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Greetings all, I just purchased a 2000 STS with 171,000 miles. Paid $3600 for the car anticipating a few issues to deal with. I wasn't disappointed. No coolant or overheating issues, need an a/c hose and a motor mount all things I can handle.

Being an old car guy, literally and figuratively, I have a miss that I would diagnose as a plug wire on any car that had plug wires. I changed, the front coil pack because I found a crack in one of the posts, changed the plugs and cleared the PO300 code. The miss is still there and it varies in severity. Raise the car to 1500 RPM no load and it's smooth, same RPM under load and it appears. Before I bring it to the dealer is there a way to bench test the rear coil pack before I buy one on spec? Is there any other obvious thing to look for? I have the FSM's but I got headache the first time I started reading.:rolleyes:

Before I insatalled the new plugs I checked the gap...read somewhere on this forum that checking the gap could ruin the plug!! Is that true? I didn't need to adjust them just used a smooth flat feeler gage to check.

Thanks in advance

ErnieR
 

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White Diamond '03 DHS (with DTS floor shift)
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Checking the gap won't hurt a thing. I am sure there is a way to check the ignition module, but I don't know how. The FSM should have the procedure. Start by taking 2 Advil. Maybe one of the techs will chime in with better advice.
 

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1992 STS / 2005 MB G500 / 2003 STS / 2006 XLR-V
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P0300 is not necessarily due to an ignition component failure. In fact, alot of times the dreaded P0300 is one of the first pre-cursors to headgasket failure. Not saying thats the case here, but you already replaced exactly what would have been my first guess as well.

I havent really heard of the ignition system failing too often in these cars.
 

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Discussion Starter #4
There are no symptoms of any coolant problems, temp remains steady, oil is clean, no coolants loss.

I noticed that in trying to isolate a bad cylinder by pulling the injector wires that the problem seemed to lessen and then for awhile disappear. It has resurfaced and I'm now looking to a clogged injector or two, comments?

Ernie
 

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99 STS
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Ya know I had the exact same symptoms in my 98 granted its an SLS, but a change of the #6 plug fixed it so, I really have no idea what to tell you, mostly just wanted to say CONGRATS on the new STS! haha

Adam
 

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Discussion Starter #6
2000 Cad Seville, 172,000 miles. On Board DIC shows P0300. Basic scan tool shows P0303. In attempt to isolate the miss here's what was done so far...2 new coil packs, new plugs, switched plug from another cylinder and then the injector with another cylinder but miss stays with #3. Sprayed carb cleaner looking for vacuum leaks--none obvious.

There are times that after I play with it enough the miss lessens and disappears for a short while but always comes back. No matter what it will always show a blinking MIL at wot in second gear at the top of the RPM range.

Here's the freeze frame...

TP 0%
671 RPM
LOAD VALUE 1.9%
AIR FLOW 7.06
MAP 51 KPA
COOLANT 199
INLET AIR 123
TIMING 5.5 ADVANCED
SHORT T FUEL TRIM 1 .7%
LONG T FUEL TRIM 1 3.9%
SHORT TERM FUEL TRIM 2 .7%
LONG TERM FUEL TRIM 2 6.2%
SHORT TERM FUEL TRIM 3 72.6%
LONG TERM FUEL TRIM 3 -70.2%
LONG TERM FUEL TRIM 4 35.9%

0 MPH
CLOSED LOOP

Can a crank sensor cause this? There is no difficulty starting and no stalling. From an old "carb and points" guy it reminds me of a shorted plug wire but there are no wires. The plug boots are OK and there was no evidence of fouling on the old or the new plugs.

When I unplug the O2 sensor in the back of the engine before the CAT there is no difference in the way the engine runs and with codes cleared it didn't set a new one.

Haven't done a compression test but the miss is not rythmic like a dead cylinder would be. In fact, there are times it goes away or lessens to a point where it's barely noticeable. That doesn't last for long though.

Thank you in advance for your help.

Ernie [/b]
 
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