02 WS6 Misfire on all cylinders

**UT Trans Am** · 11-11-2014, 02:10 PM

Hello,

Sorry if this is not the correct section, but I am hoping someone could steer me in the right direction. I just purchased a 2002 WS6 Trans Am with 35,355 mile. I had it shipped from NY to Houston and took it straight to a mechanic to get inspected to make sure everything was ok. He called me the next day and asked me if I could call the previous owner and ask him if he had made any modifications to the intake or the cams because he was getting a misfire code on all the cylinders (P0301-P0308). He said that it misfires worse in the mornings when the engine is cold and less so when it is warmed up. I bought it from a dealership who didn't have any information on the vehicle. I was able to look up last service date from my Carfax report and it shows the following:

07/16/2010 32,230 Clark's Auto Repair

State inspection completed
Engine/powertrain computer/module checked
Spark plug(s) replaced
Spark plug wires replaced
Air filter replaced
Decarbon service completed
Fuel injection system flushed/serviced

No service since then:
06/12/2012 EASTERN REGION 34,701 Auto Auction REPORTED AT AUTO AUCTION
06/20/2012 MARLTON, NJ 34,640 Motor Vehicle Dept.TITLE
07/13/2012 EASTERN REGION 34,757 Auto Auction REPORTED AT AUTO AUCTION
07/16/2012 EASTERN REGION 34,768 Auto Auction REPORTED AT AUTO AUCTION AS DEALER VEHICLE

I am almost positive that the car has been sitting in a lot since 2012 untouched (it has Falken tires with 95% tread left that are rotted from sitting on flats)

Mechanic said that he tested the pressure and everything was ok. Any ideas on simple things to check before taking the car apart to see if it has indeed been modded? Doesn't look like the engine has been serviced since 2010, maybe something simple like cleaning the MAF? Any help would be appreciated. Thanks in advance.

**35th-ANV-SS** · 11-11-2014, 02:30 PM

Well, with it misfiring on all cylinders, I'd suspect it's a vacuum leak likely. Either the intake seal itself is bad, or perhaps you have a deteriorated vacuum line somewhere. The one coming from behind the intake usually goes bad first so I would start there. You could also clean the MAF with CRC MAF Cleaner from any local auto parts store. Aside from that, simple things like the air filter, plugs, wires, etc.

Also check to make sure the car is getting enough fuel. You can hook up a fuel pressure gauge to the schrader valve and it should read a steady 58PSI with the car running.

**RONS98TA** · 11-12-2014, 03:23 AM

My 1st guess is the gas is all gummed up and bad from sitting for so long. You will need to empty the tank and get that crap out of there. Remove the fuel filter, and then just turn on the ignition key to the run position and let the gas flow from the line where the fuel filter was taken off. I would let the fuel pump do most of the work, BUT make sure you don't drain the tank completely empty and get all the crap from the bottom of the tank caught up in the fuel pump. While your at it, replace the fuel filter too. Replace the fuel with the highest octane level possible and that will probably fix you up.

**UT Trans Am** · 11-12-2014, 07:47 AM

Thanks for the responses. I have purchased some NGK V-Power spark plugs and MSD wires to rule that out of the equation. Hopefully it is simple/non expensive problem. I will keep everyone posted. Thanks again for the suggestions!

**UT Trans Am** · 11-13-2014, 07:10 AM

Just went by the mechanic shop to pickup the inspection papers I need to register my car. He said he had changed the plugs and wires, checked for a vacuum leak, cleaned the MAF and he was getting 60PSI of fuel pressure. He also said the little amount of gas that was in there was clean. He plugged the computer in and showed me the misfire readings, and the misfire count was pretty even across all 8 cylinders. He still believes that the cam was modified. He said that I should drive the car and if I don't like the way it drives then bring it back and I can have it tuned...otherwise drive with the check engine light on and wait until next November (next time I need to get it inspected) to deal with it.

I would really like to figure out what the problem is. Does anyone have any other suggestions on what to try next? Anyone know of a good mechanic that specializes in F-Body's in the Houston area?

***SMWS6TA*** · 11-13-2014, 07:13 AM

Go to autozone and have them pull the codes and post them here. Sorry if I sound skeptic here but it's not the first time a shop has made issues bigger than they are in order to get further business.

**UT Trans Am** · 11-13-2014, 07:23 AM

Ok. I am going to go pickup the car hopefully tomorrow, I will see exactly what the codes are and post them here. Thanks.

**RONS98TA** · 11-14-2014, 08:52 PM

I have installed several cams in cars before and didn't have them tuned, and never had a misfire on all cylinders. It is possible I guess, that someone has either installed a timing chain, and or cam, and doesn't have the timing chain correctly installed. Again, just my opinion. Hard to diagnose a problem over the web. There are so many different sensors that could be malfunctioning also, like a cam sensor. Could be just a broken wire or lose connection.

**UT Trans Am** · 03-06-2015, 09:02 AM

Sorry it took so long to get the codes pulled.
P0188 - Engine Coolant Temperature Sensor Circuit High Voltage
P0300 - Randon - Multiple Misfire Detected
P0442 - Evaporative Emission System Leak Detected (Small Leak)
P0410 - Secondary Air Injection System PENDING

**nathan c** · 03-06-2015, 10:46 AM

Isn't MTI located in Houston? They used to specialize in LS1 cars.

**99ss405** · 03-07-2015, 02:23 AM

has a mti lid was rated best for ls1 cars by gm high tech .. my buick was in their mag

**pajeff02** · 03-07-2015, 05:13 AM

Originally Posted by UT Trans Am

Sorry it took so long to get the codes pulled.
P0188 - Engine Coolant Temperature Sensor Circuit High Voltage
P0300 - Randon - Multiple Misfire Detected
P0442 - Evaporative Emission System Leak Detected (Small Leak)
P0410 - Secondary Air Injection System PENDING

I assume the secondary air system has been removed? It's possible the vacuum source to the solenoid was not plugged off properly and that would create a small vacuum leak. Same with the evap system, whether it is a leak in the fuel tank emissions, or a vacuum leak under the hood, is the question. Do you want a diagnostic procedure for the P0300 code?