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Discussion Starter #1
Hey guys, I just installed a replacement NPI engine in my 95 bird. Once I got the car running I noticed a misfire (maybe every other combustion stroke) on the passenger bank. I have true dual exhaust so its easy to isolate.

I let the car run for maybe 5 minutes, hoping it would smooth out but no luck.

Engine has new OEM spark plugs, gapped properly. The plug wires are motorcraft about two years old.

My scan tool tells me this:
TPS 15.3-15.7
RPM 800
LOAD 37.6%
MAF 1.40
COOLANT 119
IAT 86
IGN ADV 22.0
LT FTRM1 0.0
ST FTRM1 16.0
LT FTRM2 0.0
ST FTRM2 18.8
FUEL SYS CLOSED
O2S11 0.045-0.720
O2S12 0.285-0.380
O2S21 0.360-0.600
O2S22 0.905-0.915
ST FTRM 18.0-22.0 (I am a little confused about this one I see ST FTRM1?)

Car misfires/backfires out the passenger bank. Exhaust smells like its real rich. After I turn the car off it doesnt start so quickly (feels like its flooded out).

Checked fuel pressure it's at 29psi @ idle and 40psi @ WOT.

Not trying to be spoonfed here but I am scratching my head saying WTF!
Thanks guys.
 

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WOT Junkie and avid corn burner
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There's ST FTRM 1 and 2 because there are two banks. Since it is adding fuel, I'd be looking for vacuum leaks.
 

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Super Moderator
1997 Thunderbird 4.6, 1998 Mark VIII LSC
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Fuel pressure is off... It should be 39.5 at idle and 43.5 at WOT.
 

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You're running dangerously lean as the STFTs say, but if you are smelling raw fuel that is usually indicative of an exhaust leak near the O2. First check all the plugs to see the actual condition. You should see some brownish darkish soot if it is running rich. Check all vacuum lines and sealing surfaces prior to the intake ports and all sealing surfaces after the exhaust valves. If you can run a misfire counter on each cylinder it might help you find the problem. Check all injector O-rings as well.
 

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Discussion Starter #5
Thanks guys I will be out there in the morning with my can of carb cleaner seeing if I can find a vac leak.

Mgino- I have ST FTRM 1 and 2 and then ST FTRM with no number, thats what I'm confused about. Is ST FTRM a combo or both?

GM- Thank you. I will check plugs, vac leaks, and injector o-rings.

My injector orings are old and i've only got 7/8 of the press on gromets that sit at the very tip of the injector. I do have a fire extinguisher ready!

Terminator- I left the car sitting for 2 weeks with E10 gas in it. I'm thinking the fuel filter might be varnished up from the ethanol. I'm going to do some searching about fuel pressure, I thought I read 29idle - 40wot was normal. But that was internet info, so who knows how accurate it was.

Thanks everybody!
 

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Fuel pressure is off... It should be 39.5 at idle and 43.5 at WOT.
not for our cars with stock injectors. Idle should typically see 34psi ± a couple psi, WOT should be 39-40psi. 43.5psi (3 bar) fuel pressure is for the "newer" cars.

I thought I read 29idle - 40wot was normal.
that sounds ok. It's a smidge low a idle, but that can be due to weather/temperature/altitude variations most likely. At WOT, 40psi is perfect. The idle part is what seems a smidge low. If you would like to verify, you can take a vacuum reading of the manifold at idle. This vacuum reading can be converted to a pressure differential, which you can then compare to your 29psi idle reading. Its up to you though.
 

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Discussion Starter #7 (Edited)
One other thing I wanted to add. I installed this engine this weekend and it was seized. I was able to destroy a flywheel and get it working (thankfully I have lots of spare parts). I am wondering if the engine having a rough spot would fool the OBD2 into logging a misfire due to crank speed slowing at that point. My head is going in circles, it could be a million things wrong here.

I called my friend who is a mechanic at ford and he was sounding like "Oh *****!, Ryan needs help! This must be a major PITA that I don't wanna deal with!"

Thankfully he owes me one, I hooked him up with a front bumper, headlights, and headerpanel for his 94 SC after he rearended a customer one day leaving work. (94 SC caused $2500 damage to a 2012 Expedition, lol)

I've got gauges for refrigerant that read inHg. I'm going to rig up a vacuum gauge and see what I get. I'm interested in converting this reading to a pressure diff. Will do some research.

I'm thinking though less vac= more fuel pressure. More vac= less fuel.
 

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One other thing I wanted to add. I installed this engine this weekend and it was seized. I was able to destroy a flywheel and get it working (thankfully I have lots of spare parts). I am wondering if the engine having a rough spot would fool the OBD2 into logging a misfire due to crank speed slowing at that point. My head is going in circles, it could be a million things wrong here.

I called my friend who is a mechanic at ford and he was sounding like "Oh *****!, Ryan needs help! This must be a major PITA that I don't wanna deal with!"

