howudoin Posted June 3, 2005 Report Share Posted June 3, 2005 hey yall im a new member with a 79 eldorado biarritz with a 350 olds i just got done replacing the fast idle valve and it seems to be working better then the old one but now a new problem i cant stop it from backfiring through the throttlebody so when i advance the timing it stops but know i get a real bad pinging noise and after the car is running for about 10 mins it just dies. Its such a pretty car but ive driven it a totally of 15miles since i ought it 3 mos ago due to all this crap going on with it!. any info on troubleshooting would be very welcome.....oh and sorry for the book! great website !!!!!!!!!!!!!!!!!!!!!! Link to comment Share on other sites More sharing options...
Ranger Posted June 4, 2005 Report Share Posted June 4, 2005 Do a compression check. If it's back firing like that you may have a burnt valve. Link to comment Share on other sites More sharing options...
howudoin Posted June 4, 2005 Author Report Share Posted June 4, 2005 thx ill try that oh and not to sound dumb but if the compression is low where do i go from there. the motor was rebuilt 5000 miles ago so i would hope it wouldnt have a burnt valve Link to comment Share on other sites More sharing options...
Scotty Posted June 4, 2005 Report Share Posted June 4, 2005 As Ranger said, backfiring through the TB is associated to a valve hanging open and leaking on the compressor stroke. This can be for a variety of reasons, a cracked valve, a burned valve, an oiling problem, a valve spring collapse, dirt or debris. a valve guide.. A rocker arm hanging up would tick fairly loudly. Do you hear valve ticking? If you do, check that cylinder first. I would suspect that the idle is rough. Pull one wire at a time but use heavy insulated channel locks (or an insulated plug wire puller) and rubber gloves or you will get jolted. Don't pull the wire, pull at the boot. When you pull the plug on the bad cylinder, the backfiring will stop or change sound and it will have the least affect on the idle roughness. The good cylinders when you pull the plug wire WILL have a negative impact on your idle. Then do the compression test on that cylinder bank for comparison purposes. I'll look at my manual later to see what the compression should be. This may require that the head be removed, but if you are lucky the valve spring is collapsed and you can replace the spring. Once you isolate the cylinder I would pull the valve cover and look at the valve action and measure the stem height. However it sounds like a seating problem to me. You say 5000 miles on this engine, did the problem begin gradually or suddenly? Link to comment Share on other sites More sharing options...
howudoin Posted June 4, 2005 Author Report Share Posted June 4, 2005 actually it does tick! the problem began right after i bought it and sent it to a mechanic that my uncle knows. just to check things out on it. when i took it there it ran great but now i have had the worst luck trying to get it to run right and being on a flatbed twice since the mechanic touched just isnt setting good in the ol stomach Link to comment Share on other sites More sharing options...
Scotty Posted June 4, 2005 Report Share Posted June 4, 2005 Does the engine rebuild warranty extend to you? Is it still in effect? Are you mechanically inclined? Pulling a head on that engine is easy if you need to go there and an engine shop could do the head work. Link to comment Share on other sites More sharing options...
Logan Posted June 4, 2005 Report Share Posted June 4, 2005 May be a bad cam lobe. Did you break in the cam? If not you can easily lose a lobe. Logan Diagnostic LLC www.airbagcrash.com www.ledfix.com www.ledfix.com/yukontaillightrepair.html www.ledfix.com/ledreplacements.html www.ledfix.com/j42385toolrental.html Link to comment Share on other sites More sharing options...
