'96 850 Turbo running rich, poor gas mileage

farupp · Post by **farupp** » 27 Dec 2007, 07:14

Our 96' 850 Turbo occasionally (50% of the time) runs rich (black smoke from the exhaust), especially when we first start it in the morning. According to our added VDO vacuum/boost gauge, we have good vacuum (15 to 20) and turbo pressure (10 to 12 lbs). The engine runs great.

Our fuel mileage is less than I expected, though; 15 mpg around town with conservative driving. We don't do any highway driving. So, we are looking for the possible cause(s) of why it runs rich and the poor fuel mileage.

Air filter, plugs, points, rotor and distributor cap have been replaced along with several vacuum lines. Throttle body and MAF sensor have been cleaned as well. Also, the thermostat and coolant temperature sensor are new. No codes from the ECU. When I checked the new plugs (Official Volvo Turbo plugs), they were all equally sooty but we do not have any misfires.

My son and I pulled the intercooler/air intake hose off of the top of the intercooler and noticed that there was a little oil around interior fins and on the inside of the hose that runs to the throttle body. A little means just barely visible on the edge of the fins and a few drops inside the hose.

bobsnow100 · Post by **bobsnow100** » 27 Dec 2007, 10:23

Have you checked for any stored codes?
That's the first thing I would do. The oxygen sensor "reads your exhaust" and the ecm regulates engine componets based on those readings for it run properly so it could be many different things causing it

farupp · Post by **farupp** » 27 Dec 2007, 11:48

We have checked for codes and there aren't any, recent or stored. The check engine light does not come on.
This morning I opened the hood before I started the car, to pull off the vacuum line to the boost gauge. We started the car and it ran rich. I pulled off the vacuum line, then plugged it back in, and the engine ran fine.

However, after I turned the engine off I noticed that the Idle Air Control Valve continued to run for about 30 seconds after the engine was shut off, and I don't think this is normal. I have an extra one from a parts car so I am going to replace that, and check its hoses, at the same time I check the lower intercooler hose.

I let you know if anything changes.

Thanks.

bobsnow100 · Post by **bobsnow100** » 27 Dec 2007, 13:26

I'd check your fuel pressure regulator also maybe a leaky fuel injector. It may be leaking into the intake for the rich condition

farupp · Post by **farupp** » 28 Dec 2007, 07:28

Thanks, Bob.

Fuel pressure and injectors are next on my list also. However, all of the sparkplugs are equally sooty, so I do not think it is just a single injector.

The lower intercooler hose and the bottom of the intercooler were fine (no oil or clogging) as was the PVC valve. Haven't switched the IAC valve as yet.

What I keep wondering is why when I disconnect a vacuum line at the vacuum tree, letting additional air into the intake manifold, the rich condition, at least at idle, seems to go away. The factory boost gauge on the dash did not work when I bought the car and we found the gauge vacuum line was disconneted. It may have been on purpose.

Thanks for the response.

gradguy001 · Post by **gradguy001** » 31 Dec 2007, 17:01

I have a similar problem with an 850 GLT non turbo. Rich gas smell and 15 mpg. I have had three mechanics look at it along with numerous hours on my part. The MAF was replaced, O2 sensor tested, etc. I still have not figured it out. Tomorrow morning I am going to check a valve in front of the fuel line that I read about on this site to see if it is the problem (apparently leaks due to vibration and evaporates quickly as it trickles down onto the blower). So far everything has checked out fine from fuel regulation to vacuum. If this valve is not the cause, I am going to try and throw in a new ECU as a last resort... love the car but can't afford 15 mpg. Please let me know if you have any luck.

farupp · Post by **farupp** » 31 Dec 2007, 21:25

Thanks for your input GG001. What year is your GLT?

I'll let you know if I have any luck, too. Changing the IAC made no difference.

The next things I am going to check are the fuel pressure, the fuel pressure regulator and the O2 sensors. And, drive it with the vacuum line disconnected to see if instantaneous fuel mileage is higher on an identical route compared to having it connected.

Finally, I'm also going to see if there are any old codes stored that the parts stores maybe haven't found. Possibly there will be a lead there.

14 to 15 mpg average doesn't make me happy. My Suburban does better than that!

gradguy001 · Post by **gradguy001** » 01 Jan 2008, 06:21

The GLT is a 96.

Happy New Year

farupp · Post by **farupp** » 01 Jan 2008, 13:26

I just noticed that MadeInJapan, in a post to lynetteyross on Dec. 31 about her '96 850 GLT, said: "About mileage- these cars differ considerably depending on how well tuned up they are and what kind of driving you do. Don't expect much more than 17 in the city but you could get up to the high 20's and even 30 on the highway if things are right with the car."

So maybe the 15 mpg is not out of line for around town driving. What are other getting as an average mpg for 850 turbos and non-turbos, especially around town?

Maybe I should do a poll.

Thanks for any input.

Post by **Ozark Lee** » 01 Jan 2008, 14:07

I have 2 N/A versions, a '94 with a stick and a '96 with an auto. I don't know about the '96 since my son drives it and he has never done a full tank mileage test. I think he just dumps in $10.00 worth of gas every couple of days.

Mine (the stick) gets low 20s in the city and 30 to 32 on the highway at 75 mph.

You are right, my Suburban gets around 16 mpg. Filling the 42 gallon tank is still a killer.

...Lee