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post #1 of 24 (permalink) Old 01-05-2008, 04:08 AM Thread Starter
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Please Help Me!!! Lol

I have a 1991 Thunderbird Supercoupe (less then 70k orig. miles). It was totally rebuilt. I know about sccoa and tccoa, but there apparently s no one in this area. Long story short, I bought this SC (my second one) and had it for at least 4-5 years. the car had lower crank bearings in the bottom AND top (the oil couldn't get through the holes to the arm and pistons). I bought it this way (part of a piston was in the oil pan) You could still see the hone marks on the cylinder walls (bored +.030 over). We took the engine apart and rebuilt it from scratch (had the rods checked new pistons, rings, all bearings mounts, etc.). My dad and grandpa were VERY thorough to the point it annoyed me. Upon starting it, the car is missing VERY badly, at low RPM's. I replaced the IAC (new from ford - $120), I have 3 or 4 MAFS, Also 3 or 4 throttle bodies, along with TPS sensors. No Boost/Vac lak ... at least that I know, when it is idling, it is below the "ING-HNG" or whatever - (sorry I haven't started it in a LONG TIME - at least below -15/20lbs whatever is below "9 'oclock"). I am SO confused. Checked the fuel pressure at the rails, changed the fuel filter also.... I don't mind paying someone if they could help me out... I am just SO frustrated I don't know what to do...

Also - plugs/wires are new, as well as both O2 sensors...

91 sc - put the stockgears back on, underdrive pullyes, rear air hydraulics, headers, no cats or resonator, lowered 1 1/2", 10% pulley, cam, 70k, rebuilt engine bored .30 over, finally fixed!
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post #2 of 24 (permalink) Old 01-05-2008, 06:49 AM
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Can you take it past "low RPM's" or is it just a terrible miss no matter how hard the engine is turning?

May sound dumb, but make sure the plug wires are on correctly.

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post #3 of 24 (permalink) Old 01-05-2008, 07:15 AM
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If your car has a cam position sensor, you might have installed the synchronizer assembly incorrectly. Doing so would cause fuel to be out of sync with spark, which could be what you are experiencing.

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post #4 of 24 (permalink) Old 01-05-2008, 03:52 PM
 
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Make very sure the plug wires are on correctly, it is very easy to mix them up. If you need more info or assistance, let me know.
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post #5 of 24 (permalink) Old 01-06-2008, 10:53 AM Thread Starter
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I am positive the plugs are on correctly - I need to check the cam sensor though - It may be installed incorrectly. I remember my grandpa installing it with me, and he somehow used a voltmeter, and we installed it right when it started getting voltage as per the instructions he had. My question is couldn't it be 180 degrees off? he said that that shouldn't matter or something and I took his word for it because generally he is ALOT smarter then I am! But does anyone have the correct procedure for installing the cam sensor? Also, is there a way to tell if the sensor is BAD, or just mis-aligned?

91 sc - put the stockgears back on, underdrive pullyes, rear air hydraulics, headers, no cats or resonator, lowered 1 1/2", 10% pulley, cam, 70k, rebuilt engine bored .30 over, finally fixed!
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post #6 of 24 (permalink) Old 01-06-2008, 11:06 AM
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does your car miss at higher revs?

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post #7 of 24 (permalink) Old 01-06-2008, 11:56 AM Thread Starter
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I haven't driven it recently, but what I can remember, I don't think so - its like 4000 rpm and under. And it is like I can't pull away from even a civic! I keep hearing 2 different stories about the cam sensor - #1 it is only affecting you when your car starts (used just to tell the DIS the timing and what stroke your pistons are, etc) and #2 it is used while your car is actually running, and can make your car hesitate, miss and etc. Which is true?!?!

91 sc - put the stockgears back on, underdrive pullyes, rear air hydraulics, headers, no cats or resonator, lowered 1 1/2", 10% pulley, cam, 70k, rebuilt engine bored .30 over, finally fixed!
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post #8 of 24 (permalink) Old 01-06-2008, 12:16 PM
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The crank sensor is what controls starting, the cam sensor affects while running I believe.

