Hammerdrop

This is a high mileage 307 with trailer tow and a 3:23 axle that has over 300,000 mile and uses, perhaps, about 1 quart of 10w30 every 750 miles. Some of that oil usage is for sure due to a leaking rear main seal. Recently, I rebuilt the Quadrajet with a new air fuel solenoid and also the TPS sensor. It was after completing that job that I noticed an engine ping. Maybe I just never drove the car without the radio on. LOL. There are no trouble codes in the computer. and my scanner shows the knock count rising when the knock is audible. I should mention that I did have to replace the ECM about a year ago because of an engine miss. Prior to the ECM replacement and based on a guess, I replaced the electronic spark timing module and the knock sensor and also the ignition module inside the distributor. None of those replacements cured the occasional miss until the ECM replacement. At that time I installed the old prom into the replacement ECM. All was well, including a 3000 road trip to the OCA National Show.last year.
This pinging issue might have me stumped. The EGR is new and is the correct GM part and it is working. Raising the engine to 2000 rpm causes movement in the diaphragm and the passageways in the intake manifold are open. I am not running the air injection system or the catalytic converter. I thought maybe my low restriction exhaust system might be causing a lack of EGR flow, but reducing the tailpipe to a 3/4" diameter at the end did not lessen the pinging. Right now I have the timing set to 6° advance instead of the factory spec of 20°. I just tried going back to the 20° setting and there was a lot of pinging most noticeable when accelerating from about 15 to 40 mph. This is definitely an engine ping. Compression range is from 135 psi to 155.. The spark plug in that 155 cylinder, which is number 8, is showing a little blackness that all the other spark plugs are not showing. Oh yea, these are one heat range colder Champion spark plugs than the factory spec. My scanner also shows that the MAP sensor is working. At the 20° setting, the scanner showed a knock retard of 11° at most and now at 6°, it shows at most only a 2° knock retard. I just tried dousing the carb with Marvel Mystery Oil yesterday and letting it soak for 30 minutes, but the ping is still there!

joe_padavano

What is the O2 sensor showing when the pinging happens? Did you follow the carb adjustment procedure in the CSM when you rebuilt the carb? My first guess would have been EGR failed closed, but your testing shows that to be not the case. My only other thought is that you are lean at part throttle, which could be related to carb adjustment issues.

Hammerdrop

I think maybe I should try a replacement O2 sensor. It is a cheap attempt although the there are no trouble codes or hesitation in engine function.
Oh, and I did verify the position of the timing mark by using a piston bumper in the number 1 spark plug hole.

joe_padavano

So you subscribe to the hundred monkeys with a hundred typewriters approach to "troubleshooting"?

You did not say that you adjusted the carb after rebuilding. You did not say what the O2 sensor readings are with a scan tool when pinging. Feel free to throw money at parts replacement. Eventually you'll find the problem.

The O2 sensor is "cheap" until it breaks off in the manifold when you try to remove it...

Hammerdrop

The Quadrajet is working fine, or at least, I think it is. The air/fuel solenoid is pulsing right about 70% when the pinging is occurring and usually stays near the middle of it's range while driving and goes to right around 50% at idle, because the idle air is so easy to adjust right on top of the carb. After rebuilding, I did have go back inside the carb to adjust the float level lower because the air/fuel solenoid did not have enough range to command the a/f ratio lean enough to keep the oxygen sensor happy and not turn on the Check Engine Light. Correct me if I am wrong, but my logic says that if the ECM is happy with what is being reported from the oxygen sensor, then the a/f ratio should be good. That is why I agreed that it was a good idea to try a new oxygen sensor on the off shot chance that I had a miscalibrated unit and that could explain why I had to readjust the float. By the way, Autozone is having a $10 off sale on oxygen sensors, so a new Bosch oxygen sensor only cost me $11 with the tax, and the old one wasn't maybe a year old, so I figured "why not".

The scan tool puts out oxygen sensor voltages that are all over the range and are constantly changing. I thought the important thing was the number of "crosscounts" which is the number of times the value crosses the 0.5 volt mark.The old and new oxygen sensors both put out a hundreds of cross counts in just a short drive.

My latest thought is that maybe that number 8 cylinder with the highest compression has a lot of carbon deposits. The valve seals are original and the heads have never been off. I need one of those little inspection cameras that are getting cheaper now so I could peek inside the cylinder.

