[455'73inElCamino]

Thanks in advance for any help/ideas I can get!

The Problem:
When applying throttle moderately, like when moderately accelerating or going up a hill, my engine pings. This typically is when my engine vacuum drops to about 12" Hg, pinging starts, even when not going up a hill. I have been having a lot of trouble figuring out why.

Details for above are engine is at about 1500-2500 rpm (3rd gear in 2004r) 3.73 gears, 26" tires, engine temp @ 180 degrees.

Engine vacuum parameters - engine idles @ 12.5" Hg at 650 rpm, has 18-19"Hg at light cruise.

Engine AFR parameters - AFR will drop into 13.1-13.5 on pressing accelerator for above condition, but quickly comes up to low 15s (which of course is lean).

Engine timing parameters - has 12 degrees initial timing (mechanical only), 33 degrees all in @ 3500 RPM. Vacuum advance is 10 degrees max @ 18" Hg, starting @ 7" Hg (i.e. advanced roughly 1 degree per in Hg), which I have verified by timing light.

In above conditions, @ 1500 rpm, there is 3 degrees of addition mechanical advance (summit distributor with heavy silver and light silver spring - I used MSD timing charts for the 3 degrees plus I verified by timing light). Also, @ 12" Hg vacuum, vac advance is adding 5 more degrees of advance. So total advance at 1500 rpm is 12+3+5 = 20 degrees for the above pinging condition. As I mention below, when vac advance is eliminated, I have 15 degrees advance @ 1500 rpm.

Engine Fuel parameters - quadrajet tuned for my engine by SMI, 6 psi of fuel pressure @ idle, but drops to 3 psi at above condition. I use 93 octane from Sunoco with no ethanol.

What I have tried - besides measuring the above info on my engine.
1. I removed the vacuum advance to eliminate any timing that it may have been adding since the vac advance was not dropping to zero. I think this helped but pinging did not go away. It is difficult to tell if and how much it did help.
2. Drove it tonight when air was about 50 degrees outside (still with vac advance disconnected) and I think that definitely helped and maybe the pinging was gone.

Question:
1. Is the problem too much advance?
2. Is fuel pressure dropping too much?
3. Should I be adjusting the "piston" on the primary side of the quadrajet to add more fuel at the transition point for light/moderate throttle?
4. What else should I try?

Engine Details:
400 engine built with 4" stroke forged crank, .060" over block, edelbrock d-ports ported to flow 300 cfm, 10:7:1 compression, Sunoco 93 octane - non ethanol, quadrajet tuned for engine power level, performer RPM manifold port matched to heads, stump puller SD performance roller cam, 530 hp @ 5800 rpm and 515 ftlbs @ 3500 rpm, 2004r transmission, 3.73 gears, 2000 rpm stock stall, 3740 lbs car with me in it, 180 degree thermostat, griffon aluminum radiator with dual fans, and hose goes from waterpump to passenger side rear inlet.

[Navy Horn 16]

Go to your local airport. Get 5 gallons of 100LL and put it in your gas tank with a fill-up. That'll cure your issue.

[Cliff R]

What is the carburetor part number and how is it set-up?

The vacuum advance is a load sensing device. It should be set up so that when you go to heavy throttle it is not adding any timing. That's why most vacuum advance cans have pretty strong springs in them and start at pretty high vacuum readings. It is designed to add timing at very light load, and should not be adding timing at moderate to heavy load.

The carburetor should work in reverse, going lean at very light load and fattening things up nicely at moderate to heavy load. This keeps the engine happy and out of the detonation zone.

