Issues with mpg after walbro? Just noticed fuel system fault...help

[loganlewis]

Has anyone else installed a walbro 255 and lost mpg? I was getting like 18-19mpg after calc.vet tuning and now I'm going about 120 miles from full to half. I thought maybe it was tuning. Tried a stock tune but no change. Trims are -3 to 0. Afr on wideband shows 14.5-15.2 cruising and wide-open is 12.6-12.8 nothing has changed except a dramatic loss in mpg. My fuel status in the dashboard shows cl-fault. My rear o2 sensors are off the truck but they have been off for a long time an codes are disabled. Would that make it say fault? I wouldn't think so because all it does is tell the computer if that cat is on the vehicle... Any help is appreciated

[Mr. P.]

This is admittedly a non-authoritative answer - but I would expect to have to do the Calc.vet process again after a fuel pump change, the reason being that the rail pressure behavior will not be the same with the new pump. I am sure that the new pump gives better pressure at low RPM, hence the injectors are firing more fuel than they used to because now there is a higher head of pressure behind them. AFA mileage/economy, in my own truck tuning I've learned that the VE table is very unforgiving, being 2-3% off my MPG will tumble 1-1/2 MPG easily - the VE table has to be spot-on.

Mr. P.

[loganlewis]

Okay I guess I'll have to do it again. What is the cl- fault in the fuel system caused from?

[joecar]

CL-fault indicates that there may be a problem with the front O2 sensors...

can you pull:
- the Mode 5 data (O2 tests)
- the Mode 6 data (monitored systems tests)
if you have V2 then goto the option to record all diagnostics to .txt file and post it.

More info: CL-Fault

[Mr. P.]

Okay I guess I'll have to do it again. What is the cl- fault in the fuel system caused from?

Go to post #3 in this thread.

[loganlewis]

I have a v2

[loganlewis]

I don't know what that mode 5 and 6 are

[joecar]

I don't know what that mode 5 and 6 are

On the V2 keypad/LCD navigate down Scantool -> Diagnostics -> Read all diagnostics and allow it to record all PCM diagnostics and save to file.

test results Mode 5 (O2 tests) and Mode 6 (monitor tests) will be included in the saved file, these can be looked at to get some hints as to what may be going wrong.