Mopar electronic ignition in a '69 383 Bee - what does the ICU cutting out feel like?

[MikeyM]

Hi all,

Hoping for some ideas on what this issue is/was. When we picked up our Bee (all stock 383/727/3.23) it had a Mopar electronic ignition with the adjustable dizzy and some kind of ICU box. I have no info on the history of the setup. Presumably it's older - like 20ish years or so, based on the history I do know, but runs well. It has a 2 blade ballast resistor, 5 pin box, and has always run fine. Vacuum advance works. This afternoon after continuing to dial in the power timing of the engine (thanks to all of you) I ended up with 18* initial @ idle, 34 all in mechanical. From the looks of it and where the timing ended up, the the dizzy has been tweaked years ago to be power timed. So I went for another test drive and was paying close attention to the sound of the engine, any noises, how it idled, responded etc. Under normal and "spirited" driving it ran fine, no pinging, stumbles, smooth idle, responsive, etc. Then I hit the freeway and punched it. It pulled hard in 1st, shifted at about 5k, 2nd came in firmly and pulled hard up to about 51/5200 then all of a sudden, stumbled really bad for a few seconds like it ran out of fuel. I let off the gas a bit and then it recovered at about 65 MPH like nothing happened. Normal as it usually is. The rest of the drive back was uneventful even after a couple full throttle downshifts at a feeble attempt to see what's up. I typically don't take the engine past 5K as I'm still learning the car and getting a little more brave as we go, but this time I just let it do what it was gonna do. This is the first time this has happened so I'm wondering if the ICU might need replacing or how to test, etc. I actually was looking at replacing the coil and the ICU just because I'd like to know the parts are new from a quality source but have not yet. Upon returning home, I found no leaks, no odd smells, nothing burned out or blown up, etc.

I do know that the car sat for many years before the PO and his crew brought it back. From the looks of the dizzy, coil, and associated equipment I would say the ignition system has been on the car for quite some time. The fuel pump is a stock Carter (I have a new one on my shelf) the pump push rod seems to be fine - no mushrooming and when removed measures about 3.2ish inches so I think that's ok.

I know that asking for help on this somewhat a shot in the dark so any input is greatly appreciated.

Thanks ya'll,
Mikey

 

[R413]

How much fuel is in the tank? When low and wide open through the gears the fuel goes to the back of the tank and carb runs out, you let off, it gets fuel back up to carb and runs normal again.

 

[MikeyM]

Damn. Never thought of that. Half a tank? Maybe a touch less? My fuel gauge is sadly inaccurate. Time for Dakota digital

So what I’m hearing is…. You’re saying fill the tank to the brim and repeat the same Test test. . ??

 

[pnora]

You also may have a tank with a lot of crap in it choking off the suction screen. If filling the tank seems to correct it forget my comment.

 

[ykf7b0]

What type of carburetor? Edelbrock carbs have a great reputation of stumbling into the initial hit out of the box.

 

[Geoff 2]

Sounds like fuel starvation to me. Could be the fuel pump, fuel filter or the sock in the tank.

 

[R413]

Damn. Never thought of that. Half a tank? Maybe a touch less? My fuel gauge is sadly inaccurate. Time for Dakota digital

So what I’m hearing is…. You’re saying fill the tank to the brim and repeat the same Test test. . ??

No, I didn't say fill it. But if it's low it can do that. 1/2 tank is plenty.
I drag race with half a tank, they don't run out of fuel.

Yes it sure could be full of scale and have the pickup partly plugged.
Have you got an inspection camera to put down the filler neck and look inside?

 

[MikeyM]

Thanks all, really appreciate the input. The tank is newish and when I replaced the sending unit I did look through the filler neck while the sender was out and didn't see any junk, etc... tank looked clean. The carb is a Holley 80457-2; basically an 1850. It came on the car and I have spent a lot of time getting it dialed in as best I could. I do have a new fuel pump so I suppose I could swap it out or pressure test the line and change the filter, just to be safe.

Is it common for the ignition boxes to go out after a few years? If a box rated for 5k RPM goes past that, what happens? I know this car sat for quite some time in AZ so not sure if that has anything to do with anything.

As far as the timing goes, and I'm no expert but, 18* at idle seems to quite a bit to me. Even if I'm at 34* all in, mechanical. There was no pinging but I'm wondering if the timing could have something to do with it. Perhaps, just to be safe, I should re-power time it. Last time I did, it was only a couple degrees less but the latest timing sure seemed to wake it up a little more.

Thanks,
Mikey

 

[ykf7b0]

Regarding the timing, I have a Mopar Purpleshaft 284/484 with duratation @.050 being 241 and my compression is at 10.6 to 1 and my initial timing is set at 24*.

 

[Armyvet25]

Sounds like fuel starvation, pump can't keep up with demand, clogged fuel filter/screen even if not blocked may have restriction. To answer original question, ecm's don't normally cut in/out, usually fail or fail when hot a resume after cooling down. Tell tale sign is the backing sealant melting away

 

[Don Frelier]

I did have an orange box from around maybe 1995? that would break up at higher rpm maybe 4000-4500 it was probably 10-12 years old at the time with fairly low hours on it.

It was hard to diagnose because the car ran fine except for when you went full throttle and it kicked down a gear.
I agree it's probably not a common failure mode but I've seen it.

 

[Geoff 2]

Idle timing is mainly dependent on cam duration/overlap. A most misunderstood subject, even amongst seasoned mechanics. A large cam might need as much as 50* of idle timing.

 

[MikeyM]

Thanks, Geoff. I recall you and others chiming in another timing post I had - thanks. I have the stock HP cam and just want to be sure I'm not giving it too much advance at idle. I suppose the best way to check that would be to "power time" at idle, around 800 rpm, by turning the dizzy until you get the highest idle then back off a few degrees, check all-in mechanical timing at idle and 2500 and make sure it's not exceeding 34-36* or so. I'm at 34* all-in now and the car feels really good. I'm sure I could go more but without the proper equipment to check, I'd rather play it safe.

As for the general consensus of starvation, is there some way to confirm? I mean, other than changing the pump and filter and making sure all the filters are clean? Which I have no problem doing - I'd really just love to be able to pinpoint the root cause but it's only done it once so it might take some time.

Thanks,
Mikey

 

[Geoff 2]

Yes, you can check flow delivery. You will need an assistant [ or two....]. Get the engine warmed up. Take care doing this, can be a fire hazard if done wrong. Remove fuel line at carb & place the end into a container. Start engine & time how long the engine runs before the fuel in the carb runs out. You now have a volume of fuel & the time it took to pump that volume. A realistic HP guess for a stock 383 is 300hp which requires 25 gph. You can calculate by proportion if the fuel pumped into the container satisfies this requirement. More is ok, less no.