Using too much Fuel - 5 mpg - 930

[lomotpk]

It's obvious that there is something wrong someplace, I'm getting about 5 mpg, and while I like to think of my self as some heroic hot-foot the truth is that there's quite a bit of highway cruising involved.

So, Oh Great Pelicans... where should I start looking for things to adjust, replace, etc.

The car is a modded 84 Turbo.

[Emission]

My '86 gas mileage:

7-8 MPG on the track.
10-12 MPG in the city.
15-17 MPG on the highway

Though it is better to run rich than lean, you are DRINKING fuel. What are your mods?

[KobaltBlau]

Tell us what mods. one of them could certainly be the problem.

[RarlyL8]

More importantly - what is your CO% and A/F ratio?

I get 19.5mpg @75mph with 2.6% CO and 13-14:1 A/F with mods.

[greglepore]

Hold on a minute-go run your odo against a calibrated mile. It might well be a partial odo failure-my 3.2 did this, thought I was getting like 8 mpg until I checked the odo...

[dickster]

i would start by pulling a spark plug or two. check their condition - they should be sooty black if you're running too rich.

[lomotpk]

The Odo is fine as I run a consistant 10 miles to work each day, thus a round trip was using 4 gallons.

Mods: K&N, K-27,Bigger intercooler, twin-plugs, crankfire ignition, an un known but non-stock cam

What test equipment do I need to check co2 and A/f?

suggestions so far have run to:

- Faulty Warm Up Regulator
- Broken Fuel distributor

[dean]

I would measure your fuel pressures. That will tell you a lot. Also your commute is too short. The car just gets warmed up in 10 miles.
Dean

[dickster]

What test equipment do I need to check co2 and A/f?

a plug spanner.

[DG624]

"Mods: K&N, K-27,Bigger intercooler, twin-plugs, crankfire ignition, an un known but non-stock cam"

I thought that a twin plug engine would get better mileage (burn more efficiently). Does the turbo affect mileage?

I usually get 17/30 with no mods except synthetic oil and K&N.

[RarlyL8]

You need a CIS fuel pressure gage, A/F gage w/O2 sensor, and a Gunson gas tester for %CO.

Many things can cause a rich condition. These tools will show you changes when adjustments are made to suspected culprits.

[Amac]

At 5 mpg I'd say you have some real issues.
My cars are 600 & 800 hp and they both
get around 10mpg with normal driving.
CIS has to be tweeked to handel the mod's, as
a rule the run fat low in so they won't lean out
at high RPM's. Sounds like your tuner has it way
too fat. If you not fouling plugs or loading up at
low RPM's, you may be getting better MPG than
you think. If the inside of your exhaust is sutty
black have the fuel adjusted.
When it comes to keeping high HP engins together:
" Fat is safe"
" Lean is dangerous"

[ZCAT3]

I have nothing new to offer other than that my 3.4 twin plug CIS 930 gets about 20 MPG highway, and maybe 15 around town. At the track who knows - maybe 5. My car runs pretty rich at idle, maybe 3% and the inside of the tail pipe is pretty sooty. I cannot imagine that the car would not be choking on that much fuel if it is a rich condition causing this mileage. Have you noticed any bogging of the engine when you give it gas while cruising?

Are you on full boost all the way to work (that would be a fun commute)? If so, that would explain the mileage.

[lomotpk]

Thank you for all of your comments. And other people's MPG figures are helpful for understanding what 'normal' I should be experiencing.

Are there any suggestions for where to look, Or a diagnosis proceedure to follow?

Regards,

Lomotpk

[temo79]

Maybe wheel your wheel bearings are shot. Does the car roll freely?

[Emission]

Originally posted by temo79
Maybe wheel your wheel bearings are shot. Does the car roll freely?

If the wheels were dragging, you'd see really high tire wear rates (as if the brakes were lightly applied the whole time). I doubt it, but not a bad suggestion.

[RarlyL8]

You can start with all the components that exist on your car that would use excess fuel without seeing a leak. Examples would be the cold start injector, all 6 fuel injectors, the WUR, and the fuel head itself. Knowing the fuel pressure will isolate fuel head and WUR leaking, bad diaphagm, or being out of adjustment. Physical examination of the individual fuel injector spray patterns will shed light on their health.
Knowing the A/F ratio throughout the RPM range will also point twards the culprit. CO% is basically a static reading at or around idle speed but it is an important setting because the range is loosely based on that figure.
How much do you understand about the function of CIS? No need to tell you things you already know.
If you have no diagnostic tools all you can do is physically check the components. The fuel head and WUR have a great deal to do with fuel mileage. It would be difficult to check them without at least a pressure gage.
One thing that you can start with - does your car "hunt" at idle? By this I mean does it occillate between 500 and 1500RPMs in a rythmic manner? If so you are adjusted too rich. If not the problem may be component related.

[lomotpk]

Rarly8, Now that's what I'm talking about.

The idle is steady as a rock at about 1000 when its cold and then 900 when its warmed up.

I just bought a CIS pressure tester which should be arriving next week and then I'll do the whole WUR cold/hot pressure tests.

I would assume that the cold start injector is related to the WUR, but is it possible that it's injecting at full strength all the time, even with a good WUR?

What would be the proceedure for checking out the fuel head, or is this something that will be covered in the CIS pressure tester kit?

Thank you all, 10 MPG or BUST!

Lomotpk

[lomotpk]

Update - While waiting on the CIS tester to arrive I pulled all of the plugs and ran a compression test.

Each plug was covered with a Dry black crust. Filed it off of each plug and replaced.

Compression was even all around: 110-120 psi on each cylinder after three tests per cylinder.

[Jim Smolka]

lomotpk,

10 miles??? You are not driving your car enough... Please sent it to NC ASAP where it can be driven each weekend on the twisty mountain roads we have here

It is possible to remove one injector while the Fuel Pump(s) is/are running. You should see small stream of gas.

Also, it may be that the WUR keeps adding the additional fuel into the system. The extra fuel could be detected in the oil.