Upon several different ocassions, my astro has, usually upon start-up, begun to misfire as if it was being starved of fuel. The SES lights blinks, then stays on. I took it to the shop, and paid $70 to find out that there was a misfire on every cylinder (Duh!). They wanted to perform a tune-up for $850 (the van has 102K on it, and has not had it's 100K tune-up yet). After turning the van off for a short while, and restarting it, the problem disappeared - even the SES light turned off eventually! It will run perfectly for weeks, then the problem will present itself. At first, I thought that it was water in the tank, but that doesn't seem to be it. Could it be a clogged fuel filter or sticky EGR valve? I would appreciate any suggestions!

Changing a 10 year old fuel filter sounds like cheap insurance. Does a '96 have OBD 11? It should tell you more faults I would think. What's the weather like when it acts up? Wet weather may point to bad ignition wires, cap, etc. Anytime may be a crank position sensor? Any luck borrowing a fuel pressure guage?
Just some thoughts as no-one else has written yet

I think '96 is when ODB II arrived on the scene.
I'd start with Drew's suggestion and change out the fuel filter, then have the fuel pressure checked. Next things I'm thinking since it is a misfire on all cylinders is the coil is failing, or the wire from coil to distributor is arcing to the engine or the foil on the bottom side of the doghouse.
?? A tune up?? for $850? Even if we are talking Canadian $$$ here that's ridiculous.
For that much money you could replace every sensor, spark plugs, distributor cap, rotor, plug wires, coil and vacuum hose. Not to mention throw in an air filter and an oil change.

Hey Profg
Did you ever get your problem resolved? I just got mine out of the tranny shop thinking that there was something wrong with it. Come to find out it's fine, but they picked up a code that indicated "Random Cylinder Misfire". Last month I had the cap, rotor, ignition coil, wires and plugs all changed and it still misfires. Anyone have any suggestions other than burning the SOB.

be aware that any misfire or backfire can or will cause damage to the converter...a costly expense.

recently, while driving my coil went on the expressway. i pulled over, waited for a few minutes and attempted to restart it. it would barely run but it backfired a few times. had it towed and replaced coil, plugs, wires, cap, etc. it ran great, but the "service engine" light stayed on. i had that checked and it was code po420 bank 1.

ok, changed that oxegen sensor, reset the computer....soon after it's "on" again..same code. computer says the cat was bad. service tech tells me any misfire or backfire will burn out the cat real fast....argh!!

so, today, i will attempt to change the cat. we can't get the service engine light off to get the damn thing to pass inspection, so this has to be done.

this is a 1998 astro.

be aware that any misfire or backfire can or will cause damage to the converter...a costly expense.

recently, while driving my coil went on the expressway. i pulled over, waited for a few minutes and attempted to restart it. it would barely run but it backfired a few times. had it towed and replaced coil, plugs, wires, cap, etc. it ran great, but the "service engine" light stayed on. i had that checked and it was code po420 bank 1.

ok, changed that oxegen sensor, reset the computer....soon after it's "on" again..same code. computer says the cat was bad. service tech tells me any misfire or backfire will burn out the cat real fast....argh!!

so, today, i will attempt to change the cat. we can't get the service engine light off to get the damn thing to pass inspection, so this has to be done.

this is a 1998 astro.
I have a 96 with the same code how did u end up fixing your problem? Thanks did the converter fix it?

OK, it's me again - the one with the original misfire problem. The mechanic tried everything (almost). he replaced the plug wires, cap and rotor, along with a crank sensor. He even changed the fuel pump and filter. That seemed to clear it up....for awhile. The problem soon returned, exactly as before. He rooted around in the cable harnesses that are near the battery, and found several wires with insulation that had deteriorated away. He spliced in new sections, and the van ran fine (I did eventually have to have the catalytic converter changed). Well, here it is two years later, and the exact same problem has surfaced. This leads me to believe that he never really identified the cause of the problem. If I could afford a new van, I would push this one off a cliff!

A very common problem is an accumulation of condensation in the distributor cap. Condensation could very well return if the vent holes in the distributor base are not cleaned out and the screens, (if it has them) removed. While you're in there, make sure the coil wire is not shorting out on the transmission dipstick tube. If you do the job at night, take a spray bottle with water and direct a mist at the distributor cap and wires, you just might get a nice light show! If so, replace the cap, rotor and wires.

I had the van towed to the shop that had originally "fixed" the problem. They replaced the distributor cap & rotor, and it seemed to fix the problem. It started up right away, and ran fine for several days. Well, I went out to start it this morning, and it just keeps cranking! There is no misfiring, but this is the way that it always seems to start - first, it won't start, then the misfiring begins. I'm really getting tired of this! Is there anyone out there who can help?! Are there some other diagnostics that could be run that would only be available at a dealership?

Yep, make sure they put in a genuine AC/Delco rotor. The aftermarket rotors are about 1/8" too short on the center electrode and will cause a misfire in short order. They work for a little while, but not for long.

I agree on the A/C Delco cap and rotor, don't settle for anything else. Also you might want to check the PCV system. Make sure it is functioning properly. The PCV system is designed to accomplish several things, one of which is to reduce water vapor in the crankcase. When a warm engine is shut down, condensation forms inside. The warm moist air rises in the engine and will accumulate at the highest point. On the 4.3L engine, that happens to be the underside of the distributor cap. If excessive condensation is present upon the next attempt to start the engine, that could be all it is... an attempt to start. There are 2 vent holes in the distributor base, they must be clear. If there are screens in the holes, remove them. This will allow for ventilation of the distributor cap.

I posted back around Christmas about the same problem. Early spring I changed the cap and rotor to a aftermarket Accel brass cap and rotor. That worked for a while till around Christmas when the damp, wet, wet snow type weather started. Everyone recommended to install an AC Delco cap and rotor but the weather was cold so I put it off until we had a day of rain/freezing rain. It missed so bad, I bought a AC Delco cap and rotor and installed it right then and there. The miss disappeared and has been gone for a week now. I compared the 2 rotors and they were exactly the same, the electrode length was the same.

One thing I noticed is that the distributor shaft has some axial endplay. It seems that if you lift up and rotate the rotor opposite the normal direction of rotation, it would, in essence, add more timing advance, which would present the misfire problem at light load. Does anyone know how much axial endplay is allowed or normal?

The axial end play you are noticing is normal. The distributor gear is pinned to the distributor shaft. There is about 1/8" between the top of the distributor gear and the bottom of the distributor housing. The 2 gears are helical cut, (similar to threads) When you pull up on the shaft, you are in a sense, "unscrewing" it. You are correct with the theory of changing ignition timing, but that is not an issue. When the engine is running, the teeth on the camshaft meshing with the teeth on the distributor gear will pull the distributor shaft down so it's always bottomed out.

When the engine is running, the teeth on the camshaft meshing with the teeth on the distributor gear will pull the distributor shaft down so it's always bottomed out.

I checked that by bumping the motor with the cap off and the rotor lifts and rotates opposite the direction of rotation. That is opposite to what your saying. I did the test in hopes that the cam gear would pull the shaft down and not further advance the timing. I've also pulled the distributor to inspect the distributor gear and it was fine (about 75,000 miles). If I get a couple of years with the new cap and rotor I'll be happy. With the wet spring season ahead it will be put to the test soon.