Misfire when wet

Misfire when wet

Postby Goden [OP] » September 29th 2013, 8:01pm

Hello. I'm new to automotive forums so if I leave anything out please don't hesitate to ask for anything I've missed.

Anywhere, here is the situation:

I have a 1998 Chevy AWD Astro van. It has, recently, begun to develop the problem of misfiring horribly when it is raining outside and water gets under the hood. It can sometimes be spits and sputters but can get as bad as having to 2-foot the gas and brake just to keep the RPM's up enough to stop it from stalling. A strong smell of fuel usually fills the cabin when it misfires like this. When stopped at red lights I have to put it into neutral and push on the accelerator a bit otherwise it'll sputter to a halt and stall. When roaring down the highway the problem goes away and doesn't start to misfire again until the van slows down (and RPM's drop). The van easily turns over when starting it and there is ignition but it may not stay running for long (unless reving it) if it is wet under the hood.

I've taken it to the shop in the past for this problem and the following has been replaced: Fuel pump, fuel injection assembly, fuel filter, spark leads and plugs.

I live in Vancouver which is a temperate rain-forest so as you can imagine - it isn't going to get dry any time soon. I can't get a hold of my mechanic at the moment so if you kind folks have any input of what I can look into I would appreciate it greatly.

Thanks!
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Re: Misfire when wet

Postby safariking » September 29th 2013, 8:21pm

I noticed you haven't changed the coil if you pull off a plug wire and check the spark you'll probably find its a orange spark rather then blue I had the same problem with my 99 when it was wet changed the coil never had a problem again
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Re: Misfire when wet

Postby Jasen » September 29th 2013, 8:24pm

Welcome to A/S

With the weather we've been having here in the PNW it's probably moisture related, these vans are known for it.
Check the dizzy cap for moisture, the dist. body has 2 weep holes in it with screens in them, remove the screen's, this is a GM service notice. Spray everything with WD40 and blast it out with air.
ACdelco cap and rotor is a must, they tend not to like after market, check that the base of the cap is flat and seating properly, clean ignition/emissions related elec. connections and apply dielectric grease to keep moisture out.

Safariking point's out the next thing I would look at. Pull the dog house, get a spray bottle of water, with the motor running and in the dark start spraying everything and look/listen for arcing.
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Re: Misfire when wet

Postby Goden [OP] » October 2nd 2013, 1:48am

Sorry for the lack of response. I took it into the shop and the following was replaced as they were badly corroded/worn: Leads, spark plugs, dis-cap, PCV Valve, and coil.

When I left the shop it wasn't raining so I had no way of really testing but today it starting raining and the misfire issue returned. Considering the parts replaced, the only thing I can think of at this point is the distributor body, that's about it. It's certainly something getting wet that shouldn't be getting wet.
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Re: Misfire when wet

Postby Jasen » October 2nd 2013, 2:07am

Just tossing this out, maybe for future reference. These van's are picky about ignition parts, they tend to not like anything other then ACDelco.
Could be a cracked coil, even a crack to small to see. I run a Accel high out put coil, 2 years with no trouble. Also the leads to the coil can go bad with not outward signs. Try the spray bottle of water in the dark trick, it's free and has often brought the issue to light.
Not saying it's not the dist. or a worn dist. gear or the ignition control modal, but free is cheaper then hourly shop rate :)
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Every projects a journey man.

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