Thankfully he owes me one, I hooked him up with a front bumper, headlights, and headerpanel for his 94 SC after he rearended a customer one day leaving work. (94 SC caused $2500 damage to a 2012 Expedition, lol)
Um yea, forget about any diagnosis until you make sure the engine is freely rotating. If something is physically binding enough to cause the crank to literally slow down on it's revolutions while idling, you're gonna end up chasing your own tail and wasting a lot of people's time who might be trying to help you diagnose a "misfire" or "rich condition".
 

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What was wrong with the other engine?

EECs are known to be bad and hand injectors on certain years.

What all did you swap over?
 

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1997 Thunderbird 4.6, 1998 Mark VIII LSC
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Oh right right, my bad. 43.5 PSI is the pressure at flow rating on new injectors. 39 is ours. hehe... :facepalm:

I'll go crawl into a corner now.
 

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Discussion Starter #11
Um yea, forget about any diagnosis until you make sure the engine is freely rotating. If something is physically binding enough to cause the crank to literally slow down on it's revolutions while idling, you're gonna end up chasing your own tail and wasting a lot of people's time who might be trying to help you diagnose a "misfire" or "rich condition".
Not trying to do that sorry for the lack of complete info, I am trying though I'm sure you can see that.

What was wrong with the other engine?

EECs are known to be bad and hand injectors on certain years.

What all did you swap over?
The other engine had bad rod knock noise for a long time. I got tired of hearing it and revved her up to 5250rpm and let her go. It threw two rod ends and blew two holes through the rear of the engine block. The only thing damaged was the block (obviously), the oil pan, and the dipstick.

I swapped over all my accessories, injectors/fuel rail, balancer, timing cover, valve covers, intake manifold, exhaust manifolds. I did not take off the heads.

I am aware of the bad EEC but honestly, this car was running great up until I blew it up, so I'm leaning on the side of optimism. For now...

And terminator don't worry about it. If your terminator 4.6 runs those pressures you were right! Nobody's perfect, I sure ain't.
 

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Discussion Starter #12
Im gonna run that ***** for an hour tomorrow, checking for vac leaks lil by lil. If it fouls some plugs out, whatever, I'm not out anything. I'm not expecting miracles. If this old engine doesn't work out I didn't spend anything to get it I already had it sitting at my house for the last two years.
 

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The Parts Guy
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Provided the fuel pressure info is accurate, if you do have a vacuum leak, it will be minor.

My injector orings are old and i've only got 7/8 of the press on gromets that sit at the very tip of the injector. I do have a fire extinguisher ready!
You're missing the o-ring at the base of the injector, or the pintle cap? If it's the o-ring, there's your small vacuum leak that will throw off the AFR on one cylinder (you'll have a single cylinder miss).

One other thing I wanted to add. I installed this engine this weekend and it was seized. I was able to destroy a flywheel and get it working (thankfully I have lots of spare parts).
:eek: Uhhh...why was it seized? That throws up all sorts of possibilities: bent valve, galled cam journals, destroyed rings...

I'd start off by determining which cylinder is missing. A compression test wouldn't be a bad idea either.
 

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Discussion Starter #14
You're missing the o-ring at the base of the injector, or the pintle cap? If it's the o-ring, there's your small vacuum leak that will throw off the AFR on one cylinder (you'll have a single cylinder miss).



:eek: Uhhh...why was it seized? That throws up all sorts of possibilities: bent valve, galled cam journals, destroyed rings...

I'd start off by determining which cylinder is missing. A compression test wouldn't be a bad idea either.
I am missing the "pintle cap" on one of the eight injectors. All the orings are good. I replaced a few that were dry rotted.

It was seized because it sat without oil for the last two years, on an engine stand in my shed. The relative humidity in there can get up to 99% very often. And not to mention, my dumbazz had the valve covers and oil pan off of the engine. I meant to pull it apart and change rings and bearings but after doing my homework I decided that was a dumb move and if I wanted a motor with fresh bearings that I should go the PI explorer route considering its 2013.

Racecoug- I have a compression tester (harbor freight I'm afraid) and it is absolutly impossible to hook it up. I need a 4"-6" extension to get the adapters threaded in the plug holes. What kind of compression tester (can I rent it?) do you have/use on the 4.6's? I tried making an adapter by cutting an old spark plug and brazing a piece of copper (using flux) onto it, but the moment I tightened it I heard the weld cracking so I backed it out and said F' that. I REALLY need a TIG welder. Especially now that I have over 100 hours welding under my belt, I might actually set a bead that holds. :D
 

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The Parts Guy
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Discussion Starter #16
I got it fixed. I used a OEM lower intake manifold gasket and it solved my problems. I was first trying to use a felpro but it wouldnt line up very well. I put the OEM gasket on this morning and it works like it should, not more misfires backfires. Thanks for all the input guys.
 
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