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Shifting/Flooding problems

First, a little background…My dad’s 2006 Hyundai Elantra had a thermostat malfunction, causing the radiator to crack and the head to warp. We took care of the thermostat and radiator our selves, but took it to the dealer garage to get the warped head shaved down. While at the shop, the battery was disconnected for a long period of time subsequently causing the computer to reset. While all of the overheating issues we taken care of, we were brought upon another. While driving (particularly uphill) the transmission does want to shift into the next gear and floods the engine with too much gasoline, sometimes causing it to stall. I did a little research on the Internet about what the issue could potentially be. The commonly mentioned things were the purge valve from the Evap canister, the MAF sensor, and throttle position sensor; all which have been tested or replaced. The issue is still present. Any ideas on anything else? The mechanics at the garage say that due to the reset of the computer, all of the adjustments that computer has made for shifting the transmission throughout the past 200,000 miles, have be erased. They told us that the transmission needs to be replaced. They said that they can replace it with a used transmission with a warranty. Our key question is: What is guaranteeing that the computer and the replacement transmission are going to communicate any better? We would just like to have a few more opinions before spending more significant amounts of money.

Thank You in advance for any help or comments!

I understand that there are some tweaks that PCMs make to the trans shifting program based on driving style, but what your mechanic is describing makes no sense to me. I’d start by looking for a vacuum leak. Also, have you pulled the spark plugs? Any dark ones?

My suggestion would be to do what should have already been done; run a compression test.

At 200k miles and with a history of obviously severe overheating it could be that the engine is flat fried. The problem may not be in the transmission so much as it’s trying to keep up with a tired engine.

If the numbers are low it may be time to say goodbye to the car and this could possibly have been headed off by performing a compression test before the cylinder head repair.

So the transmission worked fine immediately before the repair but now malfunctions immediately after the repair. Same with the flooding situation. Pulling the head requires a lot of disconnecting of electrical connectors, vacuum lines, etc. I really suspect they screwed something up. Anything they touched during the repair needs to be gone over with a fine tooth comb. It may be something really simple.

Edit: Is the check engine light on?

Another thing they had to remove during the head job was the timing belt. They may not have gotten that aligned properly when they re-installed it.

If the engine is running with reduced power you would have to step on the accelerator harder to compensate. This would cause the throttle position sensor to signal the transmission to downshift sooner than it should which would seem like a transmission shift malfunction but it is just doing what it is “told” to do. I’m very skeptical that the transmission is bad.

Insightful, we did pull the plugs and they were all good.

Ok4450, the reason that the car was is the garage was for fixing the head. They shaved the warped head and put new gaskets on and did a compression test and everything seemed normal.

My 2 Cents, so what your say is, it’s not so much that the transmission doesn’t want to shift, it is that the transmission is shifting into 3rd gear much earlier than it should? Also, the car actually never had the timing belt replaced before it was in the garage this past time and we requested that they did change it so that has me wondering if they messed that up. And yes, the check engine light is on

Also I forgot to mention that when hooked up to the OBD scanner, it comes back as a misfire. I don’t know if that helps narrow it down at all because a lot of things can cause it to read misfire.

I’m a little unclear as to whether upshifting too soon or downshifting too soon.

When going up a hill it goes through first and second gear fine, but when it shifts into third gear it seems like doesn’t want to shift from that gear at all. It will stay in third for a while, even if you let off the accelerator as if trying to let it shift into fourth. Or if you go to press the accelerator further, as if you want it to downshift into second, it loses a lot of power and begins to flood the engine. You can take the pedal clear to the floorboard and it will not downshift, only floods it. By the time you reach the top of a larger hill, you have to pull off to the side and let the engine catch up and burn off all of the excess gas.

I might ask what the compression test numbers are. Quite often those are misinterpreted even in service manuals and sadly enough; even by mechanics.

At this point I would concentrate on getting the engine running properly and then see what happens with the transmission. I definitely wouldn’t replace the transmission yet. I still think they may have screwed something up when they put the engine back together. It all seems like too much of a coincidence.

Ok. That’s what we thought. Thank you for your input guys. We too felt that the decision that the transmission needs to be replaced was quite odd being that the mechanics said that it was the issue right away as if there was no potential for it being something else. We are going to question the mechanics heavily tomorrow on whether it is a compression issue or a timing issue. We really want to see why they solely feel that it is a transmission issue and nothing else.

Can I assume that the insightful advice given above was made with the understanding that “flooding” meant power loss.

And if the check engine light has been on and indicated a miss it is very poor reasoning to suggest replacing the transmission without first addressing that problem. The repaired cylinder head may have a loose valve seat causing the miss and the loss in power which results in the transmission floundering in an effort to compensate. Of course while the transmission is being replaced the head work could be conveniently rechecked…

The shops reasoning is very questionable.

Also, in the vast majority of warped head repairs the local machine shop has heated and pressed the heads. Milling the head requires line boring the cam journals and shimming the head gasket which results in uneven compression.