YACT: Bad compression...

[Toastedlightly]

I have a '98 Grand Prix SE. (3.1L). I took 3 of the plugs out (ones facing the front) and put them back in, hooked up all the wires and stuff. Now I have a really bad mis-fire. My dad believes it is low compression, but I've tried re-seating the plugs and got nothing. If I happened to cross-thread the plugs (unlikely, but I might have done it) would there be a way to fix it?

cliffs:
Maybe a crossthreaded plug, how to fix?

EDIT: My car = reincarnated Christine. Service engine soon light went out as I was delivering newspaperes and I get no more stuttering. I am scared.

 

[jlee]

Have you ran a compression test on it?

My MR2 had no compression in cyl#4 and still ran fine..I'm assuming all the plug wires are connected properly?

 

[deadlyapp]

if its low compression it will still run, just feel really laggy.

I would say check the gap on the new ones and the old ones(if you replaced them) and see if they are the same. You may not need to gap, but yah...

Other then that, make sure that you hooked the plugs in the right way, they do have a numerical order, and they fire at different times, so if you hooked it up wrong, you are fsked.

 

[Black88GTA]

Crossed plug wires? Boot not seating properly on one of the plugs? It's possible for the rubber boot to be on the plug, but the metal part inside not making contact with the end of the plug...

 

[Toastedlightly]

Originally posted by: Black88GTA
Crossed plug wires? Boot not seating properly on one of the plugs? It's possible for the rubber boot to be on the plug, but the metal part inside not making contact with the end of the plug...

Everything chekced. All wires correct. No tester for compression 🙁. Would cross threading cause bad compression? And can I fix the bad cross threading?

 

[Black88GTA]

It's also possible that one of your wires broke internally...it may look good from the outside, but the conductive part under the insulation might have broken at some point.

I wouldn't rule out cross threading either 🙁. Hopefully that's not it.

EDIT: I think it's possible to fix a cross threaded plug hole, but don't have much experience with it. I've never had to do it, so I've never looked into it.

 

[jlee]

When you installed the plugs, did you finger-thread them in? If they turned a few times by hand, they shouldn't be crossed..

 

[Rastus]

If you cross threaded one, you definately would know by now, the plug would not have gone in at all. Check the gap. Check cap and rotor if your car has one. Check the wires.

 

[Toastedlightly]

Originally posted by: CadetLee
When you installed the plugs, did you finger-thread them in? If they turned a few times by hand, they shouldn't be crossed..

They were finger threaded. My dad just told me that he is getting a bad compression code. Hmm.. not sure if that is what he says or if it is what the problem actually is.

 

[Black88GTA]

Originally posted by: Toastedlightly

Originally posted by: CadetLee
When you installed the plugs, did you finger-thread them in? If they turned a few times by hand, they shouldn't be crossed..

They were finger threaded. My dad just told me that he is getting a bad compression code. Hmm.. not sure if that is what he says or if it is what the problem actually is.

When you tightened them...you didn't overtorque them and strip the threads in the hole, did you? This isn't that hard to do in aluminum heads...(I don't know if your car has aluminum heads, but I figured I'd throw it out there anyway)

 

[Viperoni]

Broken spark plug ceramic insulator or bad plug wire.

 

[Toastedlightly]

Originally posted by: Black88GTA

Originally posted by: Toastedlightly

Originally posted by: CadetLee
When you installed the plugs, did you finger-thread them in? If they turned a few times by hand, they shouldn't be crossed..

They were finger threaded. My dad just told me that he is getting a bad compression code. Hmm.. not sure if that is what he says or if it is what the problem actually is.

When you tightened them...you didn't overtorque them and strip the threads in the hole, did you? This isn't that hard to do in aluminum heads...(I don't know if your car has aluminum heads, but I figured I'd throw it out there anyway)

nope. I did use an extension w/ a socket attached (too hard to get down in there w/ fingers) to do the initial tightening, then I did ~1/8 a turn once it was finger tight (w/ ratchet)

 

[jlee]

You may want to just pick up a set of OEM plug wires and see if that fixes it 🙂

Two people at work have had problems with their cars (running weird)..plugs/wires fixed both of them. ('97 Integra and '97 Eclipse GST, IIRC)

 

[Toastedlightly]

update

 

[lightpants]

Did you replace the plugs or just put the old ones back in?

 

[Demon-Xanth]

Yes. It is possible to fix thread holes. But it can't be done by most people in thier garages. What most likely is at fault is a spark plug wire.

 

[Eli]

Something tells me your dad has little idea of what "compression" actually is. 😛

 

[TwoBills]

Originally posted by: Demon-Xanth
Yes. It is possible to fix thread holes. But it can't be done by most people in thier garages. What most likely is at fault is a spark plug wire.

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Yep, probably the wires. Pop the hood, at night, and check for arcing while the car is running.
Auto Zone will "lend" you a compression tester. While you're there get them to read the codes, again.
Listen to your dad. Chances are he'll steer you in the right direction.
If a plug is stripped you can get a repair kit.
edit: If that car runs coil packs, that's something to suspect.