Still can't pin the problem down

Goldeneagle

Registered User
I have a random "hard" miss in this SC of mine. And when I say random, I'm refuring to it not happening on every revolution on the firing secquence. There are no codes coming up, I've changed the plugs, wires, the D.I.S., put fresh gas in it, ran sea foam through the fuel system and still can't seem to get the bug out. It doesn't seem to do it or at least do it as bad when it is dead cold, but it is quite bad after it warms up. If it is sitting at an idle it does not have the problem. I'm guessing a sensor, but which one is where I'm lost.

Thanks in advance for any help.



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describe the miss more. You are calling it "hard" but that isn't enough information. Do you feel like it is a miss in the traditional sense (a cylinder falling out) or more dramatic where every cylinder seems to fall out (whole car seems to buck)?
 
Have you replaced the cam position sensor?

Thanks for the replys, no, I have not yet replaced the cam position sensor.

describe the miss more. You are calling it "hard" but that isn't enough information. Do you feel like it is a miss in the traditional sense (a cylinder falling out) or more dramatic where every cylinder seems to fall out (whole car seems to buck)?


Yes, it does feel more dramatic, as if all cylinders seems to fall out, but only for an instant, then back to full power. Something else to note, it is a 92 engine that has been gone through and built (not by me so I have no idea the exact spec's) and has a 94-95 type blower with a 10% pully for far higher boost. When at full throttle the OEM guage pegs 15+ lbs of boost, and the after market gauge shows 28-30+ psi. Now I hane been told that "that" was not possible and that 22-24 was the most that I could achieve, so that said, is it possible that I need an even higher grade of fuel (more than the 93 I have been using)?

Thanks again for any help.

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Thanks for the replys, no, I have not yet replaced the cam position sensor.

Unplug it! Do a search on how to get the engine started with the cam sensor disconnected.

Yes, it does feel more dramatic, as if all cylinders seems to fall out, but only for an instant, then back to full power.

I have the same problem with my red car.. runs perfectly but occacionally has a hitch as if everything just drops out. I only notice it when stopped at stoplights. I plan to swap out the crank sensor as that is the closest thing I know of that has produced this problem in the past. I pull both type of codes (KOEO/KOER + Cylinder balance) regularly and everything is perfectly clean. I have also swapped out everything involved including MAF, DIS, EEC, ECT, ACT, O2, TPS, CID, plugs, wires, coil pack, upper wiring harness, and FPR. I have resealed the IC tubes, and tested every vacuum line available... all to no avail. :confused: The only thing left is the crank sensor.
 
Unplug it! Do a search on how to get the engine started with the cam sensor disconnected.

I have also swapped out everything involved including MAF, DIS, EEC, ECT, ACT, O2, TPS, CID, plugs, wires, coil pack, upper wiring harness, and FPR. I have resealed the IC tubes, and tested every vacuum line available... all to no avail. :confused: The only thing left is the crank sensor.

Yeah, sorry, I forgot to put in there that I have replaced the coil pack twice and the O2's once. also didn't put in there it has a double ic with push and pull fans. I guess I try the crank sensor. :)

Thanks.


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Thanks for the replys, no, I have not yet replaced the cam position sensor.




Yes, it does feel more dramatic, as if all cylinders seems to fall out, but only for an instant, then back to full power. Something else to note, it is a 92 engine that has been gone through and built (not by me so I have no idea the exact spec's) and has a 94-95 type blower with a 10% pully for far higher boost. When at full throttle the OEM guage pegs 15+ lbs of boost, and the after market gauge shows 28-30+ psi. Now I hane been told that "that" was not possible and that 22-24 was the most that I could achieve, so that said, is it possible that I need an even higher grade of fuel (more than the 93 I have been using)?

Thanks again for any help.

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Something is wrong if you are seeing 28-30 psi on an aftermarket boost gauge. Even with a stock cam and heads you would hard pressed to exceed 17 psi with that combo. There would have to be a major obstruction in the return plenum/intake manifold. I've also heard of clogged cats increasing boost, but not that much.

David
 
Something is wrong if you are seeing 28-30 psi on an aftermarket boost gauge. Even with a stock cam and heads you would hard pressed to exceed 17 psi with that combo. There would have to be a major obstruction in the return plenum/intake manifold. I've also heard of clogged cats increasing boost, but not that much.

