Misfiring and Backfiring - November 27th 2018 1:24 am
Hi,
New to the group and with a new to me van. Love the van and really want to become a real vanner! I've done my own car maintenance for a long long time and thought that buying an old van and fixing it up would be fun.
My prize is a 1983 GMC Vandura G2500 that has a Starcraft conversion done with running boards, fender flairs and some custom interior. The van was used as a Band van when it was new going from gig to gig. The guy I bought it from used it for trips from Oregon to Mexico. Though it had been sitting in a barn for the 9 years before I got it, it's got some miles odometer reads 3262 miles, but I'm sure it just turned over 200K. It's had an engine swap, out with the stock 305 in with a Mr Goodwrench 350 crate engine. From the skimpy records I got with the vehicle I figure the engine has between 50K and 70K miles.
I've had it for a year and a half but haven't got to do much with it. Life can be busy. When I got it I needed to take it through DEQ here in Oregon. It didn't pass. I had the entire exhaust system replaced and a new catalytic converter installed, tuned it with new spark plugs distributor cap, rotor, and air filter and it passed. Since it didn't seem to have as much pep as it should I found a mechanic specializing in carborated vehicles and had him look it over. The mechanic put it on his scope and saw that it didn't have much timing advance. He replaced the vacuum advance unit and put weaker springs in the distributor to allow even more advance. Felt peppier and smoother after that. Drove it on a short road trip and it died. Had it towed to another mechanic they replaced the ignition module in the distributor. Ran just fine on the one and a half hour drive home. When I got home I removed the distributor cap to see the new ignition module, yep there was a new fresh one in there. After my inspection, I started having a new kind of trouble. It would start to miss and backfire after being run for about 15 to 30 minutes. Park it for a half hour to an hour then it would run just fine. Went to another mechanic he said the sparkplug wires had been routed incorrectly and were crossfiring. I asked about replacing the plug wires, and he said he thought there was no reason to. And so the van was "fixed" and Life moved on. It sat through the winter and summer no time to do van stuff.
Now it is time to go through DEQ again it hasn't been used in 6 months, again. So I start driving it around to take it in to be checked seems okay, took it to be tested and it failed. CO is not allowed to be above 200 and it is in the 400 range. After racing the engine it once went back down to 201 on idle, close but still a fail. So I decided that I would replace all the rotting vacuum lines and replace those spark plug wires. I very carefully made sure that the spark plug wires were not touching each other or any thing metal. Really runs great! so smooth and powerful till it gets good and warmed up after 15 to 30 minutes then it's back to misfiring and backfiring. This is driving me crazy! It sound like the timing is way off like it has slipped a tooth on the timing chain, but when it cools off it's just as smooth and nice as can be.
Everything in the ignition is new. New coil, Dist Cap, rotor, spark plugs, spark plug wires. I'm confounded and looking for ideas.
Got any ideas? I'm all ears.
New to the group and with a new to me van. Love the van and really want to become a real vanner! I've done my own car maintenance for a long long time and thought that buying an old van and fixing it up would be fun.
My prize is a 1983 GMC Vandura G2500 that has a Starcraft conversion done with running boards, fender flairs and some custom interior. The van was used as a Band van when it was new going from gig to gig. The guy I bought it from used it for trips from Oregon to Mexico. Though it had been sitting in a barn for the 9 years before I got it, it's got some miles odometer reads 3262 miles, but I'm sure it just turned over 200K. It's had an engine swap, out with the stock 305 in with a Mr Goodwrench 350 crate engine. From the skimpy records I got with the vehicle I figure the engine has between 50K and 70K miles.
I've had it for a year and a half but haven't got to do much with it. Life can be busy. When I got it I needed to take it through DEQ here in Oregon. It didn't pass. I had the entire exhaust system replaced and a new catalytic converter installed, tuned it with new spark plugs distributor cap, rotor, and air filter and it passed. Since it didn't seem to have as much pep as it should I found a mechanic specializing in carborated vehicles and had him look it over. The mechanic put it on his scope and saw that it didn't have much timing advance. He replaced the vacuum advance unit and put weaker springs in the distributor to allow even more advance. Felt peppier and smoother after that. Drove it on a short road trip and it died. Had it towed to another mechanic they replaced the ignition module in the distributor. Ran just fine on the one and a half hour drive home. When I got home I removed the distributor cap to see the new ignition module, yep there was a new fresh one in there. After my inspection, I started having a new kind of trouble. It would start to miss and backfire after being run for about 15 to 30 minutes. Park it for a half hour to an hour then it would run just fine. Went to another mechanic he said the sparkplug wires had been routed incorrectly and were crossfiring. I asked about replacing the plug wires, and he said he thought there was no reason to. And so the van was "fixed" and Life moved on. It sat through the winter and summer no time to do van stuff.
Now it is time to go through DEQ again it hasn't been used in 6 months, again. So I start driving it around to take it in to be checked seems okay, took it to be tested and it failed. CO is not allowed to be above 200 and it is in the 400 range. After racing the engine it once went back down to 201 on idle, close but still a fail. So I decided that I would replace all the rotting vacuum lines and replace those spark plug wires. I very carefully made sure that the spark plug wires were not touching each other or any thing metal. Really runs great! so smooth and powerful till it gets good and warmed up after 15 to 30 minutes then it's back to misfiring and backfiring. This is driving me crazy! It sound like the timing is way off like it has slipped a tooth on the timing chain, but when it cools off it's just as smooth and nice as can be.
Everything in the ignition is new. New coil, Dist Cap, rotor, spark plugs, spark plug wires. I'm confounded and looking for ideas.
Got any ideas? I'm all ears.