Engine Dies at Idle - 78TA - Olds 403

[TonysTA]

Hello,

My TA will start up fine when its cold and idle for a few minutes and then dies, all while its in park.   I have to wait a minute or so after it dies and then I can restart it. I know its getting gas.

Here is an attached video showing it running. At this point it was already warm, I had it running for 45 seconds and then it cut out. You can see in the video, I tried to give it gas which didn't help but there was gas squirting out. Could this be a carb/vacuum issue? Timing?


I am running a Holly 80555c on the olds motor.

https://www.summitracing.com/parts/hly-0-80555c


Video of it cutting out
https://1drv.ms/v/s!ArwKVRvkdHS6g6Yh83xTC0_-AhhT3g?e=RveId1


Here are some pics of the carb setup, maybe I messed up by plugging a port I should not have.

https://1drv.ms/u/s!ArwKVRvkdHS6g6YqnLBoUy88nB6tKg?e=pDHNy9

Any pointers appreciated.

Thanks

[b_hill_86]

Since you have a fuel pressure gauge, are you maintaining pressure up until the engine dies?

How long has this occurred? Have you changed anything recently? I kinda thought at first maybe it was going lean from a thermal vacuum switch maybe not hooked up and opening to the atmosphere when the motor warms up but #1 I didn’t see one in your pictures or video and #2 I’m not sure only a few minutes of cooling off would cause the switch to close.

How about your ignition system? I see it’s an msd distributior. Is that controlled by an MSD box of some sort?

[TonysTA]

Hi,

I just ordered a new fuel pressure gauge since the current one is busted, but I do see gas squirt when I try to pump it before it dies which would suggest gas in the bowl(s).   The car has never been on the road since I restored it, this is me chasing out gremlins getting it ready for the road. Hard to say if it has been this way since I installed the motor or not.

I haven't changed anything lately other than finishing up the interior, power window installation, console etc. I did install relays to make the windows go up/down faster but can't see that being related.

I don't have the thermal vacuum switch installed (do I really need it?) . I say I need a few minutes to restart because when I try to restart right away, it will crank but not catch, and it does crank a little slower but that could be me killing the battery. Ignition is an MSD ready to run, no external boxes.

[b_hill_86]

No you don’t need a thermal vacuum switch it was just a stab in the dark as a cause.

Does it take a decent amount of cranking to fire back up once you leave it sit a few minutes?

I dunno, I do see gas squirting from the accelerator pump but it’s kind of hard to tell in the video. It sort of looks like in the  last few blips of the throttle you make it’s not squirting much gas. Like I said, hard to see so I could be wrong.

[firebirdparts]

It seems like you should be telling us what the choke does during all this. 

I guess there are three possibilities:
1.  The metering with the choke open or closed or whatever, something is really wrong with the metering, so bad that it won't run.  if this is the case, we need to know if you think it's really rich or not.  usually that's easy to say.
2.  Fuel pickup failure (already suggested).   Probably not as far as we know.
3.  Thermally activated event happens which kills it (already suggested).  You don't have any thermal switches at all, right?

[TonysTA]

Hi,

1.  I don't think its running rich, is there a way to tell beyond the smell of gas?
2.  I don't think its a fuel issue (could be wrong) , I say this because when I pump it, I do see the gas squirt but the motor doesn't care, it still dies
3.  No, no thermally activated switches

I am heading back out to continue troubleshooting, will post if I find the issue.

Thanks for the replies

[Maxthe222]

Carb is not tuned correctly/not the best choice of carb. The best care for that motor is the factory 403 Olds q-jet, the other carbs like Holley's are just not well suited to that low compression motor. I think go back to a quadrajet, you'll have a much more efficient motor and it will be a lot easier to run.

My 1979 403 Olds would idle out and then die out after parking, or stopping at a traffic light. Fuel was fine, wasn't due to heat issues as the car will run all day just as long as it was fed enough fuel, changed the idle, didn't do anything. Took off the carb, rebuilt it, worked totally fine after that. Not sure what it was, but choke may have been getting stuck shut at a point. I would still drive the car for months, but had to keep one foot on each pedal like it was a manual. Good ol' 17059253 Quadrajet runs without issues ever since.

[TonysTA]

Thanks Max, I will keep that in mind as an option, would be a bit drastic but I won't rule out swapping the carb. I still have the original.

As for this evening, I did more research on my ignition system. It's an MSD Pro billet Ready to Run dizzy with MSD blaster 2 coil.  Some people online reported similar issues to me with their coil dying so I tested mine.

My blaster 2 coil is out of spec, this may be contributing to my issue, hard to tell.

