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OBD-1, a 1995 850, and troubleshooting RPM bounce

Help, Advice and DIY Tutorials on Volvo's extremely popular car line -- Volvo's 1990s "bread and butter" cars -- powered by the ubiquitous and durable Volvo inline 5-cylinder engine.

1992 - 1997 850, 850 R, 850 T5-R, 850 T5, 850 GLT
1997 - 2000 S70, S70 AWD
1997 - 2000 V70, V70 AWD
1997 - 2000 V70-XC
1997 - 2004 C70

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misha
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Year and Model: '97 850 2.5 20v
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misha

Re: OBD-1 SHORT!

Post by misha » Mon Nov 05, 2018 3:58 pm

Hmmm...i see.
Car is 5 speed manual,right?
Do you have 2 ecu in ecu box or just one?
That could explain a lot if the car have LH 3.2 Jetronic management....since they are obdI.
You mentioned a slugish performance and idle is bouncing up & down....that indicates a problem with MAF.
Unplug it's connector,start the engine and see if problem disappears.
'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

villagepc
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villagepc

Re: OBD-1 SHORT!

Post by villagepc » Mon Nov 05, 2018 5:52 pm

DIAGNOSTIC UNIT “A” LED DOES NOT FLASH

1) Disconnect diagnostic unit “A”. Turn ignition on. Check for voltage at diagnostic connector terminal No. 4. If voltage is not present, check fuse and wiring. If voltage is present, turn ignition off.
2) Connect an ohmmeter between diagnostic connector socket
No. 8 and ground. Ohmmeter should indicate approximately zero ohms. If reading is not approximately zero ohms, check wiring. If wiring is okay, replace diagnostic unit “A”.

Googled around a little.

The whole push the button thing might be a little tricky. There's definitely a window of time between pushing it, and letting it go. Hold it longer than necessary, ya get nothing. Hold it not long enough, ya get nothing.
____________________________________________
1998 V70 T5M R Clone | IPD / ARD Stage 3
2001 S80 2.9 - I'm a glutton for punishment
1991 740 Turbo - a-traktor wannabe project

Blackwagon
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Blackwagon

Re: OBD-1 SHORT!

Post by Blackwagon » Tue Nov 06, 2018 1:28 am

Misha, I tried that already and it was worse so scratch that, there’s two ecm in the box...

Villagepc, I’ll try that tomorrow and get back with results 👍🏻👍🏻

Ozark Lee
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Ozark Lee

Re: OBD-1 SHORT!

Post by Ozark Lee » Tue Nov 06, 2018 6:59 am

The OBD-1 button box is has a connector on the bottom of it. My suggestion would be to remove the button box and then take it inside to a well lit area to disassemble it. There are four plastic tabs that hold it together and the outer shell needs to be pulled out at those tabs to get it apart. I use a small screwdriver to pry the shell out and then toothpicks to hold it out while I go to the next tab.

It is amazingly simple once you get inside of it. The one thing you have to be careful about is that there is a spring under the button and it wants to sail when the shell comes off if you remove the case quickly. Once inside you just need to clean the contacts and repair the flywire. I have just made a new flywire in a couple of cases by soldering the new wire on the contact and then using a crimp on "bullet" connector which you can get at any hardware store.

I also always spray the connections, both top and bottom, with electrical contact cleaner. Once the corrosion is cleaned off I have had good luck getting the box to work again.

...Lee
'94 850 N/A 5 speed
'96 Platinum Edition Turbo
Previous:
1999 V70XC - Nautic Blue - Totaled while parked.
1999 V70XC - RIP - Wrecked Parts Car.
1998 S70 T5
1996 850 N/A
1989 740 GLT
1986 740 GLT
1972 142 Grand Luxe

Blackwagon
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Re: OBD-1 SHORT!

Post by Blackwagon » Tue Nov 06, 2018 2:42 pm

Thanks, lee. I’ll try that as well. A longer wire is a good idea anyway. I have a feeling O2 sensors are the cause for the way it’s acting so hopefully I can fix the box and figure out which one it is...

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misha
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misha

Re: OBD-1 SHORT!

Post by misha » Tue Nov 06, 2018 3:09 pm

You have only one o2(front one) and idle bouncing up & down is not o2 sensor malfunction indicator.
'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

Blackwagon
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Joined: Mon Nov 05, 2018 12:43 am
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Blackwagon

Re: OBD-1, a 1995 850, and troubleshooting RPM bounce

Post by Blackwagon » Tue Nov 06, 2018 10:35 pm

C0B56418-8D2E-48F3-863E-BEC187DB1008.jpeg
You’re right lol. I just found that out when I got under it. At least I can return the other one... it does have a lot more pep now, the old one was definitely worn. I mustn’t have explained the symptoms properly; when I shifted, the RPMs would kind of wander for a second and then get up to par, and I noticed my fuel mileage wasn’t what it should be. It’s coming up on a 70K mike service and im going to service the pcv system and a tune up as well. After all that I shouldn’t have to worry about much for at least a month LOL! I’m gonna see what I can do about the obd short now so I’ll let you know...
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Blackwagon
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Blackwagon

Re: OBD-1, a 1995 850, and troubleshooting RPM bounce

Post by Blackwagon » Wed Nov 07, 2018 2:24 am

257E76E7-9B4F-4EB6-846A-4DE637176346.jpeg
So I got a longer wire soldered up which is nice, and Everything is clean now but I just realized there is no terminal 4 or 8 so... idk where to go with that but the diode still stays lit when plugged in without pushing the button (not pictured, it’s somewhere here) I used a clean wire to do the buttons job but the response was the same. Fuses are good. The coolant cap was loose... I’m done till tomorrow.
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misha
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misha

Re: OBD-1, a 1995 850, and troubleshooting RPM bounce

Post by misha » Wed Nov 07, 2018 7:40 am

Old o2 sensor doesn't look bad.....your car wasn't running rich...otherwise it would be fouled with black sooth and carbon.
What you see is just a shield,sensor and it's elements are under it.
'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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