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Fuel Problems

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

Derilas
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Fuel Problems

Post by Derilas » Mon Mar 11, 2019 8:38 pm

My car, at least occasionally anyway, stalls.

It will start, but on occasion, without a distinct pattern, will sputter, and no amount of throttle will solve the problem. If I wait / coast for a little bit, it will resolve itself eventually, but sometimes it happens after I've pulled out into a busy intersection, which, as you may have assumed, is not a very good thing, and is rather disconcerting to think about. In addition to this, the throttle has never been smooth, especially at the upper end. It will work, but it will reach a point at about 55-60 mph (80-95 Km/h) where the throttle will not increase as the peddle is pushed past a certain point, but then it will all of the sudden go full open. I've checked the throttle cable (it is a 97 850) and there is no slack, but this problem still happens every time I try to speed up to highway speeds. The check engine light comes on, but only occasionally, as a rich in bank 1 (not sure if the 5 cylinder has banks, but ok), and when I bought the car about six months ago, the catalytic converter was totally busted and was restricting exhaust flow (fixed), and also at that point it was throwing misfire codes, but I have since replaced the cap, rotor, wires, and plugs, basically a new ignition system, and these codes went away (for now). There are two other issues with the car that I have yet to fix, 1) the ATF is pretty brown, so I should replace that, and 2) there is pressure in the crankcase, and so the PCV system is likely bad, but I have done some other things to help remedy the fuel problem. I have replaced the fuel filter, and the fuel pump relay, but this problem still persists. another thing I've done, and I had to do it because of a lack of time and funds, was to completely cut out the cat (obligatory exhaust leaks resulted on account of this). I don't know how the O2 sensor(s) is set up, whether it is supposed to be before or after the cat, and that may be the cause of the issue after all (In my defense, the cat was completely blown out and useless from all of the unburned fuel), I just don't know. Does anyone have any recommendations as to what sort of tests I should run or parts to service? Any advice is appreciated.


By the way, you can hear the fuel pump when you prime the engine, it is really loud.



850 LPT
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850 LPT

Re: Fuel Problems

Post by 850 LPT » Tue Mar 12, 2019 1:07 pm

I think you have two problems to deal with here: exhaust and possibly fuel pump.

If the fuel pump is really loud, it may need replacement very soon.

But the important thing is to figure out your exhaust situation. Your car has two O2 sensors from the factory, one mounted in the exhaust manifold (primary) and one in the cat (secondary).
You can't just eliminate the cat and not do an ECU upgrade with sec. O2 sensor delete because now you have a secondary oxygen sensor with nowhere to go.

Or, you can weld a nipple with an extension into the pipe that replaced the cat so you can install that sensor again, and the ECU thinks everything is fine.

This is just my very basic knowledge of how this is supposed to work, people much smarter than me will hopefully chime in.

Dirk
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Derilas


96' 850 sedan, base, auto, pewter/charcoal, 106k miles
99' S70, base, 5-speed manual, nautic blue/ tan, 209k miles
04' V70, auto, ash gold/ tan, 222k miles
05' V70, 5-speed manual, loaded, mistral green/ tan, 142k miles
79' Ford Capri S, Euro Spec 2.8 V6, T9 5-speed manual
58' Porsche Diesel Junior
13' Honda Odyssey :oops:

Derilas
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Derilas

Re: Fuel Problems

Post by Derilas » Tue Mar 12, 2019 10:04 pm

Update: the misfire codes came back, now I'm absolutely not sure what the cause of that is.

Question: there are different types of catalytic converters on the market of varying price ranges and types. Given that I live in a state where I am not required to pass an emissions test, so I can pretty much use whatever I want, what sort of cat is the best for a non-turbo 97 850, preferably with the best fuel economy and ease of use. Where it sits now, My car will burn through a tank of gas in around 3 days. With the amount I drive, I'm used to getting about 5 days to a week out of a car with a similar advertised mpg. Something is causing my fuel economy to suffer, and I'm not quite sure what it is, so I would like to find out. I don't really want to shell out the $400 for an OEM cat, so if there are any other workable options then let me know.



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WhatAmIDoing
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Re: Fuel Problems

Post by WhatAmIDoing » Tue Mar 12, 2019 10:28 pm

Best cat for fuel economy is no cat or a free flowing cat. Crappy gas mileage can be any number of things, including worn ignition components, dirty injectors, clogged PCV, stuck brake caliper, no compression, and bad vacuum leaks.

