Author Topic: "Pop!" while driving then engine shut off  (Read 568 times)

EspriTA350

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"Pop!" while driving then engine shut off
« on: August 29, 2019, 02:06:22 PM »
Was taking the firebird on a routine evening drive yesterday when I got interrupted about 10 minutes in with an audible "pop!" noise. Engine was turning about 1800-2000 rpm until that occured. I immediately checked the gauges and started slowing down and pulling over, didn't realize until I started turning the wheel that I had no power steering (and that the engine was already off) but this all happened in the course of maybe 2-4 seconds. So I'm on the side of the road expecting to find the worst, but I didn't see any huge trail of oil, no leaks underneath, no smells, no obvious catastrophic damage like smoke or a rod sticking through the hood or the block etc. I check the oil level which turned out to be a little low, but not dangerously low. So I decided it'd be safe to try cranking a couple of times. Both times it cranked fine but no start at all. I'm suspecting maybe the timing chain failed completely (engine is at 118k and probably still on the original chain), or something with the ignition although I'm not sure what could've made that popping noise. All of the ignition components are only a few years old but I'm checking them regardless. The car is at home as we speak and I've only just started going through it, but I am admittedly something of a novice when it comes to these things. Anyone have ideas on what I should check/what it could be?
« Last Edit: August 29, 2019, 02:10:29 PM by EspriTA350 »

81Blackbird

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Re: "Pop!" while driving then engine shut off
« Reply #1 on: August 29, 2019, 02:48:34 PM »
Don't know the build of your engine but I don't think it's the timing chain since you mentioned it turned over fine.  Doesn't sound like you have piston to valve clearance issues.
Try pulling the distributor cap and check there first.  Not much but it's a start until someone else chimes in.

EspriTA350

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Re: "Pop!" while driving then engine shut off
« Reply #2 on: August 29, 2019, 03:16:21 PM »
Don't know the build of your engine but I don't think it's the timing chain since you mentioned it turned over fine.  Doesn't sound like you have piston to valve clearance issues.
Try pulling the distributor cap and check there first.  Not much but it's a start until someone else chimes in.
It's basically a stock 72 350. Has a qjet and an edelbrock intake, dual exhaust, nothing major. Also has one of those electronic ignition retrofit modules inside the distributor, not sure how those would act when they crap out but thought I'd add that piece of info. It's made by accel.

Topped off oil (1/2 qt did the job, shame on me for not checking that sooner) I checked under the dist cap and everything looks brand spanking new. Checked all my wires and I did notice that the main ignition wire coming off the coil came off a bit too easily, so I made sure it was back on there snug. I also noticed this:





looks like the upper heater hose is being kinked by part of the distributor advance, though I'm not even sure how... I did those hoses 2 months ago and there were no clearance issues.

Update: tried firing her up again to see if it was just the loose ignition wire, she catches and fires up but she sounds like absolute crap... like way less than 8 cylinders and she dies off pretty easily. Going to double check to make sure I put everything with the distributor back on tight and didn't knock anything loose.

Update 2: Re-tightened distributor cap and made double sure the rotor was tight, still doesn't want to stay running unless you keep giving it some gas, in which case it sounds like crap. Not gonna force her until I get some more advice on where to check. At least she starts now.
« Last Edit: August 29, 2019, 03:42:53 PM by EspriTA350 »

Bluebandit

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Re: "Pop!" while driving then engine shut off
« Reply #3 on: August 29, 2019, 03:50:05 PM »
looks like the upper heater hose is being kinked by part of the distributor advance, though I'm not even sure how... I did those hoses 2 months ago and there were no clearance issues.

If you didn't leave it like that then its possible the distributor hold down is slightly loose and let it turn.

