1999 Astro Cargo 168K (8th VIN "W")
Van always ran great so I did the first tune-up, cap, rotor, plugs & wires in March 2008 with the best NAPA parts. The fuel pump was changed in November 2008. Now it runs wonderful for a couple of days, and runs rough for a couple. Check engine light is off when great, and on when rough. The other day it was even flashing. Autozone said code PO304, tune up place just said mutiple misfires, and then another Autozone said plugs & wires. They didn't tell me the codes for the last two. Fuel pump pressure was checked at 58- 61. From what I've read here, I'm going to install ACDelco cap & rotor. Also, it starts and idles fine all the time. I'm leaning towards a post I read here talking about a GM bulletin on plug wires having to be routed correctly because of the aluminum foil in doghouse. Please help. :confused:

P0300 series DTC's all indicate a misfire. Flashing SES light indicates the engine is misfiring and a P0300 series DTC is being set in memory. P0304 is a misfire on cylinder #4. Most likely caused by a secondary ignition problem, (spark plug, plug wire, cap, rotor). Always use AC Delco plugs, distributor cap, and rotor. Proper spark plug wire, and coil wire routing is very important to eliminate the possibility of shorting to ground or cross firing.

Your fuel pressure is borderline low. That could be caused by any number of things and requires proper diagnostics to find the root cause. Spec is 60psi to 66psi with the ignition in the RUN position, fuel pump running, and the engine off.

I replaced the cap & rotor with AC Delco last weekend and it runs great! Went on a 300 mile trip Tuesday with no problems. I did a Techron additive treatment on the trip for the heck of it. A mechanic friend looked at the 11 month old cap and he said it looked like it had been in there for three or four years. Thanks for your help.

Well, I'm back. It was a good few weeks with no problems and now SES is on solid with PO300 & PO420. It still starts fine & runs smooth. I guess my next step is changing the blue high dollar Beldon wires with AC Delco wires and maybe the coil. Any ideas? Thanks.

Not too fast.... Belden wires are good quality wires. What brand of spark plugs did you use?

The plugs are from NAPA. The ticket says AC 12 Gap .060

Your vehicle calls for AC Delco 41-993 (Platinum) with a gap of .060

AC Delco plug #12 cross references to R44LTS, 41-601, R45LTS6, R44LTS6, R44LTS6K, R45LTS6K, and R46LTS. It has a different heat range and reach. I'd exchange them for the correct plugs and see what happens.

I changed out plugs with 41-993 and it runs great. SES came back on with the PO420. Someone told me that it's probably not the fairly new converter, but the O2 sensor before the converter. They said you should change it around 100K. I have learned my lesson about installing the exact parts. If it is the sensor, what brand should I use? Thanks for your help Old Master, you've been great!!!

Oxygen sensors measure changes in voltage. The faster they react to changes in fuel mixture, the better the fuel mileage you'll get. Oxygen sensor reaction time slows down over time, at 100,000 miles they have slowed enough to affect fuel mileage significantly. That's why it's recomended to replace them, (all of them) at 100,000 miles.

P0420 is indicating the catalyst is not operating as efficiently as it should. This does not necessarily mean the converter is bad. Nor does it necessarily mean the oxygen sensor is bad. There are 3 oxygen sensors on your vehicle, two upstream and one downstream. The upstream sensors monitor changes in fuel mixture and are located just after the exhaust manifold on each side. The downstream sensor, (after the converter) is only used to monitor the performance of the converter. When the ECM runs the catalyst monitor, it watches for a specific amount of time for the voltage to change. It gets quite technical how the test runs, but basically it watches for a slow change in voltage in a certain direction. If the voltage changes too rapidly, it can be an indication that the converter is not doing its job correctly. There are several things that can affect the voltage at the sensor, and if the ECM doesn't see the correct amount of time and voltage, it sets P0420. Here are the 3 pages of the diagnostic flow chart:

http://i561.photobucket.com/albums/ss58/cwhook/P0420page1.jpg

http://i561.photobucket.com/albums/ss58/cwhook/P0420page2.jpg

http://i561.photobucket.com/albums/ss58/cwhook/P0420page3.jpg

hey guys i got same problem here on my owns van 1999
and i only rempace rotor and make ride running good for 3 or 4 day
so i will investigate distributor i whas thinking is bad about
gear shaft and gear shaft tube i mean when i press gaz at carpet
engine running really well on 6 cyl and on scanner i got no miss fire in live data think when cams running faster push up distributor gear up maybe 1/8 inch higher and make rotor touch properly on cap
i will write here in 1 or 2 next day

I had the exact problem with my safari. It turned out to be a worn distributor gear. When I changed the cap and rotor the problem seemed to be solved but like your van the problem came back. It is definately worth looking at the gear, if there is signs of wear I would swap it out with a used distributor if you can find one with a decent gear.

ya mike but about this gears i buy new one for about 60 $ canadien from my uni select

I changed out all of the O2 sensors about 6 weeks ago with Bosch, had the SES turned off, and it's been running great and the mileage has improved a lot!!! I was afraid to post anything in case it didn't stay that way. What a pleasure to drive again without problems. Once again Old Master, thank you again for your great assistance. I'll start a new post about the bouncing fuel needle.

Old Master, I'm at my wits end. The PO420 came back on today after going great since May. Any ideas? Thanks.

Aftermarket converters are rated as to the size engine it will handle. Theoretically aftermarket converters rated for at least a 4.3L engine should be fine. I have seen several times when an aftermarket converter will set a P0420, and when replaced with an OEM converter, the P0420 never returned. This may be the cause with your vehicle. The parameters for setting P0420 are rather close in tolerance, there is a GM TSB for widening the parameter, but it requires that a GM dealer flashes the PCM with the updated specs. Who knows, doing that might keep the SES light off with your present converter. Keep us posted.