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Old 05-28-2019, 07:22 AM
Witsend Witsend is offline
Join Date: Nov 2012
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Witsend Made it to level 2!  Looks like you are on your way to becoming famous

Unhappy Pre Cat Substrate failure can trash motor

Had a guy that had a 177K 2004 Jeep Grand Cherokee 4.7 v8 that quit on him on the Highway,and it was towed here as a Crank no start. Fuel pump working fine , Misfire code on cyl 1 and pending misfire code #7. Managed to get started WOT clear flood mode but seemed to just run on 4 cylinders. I pulled bank 1 O2 sensor and it now started and ran on 6 of 8 cylinders with high pressure jetting out of the vacant upsteam Bank 1 upstream O2 bung. Took out #1 plug and it was carbon fouled with 115psi engine running compression. I burned the carbon off the plug clean with my torch. I then removed #7 plug and it was all wet with a crushed closed ground electrode and #7 engine running compression registered only 15psi. Uh Oh Also I found the brake booster hose had come off the plastic intake plenum nipple that probably came off on a backfire event and created a huge vacuum leak that made for overfueling to compensate for the vacuum leak.
Took a peak in cylinder 7 with my $60 HF sewer camera and saw piston had a ragged gouge, so figured it trashed. Guy priced a used 100k 4.7 engine from LKQ for $1800, they don't sell the used OE exhaust Catalysts to go along with engine , and his car was already on it's 3rd set of Cats (2nd aftermarket set ).Told me the OE ones cost $2K. Told my Arab former Ford Mechanic friend it's time to let it go to where all good Chrysler products go and get their 70 pounds of virgin refrigerant. The Best Volumetric efficiency it should see now is being compacted into a 3x3 ft cube
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Last edited by Witsend; 05-28-2019 at 07:55 AM..
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Old 05-28-2019, 09:21 AM
Joe Rappa's Avatar
Joe Rappa Joe Rappa is offline
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Join Date: Aug 2007
Location: North Carolina
Posts: 1,907
Joe Rappa Made it to level 2!  Looks like you are on your way to becoming famous


Looks like it ate something, no? Either way, it's chewed.

"You don't build a reputation on what you're going to do"
Henry Ford
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