FormTA

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Re: "Pop!" while driving then engine shut off
« Reply #4 on: August 29, 2019, 04:48:19 PM »
^^^^ That's my thought too. Get a timing light and see where it's at. My guess you need to back that cap up quite a bit.
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Re: "Pop!" while driving then engine shut off
« Reply #4 on: August 29, 2019, 04:48:19 PM »

oldskool

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Re: "Pop!" while driving then engine shut off
« Reply #5 on: August 29, 2019, 04:56:59 PM »
"...I did those hoses 2 months ago and there were no clearance issues..."

As said, the dist has obviously rotated some, in a counterclockwise direction. So, IF that's the ONLY problem, just rotate the dist back in a clockwise direction. This will increase the ignition timing advance, since Pontiac dist shaft/rotor turns in a counterclockwise direction.

Low timing will drastically reduce engine power, produce more coolant heat, and if low enuff, make idle very difficult.

If too high, it can cause pinging, detonation, & engine damage. Most Pontiacs seem to run best at somewhere between 30° & 36° BTDC, at WOT. Most seem to idle best at somewhere between 12° & 24°. Most will set their initial @ about 9°-12°, then use an adjustable vacuum advance to achieve exactly the best idle timing setting. Too much vac advance can cause detonation, especially with low octane pump gas.

It has been posted online, many times, that it's best to set your total mechanical advance first, THEN do whatever it takes to achieve the best initial & part throttle advance. This is sometimes referred to as the timing curve. Most say it's best to have ALL the mechanical advance in by 3000 rpm. Many factory dist don't achieve max advance til 4000 rpm or higher.

To achieve it at 3000 rpm will, most of the time, require at least one weaker spring, holding the centrifugal advance weights. Kits are available, which contain 3 sets of weaker springs. Most say the lightest springs in the kit will not hold up & should be avoided. Max mechanical advance can be determined by removing one spring entirely. Removing both springs will allow the max advance to be determined at an even lower rpm.

Once max mechanical advance is set, some combination of springs will be required, to set the rpm at which you desire the max advance to be achieved. All of this is done with the vac advance unhooked & the vac source plugged.

Once max advance rpm has been set, THEN you can work on getting your initial & part throttle advance correct for your engine. If your dist has too much centrifugal advance, you'll have to make some sort of positive advance stop, or settle for lower advance at idle, before adding any vac advance. You'll obviously need a decent timing light. If the balancer is not marked, you'll need an accurate dial-back timing light, to set your max mechanical advance, since the stock timing tab does not go high enuff. 

Crane sells a kit which contains an adjustable vac advance, plus 3 pairs of springs.

https://www.oohall.com/2019-crane-cams-99601-1-adjustable-kit-vacuum-advance

https://www.ebay.com/itm/Crane-99601-1-Vacuum-Advance-Kit-Adjustable-Vacuum-Canister-Springs-Cam-Limiter/273885434550?epid=1939755269&hash=item3fc4d812b6:g:RuwAAOSw-GtdABrF

https://www.amazon.com/Crane-Cams-99601-1-Adjustable-Advance/dp/B000CIO2KY

I'm not sure of a good quality dial-back light, for a reasonable price. Maybe some of these guys know. Some pro mechanics insist on high dollar tools, like Snap-On. Most street guys don't wanna spend that much on a tool they'll use very little. Maybe some can rent or borrow a good dial-back light.
 
« Last Edit: August 29, 2019, 05:31:32 PM by oldskool »

EspriTA350

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Re: "Pop!" while driving then engine shut off
« Reply #6 on: August 29, 2019, 05:16:49 PM »
Well I'll be damned. I thought that looked out of place but wasn't 100% that'd be the issue. Guess I know what I'm doing this weekend. Never done timing before, so this will be a first. Is it normal for these things to just work themselves loose over time, or is this something that really shouldn't happen?

oldskool

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Re: "Pop!" while driving then engine shut off
« Reply #7 on: August 29, 2019, 05:33:33 PM »
Well I'll be damned. I thought that looked out of place but wasn't 100% that'd be the issue. Guess I know what I'm doing this weekend. Never done timing before, so this will be a first. Is it normal for these things to just work themselves loose over time, or is this something that really shouldn't happen?

