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post #1 of (permalink) Old 01-21-2004, 08:35 AM
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timing ignition

I have a 1985 gmc 350 rv.
I had several problems with my distributor,
I've replaced everything and now I get spark on all wires.
I have replaced the plugs and wires.
I didn't check the timing with a light just put the distributor at no one plug with the timing mark set at 4btc
It ran fine but low power so I adjusted the distributor then it ran fine for awhile Then just started backfiring.
It will either start right up and idol fine for a few minutes then start backfiring no amount of adjustment has helped. Other times I have to open it all the way up for it to start and slowly let up on the gas, runs fine for a few then starts backfiring.
plugs appear fine or wet soaked and blackened, tried seeing if it was a tooth off and get the same thing.
sometimes it has ran for several minutes and then will start backfiring. seems to be on the passengers side.
Not much of a mechanic so need plain instructions please
Been very frustrating, been working on it for several weeks. please help.
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post #2 of (permalink) Old 01-21-2004, 07:51 PM
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Re: timing ignition

could have a bad valve. I had a new engine put in november of 2000 and it started backfiring on the right side ine the pipes a few monthe later. I took it in to have it checked and the dealer couldn't get the timing to hold either. They found out i was running on 7 cylinders(the #8 was dead). Bent valve. Don't mean to throw a bad possibility at you, but it could be the problem.
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post #3 of (permalink) Old 01-21-2004, 10:29 PM
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Re: timing ignition

im assuming you replaced the cap and rotor so
try replacing the ingnition module. that fixed mine.
or the condener (i think that is what they call it) it is a little roung thing in the distributer. the module is about $12.00 and the condenser is probly around $2-$5
i had several chevy small block do this
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post #4 of (permalink) Old 01-21-2004, 11:32 PM
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Re: timing ignition

Hi, Yes I replaced the pickup coil the main coil and had the module tested.
I did find one problem today the advance weights were sticking and not coming back to rest with on advance. after cleaning them it moved my 1 plug about a 1/2 inch. redid the distributor with 1st piston at compression and 4 btc. made sure the pickup coil prongs were in alignment. Started right up but instead of random backfires it was a steady backfire. checked the spark plug wires. No 1 wire not firing. going to check the ohms on it now.
Any other thing that will cause this?? Was working as of yesterday. and all other plugs are firing.
I'm told that the ohms should be 10000 every foot of wire????
post #5 of (permalink) Old 01-21-2004, 11:40 PM
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Re: timing ignition

My idea is to check for a worn camshaft lobe not opening a valve. It's not hard to figure out once the valve covers are off, and the all the spark plugs removed. Just turn the engine by hand and watch each and every valve spring get compressed as you turn the engine by hand. I'm thinking one of the valves is not opening, or maybe one of the valves in not opening very much. Sometimes a push rod might be the problem. I've replaced a few broken push rods, which will keep a valve from opening. Sometimes the back firing is because one of the valves is not closing. Just my idea on what might be the problem.
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post #6 of (permalink) Old 01-22-2004, 08:44 PM
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Re: timing ignition

on mine i replaced the spark plugs, wires, cap and rotor, coil,vacuum advance, timeing advance weights and springs, and module.
changing the cap and rotor helped but the thing the fixed mine for good was the module.
did the test it when it was back fireing?

and check your fuel mixture, i guess it is a stock q-jet,
one side might be running lean. but it would be alright unless it got rebuilt or changed.
post #7 of (permalink) Old 01-23-2004, 06:00 PM
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Re: timing ignition

Here is a silly possibility. I had trouble holding the timing for a while. I checked everything I could think of, but no help. One day I looked real close at my distributor hold down clamp and that foolish thing was not sitting on the distributor shaft right. Got a new one and that took care of it. I know that is a one in a million, but might be worth a look.

Good Luck,

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post #8 of (permalink) Old 01-25-2004, 08:58 AM
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Re: timing ignition

Could be a valve train problem - but that sure is coincidental it picked the same time you changed ignition parts. What are the odds?

You've already localized it to #1. A module CANNOT affect only one cylinder, neither can a pick-up coil, or even the coil itself.

I can only be from the rotor outward, rotor, cap, wire, or plug, or the cylinder itself (see above.)

If you changed caps, you had to transfer the coil to the new cap - a possibility is you used the old style long screw - the long ones can crack the cap inside, letting the rotor jump the spark into the crack to the screw - which is ground. Look at the inside bottom of the cap.
Could be a bad wire or a bad plug. New doesn't mean good.

Pull the wire at the plug end - good healthy spark?
Yes - bad plug - sometimes when putting it in you miss the hole and get dirt on the nose of the plug, sometimes they are just bad new ones - put in an old one to try it.

No - pull the wire at the cap end - use a grounded wire to test for spark at the cap terminal.
Yes - bad wire.
No - look inside the cap for that crack.

Also look at the underside of the rotor - GM's are famous for flashing through the center of the rotor.

Please post the results here - most of the inconsiderate little kids on here don't bother to post the final results. That's how they've driven the adults away to other boards. Notice how few posts there are anymore - this board may get closed from inactivity.
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post #9 of (permalink) Old 01-25-2004, 06:13 PM
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Re: timing ignition

I'm sorry to hear about the possiblity of this site closing. For I have recieved some very good knowleadge here.
Of course I will post until I write that I am running down the road trying to loosen my load.

Okay since my last post, to make it short I located the spark problem, was the rotor, looked okay to me but when commparing it to new one definitly used.
Put in new one. checked I have spark on all wires. Good strong spark tested each one. should have fixed the problem yes. no. now it only starts if I give it full gas, minunte I let up it bogs down and dies.
maybe faulty plugs. going to check that next
Stuck inside worse storm here yet been snowing constantly since last night. I just read won't stop till tomorrow night Yuck.
thanks guys.
post #10 of (permalink) Old 01-26-2004, 04:08 AM
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Re: timing ignition

sounds like a carb prob .... do you have a holley? if so all that backfiring may have blown the power valve.
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