I hope I don't have another bad ECM. That was a real joke especially after a supposedly "rebuilt" ECM turned out to have the same issue as the original unit. I ended up getting one from a junked car that finally worked.

Oh yea, and I'm the one who feels like a monkey on a treadmill here.

Cutlass Fan

If it is carbon build up in one or more cylinders causing the ping giving the engine a Seafoam or similar treatment to the engine may help.

Hammerdrop

Yea, I did give it a can of Sea Foam and let it soak back in January and 2 days ago I put 10 oz of Marvel Mystery Oil in the tank and then put the other 22 oz down the carb and let that soak. I still have the pinging with 14° less advance than the factory spec. The pinging is greatly diminished from where it would be when set at the factory spec of 20° advance although.

Funkwagon455

A sound investment for you if you don’t already have one.

https://classicoldsmobile.com/forums...ce-manual.html

Hammerdrop

Thanks, but I already have one. Doing that quadrajet or a lot of other stuff would be impossible without it.

Hammerdrop

It seems that the problem here, after all, is the EGR. After coming up dry with all other theories, I decided to go back and look at the EGR. Ok, so I have an almost new AC Delco valve on there and when it is manually depressed, the engine initially slowed a little, but then regained RPM to what it was previously. I thought this was ok, but after doing the same test on a Chevy 305 of the same era, and completely stalling the engine, I concluded that the EGR passages must be clogged even if vacuum can be felt with a finger placed over the EGR port on the manifold leading to the 2 tubes under the carb. I took off the carb, filled the passageway of the 2 tubes in the manifold to over at the EGR mount with Seafoam and let it soak overnight. After soaking, I used a brake bleeder to suck out most of the Seafoam. I then used a small screwdriver, and vacuum cleaner and a piece of spiral throttle casing like from a lawnmower throttle mounted on a cordless drill and ran it though in all directions. I thought everything would be good. I even used a little remote TV camera down the passenger side tube and could see the throttle casing at the bottom. I then used the vacuum cleaner to clean up again and sucked some brake cleaner through all three openings just to clean things up.
Now air from the air hose blew right through there nicely.

Well, you guessed it-- I set the timing back to where it belongs and still have a slight ping. I am wondering if those EGR passageways just can't be cleaned adequately enough to achieve the required flow of exhaust gas. And the engine will still not stall when the EGR is manually depressed.
As previously stated, there are no trouble codes, the engine temp is all ok and plenty of exhaust comes out of the EGR mount when the engine is started without the EGR valve in place.
Can anyone out there try manually depressing their EGR valve to see if their engine stalls because mine won't?
Is a replacement intake manifold the only solution? This engine does have 340k miles but runs fine except for the ping. Taking off the intake manifold will not be fun.

joe_padavano

The exhaust passage in the intake is the large crossover under the carb. That is not plugged. If the ports at the EGR valve are open, pull the carb off the intake and look at the two tubes that come up from the base of the intake plenum. Those can be unscrewed and cleaned if necessary, and removing them will let you look at the ports in the manifold directly under them.

joe_padavano

The other easy test you can do while the carb is off is to remove the EGR valve also and use compressed air to blow down into each of the two ports below the carb. You should get good flow out the port at the EGR valve flange. If not, maybe that passageway is plugged.

Hammerdrop

I did blow through there "nine ways to Sunday" and the air went through, but, of course, a loose piece of carbon could have come loose and could be causing issues. Those passage ways must be too restricted if the engine can't be stalled my manually depressing the EGR valve, right?

Sugar Bear

Is it running a little too warm? What does the scan tool indicate as engine temp? Does it ping before being completely warmed up?

Perhaps another member can test their 89' 307 to see if the EGR will stall the engine. My guess is it should.

May want to try a different fuel supplier if you haven't.

Good luck!!!

Hammerdrop

There is no ping until the engine gets up to operating temp. This car has trailer towing and therefore a temperature gauge which indicates normal. Yea, I need someone to verify that this engine should stall when the EGR valve is manually opened at idle speed. That would tell me that the EGR flow is inadequate for sure.

