Born Free Leap'n Lions RV Club

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It is currently Sat Aug 24, 2019 10:28 am

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PostPosted: Fri Aug 09, 2019 6:05 pm 
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Joined: Wed Apr 24, 2013 6:23 pm
Posts: 56
Location: Wandering the West, now in California
We've had our 1999 24RB for 5 years. In the beginning we were getting between 10.2-9.5 over about 50,000 miles. After a plug change and a few miles (don't know how many) I replaced all the coils with cheapies. MPG has dropped to 7.5 or so, and eventually we realized we needed a new engine. ($9000 from Ford).

Now we get no OBD errors, it purrs like a kitten, but STILL get 7.5 mpg (just one check, but mostly flat highway in CA). We keep it at 58-62 MPH. This mpg will probably increase somewhat with time, but I'm skeptical of an additional 2.5 mpg. Any ideas?

The motor came with plugs, I had bought new Motorcraft coils in my troubleshooting before getting the new engine. Could the catalytic converter be partially plugged?

What mpg do most people get (without a toad)? We love our '99, but the drop in mileage is concerning.

Thanks in advance!


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PostPosted: Fri Aug 09, 2019 6:46 pm 
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Joined: Mon Aug 15, 2005 8:05 pm
Posts: 1975
Location: Spencer, IA
I have a 26' RSB on a 2000 E450 V10 chassis now with 114,000 miles on it. It used to average 8.5 mpg pulling a 3400 lb toad but my mileage has slowly decreased to around 7.8 mpg. At 98,000 miles I had the plugs and coils replaced with Ford Motorcraft parts but that never improved the mileage. I also have cleaned the MAF mass airflow sensor which also has not helped. My next step will probably be to replace the Oxygen sensors but my Ford dealer does not think that will help either since I have not been setting any O2 codes. I am puzzled too.

Your 24'RB is lighter than mine and you didn't say if you are pulling a toad. I assume you still have your original O2 sensors?

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Bill Hemme - Spencer, Iowa
E-mail: whemme@earthlink.net
2002 Born Free (Ford E-450 V10) 26' RSB
2016 VW Golf GTI - toad


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PostPosted: Sat Aug 10, 2019 12:16 pm 
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Joined: Wed Apr 24, 2013 6:23 pm
Posts: 56
Location: Wandering the West, now in California
I honestly don't know about the Oxygen sensor. I can find out from the dealer when he put in the rebuilt engine if the Oxygen sensor was replaced. I believe it's part of the exhaust system, which would mean no. I have a bluetooth OBD reader which has shown no errors. I don't pull a toad, and the vehicle is essentially identical to the configuration 80,000 miles ago.


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PostPosted: Sat Aug 10, 2019 12:25 pm 
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Joined: Mon Aug 15, 2005 8:05 pm
Posts: 1975
Location: Spencer, IA
Well I would agree that your 24' RB getting only 7.5 mpg not pulling a toad is poor mileage. Actually, your exhaust system I believe has 3 oxygen sensors, one in each exhaust manifold output for both the left and right 5 cylinders and also one in the output of your catalytic converter.

Too bad you didn't first try replacing the O2 sensors and catalytic converter before spending $9,000 on a replacement engine.

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Bill Hemme - Spencer, Iowa
E-mail: whemme@earthlink.net
2002 Born Free (Ford E-450 V10) 26' RSB
2016 VW Golf GTI - toad


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PostPosted: Sat Aug 10, 2019 3:32 pm 
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Joined: Wed Apr 24, 2013 6:23 pm
Posts: 56
Location: Wandering the West, now in California
The problem with the old engine was repeated misfires and oil-fouled plugs. Changing to new Motorcraft coils didn't resolve it. When cylinder #4 still misfired with the new coil, I tried to change the spark plug but couldn't get the socket on the plug. The mechanic scoped a piece of plastic blocking the plug. After removing the plastic and looking at the plug, it was badly oil-fouled. He ran a pressure test on cylinder #4 and it read 70 psi. Rather than doing just the head, I opted to replace the engine. We live in the vehicle and travel without a toad, so dependability was paramount. I also had him change the exhaust studs on the new engine to stainless steel. (I had one broken exhaust stud, but have read that it was a common issue.

Do you know if the multiple misfires could cause serious backpressure from the catalytic converter? I've never gotten an oxygen sensor error on the OBD.


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PostPosted: Sat Aug 10, 2019 4:19 pm 
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Joined: Mon Aug 15, 2005 8:05 pm
Posts: 1975
Location: Spencer, IA
Well if you #4 cylinder was using enough oil to cause oil fouling of that plug, evidently that cylinder had broken piston ring(s) or other serious problems. Now I understand why you changed engines. I have never gotten an O2 sensor defect code. However I have received conflicting advice on whether I should replace my O2 sensors to see if it would improve my loss of gas mileage. My local Ford dealer says that if my O2 sensors are bad, they will set a code. However, others have told me that as the O2 sensors slowly deteriorate, they may cause loss of fuel mileage before they get bad enough to set a defect code. So I guess I may try new O2 sensors to see what happens.

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Bill Hemme - Spencer, Iowa
E-mail: whemme@earthlink.net
2002 Born Free (Ford E-450 V10) 26' RSB
2016 VW Golf GTI - toad


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PostPosted: Sat Aug 10, 2019 7:13 pm 
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Joined: Wed Apr 24, 2013 6:23 pm
Posts: 56
Location: Wandering the West, now in California
Thanks, Bill!
My next approach is fuel injector cleaner.


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PostPosted: Sat Aug 10, 2019 7:33 pm 
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Joined: Mon Aug 15, 2005 8:05 pm
Posts: 1975
Location: Spencer, IA
I would have thought your replacement engine would have come with new injectors - but maybe not?

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Bill Hemme - Spencer, Iowa
E-mail: whemme@earthlink.net
2002 Born Free (Ford E-450 V10) 26' RSB
2016 VW Golf GTI - toad


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PostPosted: Sat Aug 10, 2019 11:55 pm 
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Joined: Wed Apr 24, 2013 6:23 pm
Posts: 56
Location: Wandering the West, now in California
i'll ask, but don't think so.


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