460 Running Poorly
Thread Starter
|
2nd Gear
Joined: Aug 2025
Posts: 2
Likes: 2
460 Running Poorly
Hello all. So I have a 1989 F250 RWD 460/C6. Yesterday I had a new exhaust system installed at a local muffler shop. We deleted the CAT, left the O2 sensor in its factory location, then deleted the AIR system (it only went to the CAT). It ran ok on the way home but a little rough on idle. Now it will start but runs extremely rough and wolfs out smoke like it is very rich. No electronics were touched and this is OBD1 so there is no O2 sensor behind the work to tell on me. I did replace the O2 sensor but no change. Before I fire the parts cannon I'm hoping somebody knows what happened. I'm thinking perhaps the welding damaged the ECM. Any help would be appreciated. Thanks!
Hotshot
Joined: Jul 2020
Posts: 10,354
Likes: 2,592
From: Near Salt Lake City
First thing is a code check and see if fuel comes out the vacuum hose of the fuel pressure regulator
Second would be a MAP sensor test checking the actual Hertz coming out of the sensor for your altitude
We all used to just substitute a known good MAP sensor (that's way easier)
Correct, those older fuel injection systems have little to none self test capabilities
We had monitor boxes for them at the dealer where we could record live data, but it took an expensive monitor box
Processor damage is NOT out of the question; it will come back as a code for RAM failure or something similar if that is the case
* Pull the processor out and inspect the capacitors, give it "the smell test" for the possible welding damage (rare or non existent on Fords)
Report back what you find
Anything could have happened at tha shop, might want to check the "base" (spout unplugged) timing in case it's off
Second would be a MAP sensor test checking the actual Hertz coming out of the sensor for your altitude
We all used to just substitute a known good MAP sensor (that's way easier)
Correct, those older fuel injection systems have little to none self test capabilities
We had monitor boxes for them at the dealer where we could record live data, but it took an expensive monitor box
Processor damage is NOT out of the question; it will come back as a code for RAM failure or something similar if that is the case
* Pull the processor out and inspect the capacitors, give it "the smell test" for the possible welding damage (rare or non existent on Fords)
Report back what you find
Anything could have happened at tha shop, might want to check the "base" (spout unplugged) timing in case it's off
Laughing Gas
Joined: Apr 2024
Posts: 794
Likes: 252
From: Laramie Wyoming
I know you said you changed out the O2 sensor but have you checked the wiring on it up to where it goes? Maybe it got pulled out or a wire melted.
when you got rid of the air system did you get everything capped and plugged correctly? To include up on the engine?
when you got rid of the air system did you get everything capped and plugged correctly? To include up on the engine?
Thread Starter
|
2nd Gear
Joined: Aug 2025
Posts: 2
Likes: 2
Found It
Thanks guys! manicmechanic007 pointed me in the right direction. When I removed the AIR pipes I accidently knocked the vacuum line for the MAP sensor off the back of the throttle body where I couldn't see it. Now it idles smooth. Getting ready for a test drive. Thanks again! Mark
Thread
Thread Starter
Forum
Replies
Last Post
mykdee
1987 - 1996 F150 & Larger F-Series Trucks
7
Jun 4, 2021 09:56 AM
CaseyLandscapes
1987 - 1996 F150 & Larger F-Series Trucks
11
Feb 25, 2015 03:04 AM
Django92
1987 - 1996 F150 & Larger F-Series Trucks
5
Nov 20, 2010 05:10 PM
wantaford
Big Block V8 - 385 Series (6.1/370, 7.0/429, 7.5/460)
13
Dec 2, 2004 10:29 AM
