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Don & Michele · 10-03-2019, 10:23 AM

Short story, gas mileage went from between 7 & 8 MPG to 3 to 3 1/2 MPG lots or black smoke out the tail pipe obviously running rich. Scan gage shows no codes loop is closed and no engine light. Any guesses?

AKIQPilot · 10-03-2019, 11:28 AM

Year and chassis model would be helpful.

Depending on the year it Could be the fuel pressure regulator on the driver side fuel rail. Do you have a fuel pressure gauge?

Don & Michele · 10-03-2019, 01:36 PM

2004 WR20 30' Gulf Stream Supreme and I don't have a pressure gauge.

Soppy · 10-03-2019, 02:23 PM

Check the temperature sender for the ECM. It's most likely giving the ECM the incorrect engine temperature reading (too cold) .

FastGlassMan · 10-05-2019, 05:05 PM

Go buy one at any parts store, they are only like 20-30 bucks!

LETMGROW · 10-07-2019, 08:24 AM

You need to go to a repair shop with diagnostic capabilities and have your MH hooked up to a scan tool which can read data streams, not just a cheap code reader.
If the tech knows what they are doing they can scroll through all the sensor outputs and find the faulty one if a sensor is at fault. There are times when a sensor can read incorrectly but still be within a range where it won't trip the check engine light on.
I have used my own Snap-On scan tool which does not have the heavy duty truck software by programming in a 2002 Chevrolet Silverado 3500 with an 8.1 engine. I pinpointed a detonation sensor problem once and a bad throttle position sensor once by programming my scan tool like this.
Lynn

Don & Michele · 11-09-2019, 05:54 PM

2004 W22 8.1. Lowered tank found out I need a tool to remove the the fuel pump no screws just a twist connection. I tried every thing I could in trying to twist off no luck. All I can say is help.

rte154 · 11-09-2019, 06:15 PM

Have never dropped a tank on a motorhome but if you are talking about a 3 or 4 inch opening like are on some autos there should be some tabs sticking out on a locking ring. To loosen the lock ring take a hammer and a brass punch and take turns tapping on the tabs in the direction to loosen ring. Use judgement on how hard to hit without damaging any thing.

winniman · 11-09-2019, 06:22 PM

Shooting from the hip, but did you check the airbox and make sure no mice have set up shop in there. Probably not the problem, but it would choke the engine from getting proper air. I have seen it on other vehicles.

robertkathy · 11-09-2019, 06:28 PM

did you check the intake and the spark plugs that the 2 areas i would start at and since you got an 8.1 check the cat as well

gmtec16450yz · 11-09-2019, 07:15 PM

Quote:

Originally Posted by Don & Michele

Short story, gas mileage went from between 7 & 8 MPG to 3 to 3 1/2 MPG lots or black smoke out the tail pipe obviously running rich. Scan gage shows no codes loop is closed and no engine light. Any guesses?

Get any kind of scanner you can and look at the o2 sensor voltages. If it's truly running that rich, the o2's should be telling the ECM that it is. If it IS in closed loop with no light and no codes, but actually running super rich, there's not much else that can trick the ECM into thinking everything is ok than a dead o2 sensor. Make sure you look at the bank 2 sensor 2 readings too, that's the post cat sensor and it does also have control over mixtures.

The o2 voltages need to be switching between ~.1volt and .9volts. Check that and report back before doing anything else or throwing any parts at it.

gmtec16450yz · 11-09-2019, 07:17 PM

Quote:

Originally Posted by Don & Michele

2004 W22 8.1. Lowered tank found out I need a tool to remove the the fuel pump no screws just a twist connection. I tried every thing I could in trying to twist off no luck. All I can say is help.

Wait, why are you pulling the tank??????

Arch Hoagland · 11-09-2019, 07:54 PM

Quote:

Originally Posted by gmtec16450yz

Wait, why are you pulling the tank??????

Took the words out of my mouth!!

Have you cleaned the MAF? The MAF determines the Air to Fuel Mixture.

**Spdracr39** · 11-09-2019, 08:15 PM

Plugged air filter, Intake air sensor or Mass air flow sensor. If you don't know what your doing take it to a shop, that's what they are there for. Your fuel savings when fixed will pay for the service call and you will prevent any further engine/ catalytic converter damage.