You mentioned 200-4R and 2000 stall, but is it a LU converter and is the TCC solenoid disengaging when you go to heavy and full throttle like it should be?.....Cliff

[Formulas]

Given what you have stated target areas, apt. Primary rods, power piston springs get rid of that 15

[gtofreek]

You might try lowering the fuel pressure to around 4 PSI. Not sure how sensitive Q-jets are to fuel pressure but one thing that can happen if the fuel pressure is too high is the fuel builds up around the float in order to overcome the pressure and hold the needle seat closed. Then, when you start using up the fuel, the fuel level has to drop further in order for the float to start dropping. Now the fuel level has a hard time trying to catch up[thus the low pressure when accelerating]. With less fuel pressure, the float will shut off the fuel flow with less fuel building up around the float so when the fuel level starts to drop, the float drops with it and immediately starts letting fuel into the bowl. Seems to me that with the small amount of fuel the Q-jet bowl holds, it would be more sensitive to this issue which we call float drop delay.

[hal101]

first place i go is fix the air fuel ratio dropping to 15 to 1 dose not sound like a good mixture for any kind of accelerating

[PunchT37]

I would try a lighter power piston spring. If you have a mod quad, you might want to raise up the apt a little.

[455'73inElCamino]

Thanks guys.

Cliff -
1. carburetor is an oldsmobile carburetor from what I understand- I will look for the part number. The following link is what I believe I have, although I sent it back for a modification (which is what I have now).
https://www.smicarburetor.com/produc.../productID/839
2. 2004r - no lockup on the torque converter.

Per everyone's advice -
15:1 AFR - Ok, I will work on getting the 15:1 AFR into the mid 13s at moderate acceleration adjusting the APT. Then power piston spring. I have Cliffs book so I should be able to figure that out.

Fuel Pressure - after above, I will lower that too. Originally when I set it, it was at 5 psi (not 6) so I will lower that down to 5 again, then further if it looks warranted. BTW, should my fuel pressure be more constant? Might I need more fuel flow up against a return style regulator? As stated, my fuel pressure is dropping and it isn't even at full throttle.

Float Height - once I figure out what carburetor I have and its setup, it sounds like float level might be an issue too. But this is TBD for now.

[Cliff R]

I would think stronger PP spring to get the metering rods up quicker at a higher vacuum reading to cover the lean condition. By design the carb should richen up with increased engine demand as the pressure differential above/below the throttle plates puts more draw on the main system. I suspect a problem with the basic tune, but would have to know the carb number and what parts were used to help out.

What basically happens with a carburetors power enrichment system is that it stays in the lean mode at very light load and low throttle openings. At the same time the vacuum advance stays on to effectively burn the leaner mixtures. Both are load sensing devices so when load increases fuel delivery increases and timing falls out. Working together a lean condition is avoided as it the engine having too much timing on it, at the same time. Problems in one or both areas quickly lead to pinging and poor performance. Adding aftermarket distributors with really quick advance curves (mechanical) and light springs in the VA very quickly put too much timing on a well thought out engine build at moderate to heavy load. Combine this with the carb being lean where it shouldn't be and you'll quickly run into pinging.

The mechanical advance in this scenario seems slow if anything, but the A/F readings are a bit lean when the engine is loaded, so most likely the biggest contributor to the pining issues......Cliff

[Cliff R]

APT is there to fine tune light part throttle and the PP should be up when you go to heavy part throttle.

15 to 1 is fine for light load, but it should immediately fatten up going heavy and on to full throttle.

I'd still raise the APT, and check the float height. Check the PP hanger arms while you're in there, 99 percent of the ones I get in here will NOT be even so fine tuning with the APT system is out the window right to start with.

The later Old's APT carbs are excellent starting points for a really nice HP unit. Not quite as good as the 75-up Pontiac carbs, but same end result if you know what you are doing.

Those are also fine with higher fuel pressure. I run 7.5 psi on my 1977 Pontiac carb, and it's fine to at least 9psi but didn't pick up any at the track. With a .135" seat it will suck the bowl down below 6psi, so I run a .145" seat at 7.5 psi and zero issues anyplace for nearly 20 years now.........Cliff

[PunchT37]

My bad. Had the power piston spring advise backwards.

[455'73inElCamino]

Cliff -
Thanks for the information. It is a lot for me to take in but it is definitely helped explain the apt & power piston operation.

