pat944

I've recently developed some fuel usage problems. After filling it up today my usage worked out to be about 16mpg, this is on a RoW 1982 N/A. I started to get some issues wiht fueling after changing spark plugs but I am unsure whether it was related or a coincidence, see this thread here . I feel I shouldn't be getting this kind of fuel usage, especially as I have been making attempts to restrict the use of my right foot in order to try and track this problem down.
As well as the probs from the other thread I get a strong smell of fuel when you get heavy on the accelerator, I have noticed thought, that the smell doesn't seem to be as strong on colder and/or wetter days. Is the air or coolant temperature sensor that is used for enrichment when the car is cold likely to make this much difference to fuel economy if it is dead or faulty?

If not what other things should I be looking at chasing to fix this problem before fuel bills kill me, .

hosrom_951

How are your vacuum lines for the fuel vapor canister system?

I do not know of earlier cars have this, but there is a thermoswitch located under the intake with two pongs in it that could be your problem for fuel smell.

Did you do a full tune up? (rotor/cap, fuel filter etc)

Double check fuel lines to make certain that fuel isn't leaking ANYWHERE!

pat944

Nope, no full tune up yet, doing it stage by stage as the funds are available. Pretty sure that fuel is not leaking, it's not a raw fuel smell, it's smells like and engine that is running rich to all buggery, and is only present after spirited driving.

What kind of check do i need to do to see if the thermoswitch under the intake you mentioned is in working order??

hosrom_951

Here is a pic, look at number 25 or to where the arrow is pointing:



Also check your Fuel Pressure Regulator/Damper along with two two vacuum units (numbers 21 and 13) connected to that thermovalve (shown in pic).

Luis de Prat

pat944, the fuel smell when pressing the accelerator is indicative of a leaking fuel hose or leaking fuel injectors. Be very careful driving this car, because it's prone to have an engine fire.

Check the fuel hoses that go to the fuel pressure regulator and damper. They have metal fittings and may be leaking. Look for a strong fuel smell in the fuel rail area. This is not normal, but would indicate that fuel is leaking.

Report back after checking this.

pat944

I'll be checking those hoses then, they have recently been off and on after running the car our of petrol and having the road service guys trying to figure out why it wouldn't start, so I'll check that they are all good.

pat944

No fuel leaks or anything, the fuel is definatley being burnt, smells and runs like a car that is running rich, it has a slight hunt at idle and last time i checked the plugs they were as black and sooty as i've ever seen a set.

pat944

I'm want to see if the thermostat that tells to DME the car is engine is cold is operating properly or not, this is the one under the intake as was suggested is it not?

How do I check to see if it is working or not?

Luis de Prat

Are you getting any soot or black smoke from the tail pipe? This would indicate a bad fuel pressure regulator and cause high fuel consumption.

Does your car have a catalytic converter? In that case, have you checked the Oxygen Sensor?

Have you tried adjusting the idle with the adjustment screw in the throttle body?

Not sure about the Idle Control Valve. I hear it's a standard problem on these cars that makes the idle dip on and off, but it shouldn't affect the mileage as badly as in your case.

pat944

Everytime I wash the car the back end of it is fairly covered in black soot, I'll try and fit the fuel pressure guage I've got to the end of the rail and get a reading, what kind of pressure should I be looking at, around the 40-50 psi mark?

Nope, no oxygen sensor, so that is one thing I don't have to worry about checking/replacing thankfully.

I wasn't thinking the Idle Control Valve, I thought they were only on the 85.5 and later cars anyhow. I thought there was an engine temp sensor that put the DME into an enrichment/warmup mode for when the car was started from cold, and was thinking that could be the problem.

Luis de Prat

Yes, that's the sensor that evolved into the ICV. Whatever it's called, I believe it causes erratic dips in idle but shouldn't cause the excess fuel consumption you're getting.

As I understand it, a failing FPR will get stuck in "open mode," and essentially flood the system with fuel, hence the black soot. I'm not sure on the accurate fuel reading, but a search will probably bring it up.

FYI, the part number for the Fuel Pressure Regulator on your car is: 944.110.198.01.
In case you want to do the Fuel Damper also, it's 944.110.201.03

Waterguy

The manual suggests checking the following items in cases of high fuel consumption:

1. Ignition system
2. Air flow meter
3. Fuel pressure
4. Engine temperature sensor
5. Throttle position switch

To test the temperature sensor, unplug the 35 pin connector plug on your DME. Measure the resistance between pin 13 on the DME plug and ground. Specification is 1.45 to 3.3 k-ohms between 15 C and 30 C, 280 to 360 ohms at operating temp (80 C.) If there is a break (infinite resistance) your car will run rich. If you have a bad value, disconnect the sensor and repeat the test on it to determine if the break is in the sensor or wiring/connectors.

Fuel pressure specs are 29 psi at idle and 33 to 39 psi at static (vacuum line removed from regulator, engine idling.)

Good Luck!

pat944

The problem has been found, I pulled the vacumn lines off the regulator and dampene, the fitting on the dampener was all wet and it smelt like fuel, so I've decided to order both of the parts, I figure they're both original and the regulator diagphram is probably heading in the same direction. I'll get them on asap and let you all know if it's fixed.

hosrom_951

Replace both FPD and FPR; Drive the car for a few mins, pull out the oil dipstick and wipe it on your fingers. If you SHOULD NOT be getting any gas smell, which indicated the problem is solved