Timing Problem on 68 Impala

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  #1  
Old 12-04-04, 02:07 PM
Chevyman
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Angry Timing Problem on 68 Impala

Installed Hooker headers on a 68 Impala 396cid last week and have had deiseling problems every since. checked timing today and found it about 8-10 degrees to far advanced. Set to 4deg and tached up and it advanced again. Set to 4 again, turned off vehicle and then started - now it was 8 degrees retarded. this has an Accel HEI distributor. we repalced the coil, rotor and cap already before we discover the timing problem. I have never seen this ahppen before. Can a control module casue this problem?

I have the engine fully warmed up, choke is wide open and rpms are set to 600. I know a normally working engine will advance when tached up becasue of centrifical advance but it is supposed to return to normal. Mine will not return to normal. It stays advanced and idling about 200rpm to high which causes the deiseling (can't spell).

I figure either the control module is bad or the distributor is bad. Probelm is it repeats and always changes to the exact same values either to high or too low depending on whether it was just started or tached up. Driving sucks becasue it misses like crazy when the secondarys are opened up. Also have installed new plugs gapped at .035 and have new Accel plug wires.

Not sure why this started after the headers were installed except that we had to raise the engine quite a ways to get the dang drivers side header on.
 
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  #2  
Old 12-04-04, 02:53 PM
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Did you happen to bend or damage anything in the distributor when jacking the engine against the firewall? Are the counterweights in the distributor binding and not returning? Any weight return sprinmgs broken or missing? All the ability to change timing comes from the breaker plate turning by vacuum advance or centrifical weights moving the rotor. Bottom line, the distributor does it all.
 
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Old 12-04-04, 09:43 PM
Chevyman
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Weights

I have turned the rotor by hand and it seems to spring back into place but i have not actually checked the springs. When it was jacked up the HEI cap was still on so I don't think any internal distributor parts would have been damaged without first damaging the cap. Unfortunately while we were jacking up the engine I carefully watched the radiator hoses, fan and ground wire to the block but completely forgot about the distributor. This sure seems like somekind of an advance problem though since I can watch the timing advance when I gun it and it will not return. I was wondering about the vacuum advance possibly sticking. I am going to test it tomorrow with a vacuum pump. I will check for the springs then also. I haven't plugged the vacuum advance line when setting the timing becasue at 600rpm I don't have any vacuum but gunning the engine would put vacuum on it.
 
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Old 12-05-04, 05:17 AM
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Disconnect the vacuum advance and set the timing before you go any further.Then do your reving and startup test and see if you still have a problem.If you do it's either the distributor or something in the timing chain/gear setup.Also leave the vacuum advance disconnected and see if you still have your top end misfire,I'll bet you do because vacuum advance doesn't work at full throttle because the engine vacuum is too low more so on bigger cammed engines.Vacuum advance is for fuel economy no power is gained by having it.Do you have one of the fancy adjustable cam or crank gears?I ask because you say the timing is of by multiples of 4 each time.Also when checking timing your eye,timing pointer and center of the crank must be in a straight line for it to be accurate so if you are looking at an angle to set the timing you have no idea what it is.By the way if you didn't insulate the headers you raised your underhood temp quite a bit and that could promote dieseling.
 
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Old 12-05-04, 05:56 PM
Chevyman
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Problem Solved

Checked the vacuum advance with a pump and it would not hold vacuum - hense this explains why it the tranmission was shifting erratically. Also found the centrifical weights sticking some and gummed up - cleaned with WD-40 and work much better. Set timing to 4deg and everything seems to be working great now. Also found a spark plug loose and 2 plug wires not fully pushed on the plugs (I let my son install these and didn't want to check his work). Now I will have to replace the air divorced choke with an electric conversion from Carbs Unlimited becasue the choke takes about 20 minutes to open up. I have no problem with heat from the headers rather lack of heat to open the choke coil. Thanks for the tip on the weights - that got me going in the right direction.
 
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