David

Okay, I'll have to check the intake, get my little camera probe out and stick it in the back plate, and I don't know if the heads are any kind of an upgrade, however the car does lobe left to right, a little like my ol' big block chevy that was bilt to hilt, so I think it has a bit of an upgraded cam. As for the cats, it is two 2 1\2" straight pipes all the way back off the exaust mans. The only obstruction in them is the O2 sen's

Thanks David


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Okay, I'll have to check the intake, get my little camera probe out and stick it in the back plate, and I don't know if the heads are any kind of an upgrade, however the car does lobe left to right, a little like my ol' big block chevy that was bilt to hilt, so I think it has a bit of an upgraded cam. As for the cats, it is two 2 1\2" straight pipes all the way back off the exaust mans. The only obstruction in them is the O2 sen's

Thanks David


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I'd try another boost gauge.

Assuming this only happens at wide open throttle under boost, it may be as simple as tightening the plug gap to .040". What brand coil pack, wires and plugs are you using ?

David
 
I'd try another boost gauge.

Assuming this only happens at wide open throttle under boost, it may be as simple as tightening the plug gap to .040". What brand coil pack, wires and plugs are you using ?

David

Try a different gauge, got cha, ok. As for the coil, it's a accel super coil. The plugs are standard Autolite 103 plugs @.060 gap, and the wires are 8.2mm, Blue Taylors. I'll have to see if a local speed shop has a boost gauge I can borrow for a day or two.

Thanks once again David.


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Try a different gauge, got cha, ok. As for the coil, it's a accel super coil. The plugs are standard Autolite 103 plugs @.060 gap, and the wires are 8.2mm, Blue Taylors. I'll have to see if a local speed shop has a boost gauge I can borrow for a day or two.

Thanks once again David.


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Does it only missfire under boost ?

David
 
try and stick to one issue per thread.

On the missing issue... sounds like a cam sensor issue. If it was the crank sensor, you'd throw a code and in general they don't fail half way. Best way to check is to disconnect the cam sensor and drive the car that way a couple days. If the miss is gone, then get a new cam sensor.
 
Hmm ... One thing to check is the ignition switch. The idea of all cylinders going dead at once is pretty foreign to me. I have replaced crank sensors, cam sensors, and DIS modules, and the symptoms don't seem to match exactly. It could still be that. But I am wondering if power to all systems is getting cut off intermittently.
 
The question of does it only happen under boost should be answered. If its completely random, it could be a power, ground issue. But if its only under boost then you need to isolate the parts of the system consistent with that.
 
Does it only missfire under boost ?

David

The really hard miss or drop out only happens under full throttle hard exceleration, however, it does seem to (for lack of a better term) spit, studder, but this it only after it warms, then ramdomly spit or studder. The more I do the hard exceleration, and think about it, the way it feels, the more I am wanting to say, and I know this sounds crazy, but it feels like it's backfiring, or at least trying to, as if the car isn't just missing, but hitting the brakes, but only for an instant, then back at full power.

I want to thank everone for helping me. I will try just about anything to get this fixed:)
 
So you replaced the DIS, but was it with a new one? Is it Motorcraft? I have replaced them with used an had a bad one still.

Where are you located? Chances are someone is near you that could help out.

DIS, Cam, Crank would be the first too look at as already suggested. Has the Cam Sensor been unplugged and the car driven yet?
 
So you replaced the DIS, but was it with a new one? Is it Motorcraft? I have replaced them with used an had a bad one still.

Where are you located? Chances are someone is near you that could help out.

DIS, Cam, Crank would be the first too look at as already suggested. Has the Cam Sensor been unplugged and the car driven yet?

I have not yet unpluged the cam sensor and tried that yet, I'll do that in a little bit. As for the D.I.S. No, they are not new, I have three and borrowed one from a friend that has a DD SC 93, it doesn't seem to make any difference which one I put in. I put the ones I have in his SC and they worked good in his car, so I'm thinking they're all good, I could be wrong though. Oh, and yeah, they are all motorcraft. Do they make aftermarket ones? If they do, are they any good, or better, should I go get an aftermarket D.I.S.? Do you think that would help?

I can't thank you all enough for the help.


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