Power Loss Problems After Backfire

[cmurakami]

My '82 Fiat Spider 2000 was running very well until last week when I started it up after a week of sitting. The engine backfired and has very little power under load and outside of the 2k-3k rpm range.

Here are the symptoms:

• low, intermittent power under 2k
• low power above 3k
• can't really get above 3.5k
• engine sounds fine and revs fine when not in gear
• isn't obviously misfiring (to my ear)

Troubleshooting done so far:

• checked the timing to make sure the vacuum advance was working. It seems to be working.
• pulled the plugs. engine seems to be running a little rich, but no obvious signs of a fouled plug. Cleaned, gaped, and replaced plugs.

Any assistance is appreciated!

[ORFORD2004]

You bent the flap in the AFM when it backfired so the flap is rubbing? Or your temp sensor in the T ?

[RRoller123]

+1. Could be also that a portion of the air tube is blown out, or is off the connection somewhere, check for air leaks everywhere from the throttle back to the AFM. Unregulated air getting in will screw up everything.

[courtenay]

What Pete (Roller) said. Before you take your AFM apart to check the flap, check the big intake hose for cracks or loose connections. I had the same problem - and found I hadn't tightened the clamp that holds the intake hose to the AFM housing properly and it had come loose. Tightened clamp, problem solved.

[cmurakami]

Thanks for the quick replies.

I checked the intake hose and it looks like the clamp connecting it to the AFM had slid off. Fixed that, but the problem persisted.

So I took out the AFM and inspected the flap. The little stopper was bent, leaving a gap when the flap was resting. I straightened out the stopper and put it back together. Unfortunately the problem still persists.

I watched the AFM while pushing reving the engine and the flap appears to be moving freely. Do I need to do something else to the AFM? Or does it sound like another issue? Thanks

[RRoller123]

Check the hose connections related to the AAV, and the timing advance hose under the throttle body spring too.

[cmurakami]

Thanks. I checked all the hoses related to the AAV and the timing advance hose. They don't seem to be leaking.

I've recorded some audio of the car accelerating to help with the troubleshooting: https://dl.dropboxusercontent.com/u/344 ... -00-27.wav

Please excuse the wind noise.

[burgandy81]

Last year I had a backfire when starting which resulted in Extremely Rough running, no power, and inability to get past 3K.

In my case, I traced it back to the cam belt. My guess is that the back fire caused the engine to spin backward slightly which cause the exhaust cam to be off one cog. In any case, adjusting the cam belt returned the engine to previous running state.

Might be worth a look.

Good luck!

[cmurakami]

Thanks burgandy81.

In my case, I traced it back to the cam belt. My guess is that the back fire caused the engine to spin backward slightly which cause the exhaust cam to be off one cog.

How do you test the exhaust cam belt? Is this a relevant thread: http://www.fiatspider.com/f15/viewtopic.php?t=18840 ?

[burgandy81]

How do you test the exhaust cam belt? Is this a relevant thread: http://www.fiatspider.com/f15/viewtopic.php?t=18840 ?

Yes, that is exactly what i was describing!