I have a 92 Explorer with a 4.0L motor and a 5sp. manual trans. I got in it to start it and before it started, it popped/backfired and smoke drifted up from under the hood and thru the dash vents into the truck. The engine did not start (although when I tried it again it did start). The smoke just drifted with no force behind it (such as a fire). The smoke was present for just 2 or 3 minutes. I'm pretty sure it originated under the hood. The smell reminded me of the cap guns I used to have as a kid with the red rolls of caps. After it started on the next try, it seemed to idle a little different. It seems to take a little longer to idle down, even when shifting gears. It also seems to take the truck a little longer to warm up regardless of the outside temperature. Any ideas? The only work done lately was a new transmission and slave cylinder about 2 weeks ago. About 3 weeks ago, I also put on a new fuel filter. Since the day of the backfire, it has been running fine as usual, although there is a very slight difference in the idle ( it is so slight, that I'm not really sure if it is different).That one time is the only time it backfired. I would appreciate any help you can give me.

Thanks,
Vance

 

As opposed to "Backfiring" through the exhaust, it sounds as if it may have "Spit Back" through the intake. My 92 has done this periodically. Check all of your vacuum hoses and connections on the intake. There is a tree on the intake just in front of and below the break booster. There are 4 or 5 hoses and 1 or 2 vacuum plugs on that tree. Thats usually where something comes loose when mine spits back. This can cause a rough idle as the engine is getting too much air and the computer can't measure it.

Good luck.........

 

About 6-8 months ago, my '93 Explorer did the same thing - it backfired that one time, and hasn't done it before or since. After the backfire, the truck died. I restarted the engine; it started right up, but it ran rough and the idle was high and hunted around. I experienced the same smoke you described, but I don't recall a particular smell to it. While it idled, I popped the hood and heard a loud "sucking" sound. I tracked the sound down to a vacuum line on the top left rear of the engine that had been blown off by the back fire. Once I reattached it, the truck returned to normal, and has been ever since. I have no idea why it backfired in the first place.

 

I must have been writing as you posted, Jerry! Yes, that is exactly the area where I found the loose vacuum line after the backfire. I think that as the truck has aged, it requires a bit more crank time on the key while cold-starting. It has only backfired the one time, but I've noticed that it has some stumbling starts if I let up on the key too fast. My big truck has me spoiled - all I have to do is touch the key and it starts.

 

Thanks guys. You were right on the money. I found a little line that had blown off right where you said it would be. I really appreciate the help!

 

Just to add the solution....i also had a 92 explorer xlt and had the same problem...the reason the hose came off, was becuase of a small transmission converter or regulator (im not sure what the peace is called). since that wasnt working properly, the transmission fluid was being distributed and burning throughout the exhaust and vacum hoses, causing the vacum hose to get damp and slippery....as for the exhaust, there might be slightly more smoke comming out of there than usual. check the vacum hose you fixed and see if it has a fluid, oil like substance...if it does, chances are the regulator went bad.

 

vbl said he had a manual transmission (lucky stiff), so he won't have a vacuum modulator. Vacuum modulator is only for auto transmissions. But you are right. If you have an auto transmission and those hoses start slipping off, ATF from the vacuum modulator can cause that.