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Old 02-11-2004, 10:30 PM
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Angry engine firing but wont run

hey everyone, this is my first time using this, so any help i get is greatly appreciated.


I own a 1968 firebird with a pontiac 350 engine. my car had been running a little bit rough and i just thought that i needed to adjust my carb or timming (felt like it wanted to stall on idle). but when driving home the car back fired and I lost the engine. i coasted off the highway and when i tried to restart it, it would turn over and initially fire but would not run.
I replaced the feul filter thinking it wasn't getting gas, then i rebuilt the carb on the same concept. still the same thing. a buddy said he heard of timing chians skipping so i pulled the front of the engine apart and noticed that my chain was extremely loose and the camshaft sprocket had tons of play, so I replaced it. and still the same thing. i checked the commpression and the commpression was weird, the highest cylinder was 140 and the lowest was 105 i really don't think it's burnt valves or rings but i'm not an expert. i checked for spark and a few plugs were weak so i replaced the coil and it did nothing, i replaced the modulator, nothin, i replaced the whole distributer with a pro-form hei and then i got good spark! replaced the plug wires but not yet the plugs. found top dead center on the right stroke and connected the plug wires in the right firing order (quadrouple checked proper order and rotation) excitedly cranked it over and still the same as when i died on the highway?????? it has gas, somewhat of commpression, spark and twelve volts to the coil, but it keeps wanting to run but just burps then backfires when i get mad and hold the gas down while cranking. sorry this is so long but you can see that i have done everything that makes sence and i am soooo lost. thank you for any replies!

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Old 02-11-2004, 10:36 PM
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Have you tried advancing the distributor while cranking the engine. Your timing could be out a little.
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Old 02-11-2004, 10:39 PM
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does it only fire when cranking?
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Old 02-11-2004, 10:48 PM
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i tried turning the dist. and yes it only fires while cranking
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Old 02-12-2004, 01:11 AM
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Is it producing a red spark or a bright blue spark at the spark plug? If its a red spark then you need to replace the coil. A friends blazer was gettin a spark.. But it wasn't hot enough to ignite the fuel/air combo.
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Old 02-12-2004, 07:32 AM
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You definately have compression problems, 140 might work, but not 105, is the cam timed correctly? How many are below 140?
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Old 02-12-2004, 07:35 AM
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when u put the new distributer in did u make sure u were on the compression stroke? u could be 180 degrees off.
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Old 02-12-2004, 08:43 AM
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I'm not meaning to offend you, but when I started getting into Pontiacs, and I replaced the cap on one, I had a similar problem. I rechecked the plug wires, and it wasn't until about the 4th time of doing so that I remembered that Pontiac distributors rotate opposite of Chevys. I redid my sparkplug wires, and it fired right off. Just something to think about.

Last edited by adryan16; 02-12-2004 at 12:10 PM.
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Old 02-12-2004, 09:01 AM
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Had a buick that did the same thing after it busted a timing chain, replaced the timing chain but it still would'nt run, pulled the engine apart and all the pushrods were bent along with the exhaust valves. After replacing the exhaust valves and the push rods it started again.

But may not be the same thing, your exhaust valves might be burnt, or carb is running too lean, or too rich, timing might be off, lots of little things.
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Old 02-12-2004, 01:12 PM
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Have considered a broken crank or cam? I would remove the dist. cap, turn the crank by hand (with a socket and handle) in one direction and watch the rotor, stopping it at a straight forward or backward derection, then watch or have someone watch while you turn in the opposit direction, remembering where you started and see how far you go before the dist. starts moving. I don't know how far it will move it shouldn't be very far if everything is tight. If it back fires, its got to be firing at the wrong time (when the intake valves are open) so the fire is early (before the valve close's) or the valve is staying open late. I wouldn't think bent push rods would make valve late but early closing., although a bent valve might stick and cause it to close late. Just some food for though. Everything has to be at the right time, early causes back fire, and late causes exploion in the exhaust pipe. LOL
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Old 02-12-2004, 08:29 PM
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Quote:
Originally posted by Wrencher
You definately have compression problems, 140 might work, but not 105, is the cam timed correctly? How many are below 140?

this is the commpression before i changed the loose timing chain and cam sprocket #1- 125, #2-115, #3-130, #4-115, #5-140, #6-125, #7-105, #8-105, i haven't rechecked them since the new parts. innitially thought the commpression was wonky because i was told my timing chain skipped and you can expect weird readings but i will go and check the commpression right now. the car has always run strong, i'm not hard on the engine at all? if my timming was off, i mean way off would the commpression readings be off as well?

Quote:
Originally posted by adryan16
I'm not meaning to offend you, but when I started getting into Pontiacs, and I replaced the cap on one, I had a similar problem. I rechecked the plug wires, and it wasn't until about the 4th time of doing so that I remembered that Pontiac distributors rotate opposite of Chevys. I redid my sparkplug wires, and it fired right off. Just something to think about.

you didn't offend me at all, it was actually the third time before i figured out that the rotor spins counter! and i'm positive i have the firing right - 1-8-4-3-6-5-7-2 - and i was reading on the bulliton about the finger test to check to make sure you were on the commpression stroke and of course i wasn't so i changed that as well, each time thinking o.k. this is definitly the problem! but then feel like crying when it still doesn't run. the only thing that is different on my car then what it shows in the manual is that my
# 1 plug wire is on the front left side (looking at the engine ) rather than the back right, were it shows it is supposed to be in the manual and through other discussions, i didn't think it would make a difference though because i dropped the dist. in myself and allined the rotor with the # 1 plug, or would it ?

the only way i have been able to adjust the timing is to turn the dist. by hand then try turnning it over then turnning it a little bit more then turning it over ..... well you get the picture! if i bring a buddy over and connect a timing light to it and turn it over, even though it does not run can i get a proper reading??? thank you everyone for your input so far, i'm not an expert so with your help i hope to figure out this proplem .... i'm too stubburn to give up and take it in yet!!

Last edited by lovemy68bird; 02-12-2004 at 08:29 PM.
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