Suburban 2500 Pinging

[rockrdr]

I have a 1994 Sub when the wire is disconected from the timing (the gry/blk wire) truck run ok, but when it reconnect it it pings bad under a load.
I did set the timing to 4 deg btdc, and when looking with a timing light
the timing retards insted of advancing...

any thoughts....

[j cAT]

Originally Posted by rockrdr

I have a 1994 Sub when the wire is disconected from the timing (the gry/blk wire) truck run ok, but when it reconnect it it pings bad under a load.
I did set the timing to 4 deg btdc, and when looking with a timing light
the timing retards insted of advancing...

any thoughts....

no egr operation . pinging will cause timing to retard

[rockrdr]

Pinging doesn't happen when idling. Pings only under a load, not just sitting there. retarding is when I'm iding, i get the timing set, watch the dampener with the timing light, give it a little gas and it retards...shouldn't it advance..?

how do I check the egr

[J-Ri]

The way I remember it, the timing should be set to 0 degrees with the computer connector unhooked. It may be retarding the timing because you advanced it 4 degrees past where it should be.

To check the EGR (I can't remember which year they started using electronic solenoids, so this may all be useless), unhook the vacuum hose to it while idling. There should be no change in the idle. Using a vacuum pump, apply vacuum to the solenoid, the idle should go way down and possibly kill the engine if you pump it fast enough that the computer can't compensate in time. If it does, the EGR is flowing enough. Check for vacuum to the EGR valve. There should be none while idling. If there is vacuum, it's flowing when it shouldn't be.

Have you checked for carbon buildup in the cylinders? If there's enough, it raises the compression ratio. Going to a higher octane gasoline will temporarily aleviate the pinging, but it will come back and be worse, so clean it out if there's very much.

[j cAT]

Originally Posted by J-Ri

The way I remember it, the timing should be set to 0 degrees with the computer connector unhooked. It may be retarding the timing because you advanced it 4 degrees past where it should be.

To check the EGR (I can't remember which year they started using electronic solenoids, so this may all be useless), unhook the vacuum hose to it while idling. There should be no change in the idle. Using a vacuum pump, apply vacuum to the solenoid, the idle should go way down and possibly kill the engine if you pump it fast enough that the computer can't compensate in time. If it does, the EGR is flowing enough. Check for vacuum to the EGR valve. There should be none while idling. If there is vacuum, it's flowing when it shouldn't be.

Have you checked for carbon buildup in the cylinders? If there's enough, it raises the compression ratio. Going to a higher octane gasoline will temporarily aleviate the pinging, but it will come back and be worse, so clean it out if there's very much.

I agree that unless you have manual it is hard to say exactly what turns on egr.. is it pcm solenoid or temp controled vacuum? but any way no egr under load will cause pinging... too much egr stalling stumble . and as you also mentioned excessive carbon build up in combustion chamber this is the power killer.......

[J-Ri]

Originally Posted by j cAT

but any way no egr under load will cause pinging... too much egr stalling stumble.

Isn't it the other way around? You don't want EGR under load?

[j cAT]

Originally Posted by J-Ri

Isn't it the other way around? You don't want EGR under load?

what is the purpose of egr ? exhaust gases are sent into the intake this reduces the oxygen content by mixing a metered amount of no. this then reduces combustion temperatures this then reduces the premature ignition of the fuel.... also if this combustion chamber has carbon in it the size of the chamber is reduced this then causes the fuel to ignite before piston is in the proper power position...no no egr means a very hot combustion chamber....

[rockrdr]

I pulled the plugs and they were pretty clean, EGR might be the cause it does run hot. I did change out the PCM and the same thing. also I guess i should give some back ground on the engine, I bought it the way it is and i only know is what I put here....

454 jegs bottom end
edlebrock sq port alum heads
edlebrock shorty headers
edlebrock tpi to multi port injection, I also spoke to edlebrock and they sent me a new chip for that as well, just in case the chip was bad... really kwel of them I thought...
edlebrock mtpi manifold
4" single exhaust all the back with flow master muffler. no emissions in my area.
new aic motor, new knock sensor.
1994 K2500 Surburban

also when cold in open loop (i think) it runs great no pinging than when it switches to closed loop ( I may have this switched) it get the pinging back
this is all with the timing wire dissconnected it ping it self to death if its pluged in (hot)

I dont know if any of this has relevance but I figured i should give all the info
the timing in the manual and on emissions lable says 4 degrees BTDC.

I'll check the EGR this weekend and see what happens..

[rockrdr]

Ok, I blocked off the egr this weekend, same thing ping from mid throttle to WOT.
Oh I have changed plugs, wires, cap rotor.
stumped.....
and it is a electronic egr, with a egr silonoid...

[j cAT]

Originally Posted by rockrdr

Ok, I blocked off the egr this weekend, same thing ping from mid throttle to WOT.
Oh I have changed plugs, wires, cap rotor.
stumped.....
and it is a electronic egr, with a egr silonoid...

no egr means if egr is plugged , disconnected , egr ports full of carbon, electrical connections removed , broken ,,this all will cause pinging.......blocking off EGR will cause pinging so because you did this and it did not change symptoms I would say you are in the correct area...question is why ????????? no EGR ?????????

[rockrdr]

Originally Posted by j cAT

no egr means if egr is plugged , disconnected , egr ports full of carbon, electrical connections removed , broken ,,this all will cause pinging.......blocking off EGR will cause pinging so because you did this and it did not change symptoms I would say you are in the correct area...question is why ????????? no EGR ?????????

Another thing I just reattached, egr on top of plug....egr still connected to wiring harness, should it be disconnected as well?? I'll try that on the way home from work....There was carbon in the egr... not allot, the plunger seamed like it was sealing... but its all electrical how do you test? EGR/Silonoid ???

[j cAT]

Originally Posted by rockrdr

Another thing I just reattached, egr on top of plug....egr still connected to wiring harness, should it be disconnected as well?? I'll try that on the way home from work....There was carbon in the egr... not allot, the plunger seamed like it was sealing... but its all electrical how do you test? EGR/Silonoid ???

clean out all carbon use coat hanger if necessary vacuum cleaner to suck out particles....on egr use wire brush also a pipe round wire brush to loosen carbon....then reinstall and see if pinging lessens or disappears......


once again if the egr cannot open and send exhaust gases to intake manifold the combustion chambers will get too hot and the engine will ping....understand??

[rockrdr]

the egr moves pretty freely, there is only two holes in it one has a plunger thats moves freely the other side is a 1/2 inch hole..

why does it not ping with the timing wire unplugged...???

[2000CAYukon]

Originally Posted by rockrdr

the egr moves pretty freely, there is only two holes in it one has a plunger thats moves freely the other side is a 1/2 inch hole..

why does it not ping with the timing wire unplugged...???

Because with the EST wire disconnected, the timing is not advanced at all by the ECM.

//2000CAYukon

[bndfishing]

Pull the distributor and see if everything is tight. Sometimes the pin that holds the gear in place will wear and cause really strange timing issues. If everything on the distributor is tight and not worn replace the knock sensor. The knock sensor senses ping creates an electrical signal that tells the PCM to retard timing. The EGR's purpose is not to reduce ping it is to reduce NOx. EGR is solely an emissions part.