I have tried to get this question answered elsewhere, but I figure a Camaro site would have smarter gearheads since racing requires more attention to detail.
I have a 91 Olds wagon with a new L03 motor(GM Goodwrench) and it always pings at part throttle, around 1400-2000ish. The old wore out motor acted very much the same way.
It won't run worth a damn with 87 octane, have to put 93 in it. If you put in 87, it'll ping so bad up slight hills the check engine light comes on and the computer pulls timing.

There is a barrage of new parts underhood, EGR valve, knock sensor, plugs, wires, coil, cap, and rotor replaced, Oxygen sensor replaced, I have a heated oxy sensor in it now, the only "mod" I have done, everything else is stock. Fuel pressure is in spec at 14psi. Plugs are AC R45TS which are stock recommended. I have tried to stick to Delco stuff wherever possible. Base time set to zero per the owners manual. Temp sensor replaced a few times(first couple cheapo brands leaked, till I changed to delco brand)
195f thermostat although once it opens it seems to run closer to 160ish if the dash gauge is to be believed.
I have not changed the ESC...yet. I don't get check engine lights popping up.

It will run like a dog with rich carbon filled exhaust on 87 if I retard the crapola out of the timing, but that is horrible. I know its a heavy car with a 2.73 rear with 9.3:1 compression, but I would not think this car would leave the factory making such a racket without being brought back to the dealer. Mileage seems to be on point, 22-23 hwy, 13-15 in town.

Perhaps I need a slightly colder plug? Should I try to change the ESC module? I mean, I have already thrown a lot of parts at this thing, so why stop now, right?
Many thanks

 

Are you sure you are setting the timing correctly? With the EST unplugged?

 

Yes, unplugged the little connector under the air box. Waited till motor was up to temp, and unplugging made the timing move, so I know I got the right one.

 

What is the base timing set at? Start at 0.

 

Correct, set to zero.

 

You said your prior engine did the same thing? Did you reuse the distributor, cap and coil?

 

Sorta. The coil started going out before I replaced the engine, so I replaced it first and reused it for the next motor since it was less than a year old. I replaced the cap and rotor after I swapped the engine. It made no difference in the way it ran.

 

I wonder if you have a defective knock sensor or ECS module.

 

I have use the original, an offbrand, and a new delco knock sensor after I figured maybe the delco would do a better job. I learned on this site some time ago that the knock sensor is only there to pull time to get it into safe mode if the gas is bad and knock gets too loud, but other than that doesn't change the timing in normal circumstances.

ESC has also been my final guess by default. I have changed the TPS too with no improvement.
One thing I don't want to happen is to pay north of 75 bux for a new ESC only to see no improvement.

I'll admit its a real head scratcher, I've been trying to figure it out for over six years. Maybe I just need to bite the bullet, get one from O'reillys and save the reciept.

 

Do you have the correct balancer for the timing cover ? Balancer outer ring hasn't slipped?

 

Yup, I replaced that too. I compared the old to the new and it was ok but kept the new one as it it had new rubber in it and I plan to keep this car for a lot more years.

 

Was the new crate engine an actual LO3? Or a generic 305/350? If it doesn't have the same heads and cam as stock the stock tune will not run well with it.

 

Its an genuine L03 I ordered from Summit.

 

Didn't even know you could get one. Did you check the head casting numbers? I'm skeptical that summit had a new L03 in their inventory that long and it wasn't just some genero 305 mill.

 

I ordered it Feb. 2015 and apparently one of the last people to do so, if not the last. The casting marks looked right, has the inline valve cover bolts, no cutout for a mechanical fuel pump and roller lifters.

 

It could be but I have my suspicions. Pull a valve cover and see what the head casting is. Should be 087. Also, if it has received an overbore or already is out of range of the stock tune to account for. Might be time to invest in some DIY tuning. At the minimum get some datalogging.

 

Interesting, it was listed as a new engine. Came with the GM Goodwrench "NEW 305" foil stickers and everything, but liars are everywhere I suppose. Where would I find this casting number exactly inside, I don't want to break the seal if I can avoid it, I'm hoping its near the oil filler cap or one of the PCV holes I can snake my camera into there and have a look.

