Help Trying to Fire a 340 - Timing Issue?

[Orange Bird]

I am working on finishing a resto on a car - 71 340 Demon. All new wiring harness, running motor (I'm told) from a few years back. Motor was installed after paint, new Edelbrock carb, wires and plugs, fuel line. My friend did not finish the reassy after I painted it so it is back and I am trying to wrap it up for him. I dont know much about the motor other than it ran fine and has quite a lope to it according to him. No exhaust currently and factory mans. I an trying to start/get running to take to shop for exhaust, easier to move a running car than pushing one and having to worry about scratching it.

Carb was pulled from the box and installed, plugged rear vac port, PCV connected to front port (large orifice), dist vac plugged for now to fire. Elect choke not connected for now

Timing should be easy going back to basics since I knew nothing about the engine status. All plugs gapped, wires run 1x1 to its respective terminal on the distributor. #1 TDC on compression, gear slot for dist shaft parallel w/crank, dropped in dist to land on#1 terminal. Cranked until fuel in system. It really wants to fire and lights off on ocassion but very short lived. Seems the longer I crank the less it wants to fire. After back and forth with choke on, off, partial I cant seem to get anywhere with it.

Dist rotor never seems to land in the same spot when I recheck the timing. When at TDC to check it should be right on or 180 out. After checking a few times it seems as if the rotor is always out. I understand if I am 180 out it is simply lift and twist 180 and I am back in business but after trying several times it looks to me that the rotor gets to be 1/4 to 1/8 out of sync with where I think it should be when I rest it at TDC and look at the rotor position .

Am I missing something?

At first I thought that without the clamp holding it down the dist jumped up and lost its slot and slipped a tooth off the shaft. I can lift the gear and turn what seems to be 1 tooth and it rotates back to the correct position. It tries to fire then nothing, recheck seems to show the same thing again. Tried with the clamp in place and same thing.

I can not twist the rotor at all when it is set in place so no indication anything is out.

Could the shaft from the pump to the gear on the cam be slipping? Is it being cold (40ish) playing a major role here? My other car can be a PITA sometimes when cold but I dont really think its that bad now.



I'm lost and it is starting to bother me.

[firefighter3931]

I'm sure the cold temps aren't helping much 

With a big cam it's going to want some advance so what i do is bring the engine to TDC then advance it 20* BTDC. Then line up the rotor with #1 on the cap and snug down the distributor.

Get a space heater and place it under the hood to get the engine bay warm and then give that a try.

Make sure you have spark and fuel delivery and it should fire and run....then you can tune 



Ron

[Orange Bird]

Thank you, I will do it again tonight, this time with more advance. I do have spark and fuel. I appreciate the info.

[Cooter]

Agreed, sounds like timing is still a little late to fire and run. Try cranking it up and see what happens.

[randy73]

No when you are 180 out, and twist, you change the SP wire locations on the cap, you need to also change the wires.

[Orange Bird]

Well I have everything set, it wants to fire but I now believe it is in the wiring. I do not believe 71 had electronic ign as the wiring diagram I have is not showing it. I was told some had it and some did not? this car has the orange control box in it and I will chase down the diagram or check out the 72 diagram. I mention this as the ballast in the 71 diagram I have shows only 2 terminals and the one in his car has 4. I think I am dropping out the power to the ign system after the crank. No power on the coil when just the ign on.

Again a new engine harness and dash harness was installed. The harness purchased and installed buy him was prewiried for the ign module so maybe a late 71/early 72? I see 1 or 2 wires that need terminated under the dash but figured it/they were for accys not yet installed. Maybe one is the ign power? I will chase down some diagrams for my orange box to see if it is the same for the one installed in the car. At least that may indicate/confirm some of my wiring power paths.

[firefighter3931]

Ahhh....the old dreaded electrical gremlins are at it again ! 

Earlier you mentioned that this car was recently painted ? Have a look at the ECU grounding ; this is a common problem. New paint will often compromise the ground and prevent the circuit from completing. 

You can scrape some paint away under the ecu mounting surface, use a "star" washer or run a seperate ground strap from the ecu to the engine to see if that helps. A simple test light can tell you if it has a good ground or not. 


Ron

[Cooter]

Course, that "Orange" Box could be suspect as well.

[Orange Bird]

Well,I did more checking but forgot my meter for continuity checks to figure the wiring but this is what I found with my test light. Brown wire on coil (+)  traced out to Ign switch and it was very dim when in ign position. I thought it may have been a bad ign sw so I took another known good one and bypassed the one in the column to eliminate a crimped wire in the column, it did the same thing. I reassembled car wiring.

I went back out to the coil and removed the wires, everything brightened back up with the test light. Grounded on bat the test light to touch the + and it showed bright to brown wire. Black wire w/white tracer (-) was then connected to gnd of test light and then I touched the brown wire on the coil and too was bright - green wire with module is not used.

I have a good gnd to the ign module as I rechecked.

My meter will confirm some of the routing tomorrow but I seem to have located the coil wires to the module so I am eliminating those for now as known, it seems to match the wiring on my control module diagram by location on connector (colors are different).

I may have a bad coil?

If I have a bad coil would it dim the circuit from an internal fault?

[Orange Bird]

Im actually thinking I have a bad ballast resistor. It wants to start but as soon as ign falls back rom start  to ign then it quits. The dim light may be a factor of limited voltage through resistor?

[firefighter3931]

Some good detective work there OB 

It's definately a coil voltage issue. Using the voltmeter will point you in the right direction. The ballist could be bad or improperly specced (they come in different ohm ratings) The coil itself could have an intenal short.

A little more detective work and you'll have it licked. 


Ron

[Orange Bird]

Will check for short, proper connections and defective parts. All look new/very good used but some of this was already hooked up and not exactly sure what I am dealing with.  The guy who got the parts bought alot of new (harness) but also has some used. Neither means anything sometimes as that is why I need to confirm ballast could have been dropped or something. I just located a different diagram that appears to be the same as what I am dealing with so it will be nice to confirm - both visually and with meter.

[Orange Bird]

I found a diagram consistent with the one I had in the car. The field wires were reversed. Swapped them after confirming the other wire paths and all is well now. Fired is 10 seconds after the tracing of wires.

Thanks for the help

[firefighter3931]

I found a diagram consistent with the one I had in the car. The field wires were reversed. Swapped them after confirming the other wire paths and all is well now. Fired is 10 seconds after the tracing of wires.

Thanks for the help

Glad you figured it out ! It's the simple things that can be such a PITA ! 

When you say field wires are you referring to the alternator or the pickup in the distributor ? An MSD distributor will run with the pickup wires reversed but it will perform like poop....but it will still run/idle. 

Just seeking clarification and thanks for the update 


Ron

[Orange Bird]

 It was the wires on the alternator. I reversed them and the car fired right up. The car has a factory alt and coil with electronic ign. I did a search for the ballast resistor and when I was digging for info and found the wiring diagram I needed to confirm with what I had in the car. It was posted by someone on "For A Bodies Only"  It was exactly what I had in the car only the wire colors were a little different. Once all the wires were traced the only thing I found were the alt wires crossed.

I will sleep easier tonight.

But I still have other detail electrical things to hammer out. They are minor but it will take a bit of time.

Thanks for the help.

[firefighter3931]

Thanks for the update OB, good info for further troubleshooting should someone else encounter the same issue 

For reference on electronic VR wiring ;

(1) green field wire connects to green wire on VR plug
(2) Blue field wire connects to blue field on VR plug but that wire is also tied into the blue wire coming off the bulkhead connector (3-way splice)

Good job hunting down the problem 



Ron