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1998 S70 Runs fine cold, misfire when hot at low revs bad KAE fuel relay Topic is solved

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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WhatAmIDoing
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WhatAmIDoing

1998 S70 Runs fine cold, misfire when hot at low revs bad KAE fuel relay

Post by WhatAmIDoing » Sun Feb 18, 2018 3:09 pm

Recently developed an issue when the engine reaches operating temp it idles rough, hesitation, down on power, and I can detect a misfire. Car sat for over a week, I was sick and had no where to drive to. Went on a short drive a few days ago (less than 2 miles), didn't even hit operating temperature. Sat for about 20 minutes, came back, and started up fine. As I was pulling out of the parking lot, car started hesitating, jerking like it wanted to stall but lugged on. At idle I could detect a misfire, car was shaking. Accelerating was slow and sluggish, until about 3000rpm, then it came back to life. Repeated the same results on 2 more drives. From cold start everything is good until it hits operating temp. If I put my foot down it will hesitate, climb slowly, then roar back to life. At idle there is a miss/misses

I checked all the vacuum lines I could. Checked that no harnesses were loose or unplugged. Couldn't detect any obvious vacuum leaks. CEL is on due to unplugged downstream O2, but I don't have a working scanner with me to pull the other codes. No flashing CEL, service light is on (usually goes off after a minute of driving). At cold start it seems to be running awfully rich (ambient temp 44F). Once hot, I'm not getting the scent of unburnt fuel which usually goes with a miss. Miss isn't consistent either, so that may be why.

New parts to (probably) rule out: fuel filter, cap and rotor (solved the last misfire), wires, and fuel pump. Spark plugs have about 50kmiles on them. Air filter could use a good cleaning.

I'm assuming that since all goes bad once hot, some electrical component/sensor is to blame? Someone suggested unplugging the upstream O2 sensor (I can't seem to find were it plugs in at). If it was the MAF, wouldn't I also be having problems during cold start (has no problem starting cold or hot)? Are there specific vacuum lines I should trace?
'98 S70 T5M - 282,000+mi - forever a project
'99 S70 "AWD" - 220,000+mi - part out :cry:
Knows enough to be dangerous :wink:

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WhatAmIDoing
Posts: 761
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Year and Model: 1998 S70 T5M
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WhatAmIDoing

Re: Runs fine cold, misfire when hot at low revs

Post by WhatAmIDoing » Sun Feb 18, 2018 5:39 pm

Here's a video from the exhaust.
'98 S70 T5M - 282,000+mi - forever a project
'99 S70 "AWD" - 220,000+mi - part out :cry:
Knows enough to be dangerous :wink:

User avatar
WhatAmIDoing
Posts: 761
Joined: Sat Jul 30, 2016 1:13 pm
Year and Model: 1998 S70 T5M
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WhatAmIDoing

Re: Runs fine cold, misfire when hot at low revs

Post by WhatAmIDoing » Tue Feb 20, 2018 11:17 am

As per a suggestion, I went to unplug the front O2 sensor, but I could not get the harness to release. Could anyone explain how the locking mechanism on the O2 harness works? I really don't want to break anything.

Also noticed an exorbitant amount of condensation in the engine bay. Looks like my car just forded a river. Thinking water got into a connector. Hoping these next few days of high temps will dry everything out.
'98 S70 T5M - 282,000+mi - forever a project
'99 S70 "AWD" - 220,000+mi - part out :cry:
Knows enough to be dangerous :wink:

scot850
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scot850

Re: Runs fine cold, misfire when hot at low revs

Post by scot850 » Tue Feb 20, 2018 11:25 am

Volvo uses several different connectors so not sure which one in on that connection. Can you take a quick picture and post?

Some of the connectors use a silicon seal in them and it acts like a vacuum and along with find dirt and dust I have had to soak first with silicon oil or WD-40 and then use 2 pairs of pliers to wiggle the 2 parts apart. If the connector is the one I am thinking of, it had a
push button' on the top. You have to compress that while trying to pull apart using a lot of wiggling back and forth.

Once you have them apart, clean the connector halves and refit. Watch you don't lose the little silicon seal that sits at the bottom of the female portion and it rectangular in shape.

Neil.
2000 V70 R - still being an endless PITA
2006 XC70
2003 Toyota 4Runner V8 Limited
2015 Kia Sportage EX-L
1993 850 GLT -Sold
1998 V70 XC - Sold
1997 Volvo 850 SE NA - Went to niece in California - Sold
2000 V70 SE NA - New project and test bed - Sold

scot850
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scot850

Re: Runs fine cold, misfire when hot at low revs

Post by scot850 » Tue Feb 20, 2018 11:33 am

Check the distributor cap for moisture build up. I know you have replaced the parts recently, but worth checking.

Neil.
2000 V70 R - still being an endless PITA
2006 XC70
2003 Toyota 4Runner V8 Limited
2015 Kia Sportage EX-L
1993 850 GLT -Sold
1998 V70 XC - Sold
1997 Volvo 850 SE NA - Went to niece in California - Sold
2000 V70 SE NA - New project and test bed - Sold

User avatar
WhatAmIDoing
Posts: 761
Joined: Sat Jul 30, 2016 1:13 pm
Year and Model: 1998 S70 T5M
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WhatAmIDoing

Re: Runs fine cold, misfire when hot at low revs

Post by WhatAmIDoing » Tue Feb 20, 2018 11:37 am

I have 2 connectors styled like the right end of this connector on fcp. I figure it slides out, but I've been prying on it for an hour now and it won't budge. Not sure if there is another clip I'm missing? Is there a certain trick to it? Going to soak it in silicone.