Primary resistance:   .7 OHMs ---> Mine was .9 to 1.0
Secondary resistance:   4.5K OHMs ----> Mine was 5.30, almost 20% more that what it should be

So, I will swap the blaster 2 and see if that is why it dies once it warms up. Will post back with results.

Thanks

[firebirdparts]

If you don't think it's rich, and it won't idle after "a while", then it seems like we'd have to assume the choke opened too fast.  The fast idle cam exists because they accepted the car won't idle without it.

[b_hill_86]

If you don't think it's rich, and it won't idle after "a while", then it seems like we'd have to assume the choke opened too fast.  The fast idle cam exists because they accepted the car won't idle without it.

That’s true. The choke does look fully open in his video

[nUcLeArEnVoY]

The fact that you have to wait for it to restart almost sounds like it's flooding. When the choke is on, the throttle plates are open more, which leans out the mixture which is why it runs fine at that time. When at your curb idle, the throttle plates are near closed providing the most ideal conditions for flooding. Then again, the fact that it dies immediately after it comes off the choke may mean that something else is going on. It may be lean-stumbling, too, which means you just need to enrichen the idle mixture.

How long do you let it stay on the choke before blipping the throttle to take it off the fast idle?

Holleys are appealing to a lot of people because they're calibrated very rich to run on just about any engine. You can slap a Holley onto a weed whacker and get it to run. QJets get a bad rap because they're calibrated very lean and are application-specific, right down to the motor and options of the car they're made for. For instance, the original QJet that came on your Olds 403 is very different than the one that came on my Pontiac 400.

You don't always need black smoke to be running rich. Have you pulled the plugs to see if they're carbon-fouled?

The suggestions regarding ignition hold water, too. Luckily it's an easy and a cheap thing to rule out. Ignition components are so easy and cheap to replace that I just throw parts at the ignition system until something catches.

Also take a look at the ignition control module. You mentioned it has no boxes, so I'm guessing it's an HEI style dizzy? Couldn't tell in the video. Your symptoms point to an ICM that is overheating and then cools down allowing you to restart the car.

Often times, the worst carburetor problems are ignition problems.

And I know this sounds silly, but do a thorough once-over for vacuum leaks. Like, massive, blatantly-obvious ones. When I pulled apart my carb once, I forgot to reconnect the PCV line when I re-installed the carb and it did exactly what your car is doing. It would run while giving it throttle (which is essentially all the choke mechanism is), but would die when returning to idle. Small vacuum leaks will cause your idle to either drop or speed up depending on your mixture, but big enough ones will just stall out your motor completely.

[b_hill_86]

The fact that you have to wait for it to restart almost sounds like it's flooding. When the choke is on, the throttle plates are open more, which leans out the mixture which is why it runs fine at that time. When at your curb idle, the throttle plates are near closed providing the most ideal conditions for flooding. Then again, the fact that it dies immediately after it comes off the choke may mean that something else is going on. It may be lean-stumbling, too, which means you just need to enrichen the idle mixture.

What you described is the opposite of what happens.. A cold engine should start with a closed choke to effectively richen the mixture then gradually would “lean” it out as the plates open. His choke plates also appear to be open in the video anyway. But if the choke was causing an overly rich condition, enough to stall the engine, it would occur while the choke spring is cold when the engine first starts.

[nUcLeArEnVoY]

The fact that you have to wait for it to restart almost sounds like it's flooding. When the choke is on, the throttle plates are open more, which leans out the mixture which is why it runs fine at that time. When at your curb idle, the throttle plates are near closed providing the most ideal conditions for flooding. Then again, the fact that it dies immediately after it comes off the choke may mean that something else is going on. It may be lean-stumbling, too, which means you just need to enrichen the idle mixture.

What you described is the opposite of what happens.. A cold engine should start with a closed choke to effectively richen the mixture then gradually would “lean” it out as the plates open. His choke plates also appear to be open in the video anyway. But if the choke was causing an overly rich condition, enough to stall the engine, it would occur while the choke spring is cold when the engine first starts.

You're right, I didn't even notice the choke was all the way open...

[TonysTA]

Hi - Thank-you for the replies and pointers - it was the gas cap!

 1. Swapped out the coil, still had the issue
 2. Swapped out the fuel pressure (FP)  gauge, still registered zero. This was odd so I took a working FP gauge off a running car and put it on TA - still zero
 3. It then dawned on me that I put a new gas cap on maybe 6 weeks ago and didn't give it much thought. Once I took it off, my FP gauge started working again and the car stopped stalling

I think b/c of the wrong non-vented cap, I was sucking all the O2 out of the tank and then it ran out of gas. After a few minutes, o2 would naturally seep back into the tank and it would start again.  Guessing I should drill a hole into this cap?

https://1drv.ms/u/s!ArwKVRvkdHS6g6Y9xExWoSGtKsIEeA?e=bauhNP

[81Blackbird]

I'm surprised the engine didn't implode the tank to some degree.  Does the bottom of the tank have the correct shape?

