Willishxc

So my Dad and I have been working on my car lately trying to get it to run right after it jsut randomly stopped before winter. Garaged it and since it's been nice around me lately have been going back at it. We got it running but at higher speeds like highway driving etc it'll backfire occasionally not constantly but a good amount. As well as when coming to a complete stop it stalls out, and is hard to get started( 3 or 4 attempts) which happened alot the first few times and now is becoming a lesser problem where it doesnt do it every, less often then not. We just replaced all 8 spark plugs, oil change, and the other thing is we turned the distributor up which causes it to idle at around 1300ish rpms if im correct and about 5/6k when put into drive. Any ideas on what could cause these problems? Also I'd like to turn the distributor back down to where it was because i liked how it ran before, this was just something he thought we could try(neither of us are really big car guys so were learning) Thanks for any input guys!

Specs. 1985 Z28
350ci sbc
Machined vortec heads
Comp Cam beehive springs
1.6 Comp Cam rockers
GM hot cam .525 lift
Holley Steath intake
32lb injectors
Eagle Crank
Keth Black 10.5:1 pistons
Machined shop cylinder honed and lined honed
Megasquirt 3

Willishxc

bump

Cleric69

If it is backfiring then there are unburned hydrocarbons (read: fuel/gas) igniting in your exhaust system somewhere. If it is stalling out at idle and then taking a few cranks to get started again you may be flooding it somehow. I'm nor really smart on injectors, but if they're computer controlled there might be a programming issue or some other injector/fuel system related issue.

Alternatively you might not be geeting enough oxygen into the engine to fully combust the fuel as they mix. I'd check your air filter/hoses/intake manifolds/heads to see if there might be some restriction somewhere. I suffer similar symptoms driving at high altitudes when my carb can't suck in enough air.

Those are the simple things to check, which is pretty much the extent of my knowledge. I'm more of an interior restoration guy with a minor in body work, so take my words with that in mind.

ASE doc

My advice would be to start your diagnosis at the distributor. Weak spark will cause the hard starting and a badly worn or damaged cap/rotor will cause the backfiring at speed. With all the trouble we see with the GM HEI distributors, it is always a likely suspect. Start by performing a spark KV test. You can purchase an inexpensive adjustable spark tester at most parts stores. Set it at 40KV and check for spark at several plug wire ends. The GM HEI should easily jump the gap at $)KV with a bright, audible blue spark. If not, look at the cap and rotor for signs of deterioration or grounding. Watch the wire you are testing at for signs of arcing to ground. If the wires are old, especially if they are original, replace them with the cap and rotor.

Take a close look at the distributor. There are gear-like teeth below a round coil under the rotor. These teeth are the pole piece and timing core which, when the teeth pass each other, generate a pulse in the pick up coil they are under which the ignition module(little black box at the dist base) amplifies and uses to charge and fire the coil, it also converts this pulse into a digital signal which it sends to the ECM as a crank reference pulse. Check these teeth for heavy rust and corrosion. Check the distributor shaft for lateral runout(side to side movement) if it moves at all, the bushing is worn and the dist needs to be replaced. It may be necessary to remove the distributor and spin it to look for interference between the teeth. There should be resistance as the magnetic teeth pass each other but they should not touch. You can test the pick up coil with an ohmmeter. It should read 800-100 ohms. The module can be tested at most parts stores. Be aware that even though it passes the test, it can still have an intermittent fault.
Chances are that the dist is faulty judging by your symptoms.

Willishxc

Thanks alot guys! I should have time this weekend to get into it having friday off and the weekend due to easter. I know i looked the other day and the dist. is a Billet, and I was planning on replacing the dist. cap/rotor soon to. I'll look into the other things you guys mentioned to and let you know how it goes!

ASE doc

If the dist is Billet, it likely won't have the pole piece and timing core used in the GM HEI. Only GM liked that design. The aftermarkets(ACCEL and MSD) seem to prefer the Ford design which is much simpler and seems to be more reliable. You still need to look closely at the ignition module, cap, rotor and wires though.