Backfire, what caused this to happen?

daltar08 · Post by **daltar08** » 02 Apr 2012, 13:25

Hello everyone, 1996 Volvo 850 turbo wagon Automatic, IPD short ram with K&N, IPD silicone intercooler hoses, IPD Turboback EXhaust, ARD green tune 17 psi, ok so i was driving on the highway with a friend he wanted to see what my "mom wagon" was capable of, was accelerating at WOT hit about 96mph and BAM a loud bang, i could feel it, sounded like a backfire, checked everything and everything looked fine, have been driving for a week since and hasn't happened again, any ideas what caused this?

Post by **jimmy57** » 02 Apr 2012, 13:49

It was lean. CHeck your fuel pressure under high load like that and you'll very likely find it is low.
Things that make for low fuel pressure: filter, FPR hose cracked, FPR, or weakening pump.
I'm surprised the plug in the RH end of intake didn't pop out. The plug flying out is very common when you have an intake fart.

daltar08 · Post by **daltar08** » 02 Apr 2012, 16:06

The wire coming off the ignition coil was constricting (partly crimping) the tube coming off the tube coming off the MAF could that have contributed? I will look into the suggestions you gave me, where is this plug that could have popped off?

D_V_ENT850R · Post by **D_V_ENT850R** » 02 Apr 2012, 16:34

Pretty common to get popping in a tuned car. If everything else looks ok I wouldn't worry about it!

Post by **jblackburn** » 02 Apr 2012, 16:39

The plug on the intake manifold is on the left side behind the power steering pump.

Don't worry, if it's still going, that freeze plug is still in there. It wouldn't be running at ALL without it.

I'd check more into the fuel pressure things Jimmy talked about, or check out your spark plugs for wear. I went from 0-90 flat out one time and the check engine light started flashing at me indicating a misfire - I think it was mad at the #1 fuel injector.

daltar08 · Post by **daltar08** » 02 Apr 2012, 18:44

alright thank you

daltar08 · Post by **daltar08** » 02 Apr 2012, 18:46

how hard is it to replace the injectors or any of what jimmy suggested, ive done all the mods myself so far.

Post by **jtp** » 05 Apr 2012, 12:23

First get an old rag and wear eye protection. Put your cig out.

The fuel rail sits on top of the intake mani, right below your oil cap and valve cover. Depressurize the fuel system via the blue-capped valve on the driver's side of the rail, then unscrew the fuel line from the rail on the passenger side. Then remove the two 10 or 12 mm bolts holding the rail on, as you pull the injectors out be ready to unplug the wire from each injector's harness and then there is a very thin metal sheet holding the injectors to the rail by inserting itself in an indentation on the non-business end of each injector. That thin metal sheet has 2 or 3 small diameter bolts you'll need to remove.

Maybe I'm off here since noone else has mentioned it, but if you'll be replacing them anyway it might be a good time to upgrade to injectors with larger capacities. That will be hundreds of dollars so you may just want to see if the injectors you have need a good cleaning. There's a really good writeup for that cleaning linked to the official stage 0 list on this site.

Post by **jtp** » 05 Apr 2012, 12:35

Upon reassembly note that, per the Haynes manual, the two fuel rail bolts have torque specs of 88 in-lb, and then an additional 75 degrees after each one is at 88 in-lb.

daltar08 · Post by **daltar08** » 09 Apr 2012, 07:47

thanks everyone once again! will give this a try~