Reach down there & turn the dist with your hands. You can tighten the bolt a little at a time, to see how tight it has to be, to keep the dist from turning.

81Blackbird

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Re: "Pop!" while driving then engine shut off
« Reply #8 on: August 30, 2019, 05:18:51 AM »
If it's an accel then it's more than likely an adjustable vacuum advance pod.  But that is not the issue.  The above suggestions will get it running again.

Grand73Am

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Re: "Pop!" while driving then engine shut off
« Reply #9 on: August 30, 2019, 09:04:25 AM »
On a Pontiac V8, the vac advance should be aimed toward the driver side where there's more room, instead of the passenger side as you have it. And that would get it away from that heater hose. But, you'd need to know how to remove and reinstall and time the distributor.
Steve F.

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Re: "Pop!" while driving then engine shut off
« Reply #10 on: August 30, 2019, 10:00:03 AM »
I've found on a number of occasions on various engine brands that the stock (or aftermarket) distributor hold down isn't holding the distributor tight enough to prevent it from turning. Sometimes it's the design of the little bracket and sometimes the bolt threads bottom out before the bracket is actually tight enough to pinch the distributor flange to the block, so it "feels" tight when tightening the bolt but may not keep the distributor from rotating.
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81Blackbird

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Re: "Pop!" while driving then engine shut off
« Reply #11 on: August 30, 2019, 10:45:17 AM »
I just rec'd a new one yesterday.  The one I had, had wings on the side.  I don't know who thought that was a great idea.  You could get a wrench on it but couldn't turn the darn thing.

EspriTA350

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Re: "Pop!" while driving then engine shut off
« Reply #12 on: August 30, 2019, 03:58:13 PM »
The distributor felt too tight to turn by hand before I loosened the bracket. Not sure what's going on if it wasn't loose. I peeked at the distributor gears and they didn't look rounded off although you could tell they weren't brand new. Now I get to try re-time this thing... yay...
« Last Edit: August 30, 2019, 11:56:30 PM by EspriTA350 »

Ryoko

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Re: "Pop!" while driving then engine shut off
« Reply #13 on: August 30, 2019, 08:52:39 PM »
I think the question is why it's so far out of timing. Did it jump a tooth on the timing chain?

EspriTA350

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Re: "Pop!" while driving then engine shut off
« Reply #14 on: August 31, 2019, 12:04:59 AM »
I think the question is why it's so far out of timing. Did it jump a tooth on the timing chain?
It must've jumped timing on one or the other, dist or timing chain. Again, far as I know it's the original chain. May be the original distributor gear too, although the guts inside the dist are aftermarket. The "pop" was probably a backfire from the engine being so out from normal timing. I've never noticed any of the tell-tale sounds of a failing distributor or timing chain like the rattling, squealing etc.

Re: "Pop!" while driving then engine shut off
« Reply #14 on: August 31, 2019, 12:04:59 AM »



EspriTA350

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Re: "Pop!" while driving then engine shut off
« Reply #15 on: September 01, 2019, 05:32:29 PM »
Tried my best with what I had available. I took the distributor out, moved the engine by hand so cylinder #1 was @ TDC, reinstalled distributor, noted that the rotor was pointing at cylinder #1. I put everything else back on, went to start it and I got nothing but a little backfire in the intake. Tried advancing and retarding a little in either direction with the same result. I didn't want to harm anything so I stopped for now. I thought the procedure should've gotten me in the ballpark at least?

pancho400cid

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Re: "Pop!" while driving then engine shut off
« Reply #16 on: September 01, 2019, 06:55:21 PM »
If it was running fine before the pop, it may have jumped time due to failed cam gear if you used a stock nylon gear.  A broken timing chain is also possible.

