Community Forums

hamfam · 04-18-2018, 10:06 PM

Hey Everyone,
My family and I own a 97 Ford Tioga Class C Motorhome with the 6.8 V10 gas engine. We recently went on a long trip of 2500 miles. During the trip a "service engine soon" light came on. I had the code scanned and it is error code P1151. Which is an issue with the 02 censor and/or a rich fuel mixture issue. The motorhome performed like normal the whole trip. It never lost power, ran rough, overheated, etc. I did notice a slight drop in MPG on the way back, but we we experienced some extremely windy conditions and I attributed it to that at the time. Some of the fixes I've researched are vacuum leaks, a dirty or faulty MAF sensor, 02 censor replacement, issues with the EGR valve, fuel injectors, etc. I'm just curious if anyone has had a similar experience with that error code and how you addressed it. The only difference I noticed was the drop in MPG. I don't want to spend any money that may not be necessary. Our unit has 68k miles on it. Any help is greatly appreciated. Thanks.

Bob Hyatt · 04-18-2018, 10:33 PM

I have seen this sort of condition caused by multiple things. (1) is a possible mass air flow problem that claims more air is going through the MAF than really is, triggering a richer mixture; (2) bad O2 sensor; (3) one or more bad plugs, which will dump raw fuel into the exhaust from the dead cylinder or cylinders, which will make the mixture appear rich; (4) dirty (REALLY dirty) air filter makes the intake side run in a deeper vacuum, which starves the engine for air and can even increase injector flow and with either or both of those, you run rich. Much less frequently the ECU itself or a connector has an issue. We spent a year working on an old 1992 Mustang 5.0 my son had. FINALLY tracked it to a connector between engine sensor package on the motor and leading to the CPU. Had some of the "green gunk" you see on electrical connectors that was messing with the voltage and data to/from the O2 sensor...

Good luck...

Really pisses me off when the computer claims a sensor is bad when it is really the computer itself that has a failed A/D converter or whatever and is itself the actual problem.

hamfam · 04-18-2018, 10:41 PM

Hey Bob, thanks for the quick response. That's kinda what I was afraid of. Having to track down a bunch of stuff. I really wish the error codes were more specific. I'll probably start with the least expensive/easiest items and work my way down the list. Did your son still drive the mustang the entire year while you were diagnosing the problem? Thanks again.

Patti Jean · 04-18-2018, 11:08 PM

Cheapest thing first is to clear the codes and see if it comes back Sometimes on a longer trip with changing conditions funky things can happen.

avfordguy · 04-18-2018, 11:22 PM

New motorcraft air filter, clean mass air sensor, sounds like a k&n was installed

hamfam · 04-18-2018, 11:31 PM

I did clear the code once already and it came back on within about 50 miles or so. I'm going to check/clean the MAF sensor.

THenne1713 · 04-19-2018, 12:12 AM

Next cheapest thing to check/ (I.E. RULE OUT) is VACUUM LINES... remove one line at a time, CLEAN outside w/ SIMPLE GREEN AND INSPECT closely for cracks, brittleness or heat damage; if good, reinstall and go to next section of hose. When I had trouble w/ my little Nissan EGR a few years ago, I finally found a 2-inch long piece of vacuum hose hidden by another component that had melted. I did mine in the parts store parking lot...

spyderRV · 04-19-2018, 12:45 AM

Donja just love computer controlled engines:

A code P1151 may mean that one or more of the following has happened:

Electrical:
Short to VPWR in the harness or HO2S
Water in the harness connector
Open/shorted HO2S circuit
Corrosion or poor mating terminals and wiring
Damaged HO2S
Damaged PCM
Fuel System:
Excessive fuel pressure
Leaking/contaminated fuel injectors
Leaking fuel pressure regulator
Low fuel pressure or running out of fuel
Vapor recovery system
Induction System:
Air leaks after the MAF
Vacuum Leaks
PCV system:
Improperly seated engine oil dipstick
EGR System:
Leaking gasket
Stuck EGR valve
Leaking diaphragm or EVR
Base Engine:
Oil overfill
Cam Timing
Cylinder compression
Exhaust leaks before or near the HO2S

avfordguy · 04-20-2018, 11:37 AM

Research on ford truck forums, looks as if the most common is, intake leak (hoses) or driver side O2 sensor. Inspect and clean O2 sensor connector, there have been reports of bosh O2 sensors that are lazy, if replacement is needed use motorcraft,Denso, or NGK

Arch Hoagland · 04-20-2018, 11:58 AM

Clean the MAF. Been there, done that.

hamfam · 04-20-2018, 01:57 PM

Hey Everyone, thanks for all the responses. I'm going to clean the MAF sensor, check for vacuum leaks, and probably install a new air filter. Clear the code and then take it for a drive. I'll update the status after that. Thanks again and have a great weekend!

Waiter21 · 04-20-2018, 02:53 PM

Look carefully at the large rubber air intake hoses, they develop little cracks and breaks.

THenne1713 · 08-31-2018, 09:29 AM

Re-reading today because it popped back up, and here we are 5-months later, any resolution? (But also, in rereading), thinking I would be keeping some brand of injector cleaner/ lube in the tank w/ fresh gas, as it just sounds like injectors sticking open intermittently or continuously... which is very likely with the age and vehicle history.

Quote:

Originally Posted by hamfam

Hey Everyone,
My family and I own a 97 Ford Tioga Class C Motorhome with the 6.8 V10 gas engine. We recently went on a long trip of 2500 miles. During the trip a "service engine soon" light came on. I had the code scanned and it is error code P1151. Which is an issue with the 02 censor and/or a rich fuel mixture issue. The motorhome performed like normal the whole trip. It never lost power, ran rough, overheated, etc. I did notice a slight drop in MPG on the way back, but we we experienced some extremely windy conditions and I attributed it to that at the time. Some of the fixes I've researched are vacuum leaks, a dirty or faulty MAF sensor, 02 censor replacement, issues with the EGR valve, fuel injectors, etc. I'm just curious if anyone has had a similar experience with that error code and how you addressed it. The only difference I noticed was the drop in MPG. I don't want to spend any money that may not be necessary. Our unit has 68k miles on it. Any help is greatly appreciated. Thanks.

hamfam · 08-31-2018, 12:12 PM

Hello THenne1713, here's the latest update. So far, I have replaced the OE air filter with the same. I also cleaned the MAF sensor, checked fuel pressure, egr valve, and also checked hoses for vacuum leaks, etc. After resetting the code, the light came back on. The next thing I'm looking at, based on direction by Ford is to inspect/replace the O2 sensors. I believe mine has two upstream and two downstream. Thanks for your suggestions as well.