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ARFFMAN · 09-14-2014, 03:35 PM

I just got back from a 200 mile Rv excursion. All flat land driving (SC, Low Country) at about 80 miles into trip, started to lose power upon acceleration, my vacuum gauge in dash upon deceleration, vacuum would fall as it should and engine would back fire at 30 vacuum. At idle engine will run rich with black smoke from exhaust. These symptoms will only occurs after 80 + miles. When I started having problems I pulled over and stopped for about 20 min. Restarted and all was fine for about 40 miles. Engine coolant temp runs in normal range and never gets overheated. Going to run engine codes to see if anything comes up. Thinking MAP sensor. Anyone experience this problem? My 460 has 40,000 miles on it.

Mekanic · 09-14-2014, 07:21 PM

a bad Map sensor can cause a rich fuel mix.
You could have some loose rust in the muffler. ??
go tap it with a mallot and see if something is loose inside it?

Many early 90 Fords (late 80s as well) didn't have a check engine light. you might have a code stored.

ARFFMAN · 09-14-2014, 08:02 PM

Quote:

Originally Posted by Mekanic

Map can cause a rich fuel mix.
You could have some loose rust in the muffler. ??
go tap it with a mallot and see if something is loose inside it?

Many early 90 Fords (late 80s as well) didn't have a check engine light. you might have a code stored.

Before I bought my MH it sat for 5 years, unattended . Rust is a four letter word for this rig. What would it do to the performance if it was dislodged in muffler.
If I do indeed have loose rust in muffler, what's the remedy for the fix.

Mekanic · 09-14-2014, 11:40 PM

Quote:

Originally Posted by ARFFMAN

Before I bought my MH it sat for 5 years, unattended . Rust is a four letter word for this rig. What would it do to the performance if it was dislodged in muffler.
If I do indeed have loose rust in muffler, what's the remedy for the fix.

What can happen is this as you dive the air flowing though the muffler picks up particle s of rust and pushed them up against the smallest opening blocking air flow. then when you shut the engine off the pieces fall back to the floor of the muffler and it runs better till the air flow pics up again and whole process starts over.

The fix? if this is the problem you replace the muffler.

Nick-B · 09-15-2014, 02:09 PM

ARFFMAN - Definitely check for exhaust restrictions but a failing fuel pump will cause the symptoms you describe. Buy or borrow a fuel pressure gauge. Hook it up to the check port on the injector rail (tube) and go for a drive. Fuel pressure should stay above 30 psi and should be 38-39 psi when your foot is in it.

Actually, lets start with the EZ stuff. When was the last time the fuel filter was changed?

ARFFMAN · 09-15-2014, 05:43 PM

Quote:

Originally Posted by Nick-B

ARFFMAN - Definitely check for exhaust restrictions but a failing fuel pump will cause the symptoms you describe. Buy or borrow a fuel pressure gauge. Hook it up to the check port on the injector rail (tube) and go for a drive. Fuel pressure should stay above 30 psi and should be 38-39 psi when your foot is in it.

Actually, lets start with the EZ stuff. When was the last time the fuel filter was changed?

300 mile ago I pulled the fuel tank, cut it opened, cleaned it out, etch it and sealed it. Installed a new updated fuel pump. Flushed out steel lines and installed a new fuel filter. Check fuel pressure during road test. Idled at 30 psi. Tested about 36 wot. Changed fuel filter again last month.
I'm going to do a pressure test again. And see if I get any codes. Muffler rust sounds logistical. Since MH sat for the past 6 years. If muffler looks bad I may look into the Banks system ( tail pipe, resinator, muffler and intake plenum.) I also don't want to rule out MAP sensor, due to running rich at idle( only after engine has run for 1 hour or more)

Lt46 · 09-16-2014, 08:40 AM

Last week I replaced my starter relay and in the process managed to dislodge the rubber tubing connected to the MAP sensor. On start-up, the idle was very rough and black smoke poured into the coach setting off the smoke detector. Definitely take a look at the MAP, your description sounds exactly like what I had going on.

sknight · 09-16-2014, 08:53 AM

Walk to the front of the vehicle and check the grill. Typically, Ford circles the problem right in the middle of the grill.

Sorry, couldn't help myself.

On those engines the MAP sensor draws vacuum off the back of the air horn the throttle body attaches to. It's got a rubber 90* elbow attached to a plastic line, that elbow tends to deteriorate over time.

If you establish the vacuum reference to the sensor is solid then I'd look at the sensor.

What you're describing is a MAP sensor that for some reason is reading low vacuum.

Brockx · 09-18-2014, 07:13 AM

I had a somewhat similar experience, but no power loss during travel. After a long haul the engine would load up if left to idle very long. After a lot of conversation in my thread in this Ford Chassis forum ("need opinions") I decided to change the Idle Air Control valve, installed a new one and it made a constant load annoying noise through the air box. Cleaned the original one with Brake Cleaner re-installed and just traveled 1300 miles with no problems and 7.8 mpg with toad. It is idling at low rpm but very smooth and no sign over over-rich. Good luck keep us posted.

ARFFMAN · 12-05-2014, 05:25 PM

You people are amazing! Just finished installing a Banks power pack on my 1994 460. Wow! MH has more power, torque for hills and increased MPG. Mekanic,,Thank you, . The Banks systems is the best money I have spent on MH. Runs amazing.