Pull the wires that provide power to the distributor so the car is not firing.  Pull the distributor cap.  Crank the starter.  If the distributor rotor isn't turning, the timing chain is broken.

PS - If the chain is broken the engine cranks a bit faster than normal.
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cyber104

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Re: "Pop!" while driving then engine shut off
« Reply #17 on: September 02, 2019, 06:22:04 AM »
"Also has one of those electronic ignition retrofit modules inside the distributor, not sure how those would act when they crap out but thought I'd add that piece of info. It's made by accel."


You might want to try replacing that module...........

It seems you're focused on timing - but if the car was running down the road with the distributor in that position and it just stopped - I'd be looking for an ignition problem
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gstrandfarm9420

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Re: "Pop!" while driving then engine shut off
« Reply #18 on: September 02, 2019, 02:54:56 PM »
Find TDC on no. 1 cyl , check and see if the timing mark on the front damper lines up with the right  numbers on the cover, also see where your rotor is pointing in the distributor at that point, should be no. 1 terminal. I'd be willing to bet they are not right. Your symptoms describe a timing chain that jumped the gears. Pontiac used plastic coated gears for quieter running, eventually the plastic breaks off, not an uncommon problem.

Lewis

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Re: "Pop!" while driving then engine shut off
« Reply #19 on: September 06, 2019, 04:50:21 PM »
I have no solution to  your problem, just this. A Delco-Moraine engineer told me in 1979 that those timing sets were engineered to fail between 60 and 80 thousand miles. If you get 90 you are on borrowed time.
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NOT A TA

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Re: "Pop!" while driving then engine shut off
« Reply #20 on: September 06, 2019, 06:20:39 PM »
Tried my best with what I had available. I took the distributor out, moved the engine by hand so cylinder #1 was @ TDC, reinstalled distributor, noted that the rotor was pointing at cylinder #1. I put everything else back on, went to start it and I got nothing but a little backfire in the intake. Tried advancing and retarding a little in either direction with the same result. I didn't want to harm anything so I stopped for now. I thought the procedure should've gotten me in the ballpark at least?

Backfire in the intake under the circumstances ^^^ would indicate you were 180 degrees off. In other words you had the engine at TDC on the exhaust stroke.
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Ford5of5

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Re: "Pop!" while driving then engine shut off
« Reply #21 on: September 11, 2019, 12:40:07 PM »
Just my 2 cents but I've had 2 different Petronix units fail on 2 different Fords after a year or 2. My thought is that they are dying due to heat.
 
X2 on the dizzy being stabbed incorrect compared to factory. Someone installed it Chevy style!  :lol:  On multiple cars I've run into issues were someone pulled the distributor and reinstalled them incorrectly. The factory clocks it in certain way to have plenty of adjustment. It's likely that you're timing wasn't optimal because people tend to give up on getting the timing right when they can't get the proper amount of adjustment or they start adjusting the carb!

Best bet is to buy a new HEI distributor. Check Rock Auto, they sell a nice, complete unit with all new components that should drop right in.  Search for CARDONE 841891 Another TAC member was able to get the exact same unit off EBAY for even less money. Just be sure to check the modulator to see if it has thermal paste on it. If it doesn't add some; it's to help cool the modulator.
« Last Edit: September 11, 2019, 12:55:46 PM by Ford5of5 »

EspriTA350

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Re: "Pop!" while driving then engine shut off
« Reply #22 on: September 12, 2019, 12:30:25 AM »
Sorry everyone, got injured at work so I haven't been able to do much since my last post. Hopefully this weekend I will have time to do some more checking around.

If it was running fine before the pop, it may have jumped time due to failed cam gear if you used a stock nylon gear.  A broken timing chain is also possible.

Pull the wires that provide power to the distributor so the car is not firing.  Pull the distributor cap.  Crank the starter.  If the distributor rotor isn't turning, the timing chain is broken.

