Chevy & GMC Vans

Hello all,
Although I've been reading posts on this site for some time, I've just become a member today. And of course, I'm looking for help. I've a 2000 Safari, 4.3 auto, 210,000 km (130,000 miles). Its misfiring / shuddering. I noticed it about 2 wks ago after a fill up at a station that I don't normally frequent. I thought it was bad gas...added methyl hydrate, then octane boost, then Seafoam in throttle body (hoping to clean any possible injector issue)...nothing...gas line filter (only 8 months old but changed it anyway). I then went in the ignition direction..again, all just 8 months old, but changed dist. cap / rotor button...no change...brought it in for a scan...misfire code, mechanic said my wires are arching (again, 8 months old) but changed them...nothing...coil...no change...plugs...nothing..
cleaned MAF sensor..(engine felt more alive, but still misfiring) feels like timing is off. Smoothens out around 80 km/h (55 mph) but some days its missing pretty bad. Noticed it worse after a heavy rain. Noticed interference on radio after plug change. Engine has small antifreeze leak at intake manifold (1.5 L / year). Is it injectors or ignition? Plugs looked normal, I smelled gas of one.
I appreciate your help.

Thanks

Caper

So far you've done everything to eliminate a misfire code.

Since it is worse on wet days, I would have said cap and rotor were going bad. Only thing I can think of is maybe a weak fuel pump. Put a pressure tester on it and see what the pressure is when it misfires.

My guess is the CPI injector leaking or one of the attached poppets is clogged, or both.

I pretty much just went through the same thing. Ended up replacing fuel pump, fuel regulator, fuel filter and spark plugs and wires. Seems to have fixed the problem, but I still get a backfire in the TBI every now and then.

Hope that helps

Hi,
Here's an update...turns out I have a couple of things happening simultaneously. I asked one of my neighbours (65 year old mechanic) to take it for a drive. I went along...and he instantly said that the shudder was drivetrain related. Although I had already checked the u-joints, he figured that one had come out of round or had dried up. Sure enough, one was toast (no play, no squeel) but toast. Shudder is gone, but there is still a slight miss (like bad gas). I'm gonna look at getting my injectors professionaly cleaned and I'll get the fuel pump pressure tested.
Thanks for your input

Caper

Get a scan tool an your van & check your CMP Retard parameter. I would bet that your reading will be outside the range of 0 +/-2 degrees. If it is, adjust it to within the spec. & see what happens.