Hey guys I am back. I am getting ready to run the fuel pressure test here in a little bit and I was also contemplating doing a compression test. Would that be beneficial to a diagnosis? I know its more than likely something to do with either my cap and rotor or fuel pressure/fuel injector but I didnt know if a compression test would help.

Also as a new development, on my way to work this morning my MIL turned on and then proceeded to flash about 3 or 4 times, it would then remain solid for about a minute or two then flash again. Took it to O'reilly's at lunch and it returned the P0300 and P0452 codes once more.

About two tanks of gas ago, I ran Sea Foam through the system, for the first half of the tank it ran perfectly then it started to give me hesitations after heading off in the morning. I also notice that it sometimes will give me some issues when cold starting. I saw something earlier that it could have to do with fuel pressure.

Any ideas guys? I feel like I am getting close yet I am just oh so far away. Thanks for all the assistance thus far though.

 

Don't bother with the compression test. Flashing SES light and P0300 is a misfire, guaranteed. P0300 is almost always caused by a fault in secondary ignition ie. spark plugs, spark plug wires, distributor cap, rotor, and ignition coil. A good tune up using AC Delco parts will most likely fix the problem.

Fuel pressure: Key on, engine off, fuel pump running: pressure must be 60psi to 66psi and must remain above 55psi for 10 minutes after the pump shuts off.

P0452 is a problem with the fuel tank pressure sensor or its circuits and will not affect performance. Get rid of the P0300, then we can deal with the P0452.

 

Thats what my main focus is honestly. The p0300 has been driving me nuts, almost literally. I wont be bothering with the compression test.

I rented the tool from AutoZone since oriellys was being used by someone else, and when I went to hook it up to the tester port (back side of plenum next to the distributor cap) the cap that goes on fits but doesn't depress the ball bearing. The piece that does that job is too small to go on the port. What I intend on doing in the morning is hooking it up to the back side of the fuel filter since it comes with that piece.

Am I missing the testing port some where? I know you were suggesting right before the fuel filter anyway but I was trying to be lazy and get it done sooner than later. I will be up in the morning taking care of it.

 

Just to be sure you're on the correct service port: The EVAP test port uses a similar style fitting on a black plastic line located near the ignition coil. The fuel line service port is on the driver side of the distributor, 3/8" steel line. Usually there are a few different adapters that come with the pressure tester so it can be used on several different makes and models. Make sure you're using the correct adapter. Low fuel pressure can cause P0300 however, usually there are other symptoms involved that you haven't mentioned. Don't misunderstand, fuel pressure is critical on these systems and it should be the first thing you check whenever there's a driveability issue. With the symptoms you mentioned, I think you'll find the problem in secondary ignition. Don't go cheap with distributor cap, rotor & plugs, use AC Delco.

 

alright, so I just finished the fuel pressure check and everything checks out in that department. I checked before the fuel filter and at the schrader valve on the fuel rail (steel line, drivers side).

I looked over the wires, plugs, rotor, and cap and everything looked just fine, no issues that I could tell. Put it all back in, took her for a test ride did not get the MIL but she was running a bit rough. Not incredibly rough just enough to notice. So far starts up just fine, when applying gas from a stop and nearing the shift from 1 -2 and 2-3 is when I notice the roughness.

I know I probably have this wrong but if it was something to do with my injectors or fuel pressure for that matter, it would be running rough all the time amiright? at stop signs, drive thru's parked wouldnt it run rougher than normal since its not getting the fuel it needs?

Any other thoughts? I was going to check the coil but I honestly have no idea what I would be looking for. I do have a multimeter but no idea what setting or where to put the testers. Is there a post floating around here for that?

Edit:
I found the test page for the ignition coil. Giving that a read over.

 

What were the pressure and leakdown readings at the service port and at the fuel filter?
Without knowing the results, (post some numbers ) it's impossible to know if the fuel delivery system could be the problem.
What brand spark plugs are in it and approximately how many miles are on them?
Approximately how many miles are on the cap, rotor and wires? Any clue what brand?

