M Danger

well after finnaly getting teh car started after 6+ months(and who knows how long it didnt run before that) it back fires when it gets to 3k rpm.
I thought maybe the ignition timing was off, but adjusting the dizzy didnt seem to do much other than raise or lower the rpms.
what else could it be?
On thing i did not was that when i pushed the brake the rpms rose 3-400 rpmsany ideas?
Mike

Basket931

The "what it could be's" are just about endless.
If you have covered all the "da's" (vac leaks, seized turbo, pluged fuel filters, rotten gas, bird/bug nest under air sensor plate.)

Grab the haynes manual and start on the ignition tests( base timing and mechanical advance ETC). That should go quickly. Then check the fuel system(main line pressure, control line pressure)blah blah... You will find the problem.

BigPorscheGuy39

You know, if you have any exhaust mods, like no cat, you'll hear the normal loud rumblings of the engine. Sometimes, on decelleration, it sounds like backfiring...but it's not a problem.

Ben Allison

Mike,
If the RPMs change when you hit the brakes then it is more than likely a vacuum leak. Check the hoses and replace as necessary. This would cause a rough idle, sometimes hard starting. backfiring as the RPMs go up and a shifting idle speed as the timing gets changed =)

-ben

CBass

Keep in mind, backfiring is when the combustion charge passes into the intake. You are probably just having engine or exhaust manifold detonation, which is just a matter of timing, whether it's ignition or cam... I don't know.

There is a company called Franco Industries that makes an interesting cam gear. It allows you to advance or retard your cam timing signifigantly.

<a href="http://thorin.adnc.com/~figf/" target="_blank">http://thorin.adnc.com/~figf/</a>

If you get an ignition controller from EBay, you can save a bit on that.

go to <a href="http://www.924board.org" target="_blank">www.924board.org</a> for more help.

special tool

Do me a favor... make absolutely sure that you don't have TWO wires crossed. That sounds exactly like what you describe.

M Danger

I know i dont have 2 wire crossed i triple checked that, it only starts to back fire at 3k

special tool

Where are the backfires coming from? What regulates your fuel?

CBass

It's a 931, it's got K-jet mechanical injection. The brakes would likely be a sign of a weak vacuum system.

Is there actual backfiring coming through the intake manifold? Or is it happening in the exhaust manifold? You might just have really bad detonation. Take out your injectors, fuel lines, and pumps. Soak them in acetone or fuel injector cleaner overnight.

You probably have a very common problem, the car sat too long, and the resin and varnish and various crap in the cheap fuel the PO put in the car has gummed up your fuel system, causing it to run very lean, causing it to detonate.

Try the soaking in acetone. I have a hunch that is your problem, you said the car was sitting for a long time, right?