Poor Gas Mileage and Rich Exhaust Smell

[sjwcougs]

I want to preface post with the fact that the car really seems to run very well. Starts up EVERY time and runs very strong. Has a slight puffing backfire on deceleration. TPS sensor out of wack? With that in mind...

The problem:

Ok here it is. 1981 Spider 2000 Fuel Injected. Was only getting about 20 miles per gallon when I put her away last fall . Doesn't that seem low? Exaust smells rich. If I have the car idling long and it's not outside of my garage (door open, obviously) my clothes smell like exhaust fumes.

Could this exhaust smell be a hint as to why I'm getting such poor gas mileage? What are common sensors or adjustments on this Bosch system that could contribute to this?

I am almost certain that the auxillary air regulator is not working. The mechanic that changed the timing belt and did some brake work told me not to worry about it as it really wont effect driveability. I only notice an issue after the engine starts and warms. Idle RPMs fall, but NEVER stalls out. After it warms it is fine. I always warm it up anyways so it's not a big deal.

I really need a good mechanic in the seattle area that is familiar with fine tuning these cars if I can't figure it out myself. I bought a new multimeter to go through all the sensors, but havne't got around to that yet.


Steven

[So Cal Mark]

it sounds like the aux air regulator is working from your description of lower idle speed as the engine warms up. To really diagnose the system you need a fuel pressure gauge and multimeter. The most common failures are the temp sensor (major influence on fuel mixture) and the pressure regulator (leaking fuel into the vacuum hose)

[sjwcougs]

If the temp sensor isn't working wouldn't the car just not run. Once the car stalled our while driving and I popped the hood to discover that the sensor wire popped off. It starts and runs fine...the idle is fine at first, but then drops VERY low and the comes up, goes low again, and then when it warms it is fine. If the Aux. Air gauge is working the idle should be high initially consistently and then drop back down. Simple test with Multimeter should verify this, or through it in a freezer I guess and it should open? Can the temp sensor at the head actual be working, but malfunctioning or is it more all or nothing?

[racydave]

Most EFI computers will substitute a value for a sensor to give you a "limp-home" mode when a problem occurs.

[So Cal Mark]

the Fiat ecm doesn't have a limp in mode. The temp sensor can be out of range at any one stage. You have to test it from cold to hot, measuring resistance constantly. With fluctuating idle speed, it sounds like an air leak. Since the Fiat system primarily works on air flow, any air leaks will drive the system crazy. Start with the air filter, make sure it's not restricted or plugged. Make sure the AFM flap moves freely. If it drags or squeaks as you move it then you'll have to repair or replace it. Check the integrity of the intake boot and all related hoses on the intake system. Also make sure the throttle plate is adjusted properly. It's common to find that a PO attempted to set the idle speed by adjust the throttle stop screw

[sjwcougs]

The intake boot is brand new. The air filter looks beautiful and clean. I sprayed a bunch of throttle body cleaner, in the TB last fall. I want to reiterate the car really does idle fine after the first 3 minutes and warms up a bit. Does the aux air sensor really matter that much after the car warms a bit. How do you check the air flow meter flap?

The temp sensor definitely impacts driving as I explained the car died once when the sensor wire came disconnected. You are saying this temp sensor can actually be working, but not working correctly and therefore causing some fuel efficiency problems?

[So Cal Mark]

yes. the temp sensor can send the wrong values at any point in it's range. It may be within range through most of the temperature arc, but out of range at another point. If you look at the FI troubleshooting charts, resistance values are given for the entire temperature range of the sensor. The aux air valve should be closed once the engine gets to temp. You should also check the thermo time switch and cold start injector to make sure they operate for the proper length of time and that the injector doesn't leak after it's shut off

[gigi]

Hi- I had this same problem-
My husband kept saying it was the fuel-mix since when his vette did it, he
had to redo his carb. My spider is fuel injected so that couldn't be the
problem. Took it to my New-Awesome-Best-Ever mechanic, Coop, and he
correctly diagnosed Gigi's illness quickly: the coolant sensor. The part was
inexpensive and he had it replaced quickly. The last tank of fuel in her
prior to the repair got roughly 10 or 12 mpg. The tank after the repair
got roughly 18 or 20. For her, that is par. Rarely do I ever see over 22 mpg
even with an additive. Frankly, this repair was, by far, the most painless
of all.
On the way home from the shop, the stick was a bit 'spongy'. By
the time I got to the driveway, it was spinning in a circle and couldn't find
any gear or neutral. Turns out the transmission crapped out...but that is
a whole other story...hahaha!

[So Cal Mark]

glad to hear she's running well, but your tranny problem sounds more like a shifter problem

[gigi]

Yes, a shifter problem, indeed.
According to Coop, and I quote,
" A Bolt "
Yeah, 'a bolt' kept us off the road for
the last month or so. A bolt.
Thank goodness he had one of these
'bolts' in the bottom of his toolbox.
Ya just never know where those parts
might show up, but soooo glad it did!

[Ligotino1]

Hello,
I have the same problem that you described. Did the solution work? I replaced the temp. sensor a couple of years ago because it didn't run (as you described) and the car ran but was getting horrible values for MPG. This car has been getting 30 MPG for me since I purchased it in 1992. Recently it has been down to 17 MPG

[rlux4]

Have you replaced your oxygen sensor? If the ECU gets a signal that indicates poor combustion it will try to compensate and that may be the problem.
It's very easy to do, and if you don't know when it was done last, it should be done now anyway.
Ron

[pope]

Yes, a shifter problem, indeed.
According to Coop, and I quote,
" A Bolt "
Yeah, 'a bolt' kept us off the road for
the last month or so. A bolt.

I could be wrong, but I think Coop should have said "A Nut" not a bolt.

[rlux4]

"I could be wrong, but I think Coop should have said "A Nut" not a bolt."
Pope? Be wrong?
Nah. Ain't happening.
Ron

[Ligotino1]

I have replaced the O2 sensor. Actually I have replaced all the sensors but the two in the head. When I start it up it spews fuel from the exhaust. I thought that it might be the pressure regulator valve but I checked it while it was running and it worked. I made a mistake when I was trying to stop a backfire in the car a couple of years ago, I changed the setting on the air intake (big mistake) and I thought it might be the problem but now I don't think so. The car runs the best it has ever run (minus the poor MPG). Recently the ex gas sensor light lit up (this is the first I've ever seen this light on). I assumed it was because the car is running rich. I have been unable to find anything about the gas sensor and this problem except this post.

Please help!
Thank you