 

The valve cover gaskets are reusable so you wont hurt anything. You should see a raised casting number on the head surface where the rockers would bolt. You'll see various numbers but the last 3 should be 087 for L03 OEM swirl port heads. Anything else and it could be a hodge podge of 305 parts. I think you are.going to have to datalog and see what the engine is telling you.

 

Well, I will take the time tomorrow to carefully lift a valve cover. I'm sure its the right head since all TBI units had swirlies, and it runs great above and below the two RPM's I mentioned.

Maybe I am unlucky and somebody en mexico slapped TPI heads on it instead(or only on one side.) now that's comedy!
I thought the TBI swirl code was 187? and TPI's are 081?

I know whatever going on is minor but it'll be nice to lick this problem.

 

You might be right in the casting numbers. I'd double check. I am going from memory which is beyond dangerous 🤔

 

Shifty,
You could still get a new 305 TBI and Vortec longblock from GM until a year or two ago. Could still get new 305 blocks as well. The TBI 305 crate engine was available in two flavors. The roller cam car engine and the flat tappet truck engine. Both were built correct for the applications.

At one point in my old G20 van I ran the 187s on a flat top piston 305 with a stock 350 truck cam, headers and and edelbrock intake. I had a 700r4 and 3.08 gears in the van. Even with the higher compression ratio it ran detonation free on 87.

Does the OP car have the factory exhaust manifolds and factory exhaust system? Exhaust backpressure seems to drastically effect the way the EGR valves open. If the ECM is commanding the EGR to open and it is not opening or the EGR passageways are plugged in the intake manifold I could see it having some wicked part throttle detonation.

​​​

 

The exhaust was factory. The cat got so plugged up it wouldn't run more than 15mph, so I had to hack it off at a buddies house just to get it back home. It has since been replaced by a regular pipe. It'll stumble when the EGR is opened manually. I have tried both a Positive and Negative EGR with the cat on and off. The A.I.R pump vanes self destructed as well, I gutted that and plugged the holes. That had no effect on anything, it didn't run any worse, but I wouldn't expect that to as the oxygen sensor is on the opposite side.

The GM service manual says something about low load part throttle leaning out the motor slightly for better fuel economy, so there is a range where this is supposed to happen. At first startup where the engine runs in open loop mode at these part throttle RPM's it will not ping, but also that makes sense as its running richer in that scenario. The warmer the motor gets, the pingier it gets.
I'm wondering if these cars were tuned to run at the ragged edge of what was acceptable driveability just to get better economy. After all it says quite plainly, "If it pings put in higher octane fuel" which did fix 90% of my problem.

I am reading through the driveability section of the service manual again today, I haven't in a while, to see if I missed anything.

Maybe the EGR isn't opening like it should. The vacuum solenoid does open at the correct rpm and load conditions, I verified that with a vac gauge Tee'd into the vac line going to the EGR while driving.

While I don't have a scan tool specifically for this car, it says the threshold between rich and lean is 450mV so I can at least see what the O2 sensor is seeing with my multimeter while driving around.

 

I had some time, and some good weather today to mess around with the EGR. All throughout the forums I have read that if you give the EGR straight vacuum, it should open. Well, I bypassed the EGR solenoid and hooked the EGR up directly. It fluttered a bit but the fact remains that it idles perfectly fine with full vacuum on the EGR valve. I have tried this before and got the same result, but didn't think anything of it at the time.

I am a decent diagnostic type person, and the EGR has always been at the front of my mind. I may have replaced it a few times, but the SOB should be opening a lot more than it does. The first EGR (AIRTEX / WELLS 4F1563) I bought during the motor swap. I got another EGR from the local parts store and bench tested it with my air conditioner vacuum pump, which puts out about double the vacuum that the EGR usually sees. It failed to open. I put it on the car anyway. Still no change in operation. Took it back as DOA. I did a little more homework and found that the OEM units were no longer produced. So I ended up getting the only other unit that Rock Auto sold, the STANDARD MOTOR PRODUCTS EGV382 which is on there now.

If I can't get a functional EGR valve, what other choice do I have?