XT6 Backfiring problem...HELP

[SSJupB]

I wanted to ask you guys for advice so please help.

 

Heres the problem:

When the engine is cold I start it up and the engine will sometimes want to die and I have to give it some gas and it will backfire. Then it will do the samething sometimes when I just started driving it when I am sitting at a stoplight for example. But when I am sitting at a stoplight it doesn't backfire.

 

I took it to a shop and they told me it probably just needed a tune up. Well I got a tune up and it really did help but...it still does it sometimes, not as much as before though. So I took my car back to shop to show them what I am talking about. But of course the car will not do it when it is being looked at. So that didn't work.

 

Please tell me your ideas what you think the problem could be.

 

Thanks,

Britnie

[JonOfScio]

possible leak in the intake somewhere (the hoses, ect.)

 

Just look at the air filter box, the hose running from that to your engine, and check your exhaust for leaks. I think maybe it's a leak.

 

How BIG is the backfire, is it light? Do you get a whispy sound when you push the gas down that you don't get when you lay off the gas?

 

Mine made a noise that was pretty hearable (blown exhaust gasket) and backfired just a little. You may want to run some FI cleaner through your car (fuel injector cleaner)

[Skip]

the key here is the back fire, I will assume you mean under the hood as in through the intake system.

This indicates a lean mixture, sounds like the ECU does not know the engine is cold. This indicates a problem with the FI coolant sensor.

These do go bad but most times they just need the contacts cleaned.

 

I think I know your next question - Where is it and how do I get the contacts cleaned?

 

I do not have my factory service manual handy but if you have no other response I'll promise to dig it out of the library.

[SSJupB]

Well I put FI cleaner in about 3 weeks ago.....didn't help. And the backfire noise isn't extremely loud or quiet....but if you are near the car you can hear it. I'll look if theres a hole in the intake hose....but I don't think there is because I sealed that up about 6 months ago. But i'll check in case.

 

SKIP...thats sounds VERY possible.

[asavage]

Spark Plug Wires!

 

They're often not replaced as part of a tuneup, and they get leaky and can be the cause of misfire into the intake tract.

 

Skip is correct, a lean condition can exacerbate this, but with a modern ignition system in good condition, lean misfire doesn't (isn't supposed to) occur; instead, you just get a power loss.

 

Anecdote:

I am (I really am!) trying to get my Loyale wgn whipped into decent shape for my friend without spending as much as is my wont. This car had had a tuneup recently, I have the receipt, but they didn't replace the plug wires, and I vacillated over whether I should.

 

As a test, I grounded a long screwdriver with a clip lead, then with the engine running, I ran the tip over the wires, ends, spark plugs, and all over the dist cap. When I brought it near the coil top, it drew an arc. I shut off the engine, then removed and carefully cleaned the wire end, boot, and terminal. Retested, no arc.

 

Next day, I decided to reset the timing. I plugged in the D-check connector, warmed up the engine, removed the bellhousing plug, loosened the dist and connected the light. I decided to back off the timing a few degrees, so I put a shop rag on the cap, and with my gloved hand, tried to rotate the dist. I got zapped hard!

 

Thirty seconds later, I was on the phone, ordering a new wire set.

 

What galls me is that the day before, I couldn't get an arc to a solid ground, but next day it zapped me through a clean, dry shop rag and a layer of latex!

 

I guess I'm just a magnet for automotive abuse.