You will get misfires on a non turbo if the exhaust is dumping right where the cat should be, as you're essentially running an open header. You can fool the downstream O2 sensor by installing a spacer.
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Derilas


'98 S70 T5M - 270,000+mi - forever a project
'99 S70 "AWD" - 218,000+mi - project
Knows enough to be dangerous :wink:

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Re: Fuel Problems

Post by Sommerfeldt » Wed Mar 13, 2019 12:38 am

Okay, so it seems pretty clear cut (famous last words... :D ).

As the others have said, your problem is exhaust, and fuel pump.
Pick whichever cat fits the pipes and your budget, and don’t worry too much about it. BUT! You absolutely must either get the rear O2 back in there, or reflash the ECU with a file where the rear O2 is deleted.
Your mileage problem is the O2 and exhaust - the ECU will try to protect the engine, and dumps fuel in there to keep things nice and rich. With your current setup, gas is almost dripping out your tailpipe.

Also check your fuel pressure. It sounds like your pump is ready to crack out. :)

- S
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Derilas


'96 855 T5, R bumper and spoiler, Koni Yellows & blue H&R springs all 'round.

Derilas
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Derilas

Re: Fuel Problems

Post by Derilas » Wed Mar 13, 2019 7:46 am

Image

This is a test reply, I'm trying to figure out how to properly include photos



Sommerfeldt
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Sommerfeldt

Re: Fuel Problems

Post by Sommerfeldt » Wed Mar 13, 2019 7:50 am

Worked! Beautiful O2 sensor. :D
(There’s also a “Preview” button... ;) )

- S
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Derilas


'96 855 T5, R bumper and spoiler, Koni Yellows & blue H&R springs all 'round.

Derilas
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Derilas

Re: Fuel Problems

Post by Derilas » Wed Mar 13, 2019 8:33 am

Sommerfeldt, I looked under the car and took several pictures of O2 sensors as well as other things that concern me, and, although my exhaust is in bad shape on account of rust and things of that nature, the O2 sensors are still in place and have not been messed with. there is a section of stainless exhaust pipe welded in where the cat was, but there is no obvious problems with it, and despite the loud exhaust leak, there are no gaping holes in it. I don't think the secondary O2 sensor is cut out or not working, or if there's really anything wrong with it, but the ECU is still dumping fuel into the cylinders for some reason like its not picking anything up. Do you think my sensors are fouled? Again, my exhaust pipes are pretty bad, especially towards the back, so I hooked a shop vac to the tail pipe and switched around the hose so it blew air in order to find the leaks. there were three minor areas, one around the rear weld on the new stainless part replacing the cat, one where the cat pipes were originally flanged to mate with the muffler pipes behind the secondary O2 sensor, somebody had since gotten rid of the clamps and instead welded it together, and the entire muffler is leaky. The biggest leak, as you might figure, was where all 5 exhaust pipes meet, and it was pretty big. I take that back about not having any gaping holes in my exhaust. could that be causing all of my problems, minus the fuel pump?



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Re: Fuel Problems

Post by WhatAmIDoing » Wed Mar 13, 2019 9:06 am

Exhaust is your problem. If you have a cat efficiency code (I bet you do), unplug the downstream O2 sensor and the car will think the cat is fine, but you must disconnect the battery for 15 minutes to reset the ECU. Either get that exhaust buttoned up tight, or order a new one. Without seeing it, it's hard for me to say what would be better.


'98 S70 T5M - 270,000+mi - forever a project
'99 S70 "AWD" - 218,000+mi - project
Knows enough to be dangerous :wink:

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Re: Fuel Problems

Post by 850 LPT » Wed Mar 13, 2019 9:26 am

WhatAmIDoing wrote:
Wed Mar 13, 2019 9:06 am
Exhaust is your problem. If you have a cat efficiency code (I bet you do), unplug the downstream O2 sensor and the car will think the cat is fine, but you must disconnect the battery for 15 minutes to reset the ECU. Either get that exhaust buttoned up tight, or order a new one. Without seeing it, it's hard for me to say what would be better.
I don't want to confuse things, but are you sure you can just unplug the downstream O2 sensor?

From what I understand, people install spacers for them when they delete cats to make them less sensitive. This would prevent the ECU from throwing the inefficiency code.

I agree though, the exhaust has to be tight. That would be the very first step to solve this.


96' 850 sedan, base, auto, pewter/charcoal, 106k miles
99' S70, base, 5-speed manual, nautic blue/ tan, 209k miles
04' V70, auto, ash gold/ tan, 222k miles
05' V70, 5-speed manual, loaded, mistral green/ tan, 142k miles
79' Ford Capri S, Euro Spec 2.8 V6, T9 5-speed manual
58' Porsche Diesel Junior
13' Honda Odyssey :oops:

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