[Y88 TA]

Wow, who would have ever thought. Glad you got it figured out.

[b_hill_86]

Good deal. Glad you found it.

If it’s creating a vacuum in the tank I assume you have your charcoal can removed and the vent line that went to it capped? If so, you could install one of these at the end of the vent line or something similar. https://www.summitracing.com/parts/tnk-vvr

[TonysTA]

Hi - The tank, as far as I can tell didn't implode from too much pressure. I am running a line from the tank up to the charcoal canister, I thought I was supposed to do that to minimize gas smell in the garage/venting. If that line is supposed to equalize the pressure and prevent stuff like this, then must have hooked it up wrong. I don't have any lines from the carb to the charcoal canister. I capped them off on the carb, the canister is old and I didn't trust it - If memory serves the tank to canister was just passive venting but the carb to canister was active suction and I didn't want to risk sucking charcoal sediment into the carb.

What was the original gas cap these cars?

[b_hill_86]

Non vented I believe

Edit: I thought non vented but the manual says “To protect the tank from mechanical damage in the event of excessive internal or external pressures resulting from the operation of this closed system, a pressure-vacuum relief valve, located in the gas cap will control internal pressures” so maybe they were vented.

[Wallington]

Vented, the whole reason this post exists.

[firebirdparts]

Hi - The tank, as far as I can tell didn't implode from too much pressure. I am running a line from the tank up to the charcoal canister, I thought I was supposed to do that to minimize gas smell in the garage/venting. If that line is supposed to equalize the pressure and prevent stuff like this, then must have hooked it up wrong. I don't have any lines from the carb to the charcoal canister. I capped them off on the carb, the canister is old and I didn't trust it - If memory serves the tank to canister was just passive venting but the carb to canister was active suction and I didn't want to risk sucking charcoal sediment into the carb.

What was the original gas cap these cars?

The canister is fully open to the atmosphere at the bottom.  So the gas tank cannot be pressurized or put under vacuum with the canister hooked up.  they didn't do purge valves and all that in the 70's.  The just used a little ported vacuum to the carb that would suck on that canister a little when you're driving.  That would dry out whatever gasoline got stock on the carbon.

[nUcLeArEnVoY]

Hi - The tank, as far as I can tell didn't implode from too much pressure. I am running a line from the tank up to the charcoal canister, I thought I was supposed to do that to minimize gas smell in the garage/venting. If that line is supposed to equalize the pressure and prevent stuff like this, then must have hooked it up wrong. I don't have any lines from the carb to the charcoal canister. I capped them off on the carb, the canister is old and I didn't trust it - If memory serves the tank to canister was just passive venting but the carb to canister was active suction and I didn't want to risk sucking charcoal sediment into the carb.

What was the original gas cap these cars?

The original gas caps on these cars were non-vented. There's a line that goes from the tank to the charcoal canister, the bottom of which is open to atmospheric pressure. That's where you get your venting for the tank. The carbon/filters in the canister are what curbed the smell of fuel. Depending on the motor, the design is a little different but the end purpose is the same.

You may be able to get repro charcoal canisters for the Olds 403 if you wanted. I know they used to reproduce them for the 400's but no longer. You can also refurbish them pretty easily. I did mine in like 30 mins.

[Wallington]

Non vented I believe

Edit: I thought non vented but the manual says “To protect the tank from mechanical damage in the event of excessive internal or external pressures resulting from the operation of this closed system, a pressure-vacuum relief valve, located in the gas cap will control internal pressures” so maybe they were vented.

Correct, they are vented via pressure valve in cap as per most caps that have the insert under the lid. Non-vented is like the old valve cover twist on one-piece cap with seal. Pre-emissions fuel caps may have been different.

Original cap for a 78 were Vented and commonly Stant #560524 , NDH 32503146 and similar. The valves in them changed due to requirements but retained similar numbers. Most of these original numbers now translate into late-model black plastic cap found on several GM. Locking cap options sold by GM were by Stant and Atlas, in GM boxes.

[b_hill_86]

Who knows if my cap is original, or just doesn’t function right, but I don’t have a charcoal can and the old vent line to it is capped. If my gas cap is tight it does create a vacuum in my tank. You can hear the tank expand when you crack the cap. Honestly, for the ten years I’ve had my car I just back the cap off of tight slightly and haven’t had an issue. Maybe my cap had been replaced or just won’t release pressure (or vacuum) anymore.