Bad fuel consumption and high emissions

[Silverti]

Hi guys,

Sorry about the long post, but i'm a bit stumped.

About 2 weeks ago i noticed that i wasn't getting the usual 300 miles or so to a tank. It had dropped right down to 220. This gives me around 23-25 mpg instead of the usual 30-35.

Thought it may have been a fual leak, so checked the tank and pipes but all was sound.

Went and had the codes read and it said the pre-cat o2 was knackered. Duly replaced sensor and took on a 150 mile run, worked out mpg and still down at 23. Back to garage, no codes present. Stuck her on an emissions test and the readings were sky high.

CO was 8% (max allowed is 0.2%)
hydrocarbons were 1000 (max is 200)
lambda was around 0.8 (should be 0.9 - 1.0)

The engine is running extremely rich, the hydrocarbons reading shows that there is an excess of unburnt fuel coming through the exhaust. The Cat is most likely dead from the excessive rich running but i can't see it making the emissions go as high as they are, and i'm reluctant to change it until i find the cause of the problem, otherwise i might kill a new cat.

Driving round today, pretty cold outside and the engine wasn't getting right upto temperature until i was in traffic so i think the thermostat needs changing but the emissions seem so high that this couldn't be the only problem.

Or i guess it could be a mixture of the thermostat, lambda and cat all at the same time...

Any ideas?

Cheers
Rob

[Silverti]

Forgot to mention its a 99 compact with the m44 lump.

Rob

[familytruckster]

Could be a fuel pressure regulator, a bad injector, or a few other things. Best way to figure it out is toss a scanner on it and see what it says.

[Silverti]

Scanners been on it, and only showed the lambda sensor. After i changed it, the only code on there was for a misfire in cylinder 3, but i think thats related to the cold start issues as is was throwing misfire codes a year ago whan the fuel economy was fine.

Thats why i'm stuck

[bazar01]

huh, misfire in cylinders meant you are not getting spark or spark is getting weak not burning the air/fuel mix completely.

check your spark plug holes, it could be filled up with engine oil and grounding the high voltage spark outside the spark plugs.

ask me how I knew.

[Silverti]

Sounds like a bad experience.

Had the plugs and leads out earlier to take a look at them. The plug holes were clean and dry. Although i did order a new set of both just to eliminate them.

[familytruckster]

Coil itself could be bad.

[Silverti]

Yeah, i've found a manual saying how to check the resistence of the coil pack so when i'm changing the leads tomorrow going to put the multimeter on it and see what it says.

After i've changed the plugs, leads and coolant temp sensor tomorrow will get the codes read and emissions tested again to see if anythings changed. Think i'll also order a stat as well and change that.

[Silverti]

Well i changed the plugs, leads, coolant temp sensor and stat yesterday and this morning took her down to the garage and shes fixed All emissions are back to normal.

I'm guessing it was most likely the coolant sensor but either way its fixed now.

Cheers for all the help.

Rob