My parents have a 2005 Chevy Uplander with the 3.5 V6 / 4 speed auto (4T65E). For the past 2 years or so when driving on the highway for MORE than 1.5 hours the car will start to hesitate / surge followed shortly after by what seems to be the torque converter or 4th gear letting go. The rpms will go up to 3000 at 70 MPH (normally around 2300 or so). The trans will stay in that gear (assuming 3rd) for about 10 minutes then shift back down and act normal. This process will continue to re-occur as long as you are on the highway. So we took it to the shop today since they plan on using it for an upcoming trip and want it to be in good running order. They ended up changing out spark plug #3 due to a misfire. They said it had misfired 144 times, not sure if that was 144 times today or over the course of the last 2 years. They said they found nothing else wrong. Now, I never put the two issues together (the surging, then the following torque converter / gear drop). I understand the bad plug could cause the surging on the highway, but could that surging cause something in the computer to make the trans drop down? I really hope thats all it is, as they don't really want to put any more money in the car.
Could a spark plug cause all this trouble?
- Thread starter gregk24
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How many miles on it?
Does it have 3 separate coil packs or 6 coils on plug?
Sounds more like a bad coil.
Sounds more like a bad coil.
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This car appears to have a single ignition coil with 6 spark plug wires attaching to it, according to RockAuto. Bad plugs / wires can sometimes mimic a bad tranny.
At that mileage, not a bad idea to change all plugs / wires for peace of mind.
At that mileage, not a bad idea to change all plugs / wires for peace of mind.
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Catconverter
I have seen stranger things happen.
Would be interesting to know the service interval for the plugs. Most can go more than 100k but recommended change interval start at half that. My Chevy HHR started acting up with misfires and strange low speed shifting and the plugs were the issue. Simple cheap fix.
Originally Posted By: mclasser
This car appears to have a single ignition coil with 6 spark plug wires attaching to it, according to RockAuto. Bad plugs / wires can sometimes mimic a bad tranny.
At that mileage, not a bad idea to change all plugs / wires for peace of mind.
I don't remember exactly when, but I know they were changed. Probably somewhere 2-3 years ago.
This car appears to have a single ignition coil with 6 spark plug wires attaching to it, according to RockAuto. Bad plugs / wires can sometimes mimic a bad tranny.
At that mileage, not a bad idea to change all plugs / wires for peace of mind.
I don't remember exactly when, but I know they were changed. Probably somewhere 2-3 years ago.
Kind of unrelated but reminds me of some V6 Accords had an issue with the number 3 spark plug shooting out of the engine. Be happy that didn't happen. I think this was mostly 7th gen Accords.
Great shop to figure this one out instead of recommending a new trans.
Great shop to figure this one out instead of recommending a new trans.
Originally Posted By: zrxkawboy
It's possible. Is the cruise control set when this happens? The plug misfires, so the cc open the throttle further to maintain set speed, which causes the trans to downshift, etc.
No, its nothing like that. There is no cruise control on this van. Its not like a smooth planned shift, it surges then shortly after will clunk slightly (noting harsh) then RPMs go up. When this happens you can let your foot off the gas and the trans will let engine go down to idle...while going 70+ on the interstate, normally you would let off the gas and RPM's would stay where they should (around 2300 rpm or so).
It's possible. Is the cruise control set when this happens? The plug misfires, so the cc open the throttle further to maintain set speed, which causes the trans to downshift, etc.
No, its nothing like that. There is no cruise control on this van. Its not like a smooth planned shift, it surges then shortly after will clunk slightly (noting harsh) then RPMs go up. When this happens you can let your foot off the gas and the trans will let engine go down to idle...while going 70+ on the interstate, normally you would let off the gas and RPM's would stay where they should (around 2300 rpm or so).
That's a good honest shop if all they changed is one spark plug!
Originally Posted By: mclasser
This car appears to have a single ignition coil with 6 spark plug wires attaching to it, according to RockAuto. Bad plugs / wires can sometimes mimic a bad tranny.
At that mileage, not a bad idea to change all plugs / wires for peace of mind.
No they have three coils which are all the same and are mounted to the Ignition Control Module under it, two bolts through each coil holding down the coil and IC module to a mounting bracket. Ohm out the coils from post to post they should be fairly close to each other and make sure also the towers where plug wires go have not been rusting from arcing under ther boot.
This car appears to have a single ignition coil with 6 spark plug wires attaching to it, according to RockAuto. Bad plugs / wires can sometimes mimic a bad tranny.
At that mileage, not a bad idea to change all plugs / wires for peace of mind.
No they have three coils which are all the same and are mounted to the Ignition Control Module under it, two bolts through each coil holding down the coil and IC module to a mounting bracket. Ohm out the coils from post to post they should be fairly close to each other and make sure also the towers where plug wires go have not been rusting from arcing under ther boot.
Yes, driveability problems can frequently be mis-identified as trans problems, or genuinely cause the trans to act strange. The trans programming is not going to work well in a situation where the engine is putting out 50hp less than expected, or stumbling at high RPMs where it should be making max power.
That is an accurate diagnosis by your repair shop and I would thank them for their honesty and maybe even drop off a pizza or beer to them. I had a friend with a 2006 CTS who thought her transmission was slipping so she went to the closest transmission shop who told her yes she needed a new transmission at a $4500 cost. She called me and I said let me look at it because I knew it was just the plugs because she said her check engine light was flashing - the CEL only flashes when there is an active misfire occurring. $25 in plugs and an hour's time and car was fixed.
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