Overnite

When I bought the van about 4 months ago it ran fine. It has about 150,000 miles on it and I have put about 3000 or so on it since I bought it. I noticed a little stumble at highway speeds (55-65) a couple of weeks ago and it seems to be getting worse. I have changed the plugs, plug wires and both caps and that got no results. It gives a code 420 and it has no catylitic converter. The guy I bought it from said he bought it that way. I thought maybe a couple of cans of Seafoam through it might help but that did not help either. I checked the fuel pressure and here are the readings: after it sits overnight- 0 psi, key on and engine off- 65 psi then when pump shuts off it drops to 55 psi, engine running- 56 psi, revving engine it goes to 62 then back to 56. Are these normal readings? It always starts right up and if it is under a load like going up hill or gettin up to speed it does't miss a bit. When it levels off it acts up. Any ideas anyone? Thanks for any help!

ihatemybike

The 420 could be changing the fuel/air ratio. It's possible to pull the after cat O2 sensor back out of the exhaust fuel to change it's reading. It's a trick overland expedition drivers use when they remove the cat in Africa to run the lower grade gas there.

Overnite

So I take it out and tie it up leaving it plugged in and plug the hole?

ihatemybike

Not quite, that O2 sensor needs to provide a reading to the computer. The sensor itself just needs to be out of the exhaust flow. Best way is to make a O2 sensor non-fouler. These are the best instructions I've found.

http://forum.e46fanatics.com/showthread.php?t=486937

Overnite

Thanks . I will give that a try.

ihatemybike

Let us know if it works for you.

Overnite

Well , I tried that trick with the O2 sensor and I am still getting the 420 code. It might work on a different vehicle though. I noticed the O2 sensor was was black and sooty when I took it out. Still did not help my problem. I'm not sure what to try next since I am still not getting any other codes, but I think I will pull the spark plugs back out and see if some or all might have that look of rich fuel mixture and go from there. Thanks again for the help.

Nick Rox

First, I am a journeyman GM mechanic with 40 years of experience. I just went through the same thing.

Your problem is with the fuel injector system. You have worn out parts in the fuel injectors and there is too much fuel leaking back into the gas tank. The GM fix is 1200.00 for a new fuel injector system, as there are no user replaceable parts.

You would be better off replacing the intake and putting on a QJ carb.
Please don't fool around with the O2 system it will screw up the computer settings.

Overnite

Thanks for the help. I have replaced the fuel pump, put in a new injector cluster, fuel filter, Plugs , wires and caps and I still get the code 300. It starts right up and runs fine but when I get it up to 55 mph in overdrive it has an ocasional miss/stumble and it gets worse at 65 mph. At 55 if I drop it out of overdrive and get the rpm's up a little the it gets bad again.

ihatemybike

What about the distributor? I've seen a couple with badly worn gears. It's a known cause of P0300.

$1200? No user replaceable parts?

Sorry, injector system parts are user replaceable. This shade tree guy has done it. The 97 vans came stock with CFI, which has fallen out of favor for MFI. The hot set up on the older CFI vans is to swap out the whole injection system with MFI. This can be done with new ACDelco parts for about $425 or with other brands starting at about $250 when purchased from www.RockAuto.com.
ACDELCO Part # 2173028 $398.79

Installation for an inexperienced person with a Haynes manual will take an afternoon.

Before you think about replacing the injectors though. I'd give the van a Sea Foam treatment. It's cleared the P0300 on a couple of my van. If it doesn't then step up to the GM Fuel System Treatment Plus. One on my vans required it to clear the P0300. I have yet to replace any injectors on any of my personal high mileage vans.