Why is my explored backfireing ?

[imq707s]

My 97 X (5.0 v8 w/ 87,000 miles) is starting to backfire out the exhaust when I'm on the highway and I put a heavy load on the motor, example : passing cars or entering on ramp. The motor will stumble a second, and them pop out the exhaust. It will do it a few times then it does away. I'm not getting any type of Check Engine Light. What could it be? O2 SENSOR, MAF SENSOR? PLUG WIRES? I put new plugs in it but that didn't seem to help.

 

[TarHeel085]

your timing is probably shot. thats what usually causes it.

 

[imq707s]

Can you give me some more info. What do you mean by " your timing is shot" ???

Here is what I'm thinking.

1. Maybe one of the ignition coils is going bad.
2. Sparkplug wires are going bad
3. One of the four O2 sensors is bad.


Anyone else ever had this problem?

 

[Majisto]

Spark plug wires. Replace them. They're cheap and is probably the problem. I think if an O2 was out you'd get a CEL...

 

[Muskrat]

check to make sure that the wires are in the right sequence.

 

[97emerald]

I would also replace the fuel filter if you haven't done it recently.

 

[mattanderson31]

timing

That engine probably uses a timing chain. If that chain is stretched or if the guides have worn, your timing could be off. If the guides break, the repair could quickly get expensive. I don't have the same engine, but it is now cheaper for me to buy and install a rebuilt engine than to repair the one I have with a broken chain guide.

I'd say start with new plugs and wires. Maybe try some heet in the gas tank.

O2 sensors could be the problem - if one is malfunctioning it tells the computer to make the gas too rich or too lean. O2 sensor problems usually signal a check engine light, though.

 

[imq707s]

Well, I finally went out and bought some new spark plug wires. I got the good Borg-Warner wires for around $60. After I put the new wires on the motor ran great. Started much easier, idles smoother, and didn't backfire when I would power brake it like before. I thought my problem was fixed. But now two weeks later, it's starting to run rough and backfire again. What the hell is going on? I'm still not getting any check engine light. I checked all the wires again and they look ok. Any suggestions?

 

[Alec]

Please do not have 4 threads going at the same time with the exact same problem. The other 3 are locked. Another moderator may decide to delete or merge them.

 

[imq707s]

Sorry about that, I posted those four threads over a period of several weeks. And I just wanted everyone that originally posted on those threads to get notified that I had an update. Sorry about that.

 

[Mbrooks420]

Then you bump the tread

 

[imq707s]

what do you mean by "bump the thread"?

 

[Mbrooks420]

Everytime you post in a thread it goes back to the to top of peoples"View new threads" and people who posted to the original thread get an e mail telling them that you posted new replies.

 

[HH1]

so...changed the plug wires= truck ran great. no backfireing under acceleration.
Few weeks later= backfire is back.

I would say that your wires are are getting cut or melted on the exhaust manifolds. So your really running on 7 cyclinders and only feel it under heavy acceleration.
Try this: with the truck running using a plug pulling tool and pull one plug wire off at a time and see if the trucks engine misses a beat. the one wire that you pull off and no change will be the bad wire.

....or your timing is off. Pick up a timing light to check it.


.....or send it to a shop where they will charge you $$ and tell you nothing is wrong with it.

 

[imq707s]

It's a very strange problem. I've already checked the plug wires, and I didn't see any that got burnt at all. I'll have to check again just to make sure. It only missfires under heavy loads. Another thing that I've noticed is that even right after I put the new wires on and the motor was running great, I still noticed that the motor was surging at WOT. Kind of like it was running lean.
From a dead stop I hammered the gas and after it hit second gear and the rpms started to climb, I could feel the power of the motor surging when the rpm's were climbing. Could it be a bad O2 sensor? But that still doesn't explain the backfiring and rough running when you put a heavy load on the motor. Coil packs going bad?

 

[imq707s]

Oh, one more thing. About the timming, how could it get off? I thought that was all computer controlled. If it was off how would I adjust it? I'm got a timming light. I've got a drag car that run's 10's in the 1/4 so I know motors. I just get realy frustrated with fuel injected motors, all those sensors.........

 

[V8-X]

imq707S - Sounds kind of like we are experiencing the same problem. I have a 99 X with the 5.0V8 and Auto Trans. I've taken the truck in to Ford 2 times & to two independent shops, which no one could find the problem since the CEL is not on. I've swapped out all 4 O2's, EGR, Fuel Filter, PCV, all 8 splugs & wires, Fuel Pressure Damper, IAC and I have cleaned the MAS. I still have the problem, which has been going on since June 2002. I just purchased a new TPS & DPFE which will go on as soon as I can get to them. If you find a cure, please post and let us all know. Otherwise, if I come across the solution, I'll post any cure that I may find.

I'm just as stumped as you are, since no one can seem to find a resolution. I've just been informed that it could be one of the Ignition Coil packs, which I'm going to test after I swap out the TPS & DPFE.

Hope you find out the porblem, as it's making me crazy as well. Good luck!!!

 

[imq707s]

Some other people have also suggested the coil packs to me. I haven't replaced them yet, but I might if I can't fix the problem. I just don't understand why it ran great for a few weeks after the new wires, and now it's runing like crap again.

 

[BigOne]

You might want to check your cam position sensor. This is what the computer used to determine the timing of the engine. If your sensor is fine, then you might want to look into a stretched chain.

On the older truck we could compensate for a stretched chain by changing the timing at the distributor. On these new units we can't do that, we have to rely on the information given from sensors to the computers. If the chain has play and the cam isn't perfectly syncronized with the crank, then the cam sensor will be sending incorrect information to the computer and your mixture and timing will be off.

Very difficult problem for diagnosis as the computer thinks all is well and therefore won't throw a code. Because of this, when you put in on the computer it will say that all is well, which of course it isn't.

One way to check for chain slack is to put a socket on the nut on the end of the cranshaft and a long breaker bar. This will allow you to move the crank back and forth a bit. The cam should move with the crank. If there is movement at the crank without corresponding movement at the cam, you have a chain problem, causing your sensors to send the wrong info to the computer. The heavier the load, the significant the error will be (chain stretching under load).

 

[imq707s]

When I said that it stumbles and backfires under heavy load, I mean a constant RPM under heavy load. Example : Going up a big hill under 3/4 throttle with the tranny still in overdrive and the rpms at around 2000rpms. It's loaded pretty good, but it's not excelerating. If the motor was excelerating I would agree with your cam stretch theory, but since it's at a constant RPM the cam chain should have any excessive strain on it. Even if I'm sitting in the driveway and mash the brake and mash the gas at the same time, the whole truck just shakes and backfires. But as soon as I let off the gas it goes back into a smooth idle. I pulled each spark plug wire off the coil packs one by one and each one I pulled would decrease engine rpm so I don't think I've got a bad wire. Man, those coil packs put out quite a spark. I could hold the wire about 1 1/2" away from the coil pack terminal and the spark would jump to the wire. If I didn't have the wire near the terminal, the spark would just jump to the closest thing.