I have a 91 Legacy LS that gets a backfire through the intake.

 

any ideas would be greatly appreciated

 

i know plugs got about 10k on them. Factory wires have unknown mileage.

 

There is no check engine light on so im not sure where to look first.

if i were to give the car a tuneup would ngk wires from advance auto be suitable for the car. i know i read oem or magncor but i beleive ngk is what oem are

I have a 91 Legacy LS that gets a backfire through the intake.[...]

Under what conditions; starting, idling, constant load, accelerating, decelerating, etc.? Does gas tank level make a difference? Is the air filter relatively clean (aside from any scorching )?

Under what conditions; starting, idling, constant load, accelerating, decelerating, etc.? Does gas tank level make a difference? Is the air filter relatively clean (aside from any scorching )?

 

it only does it under acceration. air filter is brand new. also has new fuel filter on. tank level makes no difference.

Other than backfire, does it bog/hesitate when accelerated?

Other than backfire, does it bog/hesitate when accelerated?

 

yea blogs and hesitates then it will backfire sometimes

Sounds like the mixture is a bit too lean. How many miles on the car? Ever replace an O2 sensor, and if so, at what mileage?

Sounds like the mixture is a bit too lean. How many miles on the car? Ever replace an O2 sensor, and if so, at what mileage?

 

150k i have not changed the O2 sensor since i got the car had it since 138k

We had a BRAT that did this. Don't know what it was; we sold it (had bought new in '78? and used as a farm pickup). Be interested to hear what you find. I later wondered whether the BRAT was a mechanical timing issue?

150k i have not changed the O2 sensor since i got the car had it since 138k

 

 

Tune the car up with new plugs, wires, and an 02 sensor. My money is on that correcting the problem.

Id definitely check out the wires.

Id definitely check out the wires.

 

thats what im sort of leaning towards myself since im not sure how long they have been on. The oem wire are ngk correct?

I usually just get them from my dealer so I am not to sure.I would think so since the spark plugs are NGK as well.

I usually just get them from my dealer so I am not to sure.I would think so since the spark plugs are NGK as well.

 

Ill try the plugs and wires and see if that helps will prolly be a few days till i get them. any reconmendations on plugs? i like running ngk but is there a certain one thats better to run.

Sounds like a timing issue. I would recommend taking a look at your crank pully to see if the bolt has come loose causing damage to the timing belt drive sproket and key.

Even if the crank pulley bolt is tight, it's possible that the t-belt may have jumped a tooth. It could be useful to determine when the belt was last replaced; is any of the service history before 138k miles known?

 

Perhaps some testing with a vacuum gauge might help point to a possible cause.

My 2000 OBW backfired so badly that it popped the clips on the air filter housing. Changed plugs and wires and air filter and the problem immediately went away.

Even if the crank pulley bolt is tight, it's possible that the t-belt may have jumped a tooth. It could be useful to determine when the belt was last replaced; is any of the service history before 138k miles known?

 

Perhaps some testing with a vacuum gauge might help point to a possible cause.

 

no service history is known before 138k.

 

i purchased wires and plugs today will put them in tomorrow and post results if any.

no service history is known before 138k.

 

i purchased wires and plugs today will put them in tomorrow and post results if any.

 

Can't a lean mix be caused by vacuum leak?

look closely athe the bottom connection of the rubber boot connecting to the throttle body. Mine was caught enough to possibly leak.

Replaced plugs and wires today. So far its running good. Find out more once i get some more miles on it.

Drove the car some more and the problem still exist now i get the check engine light but goes off b4 i get a chance to pull the code. Im thinking that the mas is going bad.

There will be a code stored in the memory. CEL need not be on to pull codes.

 

MAF's do go bad but are not a common failure.

There will be a code stored in the memory. CEL need not be on to pull codes.

 

MAF's do go bad but are not a common failure.

 

ill see if i can pull a code and report back