View Full Version : The misfire mystery.

01-04-2008, 02:25 AM
I posted this org. on TCCOA.com, but continuously get no help so you mr. caraudio forum is my last shot.

1995 T-Bird 4.6L

151800 Miles.

Car is surging, backfiring out of intake, has a shaky idle (whole car shakes). Does it cold and hot. Give it more throttle, hesitates harder, backfires more. WOT clears up and runs strong. Let off gas, give about 1/2 throttle, begins to backfire more. Ran 89oct in it tonite and did not help issue at all.

I have a cone filter set up where filter is ran in between support fixture for original air box.

So far I have..
-Cleaned fuel injectors
-Replaced plugs and wires twice within 30k miles
-Replaced fuel filter around 20k ago
-Top Engine Clean(BG's induction clean)
-Checked Coil Packs
-Cleaned MAF
-Checked IAC
-Checked TPS

I got it scanned and I have a P1151(lean bank 1) which means its dumping fuel like mad. My gas milage went down to 8mpg!!!! I don't think it is the O2 sensor because this happened after I did a fuel rail injector clean (ran through schrader valve).

I am stumped and I cannot figure this out at all I need some help. This has been a ongoing problem since August and its getting worse.

Now I was also beginning to think bent valve or intake leak, but that wouldn't make since if the car runs fine wide open. Guys, I'm super stumped and I cannot figure this out worth a ****. It makes me wanna purposely blow this motor up and do it in style...

Any input is appreicated. Thanks

and Fernendon I'm joining Fordbastards.org, hopefully they are a little more helpful than TCCOA.com.

01-04-2008, 01:17 PM
you posted it at midnight last night...

FWIW i bumped it up for you

01-04-2008, 04:11 PM
Bad injectors? How new are they?

01-04-2008, 04:16 PM
i had a 3.8L T-Bird with 150'ish K on the odometer and it did similar things but I totalled it before I got a chance to fix it so I guess this is a losing post :(

do you have any pix of your ride? I love that body style :)

01-04-2008, 10:48 PM
It sounds like a valve train or timing problem. Back firing from the intake tells me that an explosion is going the wrong way. Either because it's pushing through a stuck/bent valve, or your timing is off enough that the intake valves are open upon ignition. I don't know if the 4.6 has adjustable timing though... If you can drive it, see if it is pulling the way it should at WOT. When it's not under load, it might rev seemingly well, even with a problem.

01-05-2008, 04:35 AM
It pulls hard at WOT, today I was driving it and it was fine.

This is the problem its intermittent.

When it misfires, I do notice a tad of black smoke if its at idle from a take off. So rich for sure.

I'm going to pull plug wires and go from there. When I pinpoint it i'll do a comp. check also.

The only thing is it feels like its more than one cylinder, but I could be wrong. Could a completely dead cylinder on a V8 cause a severe shake like that?

Also the popping from the intake. ITs only under load when it does it. Could this mean the amount of fuel being dumped and sitting in the cylinder for the next stroke too much causing the intake stroke a pre-detonation?

Also the car misfires since I have done a fuel injection clean (through fuel rail). Soon as the cleaning agent was done I started it up and the first time I drove it it acted up.

01-05-2008, 04:40 AM
you posted it at midnight last night...

FWIW i bumped it up for you

I have made the same topic about 6-7 times hehehe.

01-05-2008, 04:54 AM
have you done a compression check on all cylinders? lean bank one means you are not dumping fuel, its saying that it cannot get those cylinders to get back into the norm ( meaning the comp is going full rich on that side and still cant bring it back ) check for an air leak, if you have access to a smoke detector use it. also a friend of mine had one of these and he said it was real picky on plugs, what brand did you use? good luck.

01-07-2008, 03:08 AM
A lot of Fords tend to be pretty picky on plugs...

Autolite is good in some cases, Motorcraft is just about always ok. Brisk Turbo plugs for boosted applications. I wouldn't think a single cylinder would cause a real violent shake, if it's completely dead. Now, if it's firing out of time, then it could definitely do so.

01-09-2008, 08:21 PM
Here is another issue I ran into.

Its been wet out a lil humid. (68F out with snow on the ground).

Car runs fine. Does not act up one bit at all. No stalling. Violent shaking, ect. Ran just like it did before the injection clean.

My question what the hell is going on, how can the car run better when you can feel water in the air. This is confusing me big time lol.

I also run Motorcraft wires.

01-09-2008, 11:08 PM
Ok so it can't get as much oxygen from the air so it is running better. So the problem should be some sort of oxygen regulator I would think. Check o2 sensors again.

Again though if the injectors arn't pumping enough fuel, then less oxygen will make it run better, so check the injectors.

01-12-2008, 04:56 PM
Found O2 bank 1 lazy as a mofo. Checked injectors, did a coil test. PASS. Checked for intake leak, none found.

Did a lil wire jumping to O2 found it lazy.

Dunno why I just didn't do that in the first place. :crap:

Thanks for the input guys.