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Howdy ya’ll,
I’m back to pick your brains. I recently purchased a 1996 Ford Explorer, 4.0 OHV 5 speed manual (MR5OD I believe) 99,000 miles.
Anyway, I bought it with a catalyst code (p0420 catalyst efficiency below threshold bank 1) an EGR code (P0401 EGR flow insufficient) and a terribly rich idle. The temp gauge is temperamental, sometimes it’s in the middle, sometimes it’s closer to the C. The only time I ever plugged the scanner in and looked the ECT was 188. Story goes I rebuilt the tranny after 5th cut out, but I installed the late fifth slider backwards, so no 5th gear.
Gas mileage was unaffected for a couple weeks, then I got a misfire, tracked that down to the wires, replaced them, misfire went away, but gas mileage never really improved.
I diagnosed the cat with an IR thermometer, ordered a Magnaflow universal cat online and replaced it.
I ended up rebuilding the exhaust in the process, so everything after the y pipe is custom. I have the cat in more or less the same place as factory, maybe a little closer to the y pipe but not much, and I also replaced the downstream o2 sensor. After the cat is about 4 feet of 2 1/4 ID straight pipe running back behind the rear floor pan. I no longer have any DTCs, but my fuel economy has gone from around 15 mpg to about 10 mpg, and there’s a very subtle, inconsistent miss at idle, and a backfire at higher revs when I downshift.
Did I lose too much back pressure? Am I burning exhaust valves? Is the cat too close to the y pipe?
Any thoughts or suggestions would be appreciated, I’ve gotta get this beast back to her original 16-17 mpgs before I go home for Christmas.
Thanks in Advance
Clay
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those vehicles are prone to vacuum leaks . check over the hoses really good . especially the large pcv elbows .
So, I found a small vacuum leak at the PCV hose where it connects to the intake manifold, however when I push the hose all the way seated to the nipple, the idle doesn’t seem to change.
I plan on replacing that hose and the PCV valve this weekend, just because it’s about due anyway.
I tested my MAF with my code reader, and basically anytime I let off the throttle, it drops straight to idle reading, around .01 lb, no subtle, gradual reduction just a dead drop from whatever it’s pulling at speed down to .01, so I’ll test/clean/replace the MAF and see what happens.
My biggest concern is that backfire, it seems to be leaking from the passenger side exhaust manifold, at the y pipe. Are these taper sealed or is there a gasket?
There is also a small leak just ahead of the cat, where a stud broke inside the flange. Could this contribute to my backfire?
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