What exactly causes Intake Backfires??

E

eric91xj

NAXJA Forum User

• Jul 24, 2003

• #1

I know to some this might be a stupid question and i'm probrably just not thinking hard enough but what causes intake backfires? i get them sometimes if i'm in park and just very quickly hit the gas and let off, the motor will stumble and i'll get a pretty loud intake backfire. It happens occasionally while just driving around, not too often though. Mainly just while i'm stopped in park and hit the gas really fast.

Thanx,

Eric

 

E

eric91xj

NAXJA Forum User

• Jul 24, 2003

• #2

If it could be from a worn cam (225k), could i put the new one in with the old bearings or is that a big no no because from what i've heard those bearings are pressed in and i ain't pulling the block for that.

Eric

 

Eagle

Lifetime NAXJA Member

NAXJA Member

Location

Terra Firma

• Jul 24, 2003

• #3

Intake backfires aren't usually loud -- are you sure it's popping thru the intake, and not the exhaust? I was getting some soft "popping" last summer about this time. Finally figured out the O2 sensor was failing -- didn't respond fast enough, and when I'd let off the gas it kept pumping a rich mix for a few micro-seconds and the excess fuel was burning in the header or the cat instead of in the engine.

 

E

eric91xj

NAXJA Forum User

• Jul 24, 2003

• #4

i'm sure it is because i have a cone filter and its blown it off before. its not necessarily loud like an exhaust backfire would be, i cause it kinda sounds like when you take a paper lunch bag or a little baggie, fill it up with air and pop it with your hands.

Eric

 

Eagle

Lifetime NAXJA Member

NAXJA Member

Location

Terra Firma

• Jul 24, 2003

• #5

Check the oxygen sensor.

 

P

pec50

NAXJA Forum User

Location

sierra vista, az

• Jul 24, 2003

• #6

Also a possibility your coil is beginning to fail.

 

E

eric91xj

NAXJA Forum User

• Jul 24, 2003

• #7

hmm, i will check the o2 sensor, dang i just replaced that thing about a year ago too, oh well. What type of reading should i be getting out of it if it is bad, and if it is good? Sorry for the questions but i lost my FSM and don't have any specs on this sorta stuff. Also regarding the cam bearings question, are they infact pressed in and could i just re-use the old ones if i eventually put in this new cam that i got laying around wasting space?

thanx,

eric

 

Bones

NAXJA Forum User

Location

Mid Missouri

• Jul 24, 2003

• #8

Sorry for the questions but i lost my FSM and don't have any specs on this sorta stuff.

Click to expand...

Eric,
Get another one:

http://cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll?ViewItem&item=2424818048&category=34224

or

http://cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll?ViewItem&item=2424417010&category=34224

Bones :skull1:
#6 and eBay junkie:anon:

 

E

eric91xj

NAXJA Forum User

• Jul 24, 2003

• #9

i wish i could man but i've been unemployed for over a month now and the funds are'nt there at all.

eric

 

E

Essayons

NAXJA Forum User

• Jul 31, 2003

• #10

A new oxygen sensor just cured mine, and the one that came out looked liek it hadn't been in long and came out easily.

 

M

MarkdaleXJ

NAXJA Forum User

• Jul 31, 2003

• #11

Does anyone else think this sounds like a timing chain problem or a burnt valve? Just a hunch:anon:
J.R.

 

E

eric91xj

NAXJA Forum User

• Aug 1, 2003

• #12

thats a good possibility on that burnt valve and timing chain, or a toasted cam lobe possibly too. i dont' think its a sensor or anything, i really think its deaper than that.

eric

 

Matthew Currie

NAXJA Member #760

Location

Vermont, land of big clay

• Aug 1, 2003

• #13

When my 87 did that it was a bad Throttle position sensor. It would hesitate, nearly stall, then spit, often blowing the crankcase vent hose off. Of course 87's are a little different, but I enter that as another possibility.