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Discussion Starter #1
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...
 

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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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Discussion Starter #5
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?
 

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Discussion Starter #7
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?!?!
 

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The crank sensor is what controls starting, the cam sensor affects while running I believe.

- Stephen
 

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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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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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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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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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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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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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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.

-Stephen
 

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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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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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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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