I suspected the adjustments you (and others) mentioned needed to be done, but I was reluctant to do them because I find the quadrajet intimidating. But I will look at these adjustments tonight.

Previously, I had an edelbrock 1411 which was a much simpler carburetor. It was on a much milder, 455 @ about 350 HP, for which the 1411 was barely adequate. The rods and jets I needed to use were way off the edelbrocks tune charts so I had to extrapolate to find appropriate rod/jet combinations. That process worked, but it meant special ordering rods.

I am sure I will get more comfortable with the quadrajet. Getting the primaries and the transitions working will help.

[Cliff R]

That carb is plenty for what you are doing.

It will need some help in a few areas which is becoming obvious. I've had hundreds and hundreds of them sent here from the Left Coast shops for custom tuning, it makes up about 1/3rd of what we do here these days! I actually like the work, clean, no plating to do, just pull them down, throw just about everything inside away and start over.

Not trying to kick anyone in the nuts or steer any work my way, we're BURIED in it at the moment with no end in sight. I get the carbs simply because we specialize with these engines and know our way around the Q-jet a little more than most........Cliff

[Schurkey]

Originally Posted by 455'73inElCamino

Engine AFR parameters - AFR will drop into 13.1-13.5 on pressing accelerator for above condition, but quickly comes up to low 15s (which of course is lean).

Originally Posted by hal101

first place i go is fix the air fuel ratio dropping to 15 to 1 dose not sound like a good mixture for any kind of accelerating

Misfire will cause an O2 sensor to report "false" lean conditions.

Is it REALLY lean, or do you have some misfire along with the "ping"?

Originally Posted by 455'73inElCamino

Engine timing parameters - has 12 degrees initial timing (mechanical only), 33 degrees all in @ 3500 RPM. Vacuum advance is 10 degrees max @ 18" Hg, starting @ 7" Hg (i.e. advanced roughly 1 degree per in Hg), which I have verified by timing light.

Seems reasonable to me.

Originally Posted by 455'73inElCamino

Engine Fuel parameters - quadrajet tuned for my engine by SMI, 6 psi of fuel pressure @ idle, but drops to 3 psi at above condition. I use 93 octane from Sunoco with no ethanol.

I have NO idea why fuel pressure would drop like that. This does NOT seem reasonable.

Is this a liquid-filled gauge? What fuel pump?

Originally Posted by gtofreek

You might try lowering the fuel pressure to around 4 PSI. Not sure how sensitive Q-jets are to fuel pressure but one thing that can happen if the fuel pressure is too high is the fuel builds up around the float in order to overcome the pressure and hold the needle seat closed. Then, when you start using up the fuel, the fuel level has to drop further in order for the float to start dropping. Now the fuel level has a hard time trying to catch up[thus the low pressure when accelerating]. With less fuel pressure, the float will shut off the fuel flow with less fuel building up around the float so when the fuel level starts to drop, the float drops with it and immediately starts letting fuel into the bowl. Seems to me that with the small amount of fuel the Q-jet bowl holds, it would be more sensitive to this issue which we call float drop delay.

This is all new to me. Interesting.

[gtofreek]

Originally Posted by
Originally Posted by [B

gtofreek[/B]
You might try lowering the fuel pressure to around 4 PSI. Not sure how sensitive Q-jets are to fuel pressure but one thing that can happen if the fuel pressure is too high is the fuel builds up around the float in order to overcome the pressure and hold the needle seat closed. Then, when you start using up the fuel, the fuel level has to drop further in order for the float to start dropping. Now the fuel level has a hard time trying to catch up[thus the low pressure when accelerating]. With less fuel pressure, the float will shut off the fuel flow with less fuel building up around the float so when the fuel level starts to drop, the float drops with it and immediately starts letting fuel into the bowl. Seems to me that with the small amount of fuel the Q-jet bowl holds, it would be more sensitive to this issue which we call float drop delay.

