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Skipping motor

whity whity
New User | Posts: 3 | Joined: 12/08
Posted: 12/02/08
11:29 AM

Confused Skipping: I have a 1999 Tahoe 5.7 with a skipping problem. I've done a new tuneup with ac delco parts (plugs, wires, cap, rotor). Changed the evap. emisions, crank sensor. Had the injectors profesionaly ground and cleaned. Still have a skipping problem. The check engine light flashes and stays on for a cople days then turns off. I've had it diagnosed to a misfire. The chevy garage said it may need a valve job but they cant guarranty that will fix the problem. $2000.00 is tuff to swallow for an uncertain fix. I'm at a loss. If anyone knows of a solution I would greatly appreciate it.

Help: Steve  

Wenis Wenis
User | Posts: 132 | Joined: 10/08
Posted: 12/02/08
05:06 PM

Whity , Did you get the code that's stored? Misfires aren't that bad to diagnose, get the code for me, How many miles you have on it?

Lets fix this over the net, God I love it! Grin  

whity whity
New User | Posts: 3 | Joined: 12/08
Posted: 12/02/08
07:46 PM

Code just said misfire on cylinder 5. Milage is 145000. I always get the same code. its been coded 3 times with the same code. With the exception of 1 time for crank sensor and evaporative emisions sensor. Confused  

Wenis Wenis
User | Posts: 132 | Joined: 10/08
Posted: 12/02/08
10:20 PM

Crank sensor and evaporative emissions sensor are most likely different problems.

The PO305 tells us that the miss is happening on of course #5 cylinder. Probable causes.

1- Electrical, plugs, wires, maybe a vacuum leak, internal or external, intake gasket.
2- Injector with poor flow, or electrically weak or inop, pretty common.
3- Being it has fairly high mileage, it could be valve springs weak or broken.

Lots of maybe's, gonna need some help on this one I think.  

whity whity
New User | Posts: 3 | Joined: 12/08
Posted: 12/03/08
09:47 AM

If I use super unleaded it doesnt seem to happen as often. When the injectors were ground they checked for flow and electrical. All was ok. Did complete tune up 3 times. As far as valve spring I dont think any one checked that. Is this something that needs a tech or can I do it. Is there a posibility it may be cat. is starting to get pluged. Wet or dry outside it doesnt matter ether way.  

Wenis Wenis
User | Posts: 132 | Joined: 10/08
Posted: 12/03/08
11:20 PM

There's lots of things it could be, I'm not really sure what you mean by injectors ground, never heard that term before.

The valve spring on #5 cylinder can be checked simply by removing the valve cover and visually inspecting it, you have to look pretty close at it to see if it's broken though, they will usually break off the bottom coil. If it's broken it's probably better if a shop did this.  

While the engine is misfiring the light will flash, when it quits misfiring the light will stay on steady, you probably felt the miss if you were driving.

Example, If you accelerate hard from a stop the misfire can be felt and the light flashes, when you let off it goes away and the light will become a steady light, thus a code will be set.

It really needs someone with experience to look at it, needs to be scanned and drove to see whats really happening there.

I wish I could nail it down for you but it's hard if I can't see the truck. Tongue  

lisa Smith lisa Smith
New User | Posts: 1 | Joined: 01/13
Posted: 01/27/13
07:56 PM

i have a 2003 pontiac grand am that ran hot a few times in the past 2 weeks. last week, we changed intake gaskets. 2 days later, it ran hot again. it started skipping very bad. it fluctuates from bad to good. worse when stopped, seems like it wants to stall and sometimes will. it shakes motor and you can hear it coming out muffler. was still running hot and seemed to take alot more water than normally. we changed thermostat tonite and still running bad. don't know if still overheats. PLEASE GIVE ADVISE!!!!!!!!  

waynep71222 waynep71222
Guru | Posts: 823 | Joined: 03/12
Posted: 01/27/13
10:18 PM

any of the 3 possible motors that come in the car don't like to be overheated..

2003 Pontiac Grand Prix: Available engines
6 Cylinders 1 3.8L SFI SC OHV (found in 06% of 2003 Pontiac Grand Prix)
6 Cylinders J 3.1L SFI OHV (found in 53% of 2003 Pontiac Grand Prix)
6 Cylinders K 3.8L SFI OHV (found in 41% of 2003 Pontiac Grand Prix)

all of these motors require 50% to 70% coolant .. or straight coolant as specified by the owners manual.

diluting or running straight water will cause them to over heat..

the 3.1 motor has a bleeder screw above the water pump housing in the heater hose pipe that runs to across the front of the cylinder head..

how is the water pump...  is it leaking???   have you pressure tested the cooling system... i normally pressurize it with a proper tool to 7 to 9 PSI... and allow it to sit.. waiting for a drop or a leak...

how are the engine cooling fans.... do they work properly????  cycling on somewhere between 195F and 228F... as measured with a scan tool hooked up to the OBD2 diagnostic port..

you might also want to check the radiator cap.. that it holds pressure..

head gaskets.. warped heads from overheating.. cracked heads...  leaking heater core.. bad motor mounts tearing the tubes out of the heater core when the engine rocks backward and sometimes tearing the heater hoses...

loose injector connectors have also caused multiple issues on cars i have been second or third under the hood...   you might want to find the injector harness connector.. its got 8 or 10 wires in it.. allows easy disconnection from the main harness for engine installation..   you should ohm each of the circuits... if you narrow the engine type down.. i might get you some wiring colors for the injector harness..

you will also want to go over the items that were removed for the intake gasket replacement ..  

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