So the car was losing power slowly and we decided to do a tune up. We seafoamed the car, New spark plugs, new plug wires, New o2 Sensors, Oil Change, Cleaned the MAF and the TB out. The car started fine and idled fine. About 5 minutes later it developed a backfire. The car runs pretty crappy, it shutters under load and obviously its backfiring. Its backfiring out of the exhaust and my buddy said he saw flames (no cats but some exhaust leak in their place).

What could cause backfiring. We ruled out the o2s, plugs, wires and now its going to be expensive as we get into the bigger stuff.

Any help would be awesome

 

Need more information. Example, what are the fuel trims, O2 readings and at least IAC counts?????

The reason I ask is I had a problem for a while (showed up 2 years after installing LT's) where the O2 on the pass side showed rich. The fuel trims would show the engine was pulling fuel until it bottomed out. Then the engine would jump to open loop shortly. Then go back to closed loop and start all over again. For the brief moment it was in open loop, the engine would smooth out. The problem turned out to be burned O2 wires.

When it runs lean, backfires are to be expected.

Your problem sounds like it's ok in open loop but after it enters closed loop there is an issue. I'm stabbing at it from where you said after 5 minutes it started running crappy. One way to tell if it's control problems is unhook one of the O2's and see if it runs better.

Don't be a shotgun mechanic and don't assume since you changed what thought could be the problem that it has to be something major. I doubt your problem is that involved.

Look on the passenger inner fender running down to the bottom. See that bundle of wires???? Near the header.

 

i pulled the o2s to see if that was the problem and it didnt change.. I dont know what you mean with the bundle of wires tho..

 

I am having the same issue with my Z28 after putting a set of long tubes and new wires on.

I have not fixed it yet, but yesterday I found a potential culprit. The wire terminals on the opti side are corroded very badly. I never checked this when I replaced the wires, but the corrosion is bad enough that the tips are gone on a couple of terminals. This is most likely my problem, you should check yours. I have a new opti on the way, so I will let you know if this is what fixes my car.

speedygonzales

I am not ruling out the O2's. They are new O2's, but I had to extend the wires, so anything goes. My car never runs smooth though. About 20 seconds after start up there is a period that it will start to run a bit smother, but that does not last long.

I just bought a cable to link my laptop to my car. What program do you use to view the fuel trims, O2's, and IAC. And what does the Idle Air Control do for you?

 

TTT any other ideas?

 

will reseting the PCM lose the tune I have on it? I was thinking about pulling the fuse to reset it but I wasnt sure if that would lose my tune

 

nodnarb481

Did you ever check the terminals on your Opti? Disconnecting the battery won't loose the tune, it is written in EEPROM. Very similar to those memory sticks eveyone has nowadays.

 

You might want to start a new thread specifically for your problem. Although it may be similar to the original post, it confuses the answers for the original poster.

You need scan software that is compatible with your PCM (OBD-I or OBD-II). You don't provide any info on the year of your car, so no one can give you a specific answer on the required software. Might want to add a "signature" with basic info about your car.

The Idle Air Control is a little stepper motor on the base of the throttle body that opens and closes the idle air passage to control idle speed. Knowing the IAC counts may provide some insight on whether the PCM is able to respond correctly to idle speed errors, or possibly indicate a vacuum leak that is allowing air to enter at idle other than through the IAC passages.

No. The "tune" is stored in non-volatile memory. The only thing you "lose" when you reset is the long term fuel corrections and learned IAC value.

 

am I going crazy or do I have a misprinted Haynes Manual.. On the Optispark: cylinder four is on top and cylinder two is on the bottom. I found these were mixed up in the very beginning. Today I went to the shop the cars at today to take a look at a few things.. besides an ugly *** spark plug wire job that needs some real cleaning up and two boots not being snapped on the spark plugs.... I had my dad pull on wires and me under the car pulling back to find out if they were all correct. Sure enough he pulled on a wire and i found it went to the top.. I said that should plug into the second cylinder.. he says "no its plugged in the first" So i grab the wire connected to the bottom terminal and tug a little until he finds it.. and i say wheres that one? and he says "in the second cylinder back"

so do I have a misprinted haynes manual or did the mechanic that I took the car to and said that all I know so far is that 2 and 4 were mixed up.. mixed them up again?!? (I had to take them out and damaged them so I never got the chance to just swap them back and see what happened before I took it to the shop)

WTF?

 

We KNOW the info on Shoebox's site is correct.... probably a better place to start, if your Haynes looks any different than this:

http://shbox.com/1/opti.jpg

 

nope thats what it looks like.. so my plug wires that were mixed up (2 and 4 crossed) were now just done by a mechanic who once again.. crossed them. I even said.. they were crossed and he.. crossed them. I hate everything i havent had my car for over two weeks because of this

 

I finally got my car fixed. No more backfires and missing. I replaced the Opti to correct the corroded tip issues. While I was doing this I noticed I had gotten a bit crazy tightening down the large washer and bolt that retains the plug wires on the passenger side of the block, next to the opti. This very well could have been part of my problem. The wires were squished very badly and were surely not functioning correctly. Hope this helps you

 

went back over there today with my spare keys and switched 2 and 4.. started her up and she was smoking a little for a minute or so but that eventually went away. Then I took it for a test drive and made sure it got into closed loop and it never backfired once.