popping/backfiring repeatedly only at 3/4-full throttle


91stranger

Well-known member
Joined
Jul 28, 2010
Messages
1,141
Reaction score
131
Points
63
Location
ohio
Vehicle Year
1999
Make / Model
FORD
Engine Size
3.0
Transmission
Automatic
So I recently had to weld my exhaust where the flange is at in the middle of the truck and I couldn't get the bead around the top of the exhaust since I can't get at the top very well with the welder so I'm sure there are some spots that didn't get welded there at the top. However, ever since the repair I've noticed popping noises/backfiring noises whenever I give it more than 3/4 throttle. Could this be from the exhaust not being welded all the way? I never had it happen before and I've fixed this exhaust twice now with it never doing it before. Could I be overlooking something? Check engine light is on but it has been on for an evap leak (bad charcoal canister) which I have a scanner and could check it if needed. Any thoughts? Been thinking about cutting it off at the weld and just getting a thrush or flowmaster muffler put on. Basic info is 99 2wd, 3.0 flex fuel, auto trans, 124,000 miles, new spark plugs in october (didn't do wires though), new t-stat, ETC sensor, cam synchro, IAC, ignition coil, and i've cleaned the MAF sensor. Truck idles perfectly around 900 RPM with no weird revs or drops while idling. Any ideas?
 


Rock Auto 5% Discount Code: 248EE46702D889 Expires: October 1, 2019

RonD

Well-known member
Joined
Jun 2, 2012
Messages
13,589
Reaction score
425
Points
83
Location
canada
Vehicle Year
1994
Make / Model
Ford
Transmission
Manual
Not from exhaust weld, may have a burnt exhaust valve, any misfires at idle?

First recheck firing order on the coil pack, very very easy to reverse 2 wires on these
[3 4]
[2 6]
[1 5]
front

The 5 6 4 side gets mixed up

If you have or can get a vacuum gauge you can use it to test for partially blocked exhaust, this limits RPMs and causes what you describe

And so can lower fuel pressure, as demand goes up pressure drops too low and you get misfires and backfires
 

91stranger

Well-known member
Joined
Jul 28, 2010
Messages
1,141
Reaction score
131
Points
63
Location
ohio
Vehicle Year
1999
Make / Model
FORD
Engine Size
3.0
Transmission
Automatic
I have not tried lookin at it. our lift has been tied up for the past week and I can't see squat from the ground laying down. I ended up buying a Thrush welded muffler and an adapter so I can cut off the exhaust at the flange and put the better muffler on instead of trying to weld rust to other rust and hope it works lol. Anyone use the Thrush welded style muffler?? It wasn't the cheapest they had ($39.10) but seemed like a good one. I've heard of good things about Thrush mufflers but that's on v8's not a v6. It's gotta be better than mine now which sounds like a drumline when giving it full throttle lol.
 

91stranger

Well-known member
Joined
Jul 28, 2010
Messages
1,141
Reaction score
131
Points
63
Location
ohio
Vehicle Year
1999
Make / Model
FORD
Engine Size
3.0
Transmission
Automatic
I forgot that it can't be the ignition coil as that was replaced last year around this time lol. I'm very careful when changing plugs and wires. I do them one at a time as well as label what wires were where with a sharpie so I can't mess it up in case some idiot pulls all the plug wires out when i'm not looking.
 

rusty ol ranger

Well-known member
Joined
Sep 22, 2007
Messages
4,221
Reaction score
457
Points
83
Location
Michigan
Vehicle Year
1987
Make / Model
Ford
Engine Type
2.9 V6
Engine Size
2.9L
Transmission
Manual
2WD / 4WD
2WD
My credo
A legend to the old man, a hero to the child...
I doubt the weld has anything to do with it.

Longshot, but you didnt burn up an O2 wire while you were welding did you?

Did you unhook the battery before welding?
 

RangerFabWorks

Forum Staff Member
Forum Moderator
Supporting Member
V8 Engine Swap
TRS 20th Anniversary
Joined
Jan 31, 2009
Messages
4,630
Reaction score
148
Points
63
Age
28
Location
Long Island, New York
Vehicle Year
1990
Make / Model
Ford
Engine Size
302
Transmission
Manual
I didn’t use a thrush. But I used a summit racing street strip muffler. (There brand of a flowmaster) welded on my 00 with a 3.0. Sounded great. Little popping noise when letting off the throttle. Nothing that I would be worried about.
 

91stranger

Well-known member
Joined
Jul 28, 2010
Messages
1,141
Reaction score
131
Points
63
Location
ohio
Vehicle Year
1999
Make / Model
FORD
Engine Size
3.0
Transmission
Automatic
No I didn't unhook the battery. Never have in the past. I wasn't real close to a sensor wire, probably about 18 inches or so. I think I may have too much bubblegum welds and it is restricting the air flow because I was going heavy with wire to try to weld rust to rust lol. Don't know but I already bought the Thrush and an adapter so I was going to test fit it on lunch but I forgot my Sawzall and I don't know if our shop has any more metal cutting blades so it will have to wait until tomorrow. Saw some videos of a 3.0 with the thrush welded muffler and they sound pretty good.
 


Top