Venture misfire puzzling me

I've noticed what seems like a slight misfire whenever the van is climbing a slight grade at freeway speeds. If the cruise is on, it downshifts readily. I don't recall it downshifting quite so frequently in the past. Once downshifted the misfire is gone. This is the only time it does it, I can't recreate the problem on overpasses in town or highway driving at lower speeds. I didn't think it was to much of a problem until I checked the gas mileage over several fillups. Used to average 32mpg, now it's 23 (Canadian). The van is a 98 with 100000 Kms. A few months ago I changed the sparkplugs,pcv valve, air and fuel filters. I checked the 3 front plugs (the easy ones), they looked good. Tailpipe doesn't have carbon in it and there is no check engine light on. If anyone can offer any advice I would appreciate it. Thanks Matt

Reply to
Matclark
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Have the codes read out of the computer. The problem probably hasn't reached the threshold for the check engine light but still could show up in the computer...

Reply to
Woody

Probably a bad plug wire. A friend with an Aerostar van had similar symptoms while towing. He spent a lot of time and money chasing the problem. In the end, replacing

1 plug wire made it go away.

Erich

Reply to
Kathy and Erich Coiner

It could also be one or more of the fuel injectors. My Aerostar had the exact same symptoms, with the exception of the downshifting in cruise, & absolutely terrible mileage. I replaced all the injectors and now it runs like new, and the mileage is way up.

Reply to
Mark Olson

"Matclark" wrote

Pull the plug wires off of the coil packs and see if you have any signs of corrosion at the coil pack posts or inside the wire ends. Pretty common on the 3100/3400 engines to see problems with the spark plug wires at the coil end.

Ian

Reply to
shiden_Kai

when replacing the plugs, how difficult were the wires to remove? how difficult to reinstall them? dielectric grease installed? i'd look there and make sure the plugs have been gapped correctly.

Reply to
Ron

Removing the wires was the hardest part of the job. Only because of the location, and very easy to reinstall. I didn't apply any grease. Didn't know that I had to. I'm sure the gap is correct. I'll get some grease and check both ends of the wires as was suggested by Ian in another post. Still puzzled why it only misses at high speed though, You'd think a wire is a wire, and a spark is a spark at any speed.

Reply to
Matclark

"Matclark" wrote

You may well have another problem, other then the wires. But as with any vehicular diagnosis and repair, it is always smart to start with the simple and obvious things.

Ian

Reply to
shiden_Kai

Pulled the wires off, the posts were shiney and clean, inside of the connectors look good too. But I can't rule them out completely. There is a considerable amount of static on the AM radio. I don't drive the van too often, but I know the static wasn't there before. Boch wires are on sale here, maybe worth trying.

Matt

Reply to
Matclark

Matclark wrote in rec.autos.tech

The wires can look good but still be going bad. There is 60 thousand volts going to the plugs, and that kind of voltage does not take much of a degradation in the insulation to start arcing. And that arcing will cause static in the radio. Plug wires will cost a bit, but they do need to be replaced fairly often.

Reply to
Dick C

usually after heat, time and high voltages, the wires break down inside. under load the engine requires a stronger spark to ignite the air/fuel mix. the built in resistance of the wires to eliminate the interference in radio reception also increases as the wires degrade causing misfire under load and at higher speeds. the grease helps to make a watertight connection and prevent corrosion which increases in higher voltage situations. i'd say a good set of plug wires would take care of the problem. hth.

Reply to
Ron

try not to get the cheap wires, you mentioned how hard they were to remove. you don't want to have to do that again soon would ya? the better ones will cost more, but will last longer, perform better and save $ in the long run.

Reply to
Ron

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