: P 0300 code 2005 DTS - can't find the miss



bigmikeb4747
03-31-13, 06:00 PM
ok ive got a 2005 deville dts , it has 140000 miles on it was running fine then started having rough idle out of nowhere mostly feel it only at idle ...i cleaned throttle body and maf sensor and put some redline fuel treatment in ...then couple days later i was checking for vaccum leaks couldnt find any but while car was idlein in driveway service engine light comes on ...use onboard diagnostic and says p0300 random misfire ...go to oreillys have them check with scanner hoping to find what cylinder and only thing was p0300 random misfire ....i changed plugs about 8000 miles ago with ac delco 41-987 i had coil go bad and changed rear coil about year ago just in case i changed the front coil out with a new one seemed to help a lil but code came back ..i then changed out both ckp sensors and tryed to do a manual relearn that i found online on highway car does fine service engine light flashed and came on again in my driveway for few seconds then went off same code ....i changed fuel filter just in case ....i checked fuel pressure turn key on and got 45 psi then about 35 after it started and idles but as soon as i turn off key pressure almost drops to 0 ..shouldnt it hold pressure at least for few minutes ? took vaccum line off fuel pressure regulator no sign of fuel does this mean leaking injectors ? could not find any idle change sprayin intake manifold hoses dirty or clean pcv line or plenum ....tightened intake manifold bolts as seemed couple were pretty lose ...where do i go next any ideas would be appreciated ....thanks mike

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sorry about the long post just trying to give as much info as possible ......dont think i have head gasket problem coolant level been fine .....smelled overflow bottle dont smell any exhaust gases ...also took overflow lid off and started and watched for bubbles no sign of any ...im stumped dont really even trust taking to local mechanic ....is dealership my best option to diagnose have asked around and havent found any good northstar techs in dfw texas area

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oh yeah after i changed fuel filter and checked fuel pressure had idlein in driveway and if i give it gas seems to bog down which didnt happen at first and looked like lil white smoke out exhaust when i gave throttle ....and thats about all the info i can think of ...lol thanks guys for any help

Submariner409
03-31-13, 07:03 PM
Sounds like a stuck injector (uncommon) - listen to each at idle with a mechanic's stethgoscope - you should get a steady tick, tick, tick, tick ....

Fuel pressure should go to ~40 psi at key: ON and be 41 - 47 running. No fuel at the FPR vacuum nipple usually means the FPR is OK.

daveyhouse
03-31-13, 07:55 PM
On my P0300 I took a pair of insulated pliers and pulled a plug wire one at a time while engine was idling to see which one was not firing. That told me which cylinder it was. My case it was a bad injector (As Sub mentioned), putting too much fuel in. Except it wasn't stuck ??? When engine was off, it held pressure in the rail???

bigmikeb4747
03-31-13, 10:47 PM
ok thanks submariner and davey house ...but i did listen to the injectors and they seem like they are tick tick in ...i dont have plug wires to pull ...whats the best way to figure out if i need regulator or injectors or fuel pump and if it is injectors is there a way to check them ? no fuel in line on regulator so does that mean my best bet is injectors ? and if so how to narrow them down or just try and do ALL 8 ...

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no visible fuel in line going to regulator ...and im pretty sure when i tested fuel pressure it was 45 for initial burst with key on then like 35 or 36 running in park is that enough or do i have a weak pump ?

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and do yall know what the best brand of injectors ? i was gonna try borg warner bwd .....anyone had any experience ?

daveyhouse
03-31-13, 11:17 PM
No plug wires? Is there a way to disable one injector or coil at time while idling to find the troubled cylinder? Try to pinpoint first before throwing parts at it.

Ranger
03-31-13, 11:57 PM
2000+ engines are COP (Coil On Plug) ignition so they have no plug wires.

Might be able to disable injectors with a Tech II. I think we lost that capability with OBDII.

bigmikeb4747
04-01-13, 10:24 AM
ok guys thanks im not sure of a way to disable injectors or coils ...thanks for all the help ....

Submariner409
04-01-13, 11:09 AM
Not sure in a 2005 - does each injector still have a safety-locked electrical connector ? How about the coil trigger wiring ?? If they're separate connectors off a harness you could tediously pull one connector at a time and figure out which coil/injector did not change idle speed when disconnected.

bigmikeb4747
04-03-13, 05:01 PM
i think each injector has the connector you mentioned .....thanks submariner ...ive ordered a set of acdelco new injectors just waiting for them to come in i sure hope this gets her back on the road thanks for all help will update once i get injectors in

Submariner409
04-03-13, 06:59 PM
That's a heck of a lot of money to spend on easter-egging parts with no basis. I'll bet the problem is NOT injector(s). You could have done a good fuel system cleaning with a 20 oz. jug of Chevron TECHRON and a fill-up of Top Tier gasoline.

I suggest that you subscribe the car to www.alldatadiy.com - there are things you'll need to know when pulling the fuel rail - pressures, tests, fuel rail quick-disconnect procedure, re-priming.

bigmikeb4747
04-03-13, 07:43 PM
well because it didnt hold fuel pressure as soon as i turn key off and you had also mention it sound like a stuck injector so i thought that was my best bet was to go ahead and replace the injectors ...i ran a bottle of redline fuel treatment and before that had ran some seafoam .....