Scotty Posted June 4, 2005 Report Share Posted June 4, 2005 May be a bad cam lobe. Did you break in the cam? If not you can easily lose a lobe. Logan, but if he wiped a cam lobe the valve would not open am a wrong? If he is backfiring, the valve is staying open or leaking. Or are you thinking that its due to the valve not opening at all and popping back because of pressure out of the valve that is opening? Link to comment Share on other sites More sharing options...
growe3 Posted June 4, 2005 Report Share Posted June 4, 2005 I don't know exactly what you have been doing, but have you or someone else distrubded you spark plug wires? Verify that each plug wire is placed correctly. If two wires are mixed up the car will still run, but rough and tend to backfire. Often I see #5 and #7 swapped. -George Drive'em like you own 'em. - ....................04 DTS............................ Link to comment Share on other sites More sharing options...
johnnydone Posted June 4, 2005 Report Share Posted June 4, 2005 i think on a 350 engine i would replace the dist cap it might have a crack and of course check the plug wires 5 and 7 usually the firing order should be something like 18436572 Link to comment Share on other sites More sharing options...
KHE Posted June 4, 2005 Report Share Posted June 4, 2005 I would verify the firing order (it is cast into the intake manifold) and make sure all the plug wires are hooked up in the correct order as a preliminary step. It started acting up right after the mechanic looked at? It is possible something was disturbed while it was being inspected.... Kevin '93 Fleetwood Brougham '05 Deville '04 Deville 2013 Silverado Z71 Link to comment Share on other sites More sharing options...
runar Posted June 7, 2005 Report Share Posted June 7, 2005 Hi I am with Logan on this one.In1992 my 4.1 started out of the blue one day firing through the trottlebody. One lobe on the camshaft was gone. My mechanic changed the the cam without removing the engine. I was very impressed.It came out through the right wheel well. Regards Runar Link to comment Share on other sites More sharing options...
Randy_W Posted June 7, 2005 Report Share Posted June 7, 2005 It could be as simple as poor spark advance, I can't remember how the timing was controlled on those FI Olds engines. If it has a regular distributor check the weights and springs. My 1980 Grand Am with only 46k was very cold natured and had no power, if I advanced the timing enough to run decent, it would spark knock it's *smurf* off. I found the springs in the distributor so rusted they had no elasticity and wouldn't let the timing advance. I pulled the weights and springs, lubed everything with dielecteric grease and put on new springs, set the timing to stock. All is well now. My 301 H.O. also has the GM electronic spark control. Link to comment Share on other sites More sharing options...
Oldgamer Posted June 7, 2005 Report Share Posted June 7, 2005 ...when i advance the timing it stops but know i get a real bad pinging noise... That pinging noise is a detonation, because you advanced the timing. I would restore advance like it was before and than hunt for real cause of failure. Link to comment Share on other sites More sharing options...
OynxSTS Posted June 7, 2005 Report Share Posted June 7, 2005 Backfire, back up through the carb/throttle body sounds like an overly lean mixture... Does it backfire all of the time... just of idle... just when you gas it? Backfire at transition from idle to midrange... Under any kind of load... back up through the intake... I would check all of the culprits that generate a lean backfires… Start with a bad O2 sensor on FI cars. Easin' down the highway in a new Cadillac, I had a fine fox in front, I had three more in the back ZZTOP, I'm Bad I'm Nationwide Greg Link to comment Share on other sites More sharing options...
franey Posted June 8, 2005 Report Share Posted June 8, 2005 I do not recall your saying what the age of the engine is. IF it is an older 350 , with several miles on it , you may have one that has jumped time due to worn timing gear or strtched chain or a combination of both. If it is one tooth off it will still run and drive but it will backfire through the intake, timing it to the mark will not cure it since it is out of time. Bring number one piston to the top and the timing mark should be dead on the 0 MARK, with the rotor cap pointing dead on number one piston plug wire. IF they all do n ot line up it has jumped time on you. Link to comment Share on other sites More sharing options...
KevinW Posted June 8, 2005 Report Share Posted June 8, 2005 It is surprising how many mechanics assume that an Oldsmobile V8 distributor turns in the same direction as a Chevrolet V8, when in fact it turns in the opposite direction (anti-clockwise). Verify the firing order, then if a compression check shows a dead cylinder or two, pull the rocker arm covers to check for broken valvesprings or bent pushrods. Someone could have over-revved the engine while having some 'fun'. ___________________________________________________ Link to comment Share on other sites More sharing options...
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