Originally Posted by Schurkey

This is all new to me. Interesting.

This may be more of a problem with Holley carbs than with Q-jets since the Holley float level is adjusted to a level visible through a site glass hole rather than an actual float height like the Q-jet.

[455'73inElCamino]

Schurkey

"Misfire will cause an O2 sensor to report "false" lean conditions.

Is it REALLY lean, or do you have some misfire along with the "ping"?"

Engine runs as smooth as can be until it starts pinging, and it still runs pretty smooth even then..

"I have NO idea why fuel pressure would drop like that. This does NOT seem reasonable."

"Is this a liquid-filled gauge? What fuel pump?"

The fuel pressure gauge is in the cab and not under the hood. It is electric.
I dont have the model # on the electric pump, but it is an edelbrock pump. I suspect it is the 1791 which is only a 6.5 psi pump. While this is undersized for the engine combo, it should be sufficient for cruise and moderate acceleration. But, then again, maybe this pump is getting weak?

[Schurkey]

Fuel pump voltage/amperage testing is warranted. Remember that voltage testing must be done as close to the pump as you can get. Amperage testing can be done anywhere in that circuit. Also the usual pressure and VOLUME testing.

"I" would stop focusing on the "ping" problem and the "lean" problem until after the fuel pressure problem is solved.

[455'73inElCamino]

Fuel pump voltage/amperage testing is warranted. Remember that voltage testing must be done as close to the pump as you can get. Amperage testing can be done anywhere in that circuit. Also the usual pressure and VOLUME testing.

I have measured the voltage and it is 13+ volts, but now that I think about it, that measurement is not with car driving. I don't have a way to do measure amperage. I am driving pump with a relay, and am using a heavy gage + and - wires to/from the pump.

"I" would stop focusing on the "ping" problem and the "lean" problem until after the fuel pressure problem is solved.

I was hoping to not have to swap out the pump until this driveablity issue is resolved. But as you say, it might be the culprit.

Since I dont have another pump at this time, and need to add a return line to my gas tank, I am going to attempt the carb tuning first. If that doesn't work, then I will need to address the fuel pump & return line. I already have a regulator with return (just no installed).

[Navy Horn 16]

I had a fuel delivery gremlin back in the spring. One day after a drive I checked my fuel pressure at idle and it was way low, so I adjusted the regulator to put it back at 6psi. Next time out, car is flooding and generally running like crap. I'm annoyed, but decided against fooling with it because it was hot out. Fire it up when it was cool and had some shade, and I've got double the pressure that I need. WTF?!?! Dial down the pressure to 6, go for a drive and it runs like a champ.

I get home and look to make sure pressure hasn't changed, and I've got 1psi. WTF?? Come on here, and I get told how Holley pumps have to be "sumped" and have a high failure rate and all the other stuff I did wrong. Long story short, the bellows in my liquid filled gauge had failed. It would read normal at first, but then the pressure in the gauge would equalize with the line pressure and it would be AFU. I spent the $ on a new regulator, so I've got one of those sitting around in the off chance that I ever need one.

My question would be if you have done something recently to the car before it started having issues? My problems were because of an equipment failure giving me a faulty indication. Still, I should have thought to myself "Is there really a problem? The car is driving fine."

[455'73inElCamino]

It has had a problem since day 1.

The original carb sent to me was just way off, so it was replaced at no cost to me by the vendor. This one is much better. I suspect the engine builder supplied me the first quadrajet but did not actually dyno test on that carburetor. I think that the carburetor was faulty/damaged. The actual vendor for the carburetor graciously supplied me a new one without me having to make a fuss. I am very thankful for that and appreciate what this vendor did.

I did adjust the APT on the new carb (the one I have now) because in the colder weather, the carb would periodically run an AFR in the 10s at idle/light cruise. I have not seen it do that since, and the AFRs seem to be pretty steady. Possibly it had contamination? I need to readjust the APT back to original settings as a start.