Helping your MPG

[Bleyseng]

How does the exhaust smell? rich?

[Amskeptic]

Russell, I look forward to your spark plug color report, and your brakes are not slightly dragging and your tire pressures are above 33/40, yaah?
Colin

[RussellK]

Checked a few things this morning. Tire Pressure is OK. Odometer is a tenth pf a mile per mile off when checked against a GPS. Not enough to impact MPG. Inspection of tailpipe reveals dry black sootiness. Will pull plugs and check vacuum next.

[drober23]

A tenth of a mile per mile would impact your MPG by 10%

My odometer does the same thing. If the Speedometer says 70 MPH, a GPS will say 68 MPH. But if I drive 200 miles by the highway mile markers, my odometer will say I went 180 miles. I now factor that in when I figure MPG.

Hmmm...

Good luck with the search for answers!

[RussellK]

A tenth of a mile per mile would impact your MPG by 10%

My odometer does the same thing. If the Speedometer says 70 MPH, a GPS will say 68 MPH. But if I drive 200 miles by the highway mile markers, my odometer will say I went 180 miles. I now factor that in when I figure MPG.

Hmmm...

Good luck with the search for answers!

Thanks. What I meant to say and see that I didn't is that the 10% isn't enough to get my mileage to the level it should be at.

[Bleyseng]

Checked a few things this morning. Tire Pressure is OK. Odometer is a tenth pf a mile per mile off when checked against a GPS. Not enough to impact MPG. Inspection of tailpipe reveals dry black sootiness. Will pull plugs and check vacuum next.

"Dry black sootiness" means you are running really rich and your mileage shows it. Have you checked the CHT or installed a known good one? Checked the Cold start valve for leaks? I'd just bypass it for now.

[RussellK]

Checked for vacuum using the starter fluid test. No vacuum leaks but at the Cold Start Valve a shot of starter fluid would kill the engine. I put in a new gasket and tried again with the same result. Not sure how that fluid is getting in. I noticed while the engine was running the large hose that Ts off of the hose between the air distributor and brake booster and runs to the decel valve was collapsing. Enough to choke off anything running to the decel valve. I replaced that hose with a stronger hose. Pulled the Number 4 spark plug and as I suspected it was sooty black. I'm definitely running rich for some reason. I'll pull, clean and gap the other plugs and lean up my mixture a little. Also check that cold start valve for leaking although its only about a year old. I have a CHT gauge but its a VDO mostly good for show and tell. Its attached to the #3 and never gets above 250 even on a hot day.

[Bleyseng]

Do you have a Ohm meter? pull the Temp2 sensor and check the resistance! I bet that is the problem as they start to fail and the mix goes rich...total fail and you can't start the engine as fuel is dripping out of the exhaust.

[DjEep]

Fuel pressure? If the pressure regulator gets plugged, the high pressure can severely richen the mixture while the electronic functions in the FI system are all singing in harmony.

Also, the cold start valve always seem to leak vacuum a bit, I think it's between the metal and plastic of the body. But a shot of ether there actually killing it definitely sounds like things are already very rich.

[bretski]

Do you have a Ohm meter? pull the Temp2 sensor and check the resistance!

+1

Where's RandyInMaine when we need him?!?!?!?

[RussellK]

I have an Ohm meter and will check that tonight. I'll check that pressure regulator too. I leaned up the mix by 3 turns CCW on the CO screw last night and took it out for a spin. The performance was fine.

[bretski]

Do you have a spare TSII, Russ? It's a bit of a PITA to test it properly (getting ambient to 68*F, avoiding touching it with your fingers, etc). This is an FI part that I don't have a problem replacing as a maintenance item if you've owned your bus a long time and have not replaced it previously.

edited to add: The TSII is a part that should be in your "on-bus" repair kit, as a fuel injected pilot.

[RussellK]

I checked the Thermotime switch and it shuts off after 5 seconds when its 75 degrees out so I'm good on that. I checked the Ohms on the TSII and it read 2600 resistance so I think thats in the range. I need to get a pressure guage and I'll check out the pressure regulator then. Thanks for all the suggestions and help. The exhaust smelled a lot better after I adjusted the CO last night. Still I need to know why the sudden change.

[RussellK]

With everything checking out OK and simply readjusting the mixture I'm was at a nice 17 mpg on last weekend's trip. I must have had a real brainfart and adjusted the wrong way the last time I did an adjustment. Its all I can figure. I still need to get this tewaked a bit more.

[Randy in Maine]

More important that what number you get for the TSII is that the resistance changes (downward) as the engine temperature changes (upward).

And bretski, Randy has been busy working in his new garage lately (plus he recently discovered his siatic nerve). Woodshop dust collection system in now in and most of the shelving is up.