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96 850 Turbo Starts but runs rough then dies. Backfires.

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
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New2Volvo96
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Joined: Sat Sep 07, 2019 9:15 pm
Year and Model: 1996 850 Turbo
Location: Oregon

96 850 Turbo Starts but runs rough then dies. Backfires.

Post by New2Volvo96 »

Hi all. I am posting this in hopes to help my father in law figure out what his problem is with his 96 Volvo 850 Turbo. I helped him replace the PCV system and he replaced the PNP switch but after it all got put back together it now will start but dies after about 5 seconds or less. If you keep on the throttle it will keep running albeit very rough, but it backfires and there is a strong gas smell. We tried checking the fuel pump relay and bypassed it didn't help and it sounds like the fuel pump is working though we haven't tested the fuel pressure yet. I haven't cleaned the MAF yet but I scanned for codes and found nothing and can't imagine a dirty MAF would cause this many problems. I'm hoping someone might have some insight as to what might be causing these issues. Possibly didn't get something put back together correct. Vacuum lines look good but it's hard to test them when it's running so bad. Any suggestions would be much appreciated. Also I should note that his car has something draining the battery so it only starts up when being jumped. Thanks guys!
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Re: 96 850 Turbo Starts but runs rough then dies. Backfires.

Post by Clemens »

what about the intake manifold gasket? if there is a leak, it will run horrible.
are all the injectors seated and connected properly?
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Re: 96 850 Turbo Starts but runs rough then dies. Backfires.

Post by abscate »

It’s really easy to pinch something between the manifold doing the PCV

Replace all the vacuum lines that you have no history on, at 20 years old +, they leak now.
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rguzz
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Re: 96 850 Turbo Starts but runs rough then dies. Backfires.

Post by rguzz »

Second the distinct possibility of an air leak at the intake manifold, ie the gasket. It can tear most easily in the upper right corner when replaced, I believe around the upper stud located there, but that is from memory. If it was running fine before taking on this job you will need to retrace your steps, unfortunately. Twice as fast the second time! Get a new gasket regardless. There are numerous step by step guides to help you if need be.
New2Volvo96
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Joined: Sat Sep 07, 2019 9:15 pm
Year and Model: 1996 850 Turbo
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Re: 96 850 Turbo Starts but runs rough then dies. Backfires.

Post by New2Volvo96 »

I was really hoping it wasn't the intake manifold but I had a sneaking suspicion it might not be on correctly or a bad gasket. I'll dive back in there and see what I can find. Thanks all. This forum is super helpful.
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Re: 96 850 Turbo Starts but runs rough then dies. Backfires.

Post by bmdubya1198 »

I agree with everyone else, make sure your intake manifold gasket isn't leaking. Also check over all other vacuum lines.

It's unlikely given that this wasn't a problem before this work was done, but the car will struggle to run if the voltage is too low. Definitely do a parasitic draw test once this idle issue is knocked out.
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'03 S60 2.4T Silver/Black 117k
'07 XC90 V8 AWD Sport Titanium Grey/Black 174k
'91 944 Turbo Dark Green/Beige 175k
'92 245 Base White/Beige 249k
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2000 S70 GLT Mystic Silver/Taupe 253k
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Re: 96 850 Turbo Starts but runs rough then dies. Backfires.

Post by erikv11 »

You're in good shape with all the comments IMHO. A peripheral comment -
New2Volvo96 wrote: Sat Sep 07, 2019 9:32 pm ... can't imagine a dirty MAF would cause this many problems. ...
If the MAF isn't visibly oily or grungy, cleaning it will almost never make any difference, not even a small one. Basically not worth spending for the cleaner. Do an unplug-the-MAF test first.
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'96 855 NA, 145k
'98 S70 NA, 220k (living out west)
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gone: '96 NA 850 210k, '98 NA V70 182k
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