SBC with 7-pin HEI hates advance... Pops and bucks

[kccampro]

It starts and it runs so much progress has been made. But now I'm trying to get the ignition dialed in and I'm far from an expert. Within the last few weeks I converted from a centrifugal/vacuum distributor to a 7-pin HEI. I have set the base timing (with the B pin of the relay disconnected) to 0 degrees advance and set the timing advance in TS to match per the manual. However, I get horrible popping, bucking and general poor running when the timing map is populated with normally acceptable advance for a SBC (up to 30-36 degrees maximum advance lets say). The motor will only run well with 16 to 17 degrees maximum advance. And even with 16 degrees maximum advance I get pinging under hard acceleration even though my AFRs look good through the entire pull. I'm thinking that there is something that I haven't set up properly. I was thinking about pulling the #1 plug and finding TDC and pulling the rotor cap off just to confirm visually where the rotor is relative to the #1 spark plug post on the cap, but that might not tell me a whole heck of a lot. Anyone have any suggestions? I'm a bit of a newbie when it comes to electronic ignitions. Thanks!

[Matt Cramer]

Can you check with a timing light to be sure the timing you're commanding is what you're actually getting?

Any chance the balancer is starting to come apart and the marks have moved?

[kccampro]

I'll checking the timing again with the light and also the condition of the balencer. I'll report back. Thanks Matt

[kccampro]

I'm stumped, the timing light shows me right at TDC and the balencer looks good... the Spark Advance Table is engine advance not distributor advance right? So 30 degrees on the Spark Advance Table refers to when the engine is at 30 degrees advance (so 15 degrees distributor, right)? Just for reference, here's a screen shot of my basic ignition settings and my spark advance map (the one that runs very poorly).

[Matt Cramer]

The spark advance table is the timing in absolute numbers.

[kccampro]

Next steps, here's what I'm thinking ill do next: I've added a timing tape to the balencer that shows me the timing marks all the way through 45 degrees BTDC on the balencer. I'm going to bring the motor to normal operating temp and load a spark advance table where every cell value is the same, say 10 degrees BTDC and read the balencer with a timing light to see if I in fact get the same value on the balencer that I get on my spark advance table. Then, maybe ill try a different spark advance table value like 5 degrees BTDC and again see if it matches. I'm just curious how my spark advance table is translating to the actual engine timing. More to follow...

[Matt Cramer]

Sounds like a plan.

[440roadrunner]

Just a thought, but have you actually checked that the timing marks are correct with the crank, IE use a piston stop to check them?

[kccampro]

Just a thought, but have you actually checked that the timing marks are correct with the crank, IE use a piston stop to check them?

At this point ill consider double checking anything. When you say the timing marks are correct with the crank, do you mean the timing marking on the tab that's affixed to the timing chain cover matching the markings on the balancer? Anything is possible because something is clearly way off. A properly set-up SBC will run 30 degrees advance at 3,000 rpm all day long... The mystery continues. Tomorrow I'll be comparing the spark advance table to actual crank timing and i'll report back with my findings.

[440roadrunner]

Exactly what I meant, a common problem, caused not only by mixing parts over the years, but the balancer outer ring itself can slip. You check this with a "piston stop" which you can make or buy.

Remove the no1 plug, make sure the piston is "down a ways," remove the battery ground, and insert the device. You may have to adjust the length of the device. You are NOT trying to stop the piston at TDC, but rather down in the bore some amount.

Now rotate the engine with a wrench until the no1 piston stops against the device. Make a temporary, accurate mark under the timing tab at TDC onto the balancer.

Now rotate the engine CCW and make a second mark the same way.

Now you'll have two temporary marks some distance apart, and true TDC will be exactly halfway in between. If the original mark is accurate, that is where it will be

[kccampro]

Update... d'oh! have I done wrong? LOL. Clearly, something is off because here are my findings: at idle, with 2 degrees BTDC on the spark advance table, the actual timing on the crank is 28 degrees BTDC!!!!! At 5 degrees BTDC on the spark advance table, the actual the timing on the crank is 38 degrees BTDC. No wonder it pops and bucks at 30 degrees BTDC on the table, I'm probably running 60-70 degrees advance on the crank!

I'm stumped because I set my base timing to 0 degrees on the crank with the B terminal disconnected and set my trigger wizard to match on TS. What would explain such a huge difference between the spark advance table and the actual engine advance??? Any thoughts?

[kccampro]

The saga continues... I think I'm getting centrifugal advance and didn't realize it. With the B pin disconnected AND every cell on my spark advance table populated with 5 degrees BTDC, if I put a timing light on the balancer and blip the throttle with my hand, I go from base timing (TDC) at idle to 10-13 degrees advance when the engine revs and then back to TDC... there's no vacuum canister on this distributor so I looks a heck of a lot like mechanical advance to me. I'm going to pull the distributor and have a look. Maybe there has been centrifugal advance added on top of my advance in my spark advance table and I didn't realize it?

[kccampro]

damn... I thought I had it figured out, there's no mechanical advance on this distributor. So where do I get 10 degrees advance from when every cell is populated with the fixed value (5 degrees for test purposes) with no vacuum or mechanical advance???

[Matt Cramer]

Could you post a copy of your tune file? Something may be set backwards...

[kccampro]

Yes, I'll definitely post my tune. My new theory is that I didn't understand how to set the trigger wizard because if I tweak that value I can get the car to run properly. I thought that I set the trigger wizard to what ever the actual timing what with the b relay disconnected. In my case it's 0 degrees TDC. However, if I move the trigger wizard value to 17 degrees BTDC then I can run reasonable values on my spark advance table the car runs well. So, did I just misunderstand the correct way to set up the trigger wizard or am I just masking a bigger issue? Tune to follow...

[440roadrunner]

I can't help you with the specifics of Megasquirt, but some general comments

1--The very first thing I'd do before ANYTHING else is to check the timing marks with a piston stop, PERIOD

2--I'm not sure what you have for a dist/ module. Is it possible the trigger pickup wires are reversed?

3--Are you generally familiar with what has become known as "rotor phasing" and if so how are you verifying this?

4--What are you using for a timing light? Certain "dial back" timing lights can add their own nonsense to the mix.

[kccampro]

Matt, I've attached my current tune. I'm still getting some occasional pinging even though the timing is very retarded. I;m sure there's something I've done wrong... if anyone sees anything in the tune, let me know.

[Joe]

I think the 10 advance with EST bypassed is built into the module. I know for sure it is on the 8-pin version just not 100% on the 7-pin module. It's a fail safe to keep the vehicle drivable if you loose the EST signal. You should not get the additional 10 when the module is under MS control for timing.

Rotor phaze-

Early HEI setups had some issues with the magnet moving on the distributor shaft. Easy to check. Just take a screw driver and push on the magnet that's attached to the dist shaft . If you are able to move(spin) the magnet with the dist shaft stationary you will never get your timing sorted out.(Needs Shaft replacement) You will also end up firing spark when the rotor tip is to far from the dist cap electrode. All your spark energy will be used jumping the gap between the rotor tip and cap not leaving much for jumping the plug gap.

Joe

Edit- Sounds like you used trigger wizard corretly- If you set your trigger to 17, command 20 degrees timing. Measure 20 degrees timing at the crank, that's as good as it get's. This is with MS controlling timing of coarse.