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1993 7.5L E350 - EGR/Air injection problem

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1993 7.5L E350 - EGR/Air injection problem

Old 05-15-2011, 10:43 PM
rgnprof is offline
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1993 7.5L E350 - EGR/Air injection problem

I have done quite a bit of work on this motorhome since buying it last summer. Replaced the fuel pump and filter, plugs, wires, cap and rotor and the idle speed control motor (it was really loud). The coach has 58,000 miles...

On the way home today, the coach ran great for about an hour - at 35-55 mph, or so. Got on the freeway, and the thing just wouldn't go so I pulled off and started looking around and saw the front most spark plug on the passenger side sparking! The boot had come into contact with the exhaust manifold, I guess, and was melted through. Fortunately, I had some extra wires and I was able to replace it and get home.

BUT, the thing didn't run right the whole trip home - limited power, and couldn't go much above 55-60 on the highway. And, intermittently - when the load changed I would get a loud rumbling noise from under the doghouse (not just on acceleration, sometimes on deceleration, but you could usually get it to roar by goosing the gas pedal a little and then letting up etc). So, a friend drove and I pulled the doghouse back to take a look and isolated the noise to the air bypass/diverter valve - a multi-hosed valve that leads from the air pump to both exhaust manifolds and it also has a vacuum tube attached. This valve has some holes in it and you could really feel the air being pushed out from these holes when it started making the noise. I don't know if this could affect the power, but the coach didn't run right and when this thing started 'leaking', it was pretty loud!

I pulled a code 334 last night - EGR closed valve voltage high, and a code 542 - Fuel pump secondary circuit fault. There is a pink vacuum line that runs from the air bypass/diverter valve that is running over to the EGR vacuum solenoid (I think??) - I'm thinking that this air bypass valve "leaking" air is somehow related to the EGR system.

Anyone offer some help here? I am really encountering one problem after another...

I'm going to check all the wires, but once I replaced that bad wire it did run better...

Thanks, ryan
Old 05-18-2011, 10:35 AM
rgnprof is offline
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Can anyone help here??
Old 05-24-2011, 09:13 AM
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I have had some air pumps and diverter valves make lots of noise especially at different throttle openings. Obviously it sat a lot, you might have wasp nests in your air intake, a blocked fuel filter from sitting, or the fuel pump might be giving up (if its noisy when you turn the key on its probably the culprit) they get loud before they quit, when the engine is idling if the whirr of the fuel pump is able to be heard then its louder than it should be. Check for bug nests all over that thing, you might have a builder in just the wrong place.
Rats eat plug wires, wiring, and hoses so its systematic searching to find it. I just replaced my coil on my 92 5.0 and it sparked when I turned it over with the starter but ran like trash when going down the road. Don;'t throw money at it, that system is usually pretty bullett proof, I checked everything but found nothing wrong and it was the coil $20.
A rare problem can be some obstruction in the exhaust
Old 04-03-2017, 01:14 PM
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I'm having an issue with the air injection system also. On mine the loud roar was the hoses that connect to the exhaust manifold burst and it became a huge exhaust leak. I tried replacing the hoses with hose that is rated for 500 degrees thinking that i just needed to fix the hoses. But the turbo hose burst as well after an hour driving. Now i have to figure out why the hoses keep bursting. I did have to take the check valve that was inline off since it seemed fried with loose particles inside.
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