I have an odd misfire

Vyper202

Member
Jul 8, 2019
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53
Virginia
OK guys, heres whats happening... 1998 GT, auto... all bone stock, 102K miles. I was checking under the hood Monday, oil, water etc... I noticed #2 injector had fuel puddled around it. It appeared the fuel rail bolts had loosened up enough to let the rail raise a bit and #2 was leaking from the top oring. OK, no big deal, i will just tighten the rail bolts I said. When i did I noticed a cut piece of oring on the injector body. Loosened the rail bolts, popped the rail up enough that #1 & #2 were out, pulled off #2 and replaced the oring with a spare I had. All went back together well, fired it up, no leaks, but idled rough, thought still has air that has to bleed. Took it down the road, I could feel the miss and it flashed a CEL. Get back, check under hood, everything is dry, nothing left unplugged, all looks good. Then i scanned it, misfire on cyl3???WTH??? Checked plug on #3 injector, plugged in solid. Got my meter and checked resistance, all were at 12.3. Pulled #3 plug, looked good, right color. Fired it up, put the trusty long screwdriver to my ear, all injectors clicking and firing, but still could feel a little miss. Took it back up the road, hard miss under load, CEL again, scan again, misfire on #3. Repeat all the above checks, everything still looks good.
So before I buy a replacement #3 injector, does anyone have any insight on anything else it may be before I pull it apart again? Thanks
 
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MustangIIMatt

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OK guys, heres whats happening... 1998 GT, auto... all bone stock, 102K miles. I was checking under the hood Monday, oil, water etc... I noticed #2 injector had fuel puddled around it. It appeared the fuel rail bolts had loosened up enough to let the rail raise a bit and #2 was leaking from the top oring. OK, no big deal, i will just tighten the rail bolts I said. When i did I noticed a cut piece of oring on the injector body. Loosened the rail bolts, popped the rail up enough that #1 & #2 were out, pulled off #2 and replaced the oring with a spare I had. All went back together well, fired it up, no leaks, but idled rough, thought still has air that has to bleed. Took it down the road, I could feel the miss and it flashed a CEL. Get back, check under hood, everything is dry, nothing left unplugged, all looks good. Then i scanned it, misfire on cyl3???WTH??? Checked plug on #3 injector, plugged in solid. Got my meter and checked resistance, all were at 12.3. Pulled #3 plug, looked good, right color. Fired it up, put the trusty long screwdriver to my ear, all injectors clicking and firing, but still could feel a little miss. Took it back up the road, hard miss under load, CEL again, scan again, misfire on #3. Repeat all the above checks, everything still looks good.
So before I buy a replacement #3 injector, does anyone have any insight on anything else it may be before I pull it apart again? Thanks
Swap your coil packs and see if the misfire moves to the other bank. You can also swap plugs between that cylinder and another to the same effect.
 

MustangIIMatt

Easy there, this ain't a dating site.
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Mar 7, 2002
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Yes Id planned on that this weekend thanks... Its just odd that #2 had the leak issue and now #3 is the miss....
Crazy stuff happens on cars. I worked on a 2018 M5 today that was just in the shop two days ago for an evap system repair. That was fixed, on the other end of the freaking car, by another tech. Today it comes back because it's stalling on cold start and I figured out it had two bad fuel pressure sensors (wasn't throwing codes, but the were reading at 6.0bar and 8.3bar without any fuel in the rails).

Sometimes it's more like playing whack-a-mole than it is fixing things.
 

McFly2

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Nov 21, 2020
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Just maybe when fuel rail was lifted; some debris got into #3 injector. Consider the injector swap when convenient.
 

Vyper202

Member
Jul 8, 2019
36
18
18
53
Virginia
OK guys, it was a couple of things if anyone else has this issue. Replaced the #3 injector, swapped #3 and #1 plugs, still had a little miss. Inspected the #3 plug boot and found a pinhole in rubber boot. It had carbon trace around the hole so I wrapped it a few times with electrical tape and it cured the miss. Now to get a new set of wires....
 
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