Sudden backfire issue

[Zaffer]

I searched the forums and couldn't really find any info on the fuel injected cars. My car has suddenly decided to backfire through the intake. It didn't used to do this, and the car won't start for long. I just replaced the fuel pressure regulator as my old one wasn't working properly, but the backfire started before this.

I checked t-belt timing and it is spot on. The intake pipe is brand new. The MAF sensor is rebuilt. The fuel pump and filter are new. The fuel line is new. The cap, rotor, and module are new. The setting on the distributor is correct, or was when it ran last, about 2 months ago. I also replaced the ignition switch as I was having a starting issue, which this resolved. The coolant temp sensor ohms out correctly.

The car will start, but dies after about 5 seconds. Re-start, dies after about 3-4 seconds. Re-starts, dies after about 2 seconds. Finally, won't re-start. If I block off the fuel return line (prior to replacing the pressure regulator), car would idle and run fine. I haven't had time to check anything else lately, so any ideas would be great. Also, the car now backfires through the intake sometimes, which it did prior to the PR replacement.

Also, my vacuum diaphragm on my distributor is shot, but this shouldn't cause the above issue, correct? I have a new one coming next week from Auto Ricambi.

In the interest of all, I posted about this a couple of months ago but couldn't find the post.

[RRoller123]

Verified ignition timing? Distributor shifted somehow?

[Zaffer]

I haven't verified it since setting it before this whole thing started, but I guess I should. I just can't see why it would run and idle fine by restricting the return line.

[Frog2Spider]

Here's the problem:

The air cleaner intake plumbing has come of. Fit the black tube back on the housing and tighten the clamp.

You're on your way!

Dave.

[courtenay]

It does sound like there's air getting into the intake system between the AFM and the intake. I'd follow frog's advice and check the connections as well as the pipe itself to ensure there are no cracks.

[mscafide]

Backfire.

AFM, flapper for air intake could now be binding if it bent.

Fix the binding by filing or sanding the flapper so it operates freely.

[Zaffer]

I pulled the AFM and checked the door and luckily nothing was damaged, the door still moves freely. I did discover that there is a loose wire at the connector as when I had the ignition on, the fuel pump wasn't turning on when the door was moved, but moving the harness slightly got it going, so it MAY be loose wires at the connector causing the issue. I'll check the harness, timing, intake boot, and other air lines for any potential issues next weekend.

Frog2spider,

I checked the intake boot at both the intake and AFM connections and everything was tight and sealed there, but thanks for the heads up.

Thanks for the advice and I'll let you all know if I find anything, which hopefully I will.

[Zaffer]

Well, I removed the intake boot and it is fine. I removed the AFM, inspected the connectors and found corrosion on the pins and connectors! This is a little weird as the car is garaged, granted in a shed with no door, and not driven in the rain since I got the AFM rebuilt. Well, I'll be cleaning the connectors tomorrow at work since my contact cleaner and wire brushes are there and update accordingly.

[76was124]

My guess would be timing...either due to incorrect setting of the distributer, cams,, or the timing belt jumped. I suppose a stuck intake valve could be a cause as well.

[kilrwail]

Backfiring through the intake generally points to a lean mixture. As suggested previously, look for air leaks everywhere.

[76was124]

look for air leaks everywhere.

Sometimes the AAV can have a major leak through the housing itself. You could clamp off the hose on the intake end to see if it makes a difference, or disconnect both hoses, block one end of the AAV, and blow through the other end. If the housing is shot, you'll feel the air come out of the seam.

Also, because it doesn't,sound like the engine is idling well at all, any chance you have any of the plug wires swapped from your distributor work?

[Zaffer]

I checked the plug wires and they are correct. This whole issue was a sudden one. I had been driving the car for a few months and it was running well, less a working vacuum diaphragm. I let it sit for a month due to weather, went out to start it, and that's when the above issue(s) started, all at the same time.

I removed my AFM, cleaned the corrosion off of the contacts, and then decided to unscrew the connector on the AFM to make sure the corrosion hadn't spread to the inside. When I pulled the connector out, Pins 1 and 2 have melted plastic on them and there is a spring arm(?) attached to pin 2. weird. I'll need to call the rebuilder for a warranty issue, I guess.