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350 Chev Ign. timing problem


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12-20-02, 05:37 AM   #1  
350 Chev Ign. timing problem

This is on an '84 K1500 p/u with a 350 and AT. Factory was 305H. Just swapped motors in this... replaced motor with rod knock with one from a '79 p/u (quiet and didn't smoke). Reused carb and distrib that were on the truck (84). I think the only thing original under this hood is the distributor as it has a specific elec. connector.

Starts and runs ok. I went to set the timing (been a while since I've done this), unplugged the vac. line, turned the distr. to get around 6deg on the tab. There seems to be an advance problem, or maybe its supposed to do this. When I give it some gas, slowly... the timing mark shoots to the Left (drivers). Then with more gas it comes back to the tab and passes it going the other way. Seems to create a big bog or flat spot. I thought the timing should go only toward the pass side. It does this with vac. line off or on.

BTW: most of the factory vac. lines have been removed and/or plugged including the Thermal/vac. switches. The dist vac source is carb direct... and I didn't check for vac signal timing, yet.

Any ideas appreciated.

Steve H.

 
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12-20-02, 07:17 AM   #2  
Joe_F
It will always run half-baked.

1) The reason the '84 has that connector on the distributor is for electronic timing advance. It is required.

2) You cannot plug off all those lines. Those emission controls are there for a reason. Another reason it runs poorly.

3) The timing chain likely has slack in it at this point. It should have been replaced with the "new" motor out of the truck. It is best to do a freshening up on a motor like that (spend a couple hundred on it) before dropping it in.

4) If anything, it should have all of the 1979 engine's controls (distributor, carb, etc). However, the vehicle still has a electronic spark control computer (in all likelihood) and will be less efficient than if you replaced it with a '84 engine. A rebuilt '84 350 should be dirt cheap.

My coworker bought a 50 dollar Olds 307 motor from a guy for his commuter wagon and spend 300 bucks initially in gaskets, maintenance parts and paint to freshen it up. Money well spent----over 30,000 trouble free miles since.

 
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12-20-02, 08:04 AM   #3  
Joe,

Thanks for the reply. I realize that the "new" motor could have used some freshening up... if it was my vehicle I would have done so. But the replacement motor was $200 and anything "rebuilt" was $700. I hadn't told you this was a low,low budget swap for a friend of my father, so I was using as many good existing parts as possible. The truck was For Sale then developed this rod knock... so it was decided to throw something in it "cheap" to sell it as a running vehicle.

The truck came to me without the emission hoses, etc. , and the bad motor was a pre'80 anyhow (LH dipstick). I would hook up the vac. lines but I'm unsure what to route where due to the mismatch of current manifold ('79), truck ('84), and carb ('??). There is no air pump and the truck has headers. No charcoal cannister either.

Anyhow, can I just put the '79 distributor on the motor and run it without being hooked to the Elec. timing control. I'm sure I could just try it and see what happens.

Any ideas on what might be causing the orig. timing problem as I had described. Although everything else is mismatched... the ignition/timing should be a stand alone system (unless it is also controlled by the knock sensor or something else).
Sorry for the long post, hope the desriptions help.

Thanks
Steve H.

 
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12-20-02, 11:45 AM   #4  
Joe_F
Eeek, I'll stay far away from that one . Illegal, cobbled together and a ton of trouble. LOL.

Again, the vehicle is made to work with EST. Bypassing it is futile, and that's why the truck runs like crap. It could also have a bad carburetor, choke problems, in need of a general tuneup and again, with missing vacuum hoses, there are likely a ton of vacuum leaks.

Swap in everything from the '79 engine into the truck as a unit. Again, it will still run like crap depending on the condition of the motor itself, the carburetor, the tuneup items. If the basics aren't gone through, it will likely run like crap .

My vote: Do the basics, get it running as best as you can and in "God's hands". Tell the owner that since it's a collaboration of parts, it will never really run 100% and sell it as is and cut his losses .

 
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12-20-02, 06:16 PM   #5  
there is something obviosly wrong with the advance take your cap off and check to make sure the mechanical advance weights are not frozen and also check and see if your vac advance is working also, if it has esc it will have a 4 wire connector coming from the distributer if the machanical and vacum advance is ok you can cut the a and c wires on the distributer side of the connector and connect the wires that you just cut coming from distributer together to disable the esc from retarding the timing,this was a common practice for 5.0 liter chevy trucks, that and up the jet size in the carb.

 
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12-20-02, 06:32 PM   #6  
knuckles
You can bypass the EST w/ no problem. GM actually RECOMMENDED this for 'uncurable' EST problems. Shows you how much faith they had in that system!

Since the truck is already a cobbled up nightmare, you might as well swap in the '79 distributor & be done with it.

 
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12-20-02, 10:49 PM   #7  
knuckles,
You got me interested...
What (and when) EST problems was GM trying to cure??? What were symptoms?

 
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12-21-02, 12:48 AM   #8  
One of the best things I ever did for my '85 C10 was to install a regular HEI distributor and forget the ESC. The performance and economy went up quite a bit.


"Who is John Galt?" - Ayn Rand (Atlas Shrugged)

God bless!

 
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12-21-02, 08:48 AM   #9  
Joe_F
Dan:

Poor drivability, stalling, stumbling, general diagnostic headaches, gazorches, etc.

I remember bypassing one on a 82 Chevy Van with a 305 that came to us. The truck was a heap and not worth bus fare, but the lady had hardly any money and we just cobbled it together for her. We told her the truck was in poor mechanical shape and she'd have to start putting money into it or pitch it.

She gladly paid her bill and drove the truck for a while longer.

 
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12-22-02, 09:28 AM   #10  
OK, so if you disconnected the EST, what controlled the timing advance???

 
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12-22-02, 11:37 AM   #11  
Update...
I was going to bypass the EST as suggested on the '84 distrib. in the truck. But, I tested the vac. advance first and found the diaphragm leaking. The advance weights/springs were not frozen. So I just swapped in the '79 distributor (weights not stuck and vac. adv. worked). So now it uses the weights as the mechanical advance and the vac. adv also... no other timing control.

I set the initial timing (vac. line off) at 6 deg. As I gave it some throttle the timing mark moved to the advance side like it should. Seems to idle good and accelerate good. I sourced the distributor vac. from the lower front port of the carb. This was a timed port giving no vac. at idle.

I did try to hook up some of the emission hoses to the charcoal cannister and the air cleaner housing. The EGR diaphragm leaks so it's not hooked up. Nothing hooked up to the thermal vac. switches. I'll probably leave it as such and get the beast out of my hair.

Thanks for all of the information and everyone's ideas.

Steve H

 
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12-22-02, 03:44 PM   #12  
Joe_F
Dan:

The replacement motor used in my example was a non EST, old style vacuum advance distributor. As I said, it was a low buck, taillight warranty to the customer. She was aware of that.

Original poster: You have the right idea. This truck is a heap and not worth bus fare as too many hands have been in it. I know what it's like when you have to deal with family and what not, but it's time to cut your bait with it and it's in the owner's hands now to get rid of it.

Depending on the state you live in, the vehicle is illegal to drive as the emission controls have been defeated, it probably won't pass an emission check and sounds like it's a general menace on the road.

Let it go and you did your best for the owner .

 
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