Question about 2003 Cadillac Deville

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2003 Northstar 4.6 L V8 VIN #Y. Engine runs rough. No problem with acceleration though. Replaced spark plugs and coil boots to no avail. Warning engine light still lights. OBDII says lean on banks 1 & 2. My mechanic syad I neede to replace the coil packs but, I don't see how that would help. Any suggestions?

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Posted on Jan 02, 2017

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Try running some fuel injector cleaner through your fuel tank. What you may have are a couple of plugged or missfiring fuel injectors. I would suggest checking all of your wiring to your injectors to insure good connection, replace your fuel filter and check for vacuum leaks.

Posted on Jul 20, 2009


SOURCE: 1999 deville 4.6 northstar engine

say what?

Posted on Aug 18, 2008

  • 41 Answers

SOURCE: car won't pick up speed on acceleration

You're not getting enough fuel. You should check your fuel pressure. If you have enough fuel pressure, your injectors are probably clogged up. Run a lot of fuel cleaner through your tank when you put gas in and see if it makes any difference. Lucas fuel treatment is the best to use.

Posted on Apr 26, 2009

  • 1071 Answers


there is only one bank on a pt cruiser and yes it could be a fuel pump or a vacuum leak

Posted on Aug 06, 2009

  • 44 Answers

SOURCE: 2004 caddy deville customer changed

change coolant temp sensor. it will be reporting wrong leading to the misfire.

Posted on Aug 21, 2009

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P1312 2003 rodeo 3.2L and poor acceleration

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Engine Performance problem 2002 Ford F150 V8

Hello Bret.
These codes are indicating engine misfires. 303 is cylinder #3 and 304 is cylinder #4. The 316 indicates that the misfire happened in the first 1000 revolutions.
These trucks are notorious for misfires. The most common issue is ignition coil failure. Failure on these coils can be accelerated though by spark plugs that are worn and contamination from oils, antifreeze leaks and water.
If it has been some time since you have replaced the spark plugs this may be an opportune time to do so. This job isn't for the faint of heart or those with little patience. Some of the coils and plugs are difficult to access, especially #7 and # 8. I also recommend torquing the spark plugs properly as there are some thread stripping issues on the spark plug threads with these engines.
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Where are the spark plugs located? and how do I get to them?

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2 Answers

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I'm not sure if the Northstar has it anywhere. Just for your info though, the firing order is as follows:


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Hope helped (remember rated this help) Good luck.

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2 Answers

Rough running.

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