- Stephen

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post #9 of 24 (permalink) Old 01-06-2008, 01:58 PM
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Quote:
Originally Posted by 94mncougar View Post
The crank sensor is what controls starting, the cam sensor affects while running I believe.

- Stephen
No, it's the other way around as far as starting. Cam sensor syncs the fuel and spark, crank sensor is used while running. Now I don't know for sure if a bad cam sensor will cause it to run rough, but I do know 100% that it is used during starting.

I've never owned an SC so I don't know the specifics of this engine like how the synchronizer works and such, but I'm certain this is how the sensors are set up.
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post #10 of 24 (permalink) Old 01-06-2008, 02:17 PM
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also, try www.tstacc.com, or www.mamn12.com there's people in DE, PA and NJ that might be near you and that could lend a hand.

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post #11 of 24 (permalink) Old 01-06-2008, 05:21 PM
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I know Ben999 is reasonably close to you. I would offer to make a trip out but my supercoupe tech is lacking.

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post #12 of 24 (permalink) Old 01-07-2008, 12:47 AM
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Yes the cam sensor is used during startup. If it is installed incorrectly, the PCM will be commanding fuel to be delivered at the wrong time during the 4-stroke cycle. Installing it 180* out would cause backfires and such through the intake manifold.

There is a special tool needed to install the synchronizer assembly. The tool locks the spinning shaft to a specific point in relation to the base of the assembly, and then the synchronizer is installed with the crankshaft at a specific timing point.

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post #13 of 24 (permalink) Old 01-08-2008, 12:14 AM
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i doubt it is 180 off if it actually runs

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post #14 of 24 (permalink) Old 01-08-2008, 12:28 AM
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Did you have the head's redone?

Could be a slightly bent valve or a broken valve spring.

Do a compression test just to be sure.

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post #15 of 24 (permalink) Old 01-08-2008, 09:01 AM
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Quote:
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i doubt it is 180 off if it actually runs
I dont know about these motors as much but you would be surprised how simple fuel injection can be. My XK6 had "batch injection" Meaning it would fire the injectors (all 6) twice per crankshaft revolution, with the events not timed to any cylinder. And yes the injectors were right next to the intake valves. Its definately not the most efficient (people have seen 30-40 hp gains by going to a better management system) but it does run and make about 200 hp.

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post #16 of 24 (permalink) Old 01-08-2008, 10:59 AM
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The cam sensor can not be causing your problem. You wouldn't notice any performance difference regardless of when the injectors are fired because the fuel will not have enough time to fall out of suspension, and when the intake valve opens, it will suck in the same air/fuel mixture regardless of when the injector sprayed.

Does the engine rev up fine in neutral? Is this misfire problem only present under load, or in neutral as well? If the problem is dependent on rpms, but not load, I would suspect something in the ignition system, maybe a bad coil pack or ignition control module or something like that. If it only misses under load, then it could be a bad plug or wire, or maybe a vacuum leak somewhere. Just because the gauge reads fine doesn't mean that there isn't a vacuum leak. With the car idleing, search around to see if you can find any leak. Use a can of carb cleaner to confirm leaks if you need to.

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post #17 of 24 (permalink) Old 01-08-2008, 05:24 PM
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Quote:
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No, it's the other way around as far as starting. Cam sensor syncs the fuel and spark, crank sensor is used while running. Now I don't know for sure if a bad cam sensor will cause it to run rough, but I do know 100% that it is used during starting.

I've never owned an SC so I don't know the specifics of this engine like how the synchronizer works and such, but I'm certain this is how the sensors are set up.
Why is it then that 4.6L V8's have to always mess with the crank sensor or its connector to get the engines to start? I'm not saying you're wrong, just getting clarification.

