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Backfire Then Engine Dies in 76 930

Last summer I drove my stock 76 930 on the freeway. Got stuck in some traffic and while just barely starting to accelerate from a dead stop in traffic, I heard a loud backfire. Not sure if it came from the intake or exhaust, but I would say more likely an intake backfire. Sounded like it was right behind me. The engine then died. I coasted to the side of the road and then tried starting the engine. It started right up and I was able to accelerate back into freeway traffic with no problem. It happened a second time a couple of days later under similar conditions. What would cause this? Recommendations on where to start troubleshooting? It's one of those intermittent issues.

Old 03-30-2018, 10:30 PM
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Possible bad connection (relay, connector, fuse etc.) resulting in intermittent fuel pump shut down.
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Old 03-30-2018, 10:38 PM
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Thanks, but would that also cause an intake backfire? The backfire and the engine shut down occurred at the same time.

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Originally Posted by slyguy View Post
Possible bad connection (relay, connector, fuse etc.) resulting in intermittent fuel pump shut down.
Old 03-30-2018, 10:40 PM
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Hard to say the cause without more information but FYI backfire from intake is usually lean on fuel and backfire from exhaust is rich or excess fuel in exhaust.
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Old 03-31-2018, 03:24 AM
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I would say it's a lean condition that gets to the point of an intake backfire when the engine gets hot. Idling in traffic would be one of those times. Whatever controls the fuel flow rate on acceleration from idle is going to be the issue. I'm just learning about these engines but I would guess a problem in the WUR.
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Old 03-31-2018, 06:54 AM
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Do you have an AFR gauge installed? It would not be original but well worth the effort. Also, these early turbos run so great all the time we sometimes neglect the basics...we just get in and go. If you haven't done a routine tune up I would take the time to do this including a new fuel filter. If you so not have the CIS fuel system gauges I would get those too and learn how to use them, not too difficult. This may be all you need to analyze this issue.

Best of luck,

Rahl
Old 03-31-2018, 08:03 AM
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It could also be a vacuum leak in your turbo system. Check all the O-rings and such.
Old 03-31-2018, 11:36 AM
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^^^ That! The hoses on my car were so rotted most turned to powder when removing them. A vacuum leak will cause a lean issue for sure.


Sent from my iPhone while Driving
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Old 03-31-2018, 03:58 PM
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Thanks guys. I'll check my CO level and check for vacuum leaks. What is the correct CO level for a 76 3.0?
Old 04-01-2018, 10:08 PM
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I am thinking electrical.
perhaps coil, CD or maybe power to the CD.
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Old 04-02-2018, 03:29 AM
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Quote:
Originally Posted by T77911S View Post
I am thinking electrical.
perhaps coil, CD or maybe power to the CD.
I agree based on the following dumb ass maneuver that I did to my 76 the other day:

I made the mistake of warming my car up using the hand throttle, without thinking i turned the key off without releasing the hand throttle (it was reving at 2k). Sounded like a shotgun blast.

I went back and checked hoses coil etc. all looked ok, so I restarted (hand throttle released of course). Started up fine, slightly missed for a few min, but now runs fine. I still need to recheck timing and pressures, but it appears ok.
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Old 04-02-2018, 06:11 AM
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Quote"Thanks guys. I'll check my CO level and check for vacuum leaks. What is the correct CO level for a 76 3.0? "

From memory it is 1%-3% IIRC. If smog check is not due soon you can tune it by ear, like a carburetor.

Rahl
Old 04-02-2018, 07:39 AM
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Thanks Rahl. My CO was measured today with engine warmed up. CO level at idle was 6.5% to 7.0%. So maybe the backfire was actually from the exhaust?

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From memory it is 1%-3% IIRC. If smog check is not due soon you can tune it by ear, like a carburetor.

Rahl
Old 04-04-2018, 10:37 PM
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Ignition, most likely. Start with the lead from the trigger unit in the distributor to the CDI box, then check the CDI box. Intermittent problems with the CDI box are not unheard of. Send it to Bob Ashlock, AshlockTech.com, great guy, very skilled, and fair on pricing. Bob has a special hot box to simulate temperature conditions in the engine bay, which he uses for testing.

If you can put your hands on a spare CDI box, known to be in good condition, you can check this for yourself. A six-pin can be used in place of the eight-pin, provided that you have a spare six-pin male connector. If you compare the six-pin with the eight-pin wiring diagram, you should be able to figure it out.

Old 04-05-2018, 03:25 AM
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