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1988 E 350 motorhome no power uphill / poor fuel mileage
07-20-2008, 04:46 PM
Post: #1
Question 1988 E 350 motorhome no power uphill / poor fuel mileage
Our 1988 Ford Econoline 350 motorhome has a 7.5l engine and automatic trasmission with A/C. It sounded fine idling in the driveway before our latest trip. Once it warmed up it had no power up hills and had trouble restarting. We used about 45 gal of fuel for a trip normally requiring half that amount. While camping we changed plugs wires cap and rotor. Again ran and sounded great on site until warmed up it ran poorly all the way home! We ordered a new oxygen sensor today and wondered if there are any other things to look for to solve this problem?
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07-23-2008, 11:42 PM (This post was last modified: 07-23-2008 11:42 PM by CaryJoeYork.)
Post: #2
RE: 1988 E 350 motorhome no power uphill / poor fuel mileage
I would suspect a clogged exhaust. Cat. Convertor? Have the cat. conv. checked for restriction and excessive back pressure.

Cary Joe York
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07-27-2008, 01:06 PM
Post: #3
Sad RE: 1988 E 350 motorhome no power uphill / poor fuel mileage
CaryJoeYork Wrote:I would suspect a clogged exhaust. Cat. Convertor? Have the cat. conv. checked for restriction and excessive back pressure.

Thanks Caryjoe, Since last post we replaced the O2 and map sensors. Then we removed the CAT and found no changes in performance. Exhaust/ muffler appear to be operating fine. On a 5min test drive the RH exhaust manifold turned cherry red when trying to get up to 55 mph. Something must be causing excessive fuel to dump into multiple cylinders to cause such a quick drain of the fuel tank. Our next focus will be the EGR valve and then the computer. eb
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07-28-2008, 09:49 AM
Post: #4
RE: 1988 E 350 motorhome no power uphill / poor fuel mileage
Have an injector leakdown test done .Could be one or more injectors leaking or stuck open
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07-28-2008, 09:00 PM
Post: #5
RE: 1988 E 350 motorhome no power uphill / poor fuel mileage
Retired, thanks for your response. Will report back by weekend after test completed. eb
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07-30-2008, 11:01 AM
Post: #6
RE: 1988 E 350 motorhome no power uphill / poor fuel mileage
Another thing that will cause cherry red manifolds, poor power, and poor MPG is timing.

Look at anything that may cause the knock sensor to go full retard. It could be rust, lose wires, or something that throws a false "noise" to the sensor. At 20 years old that could include engine / trany mounts that are rotted (metal to metal) or even linkage rods (to various places) that no longer have their bushings intact. The sensor may pick up the noise as engine ping and pull the timing back 25 degrees. That will certainly give those results.

BTW, double check for slop in the distributor bushings and see if the advance stuff (if it has any) works freely. Also check the base timing as there may be other issues. (timing chain skipped?)

Rupe
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07-30-2008, 08:16 PM
Post: #7
RE: 1988 E 350 motorhome no power uphill / poor fuel mileage
Another thing to throw out there----Is the coil putting out the proper voltage? We had a Crown Vic (1991) that had a weak coilo that had exhaust manifolds glowing.

Being way2old is why I need help from younger minds.

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07-30-2008, 11:03 PM
Post: #8
RE: 1988 E 350 motorhome no power uphill / poor fuel mileage
When checking fuel pressure we only showed 35 to 40 psi. This seems to be low for a high pressure pump. Can anyone tell me what the pressure should be for this unit? If this is too low could it cause the injectors to perform poorly and drip instead of spraying into the combustion chambers? All feedback much appreciated. eb
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07-31-2008, 08:13 AM
Post: #9
RE: 1988 E 350 motorhome no power uphill / poor fuel mileage
Key On Engine Off 35 - 45 psi
Key On Engine Running 30 - 40 psi
This is per Alldata Pro.

Being way2old is why I need help from younger minds.

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07-31-2008, 09:07 AM
Post: #10
RE: 1988 E 350 motorhome no power uphill / poor fuel mileage
Got to thinking about the comment of excessive fuel use (rich mix?) and since you have already changed the plugs did you happen to notice if they were all (some?) black with carbon? That would indicate a rich mix problem.

If they were not black I'd be leaning (pun intended) toward the other things. It's fairly common to have power loss problems eat up fuel due to compensating with your right foot.

BTW, did you check or replace the fuel filter? A restricted filter can cause a lean condition under loads. Retired mentioned a weak coil, which can act similar except that there's usually a mis-fire under load.

Rupe
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