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post #18 of 24 (permalink) Old 01-08-2008, 07:18 PM
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Why is it then that 4.6L V8's have to always mess with the crank sensor or its connector to get the engines to start? I'm not saying you're wrong, just getting clarification.

-Stephen
Because the crank sensor is used while starting AND while running. Hotbird didn't say that explicitly but I think that's what he meant. After the PCM gets the fuel sync info from the cam sensor, it is no longer needed to run.

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post #19 of 24 (permalink) Old 01-08-2008, 08:34 PM
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On a 4.6
Crank sensor is ran by the 36-1 trigger. the trigger wheel makes one full rotation per single crank rotation that tells the ecu what position the rotating assembly is on. this then triggers edis to fire (waste spark so even if the cyl is on its exhasut stroke it still fires the plug) the cam senor is triggered by the bump on the cam sprocket. this will tell the ecu whether a paticular cyl is on its exhasut stroke or the intake. it can tell this because the cam sprockets make one rotation per two crank revolutions wich will be a complete cycle. This will allow the ecu to know what injector to fire. Im no expert that is some of what i understand

the 4.6 runs sequential injection. the 3.8 runs batch or known as multi port fuel injection where it fires batches of injector at a time. I thought 3.8s were sfi shows how much i knew haha

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post #20 of 24 (permalink) Old 01-09-2008, 09:51 AM
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sc engine

did u check ur dis-mod, did u take it off on the from the plate,.if i did did u put it back on without the grease?..check ur ic pipeing if u didn't reseal them ur could be getting a very bad mis...just my 2 cents.
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post #21 of 24 (permalink) Old 01-09-2008, 10:30 PM
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the 4.6 runs sequential injection. the 3.8 runs batch or known as multi port fuel injection where it fires batches of injector at a time. I thought 3.8s were sfi shows how much i knew haha
I don't know about the earlier ones, but the 96+ are most definitely SFI. It couldn't be OBDII compliant otherwise.

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post #22 of 24 (permalink) Old 01-18-2008, 02:19 PM Thread Starter
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how do you check to see if the DIS is good/bad? I have taken it off before (and put dielectric grease back on). Or could my FPR be bad? Could that be causing the computer to think its running lean? I remember there was god pressure at the rails, but I don't remember if it de-pressurized quickly... could this be why I am getting a lean reading for both banks, and the missing, but then when the car gets going (above 3500 rpm) it starts to pull boost and doesn't drive as badly? I would think if I had a fuel problem, I would have opposite problems (like under load not running right). Arrgh I want to flip out because I have been trying to troubleshoot this for years now...

91 sc - put the stockgears back on, underdrive pullyes, rear air hydraulics, headers, no cats or resonator, lowered 1 1/2", 10% pulley, cam, 70k, rebuilt engine bored .30 over, finally fixed!
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post #23 of 24 (permalink) Old 01-18-2008, 04:04 PM Thread Starter
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ok - well I took my DIS and got it tested - it is fine - they ran the test 3 times to make sure it stayed good even when it got hot. Is the FPR beneath the intake plenum on the pass side? I remember smelling gas under the hood at one point in time - its been so long (1 1/2 years) since I really drove it, and that was the last time I did the KOER test. All I remember was 2 codes being thrown - engine running lean on bank a and bank b. I will have to check the idle again, but I remember putting on a different TPS and TB, and from what I can remember now it seems to idle normally, but still gets the CEL light randomly when driven.

91 sc - put the stockgears back on, underdrive pullyes, rear air hydraulics, headers, no cats or resonator, lowered 1 1/2", 10% pulley, cam, 70k, rebuilt engine bored .30 over, finally fixed!
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post #24 of 24 (permalink) Old 01-22-2008, 04:30 PM Thread Starter
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bump to the top - any answers here???

91 sc - put the stockgears back on, underdrive pullyes, rear air hydraulics, headers, no cats or resonator, lowered 1 1/2", 10% pulley, cam, 70k, rebuilt engine bored .30 over, finally fixed!
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