Engine suddenly starts to ping (detonate)

[gthmcty1]

Was driving yesterday and my car started to detonate all of a sudden (85 Regal V6 NA) and no prior indication to any issues at all, thought it may be timing checked that and that was solid. The car had been driving perfectly and then all of a sudden...BAM pinging on acceleration at idle car shakes I am baffled.
Been putting in the same fuel from the same gas station as well
Any suggestions

 

[84cutlass383]

had the same problem when i had my 355, check the carb make sure u got the rite mix ratio first, if no luck which happened to me, i replaced my carb and tuned it.

 

[khan0165]

need more info...
what rpms is the pinging occuring? Under heavy acceleration, or normal? You checked the timing, what was it set at? At idle? At 3500rpm? Distributor clamped down good?
What kinda carb? Do you see fuel trickle into venturis when you rev the motor? Vacuum lines, check for vacuum leaks. Any pinging at idle? Is the idle smooth?

 

[gthmcty1]

need more info...


what rpms is the pinging occuring? Roughly at about 2000 RPM


Under heavy acceleration, or normal? Under moderate to heavy accel


You checked the timing, what was it set at? At idle?15 Degrees BTDC At 3500rpm? (Did not check that one

Distributor clamped down good? YES
What kinda carb? This is the stock 231 V6 with the 2 barrel carb

Do you see fuel trickle into venturis when you rev the motor? NO


Vacuum lines, check for vacuum leaks. Yes checked vacuum lines no leaks

Any pinging at idle? Is the idle smooth?

No ping at idle but the car does idle rough now

 

[pontiacgp]

sounds like something to do with your timing like the chain jumped....have you checked your timing with a gun yet?

 

[khan0165]

you should see some fuel squirt at the venturi's in the carb when you rev the engine. Check for cloggs in the fuel line, maybe at the filter.
..... it's idling rough, vacuum lines are good, ping at moderate acceleration, timing is good, I'm thinking it's fuel starvation. Same symptoms show up on my car when the fuel filter got clogged.

I don't know what kinda fuel system plumbing you have, but grab a small pressure gauge and a T-fitting, and check fuel pressure before the carb/after filter. I think you should see around 5 or 7psi? (not sure, hopefully someone can correct me if I'm wrong)

 

[Bonnewagon]

Check EGR valve, it won't cause the pinging, but the advanced timing used with EGR cars will causae detonation without the EGR diluting the mixture.

 

[gthmcty1]

you should see some fuel squirt at the venturi's in the carb when you rev the engine. Check for cloggs in the fuel line, maybe at the filter.
..... it's idling rough, vacuum lines are good, ping at moderate acceleration, timing is good, I'm thinking it's fuel starvation. Same symptoms show up on my car when the fuel filter got clogged.

I don't know what kinda fuel system plumbing you have, but grab a small pressure gauge and a T-fitting, and check fuel pressure before the carb/after filter. I think you should see around 5 or 7psi? (not sure, hopefully someone can correct me if I'm wrong)

Kahn appreciate the suggestions, I actually did see fuel squirt into the bowls when the engine was revved. Will check fuel filter as well pressure is correct just installed a new fuel pump on the car about 3 weeks ago.

 

[gthmcty1]

Check EGR valve, it won't cause the pinging, but the advanced timing used with EGR cars will causae detonation without the EGR diluting the mixture.

Can that be checked while still on the car? If so how?

Also would a clogged or defective EGR valve cause the SES light to trigger?

With the car in gear and my foot on the brake it sounds as if there is a "miss" and like I said it ran great up until yesterday and all of a sudden just started detonating.

 

[khan0165]

you're welcome,
I wish I knew anything about EGRs, lol, gonna have to keep an eye on this thread