SBC runs at 55deg advance? Why? Dave? Anyone? - Off-Road Forums & Discussion Groups
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post #1 of (permalink) Old 09-03-2001, 02:16 AM Thread Starter
 
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SBC runs at 55deg advance? Why? Dave? Anyone?

Okay, my friend bought an 85 suburban from Homer Simpsons dumber brother. The motor in it was blown, but he gave him a "good engine" to go with it. Now, the motor runs great if its 55 deg advanced (used an advance timing light with dial), but is hard to start if it sits for an hour or so. We have pulled the distributor out several times and reset it. The timing marks also line up at TDC on compression.
Now, for the Question!
Can an engine run this far off (even though this does) with everything else good? Could the cam have been setup wrong? We have played all day without coming up with a good fix. I dont want to pull the front of the motor off just to see the alignment marks are good.
What could cause this?

TJ

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post #2 of (permalink) Old 09-03-2001, 10:41 AM
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Re: SBC runs at 55deg advance? Why?

Does the distributor have a vacuum advance canister? Does the distributor have the 4 pin, 5 pin, or 7 pin ignition module?

I think it is possible the firing order out of sequence. Maybe the timing light is not connected to the #1 cylinder, because the firing order is out of sequence?
dave

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post #3 of (permalink) Old 09-03-2001, 11:34 AM Thread Starter
 
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Re: SBC runs at 55deg advance? Why?

It is a vacuum advance dist. Also, I am on the #1 cylinder (front drivers side). As far as the ignition module, Im not sure. It has the GM HEI with the 3 prong plug closest to the dist and the red ignition on the pos terminal on the cap.
I just didnt think it was possible for an engine to run this way.
How would the ignition module effect the timing?

Thanks
TJ

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post #4 of (permalink) Old 09-03-2001, 02:31 PM
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Re: SBC runs at 55deg advance? Why?

[img]/wwwthreads_images/icons/crazy.gif[/img] You are actually running ten degrees advanced, and the wire you are checking is one hole off on the distributor cap, which gives you the other 45 degrees. The most probable reason that the sub is hard to start is that the Q-Jet is leaking/draining gas into the engine out of those pesky little plugs in the bottom of the carb while the fuel pressure is still high and keeping the carb over full. Check to see that the by-pass line to the fuel tank from the fuel pump is actually open and hasn't been plugged with a ball bearing like my pickup was or with a piece of welding rod like my suburban was.[img]/wwwthreads_images/icons/crazy.gif[/img] The first thing dummies do is plug that line.[img]/wwwthreads_images/icons/frown.gif[/img]

CJDave
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post #5 of (permalink) Old 09-03-2001, 07:07 PM
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Re: SBC runs at 55deg advance? Why?

Some 1985 GM light truck vehicles were equipped with the Electronic Spark Control (ESC), which is designed to work with a knock sensor to retard timing as much as 20 degrees. The ESC system uses a computer. My guess is the former Homer Simson owner had a problem with the ESC distirbutor and has installed a distributor from something else.

The ignition module I'm talking about is located under the distributor cap. The wires you descripe are commom to all GM HEI distributors. I've seen some real creative "Homer Simson" mechanics. I really need to know what type of ignition module your distributor has. If there has been a real creative "Homer Simson" mechanic working on an ESC system, it will easily explain why the engine runs at 55 degrees advance.
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post #6 of (permalink) Old 09-03-2001, 08:33 PM Thread Starter
 
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Re: SBC runs at 55deg advance? Why?

Okay, after further digging, the ignition module has a plug with 2 prings going into it. As far as the other computer you were talking about (would it be a large flat plug with 4 prongs above the dist), there is a plug that is not used. It didnt match anyother plugs. He has another dist that has a similar plug coming from the dist, but they dont mate together (maybe from a different year ESC?). At this point, he is happy that it runs, and willing to overlook why it might be off the way it is.
I will pass on the info (THANKS ATON TO ALL THAT REPLIED), and see what happens.

Thanks.
TJ

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