Had a bad exhaust leak on this vehicle. Could not get any local mechanics to agree to do repair as all had the excuse they were worried about breaking off a bolt in the head. I understand their concern, but needed to get the job done. Having some mechanical experience, I did the job myself. Used all new bolts, though they were not exact lengths of the originals removed from the vehicle. Some, I had to use washers to keep the bolts from bottoming out. Everything went smoothly despite doing the job on two of the hottest days of the century. Because a lot of WD-40 was used in loosening the bolts, after having restarted the vehicle, there is a lot of smoke - I imagine from the WD-40 burning off.

Motor ran smoothly and after a few minutes, I decided to do the test drive. Didn't even get to the end of my street when the vehicle lunged. I believe it was going into second gear when that happened. I returned to the work area and when things cooled down, I looked everywhere I could imagine for a loose wire or vacuum hose I thought maybe I had, inadvertently, pulled off. Can't find a thing. Thinking about having it towed to my local mechanic (where I take the vehicle for tune-ups, oil changes and inspections) to see if they can find the problem.

But, thought I'd put the question here first. Does anyone have any kind of idea of what may be happening here?

 

Can you duplicate the concern?
If it was a one time thing, may not happen again. If you can duplicate it, need to know the conditions when it takes place.
Things like speed , load, engine temp, trans gear selected, running in, anything you can think of that you can recall.
Maybe something simple like leaving off a ground wire at the back of the engine?
PTO ?

 

Thank you for commenting on this. In answer to your questions, what happened when I test drove the vehicle was that I left my driveway at a low rate of speed and when it seemed like the vehicle was shifting into second gear (it's an automatic transmission), the vehicle lunged (very noticeable). I turned around to come back down the road to my house and it did it again, though not as violently as the first time. One thing I did forget to mention on my first message was that the Check Engine light was on. It has never been on before but it came on soon after I started the vehicle. Speed was low, there was no load to speak of on the engine, the engine temperature was probably normal, it was in low gear to start off and, I think, probably shifting into second. I'm leaning towards a disconnected wire or vacuum hose, but just can't locate one that's come off.

I think I will try again when I get home today after work to see if it's still happening. Will let you know what I find.

Thanks again.