Figured I'd pull the distributor and check, but the fact that it runs fine under cold start sequence makes me think it's not spark.
'98 S70 T5M - 282,000+mi - forever a project
'99 S70 "AWD" - 220,000+mi - part out :cry:
Knows enough to be dangerous :wink:

scot850
Posts: 5938
Joined: Mon Apr 05, 2010 2:46 pm
Year and Model: 2000 V70 R
Location: Calgary, Alberta, Canada
Has thanked: 12 times
Been thanked: 211 times
Canada
scot850

Re: Runs fine cold, misfire when hot at low revs

Post by scot850 » Tue Feb 20, 2018 12:12 pm

Condensation becomes warmer and therefore easier to get into places when hot so worth a quick check.

What brand of parts did you use in the electrical ignition parts? Volvos are particular what works for them.

Neil.
2000 V70 R - still being an endless PITA
2006 XC70
2003 Toyota 4Runner V8 Limited
2015 Kia Sportage EX-L
1993 850 GLT -Sold
1998 V70 XC - Sold
1997 Volvo 850 SE NA - Went to niece in California - Sold
2000 V70 SE NA - New project and test bed - Sold

scot850
Posts: 5938
Joined: Mon Apr 05, 2010 2:46 pm
Year and Model: 2000 V70 R
Location: Calgary, Alberta, Canada
Has thanked: 12 times
Been thanked: 211 times
Canada
scot850

Re: Runs fine cold, misfire when hot at low revs

Post by scot850 » Tue Feb 20, 2018 12:14 pm

Sorry, not seen or used that part/connector before. Definitely looks like a slider and they can be hard to work with especially when cold. Try the silicon oil and if you have a wide thin flat blade to help prize it apart.

Neil.
2000 V70 R - still being an endless PITA
2006 XC70
2003 Toyota 4Runner V8 Limited
2015 Kia Sportage EX-L
1993 850 GLT -Sold
1998 V70 XC - Sold
1997 Volvo 850 SE NA - Went to niece in California - Sold
2000 V70 SE NA - New project and test bed - Sold

scot850
Posts: 5938
Joined: Mon Apr 05, 2010 2:46 pm
Year and Model: 2000 V70 R
Location: Calgary, Alberta, Canada
Has thanked: 12 times
Been thanked: 211 times
Canada
scot850

Re: Runs fine cold, misfire when hot at low revs

Post by scot850 » Tue Feb 20, 2018 12:21 pm

Sorry for all the notes, but ran out to the garage to check if I had a connector like that on one of my old O2 sensors. Problem was I only have the male end on the sensors. It looks like the other end in the link you made as you sometimes need that extender cable for the rear O2 sensor. I'm guessing the slider will be the same on the car end too, so it will need to slide out and then allows you to depress the tab to separate the joint.

Neil.
2000 V70 R - still being an endless PITA
2006 XC70
2003 Toyota 4Runner V8 Limited
2015 Kia Sportage EX-L
1993 850 GLT -Sold
1998 V70 XC - Sold
1997 Volvo 850 SE NA - Went to niece in California - Sold
2000 V70 SE NA - New project and test bed - Sold

User avatar
WhatAmIDoing
Posts: 761
Joined: Sat Jul 30, 2016 1:13 pm
Year and Model: 1998 S70 T5M
Location: North America
Has thanked: 66 times
Been thanked: 56 times
Canada
WhatAmIDoing

Re: Runs fine cold, misfire when hot at low revs

Post by WhatAmIDoing » Tue Feb 20, 2018 1:02 pm

scot850 wrote:
Tue Feb 20, 2018 12:12 pm
Condensation becomes warmer and therefore easier to get into places when hot so worth a quick check.

What brand of parts did you use in the electrical ignition parts? Volvos are particular what works for them.
Bosch cap and rotor. Plugs as far as I know and wires are NKG. Coil is original.
scot850 wrote:
Tue Feb 20, 2018 12:21 pm
Sorry for all the notes, but ran out to the garage to check if I had a connector like that on one of my old O2 sensors. Problem was I only have the male end on the sensors. It looks like the other end in the link you made as you sometimes need that extender cable for the rear O2 sensor. I'm guessing the slider will be the same on the car end too, so it will need to slide out and then allows you to depress the tab to separate the joint.
Thanks. I tried prying with a butter knife, but couldn't make it budge. I appear to have misplaced my can of Blaster silicone. Looks like I'm walking to the nearest hardware store. Fortunately it's a beautiful day here for a walk.

On a side note, the exterior of the O2 sensor (part outside the exhaust) is covered in oil due to bad RMS. Could this have had a detrimental effect on wiring?
'98 S70 T5M - 282,000+mi - forever a project
'99 S70 "AWD" - 220,000+mi - part out :cry:
Knows enough to be dangerous :wink:

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