Just because a part is new, doesn't necessarily mean it's good, and you can't always tell if it's good or bad just by looking at it. With that in mind, I doubt very seriously that the cause of your misfire can be pinpointed without using a good scan tool or an oscilloscope. The PCM in your vehicle is an invaluable piece of diagnostic test equipment, it's saying there's a random misfire. There are two common possiblities that need to be explored. Checking fuel pressure and leakdown is easy, cheap, quick, reliable and gives us a ton of valuable information. If pressure and leakdown are within specs, secondary ignition is the next step. Unfortunately, without that expensive test equipment, it's tough to pinpoint the problem, so we need to be certain that good parts are installed. Now is not the time to experiment with cheesy aftermarket stuff from the chain type auto parts stores.

It's a teachable moment when customers bring me their vehicle and tell me they just installed, (cheesy) parts, and they're sure it can't be the problem. It makes a believer out of them every time, when good quality parts fix the problem. Bottom line: They not only lose the money they spent on cheesy parts, now they have to buy good parts, and pay someone to diagnose and replace it again! Waaaay cheaper to install good parts to begin with.

 

I completely agree about the cheesy parts. And I can tell you right off the bat that the cap and rotor are both Duralast (yeah i know, shame on me) i was being cheap. I am looking trying to find a place near by that carries Ac Delco cap and rotors. Scumbag O'Reillys only has them in certain stores.

Honestly I don't have the numbers from the testing. At both the port and fuel filter held steady at 55 while the engine was on. After about 5 - 10 minutes (key off) it would go down a PSI unit about every minute - minute and a half. I will probably rent the tool again next weekend and check the readings and write them all down this time and compare them to what they should be. I didn't notice anything alarming from what I have been reading in other posts, but I am no pro.

As far as mileage goes, I put new sparks in June 2010 (roughly 15-20,000 miles), new cap and rotor in september/october 2011 (roughly 5 or 6k). And if I am thinking correctly about the time that replaced the cap and rotor is about the time that the issue started (go figure right). It was actually about a month or so, nothing too long after I replaced them that I began getting the P0300.

 

Ahh, the truth comes out Duralast, I can't tell you how many of those have hit the trash barrel... oh wait, yes I can, all of them! And what brand are the spark plugs?

In a pinch, a GM dealer will have AC Delco, but at twice the price. Usually Amazon has the best price and free shipping. Distributor cap #D328A and rotor #D465. When you install the cap, put a dab of silicone dielectric grease on each terminal, inside and out. Be very careful, don't strip the threads in the distributor housing. Autolite Professional Series wires, (#96871) have better specs than AC Delco, at 1/3 the price. Put a dab of silicone dielectric grease in each boot. As for spark plugs, AC Delco 41-993 with a gap of .060"

GM does not publish any "engine running" fuel pressure specs for the 4.3L because there are too many variables involved. When you check fuel pressure at the fuel filter, fuel flow must dead end into the pressure tester. It will require some "creative plumbing" to accomplish this or, you can make one like in post #8. I can send you the parts list if necessary. Should be 73psi to 108psi while the pump is running and must remain above 55psi for 10 minutes after the pump shuts off.

 

The sparks are AC Delco double plats.

I saw the rotor and cap on amazon for almost half the price which I might just have to get them soon.

Out of shear curiosity. I'm hoping worst case scenario here. If I have to replace the spider is the reman just as goods if I were just to buy a brand new one? Or would it be best to buy a new one with the redesign?

 

Good job on the plugs

If the 8th character in your VIN is an "X", you already have the upgrade. If the 8th character is "W", again, Amazon is your friend: Amazon.com: Delphi FJ10565 Fuel Injector: Automotive



The image above is an AC Delco, Delphi is the same thing now and comes with the necessary bracket. Some of the kits even come with the upper plenum gasket. Simple job, takes under 2 hours to make the modification. The new design eliminates the poppet valves and relocates the injectors to the intake ports. It's plug & play, nothing needs to be done to the PCM. Even if there are no problems with the original spider assembly, there is a noticeable difference in performance when upgrading to the true multiport injection system.