Hammerdrop

I recently checked the EGR passageway/tubes in the intake manifold and found them to be clogged, especially the one on the drivers side. The best tip I can give for cleaning is to first use a screwdriver down the tubes, suck them out with a vacuum cleaner, and then, while leaving the vacuum connected to the tubes, suck through a piece of nylon string. Tie the end of the string to the looped end of a piece of 1/16" aircraft cable and spot weld the end of the 1/16" cable to a piece of 1/8" cable and now you can ream things out with the 1/8" cable.

I now advanced the timing to 16° but not quite the specified 20°. I still have a slight ping, but not a bad as prior to the port cleaning. The EGR is a brand new Delco unit.

The one little twist here is that I have previously reduced the exhaust back pressure with a full 2-1/2" system and no more catalytic converter. I am beginning to wonder if maybe that positive back pressure EGR valve is not getting enough positive back pressure to open properly. Does an older kind of EGR Valve exist to maybe solve this problem? What's next?

olds 307 and 403

Doesn't the 89 have a knock sensor? You could try a different brand EGR valve.

Hammerdrop

Olds 307, you are right, it does have a knock sensor, but being such a primitive ECM system, I wonder how well it can be expected to work. I should look at that. When I previously scanned it was reporting a retard, but whatever it was doing, it wasn't enough. I will check if it is still doing the same.

olds 307 and 403

Get a new sensor and it must be properly torqued to 11 ft/lbs of torque.

Hammerdrop

I hooked up the scanner and It reports a maximum of 11° of "knock retard".
With the EGR valve disconnected, it still report 11° max, but, I would say, it does seem to be running, on average, maybe 2-3° more retard on my test loop. What is crazy is that I can still here the light pinging even with the spark retard going on.

The knock sensor is actually only about maybe 15 months old.
I will be testing next while bypassing the control solenoid and just hooking the egr straight to the carb port although there is the requisite amount of vacuum called for in the shop manual.

I think the EGR is not opening because of the lowered exhaust backpressure caused by the lack of a catalytic converter and a 2-1/2" system. At least that is my theory. Maybe I need one of those EGR valves that just opened up with vacuum applied and didn't rely on exhaust back pressure to function.

The other nutty thing is that after I cleaned the EGR passageways to under the carb, I manually opened the valve with the engine idling and the engine immediately stalled. I did that 3 times with the same result. But now when I do the same thing, the engine does not stall, but just slows down.

Hammerdrop

The good news is I found the problem and, as I suspected, the exhaust does not have enough restriction to feed the Positive Back Pressure EGR valve. I hose clamped a beer can with a 1" hole on the end of the tailpipe and no more knock retard and no pinging. That little trick forces enough exhaust through the EGR Valve. I tried this trick before, but that was prior to cleaning the EGR passageways in the intake manifold and did not yield this result. Oh, and the engine does die out when manually opening the EGR valve, but only when the Air Conditioner is on. When the Air Conditioner is off, the engine just slows a bit and gets rough.

The bad news is now I need to try a Negative Back Pressure EGR valve but I don't know which one might work. This would be a valve that, when tested with a vacuum pump connected, will show movement in the diaphragm when the engine is off. Maybe the pre-ECM engines used an EGR valve like this. Anyone have a answer?

olds 307 and 403

GM has used both over the years. You need to find one that fits the Olds intake pattern. It should have a N marked on it somewhere for negative. Your current EGR should have a P on it.

Hammerdrop

I just need someone to check a 70's manual and see if the EGR valves of the era could be tested with a simple vacuum pump. Thinking. Thinking..........

Hammerdrop

The answer to the pinging issue here is the replacement of the EGR valve with an EGR valve for a 73 - 74 350 or 455. These valves are from a era of no catalytic converters (not installed until 75) and low exhaust restriction and are simply controlled by the ported vacuum signal from the carb and do not rely on positive back pressure in the exhaust system.
I can report no pinging, and the maximum "knock retard" reported by the scanner has dropped from 13° down to 2°. I will consider the issue resolved for now.

I guess this could be an issue any time the exhaust restriction is lowered on any CCC Olds 307.

olds 307 and 403

Very good info, that is a huge difference over 10 degrees. No doubt runs better with the proper timing set up.

Sugar Bear

Nice work, it was refreshing to follow the persistent steps and experiments arriving at a fix.