98
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S70 2.5t misfire

Post by radek93 »

I have S70 2.5t 98r B5254t and I have no idea. I replaced:
Spark plug
Ingition cable
Rotor
Cap
Ingition coil
Crankshaft sensor
Camshaft sensor
TPS
O2 sensor
Coolant sensor
Compresion is ok. No air leak i thing. No fault code.
When I drive, car have 1s misfire on 20 kilometers. Sometimes more often, sometimes less often. Sometime when engine working on idle, rotation degrese to 500 a grow up back to 900 in one sec.
I have idea that a ecu is broken.
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misha
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Re: S70 2.5t misfire

Post by misha »

Parts that had been replaced....are they OE,OEM or aftermarket?
Which spark plugs are used?
'97 850 2.5 20v / fully equipped / Motronic 4.4 from the factory / upgraded with S,V,C,XC70 instrument cluster / polar white wagon
'91 Citroen XM 2.0 SI /fully equipped/mandarine red metallic
History of Volvos in the family:
'71 144 S
'73 144 De Luxe
'78 244 DL
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radek93
Posts: 32
Joined: Sat Dec 07, 2019 2:43 pm
Year and Model: S70 98
Location: Home

Re: S70 2.5t misfire

Post by radek93 »

I used oem cable, tps. Other parts aftermarket. I used three brand of spark plug. First on oem. I forgot to add, car have LPG. On LPG or petrol is that same.
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misha
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Re: S70 2.5t misfire

Post by misha »

Rotor & cap,o2 sensor,crankshaft,camshaft sensors...coil MUST be OEM Bosch.
ECT especially MUST be OE Volvo or at least Vernet.

Since almost all parts are aftermarket it's hard to diagnose the problem.

LPG could also make problems.

Spark plugs should be OE Volvo for turbo engines or cheap copper ones (NGK or Bosch)gapped properly because gap is critical for turbo engines.
'97 850 2.5 20v / fully equipped / Motronic 4.4 from the factory / upgraded with S,V,C,XC70 instrument cluster / polar white wagon
'91 Citroen XM 2.0 SI /fully equipped/mandarine red metallic
History of Volvos in the family:
'71 144 S
'73 144 De Luxe
'78 244 DL
'78 244 DL
'79 244 GLE
'85 340 GLS
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RickHaleParker
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Re: S70 2.5t misfire

Post by RickHaleParker »

radek93 wrote: Fri Jan 31, 2020 3:41 pm When I drive, car have 1s misfire on 20 kilometers. Sometimes more often, sometimes less often. Sometime when engine working on idle, rotation degrese to 500 a grow up back to 900 in one sec.
Sounds more like something dragging the engine down but it is intermittent, like an Alternator bearing starting to go or a A/C compressor clutch going out and binding. Check everything on the Timing belt and the Auxiliary belt.
Last edited by RickHaleParker on Fri Jan 31, 2020 9:39 pm, edited 1 time in total.
1998 C70, B5234T3, 16T, AW50-42, Bosch Motronic 4.4, Special Edition package.
2003 S40, B4204T3, 14T twin scroll AW55-50/51SN, Siemens EMS 2000.
2004 S60R, B8444S TF80 AWD.
2005 XC90 T6 Executive, B6294T, 4T65 AWD, Bosch Motronic 7.0.
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wizechatmgr
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Re: S70 2.5t misfire

Post by wizechatmgr »

Put the old plugs back in. I know someone recently that got a plug that went bad after a week or two. Drove the guy nuts...
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1999 V70 XC AWD - ~193k miles
radek93
Posts: 32
Joined: Sat Dec 07, 2019 2:43 pm
Year and Model: S70 98
Location: Home

Re: S70 2.5t misfire

Post by radek93 »

wizechatmgr wrote: Fri Jan 31, 2020 9:34 pm Put the old plugs back in. I know someone recently that got a plug that went bad after a week or two. Drove the guy nuts...
I have this problem since four years. Oem volvo plugs. Ngk plugs. Brisk plugs. All that same problem.
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misha
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Re: S70 2.5t misfire

Post by misha »

Then...LPG system might be the cause of your problems.
'97 850 2.5 20v / fully equipped / Motronic 4.4 from the factory / upgraded with S,V,C,XC70 instrument cluster / polar white wagon
'91 Citroen XM 2.0 SI /fully equipped/mandarine red metallic
History of Volvos in the family:
'71 144 S
'73 144 De Luxe
'78 244 DL
'78 244 DL
'79 244 GLE
'85 340 GLS
radek93
Posts: 32
Joined: Sat Dec 07, 2019 2:43 pm
Year and Model: S70 98
Location: Home

Re: S70 2.5t misfire

Post by radek93 »

misha wrote: Sat Feb 01, 2020 2:13 am Then...LPG system might be the cause of your problems.
It was like this before lpg assembly
michael8888
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Re: S70 2.5t misfire

Post by michael8888 »

I found after going over a year with the same issue and replaced everything that the culprit was the thermostat sensor that's at the thermostat housing. A $13 part plus a new thermostat while I was there. ECU reads the temp wrong from the sensor and adds more fuel to the mix to cool the temp.
Also, check that all electrical connections are good and clean. use some dielectric grease. Be sure the wires from the cam sensor are not near the ignition wires. that may cause some em feedback.
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