Loud Backfire and then Silence

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San Jose Steve
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Loud Backfire and then Silence

Post by San Jose Steve » Fri Oct 19, 2018 11:58 am

Cruising through a residential street last night my 124 experienced a loud backfire and just died. (Don’t think I’ve ever experienced a backfire before in that car.) I pulled the coil lead off the distributor cap, held it close to the cam tower and observed no spark while my wife cranked the motor. The battery appeared to be strong as the headlights remained bright and 2 years ago I installed a NOS Sipea ignition switch and did the "Brown Wire Fix".
I suspect that the Crane Cams XR-3000 ignition I installed 16 years ago bit the dust. Now that the car has been towed some 30 miles back to the house, I will do the basic troubleshooting steps to confirm my suspicion. IF the Crane is indeed dead and I need a new electronic ignition, should I get another one? I see stories online were people claim to have lots of trouble with them, though my experience wasn’t bad. (Until last night.) I probably put ~30K miles on my Crane unit in that time so if I look at it that way, maybe it’s not so good. I originally purchased this thing because it kept my engine looking stock. (The box is tucked up under the dash.) If you had to buy an electronic ignition today, what would you buy?
Oh...... and please don't ask why I didn't keep the original points and condenser in a little bag in the trunk. I had to answer that question repeatedly from 10pm to midnight while my wife and I sat in the car waiting for the AAA guy to show up. The heated seat kit I installed on the passenger side paid for itself 100 times over last night! Thanks, -Steve
spider2081
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Re: Loud Backfire and then Silence

Post by spider2081 » Fri Oct 19, 2018 4:42 pm

I pulled the coil lead off the distributor cap, held it close to the cam tower and observed no spark
I have fooled myself doing this also. The cam covers often are completely insulated from ground by their gaskets. So I now use the hood release on the firewall when checking for spark.
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rridge
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Re: Loud Backfire and then Silence

Post by rridge » Fri Oct 19, 2018 7:52 pm

Backfires through the intake side often result in the hose from the AFM to the throttle body popped off one end or the other, silencing the engine. If the hose does not separate and the gases exit out the AFM they can bend the flapper door causing it to stick.
Richard
'81 Turbo Spider
Rockville, MD
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blaze
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Re: Loud Backfire and then Silence

Post by blaze » Sat Oct 20, 2018 6:09 am

FWIW Here's my exprience with a Crane XR700. I installed one in 2003. 3 years and 10,000 miles later the optical trigger failed and I had to replace it. 10 years and 50,000 miles later the control unit failed. I had purchased a spare unit and trigger "just in case" sometime ago and when I swapped out the failed control unit the spare, it was bad out of the box. Of course it was too late in the game to return it.

Crane no longer makes these units or perhaps they just don't brand them with the Crane name. They are still available though but under the brand name FAST.

If you want to retain the stock look and use the same dizzy, most people are installing the Pertronix ignitor set up these days. I decided to go another route and installed one of the electronic units that were used on the later cars.

Good luck,

Blaze
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atruscott
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Re: Loud Backfire and then Silence

Post by atruscott » Tue Oct 23, 2018 5:55 pm

Before we embark on troubleshooting an AFM.... what motor are we talking about?
1960 Autobianchi Bianchina Transformabile
1970 238 Camper OHV
1974 124 Wagon TC
1974 124 Special TC
1975 124 Sport Coupe
1976 124 Sport Spider (The Racer)
1981 Spider 2000 (The Resurrected)
1985 Pininfarina Azzurra
2017 124 Spider Abarth Elaborazione
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rridge
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Re: Loud Backfire and then Silence

Post by rridge » Tue Oct 23, 2018 6:33 pm

Good point.
Richard
'81 Turbo Spider
Rockville, MD
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San Jose Steve
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Re: Loud Backfire and then Silence

Post by San Jose Steve » Wed Oct 24, 2018 11:57 am

It's a 1600 motor in a 72 124. We had our floors sanded and refinished last week so I've not had time to work on it. The Best of France and Italy show is in LA in 2 weeks so I need to get this fixed if we're to make the ~700 mile round trip. Trouble is, I get some serious stink eye every time I stop dusting an go to pick up a wrench.

Refinishing wood floors makes a huge mess. I think the vacuums on the contractors sanders are there only for looks!
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AZRuss124
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Re: Loud Backfire and then Silence

Post by AZRuss124 » Wed Oct 24, 2018 12:30 pm

The first thing I would have check was the timing belt. A 72 is an interference motor. I hope you are correct about it being an electrical issue
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davedecker4
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Re: Loud Backfire and then Silence

Post by davedecker4 » Wed Oct 24, 2018 9:41 pm

Yes, I would check the timing belt first. If that's alright you might verify compression. Then ignition system troubleshooting. A flow chart can be helpful for this. I have one for an old ford I use. Basically you want to check for spark at each location. Good luck. Let us know how it goes.
Dave Decker
a 'couple' Fiats and Lancia's
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San Jose Steve
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Update Re: Loud Backfire and then Silence

Post by San Jose Steve » Tue Oct 30, 2018 12:20 pm

So I finally got some time to investigate this further. I purchased a new Crane (Now called FAST) XR-3000 ignition module. Unplugged the old unit and installed this one, leaving the original units optical trigger installed inside the distributor. The car immediately fired right up. The original one I had installed under the dash high up on the passenger side. Great hiding spot but it precluded me from seeing the little diagnostic LED lamp on the unit. I installed the new one under the washer fluid bag so I could easily get at it and could see the LED if I needed to by simply removing the bag.

Looking at it this morning, I am now double thinking this choice as maybe only 12-14 inches away from the exhaust manifold. Hummmm...... Thinking that may not be the best place and that going back up under the dash would be a better option. Taking the wife to the Best of France and Italy show this weekend. A 700 mile round trip across 4 days. If this thing fails again, I will get more than just "stink eye" from the right seat. Ha!

Oh...... and I now carry a set of points, condenser, screws and wire nuts in a small bag under the spare tire cover!

-Steve (The Fiat Driving) Ferrari
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