KA -BOOM!!! Help.

[1978911sc]

Trying to determine exactly what is going on.

while driving, a sudden loss of power then a huge back fire! Scarred the hoo haw out of me. It happened three times over ten miles as I was trying to make my way home. Other than that the car ( 78 SC ) started fine and runs strong.

Thoughts?

[faverymi]

Distributor with problems in timing and or advancement.

Normally timed until the internal mechanism rotates out of time and back in time igniting the mixture and KA-BOOM.

That happened to me.

Hope it helps.

[pors1968]

Crack dist cap.

[Quicksilver]

The real question is now your airbox. If your airbox didn't have a popoff valve it is almost certainly toast. If it does have a popoff valve then after a big backfire the valve probably needs to be re attached to the airbox.

You have one of the best air cooled resources in the country just on the other side of the water: John Walker's Workshop. You can also PM him on this board at http://forums.pelicanparts.com/private.php?do=newpm&u=4662.

[bugstrider]

+1 on the possible distributor idea. Lost ours on our 78 SC last July and the car is still down. The internals ate themselves and finding a replacement for a two year only distributor was a PIA....

Look up my posting on the distributor and look at the carnage it did to itself. I seriously wished I had a Kaboom type warning before mine imploded and said "game over man, GAME OVER!". Just recommending a solid check on all distributor related components as well as your internal shaft free play.

Good luck

[snbush67]

Intermittent CD failure which possibly a fried the distributor rotor, that is what my money is on, was it raining when this happened?

[Bob Kontak]

Originally Posted by 1978911sc

It happened three times over ten miles as I was trying to make my way home. Other than that the car ( 78 SC ) started fine and runs strong.

In that last ten miles all was well except for the sudden loss of power and backfire (times 3)?

If so, were you cruising at a constant RPM or did you give it some beans when it did a face plant?

If all was well, I lean towards the distributor. If it ran like crap that last ten miles, I lean towards a significant vacuum leak.

I have not experienced a distributor/cap failure. First hand experience (as noted above) carries a lot of weight.

[tirwin]

An airbox backfire could also be an indication that your mixture is off. The CIS cars tend to run lean and something as simple as a cracked intake runner boot can cause it to lean out even more.

Definitely make sure you don't have a cracked airbox, but if it is starting fine and running fine after the kaboom then it's probably fine. Tony (boyt911sc) has posted several tips on identifying cracked airboxes. Use the advanced search capability to search based on his username and you will find it.

Another possibility is an exhaust backfire. Hard to say without hearing it over the interwebs.

[T77911S]

CD or coil is going bad. problem will get worse until it cuts off.

maybe power loss to CD unit. more likely above.

[1978911sc]

Thank you everyone for your ideas. I've got some trouble shooting to get to tomorrow. I'll keep you posted as to what i find out.

[T77911S]

problem is you cant fix it when it is working.

[kodioneill]

Pull off the dist cap and inspect the rotor cap etc...start it up jiggle some wires in the cd area and see if you can duplicate the problem. Check the green wire from the dist also.

[1978911sc]

UPDATE - new fuel filter. needed but no real change in condition.

I just spent 4.4 hour with a buddy of mine swapping out the CDI and coil to the MSD system. ( Thanks John!) On initial observance I believe this has solved the problem. Tuesday will be the true test as I have a road trip planned. So far the performance gain has been VERY noticeable. There are still a couple of things to sort out but I have high hopes that this will be the solution.

thanks to everyone for your input and suggestions!

Craig

[reesestewww]

I'll bump in thread for nut, however may start new one as well.

82SC -

Starts and runs fine, slightly high idle but not terrible. After about 30 minutes on the road the car started to sputter and serge slightly at speed. Getting to first stop sign after I noticed these symptoms the car stalled and backfired. I let it rest for about 5 minutes on the side of the road, then it fired right back up and I was able to get it home.

Once in the garage I let it idle until and it sounded fine until suddenly it started sputtering again. Then, it stalled and backfired a second time. While it was in the garage I notices a rich exhaust smell as it stared to sputter. The idle and sputtering got worse until it died and backfired. I happened to get it all on video too, of course you can't smell it

Any thoughts? TIA

[tirwin]

Start a new thread.

First thought is it could be a failing CDI. They get hot and then fail. Cool off and they work until they get hot again. But it could be other things too.

Is your car US or RoW?

What CDI do you have? Bosch, PermaTune or other?

Things to check:
- fuel pump relay
- fuel pump
- CDI and coil

[reesestewww]

Originally Posted by tirwin

Start a new thread.

First thought is it could be a failing CDI. They get hot and then fail. Cool off and they work until they get hot again. But it could be other things too.

Is your car US or RoW?

What CDI do you have? Bosch, PermaTune or other?

Things to check:
- fuel pump relay
- fuel pump
- CDI and coil

tirwin,

Thanks for responding. The car is a US.

I just read this entire thread and see your comments in there as well. Mike's symptoms are the exact same as mine. Runs great, 20-30 minutes dies, let it sit 5-10 minutes fires right back up and will run for a bit, then process repeats.

I've just put together a project list for new MSD 6AL, coil, plugs, ect.

[tirwin]

Check out the MSD Streetfire instead of the 6AL. There are other aftermarket alternatives too.

[reesestewww]

Originally Posted by tirwin

Check out the MSD Streetfire instead of the 6AL. There are other aftermarket alternatives too.

Great advise. A quick search offers a $100 savings over the 6AL

[tirwin]

If you decide on the StreetFire read this thread completely:

MSD Streetfire install

[reesestewww]

Originally Posted by tirwin

If you decide on the StreetFire read this thread completely:

MSD Streetfire install

Thank you, will do.

One more question one my quest to validate the possible CDI. As it starts to sputter the exhaust smells rich. In my logical mind it does help validate possible CDI as I'm thinking a weak spark that's leaving unburnt fuel in the cylinder? Then of course it all ends with a stall, knocking and a backfire.

Thanks!