PS - If the chain is broken the engine cranks a bit faster than normal.
Good thinking, I'll definitely give a quick check under the distributor cap and see if it turns. Far as I know it's still the stock timing gear, so it wouldn't be the first nylon timing gear to fail.

"Also has one of those electronic ignition retrofit modules inside the distributor, not sure how those would act when they crap out but thought I'd add that piece of info. It's made by accel."


You might want to try replacing that module...........

It seems you're focused on timing - but if the car was running down the road with the distributor in that position and it just stopped - I'd be looking for an ignition problem

It was turned clockwise a bit more beforehand. I'd stake my life on it, because when I did the heater hoses there wasn't any vacuum advance in the way.

Backfire in the intake under the circumstances ^^^ would indicate you were 180 degrees off. In other words you had the engine at TDC on the exhaust stroke.

Crap. Well I feel silly now but at least that's an easy fix. It wouldn't have hurt anything, would it?

EspriTA350

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Re: "Pop!" while driving then engine shut off
« Reply #23 on: September 13, 2019, 03:58:14 PM »
Well I did a quick check of turning the motor while watching the distributor rotor, and it turns with the engine. So the chain isn't broken but that doesn't mean it isn't stretched at the least. Also snapped a few pics of my distributor. You can definitely tell it's an old unit. I'm not sure where the line is between healthy and unhealthy looking distributor gears so I snapped a few pics. Definitely a little wear but nothing rounded off or chipped.









« Last Edit: September 13, 2019, 03:59:53 PM by EspriTA350 »

highway star

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Re: "Pop!" while driving then engine shut off
« Reply #24 on: September 13, 2019, 08:54:41 PM »
Checked carburetor?

EspriTA350

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Re: "Pop!" while driving then engine shut off
« Reply #25 on: September 13, 2019, 10:01:56 PM »
Checked carburetor?

I checked it briefly the day it happened. Everything looked clean inside and out so don't think that'd be the issue.

Ryoko

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Re: "Pop!" while driving then engine shut off
« Reply #26 on: September 14, 2019, 07:07:21 AM »
Since the distributor gear appears to be in working order, it's time to start thinking about the timing chain gain. Yeah, those are no fun. As an easy spot check, you might put a breaker bar on the crank pulley and rock it back and forth to gauge how much slack is in the chain. How many degrees do you need to turn the crank before the distributor moves?

Ford5of5

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Re: "Pop!" while driving then engine shut off
« Reply #27 on: September 14, 2019, 09:59:30 AM »
Like others have said, it's possible that the distributor clamp just loosened up. The rotor and shaft turn counter-clockwise and that could have caused the unit to hit the coolant hose. First thing I'd try is setting the dizzy back up correctly. Correctly is a loaded word but I'd aim for factory style, it takes out guess work if you have issues later on.

Did your timing mark move around when setting timing before this incident? Do you hear any crustyness in the bearings of the dizzy? End play of the shaft should be around .015-.020 and can be checked with feeler gauges. The shaft does try to move up and down with changes in RPM. Do you notice any side to side play in the shaft bearings? Distributors are fairly stout but do wear out.

This is how the points dizzy should look when viewed from the rear of the engine. Like someone else said, yours looks to be 180* out:
dsfg by Chris Ford, on Flickr


This is a HEI from the front:
1979 TA (297) by Chris Ford, on Flickr


This guy has a good video for checking the slop on a timing chain:
https://www.youtube.com/watch?v=4_f5ukZVri8

firebirdparts

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Re: "Pop!" while driving then engine shut off
« Reply #28 on: September 15, 2019, 07:18:44 AM »
If you time to TDC on #1 you have a 50% chance of getting close.  It sounds like you got it 180 out.

You need to address that first.  It’s a lot of work to inspect that timing chain.
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Re: "Pop!" while driving then engine shut off
« Reply #28 on: September 15, 2019, 07:18:44 AM »
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