Suburban 2500 Pinging

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....

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

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

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.

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.......

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?

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....

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..

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...

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 ?????????

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 ???

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??

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...???

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

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.

The EGR's purpose is not to reduce ping it is to reduce NOx. EGR is solely an emissions part.

Some cars that have a barely adequate cooling system (or partially blocked radiator) can overheat if the EGR is inop. It's not 100% for emissions 100% of the time.

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.

I already replace the knock sensor, tapped the block and the snapon diags saw the knock, so I suspect its working correctly... I check the distributor do you know where the module is supposed to be pointed for cyl 1 at top dead center?
I know the rotor should point to number one...

thanks

The module turns!?... That doesn't seem right... you may have found your problem. Only the shaft and rotor should turn.

The module turns!?... That doesn't seem right... you may have found your problem. Only the shaft and rotor should turn.

no it doesnt turn by it self, just meaning I want to check the timing via the distributor, as to relation to the rotor pointing to #1 and where the distributor should be facing with the timing correct...
example....

if timing is correct the rotor pointing at #1 with #1 at TDC and the distributor module facing towards the firewall etc... I know on older cars the vac module had to face a certian way than the rotor lined up...something like that...
weather here has been bad outside no garage, so I havent checked the shaft play, figured I would pull the distributor when I pull it to get everything line up...

-Jason

Some cars that have a barely adequate cooling system (or partially blocked radiator) can overheat if the EGR is inop. It's not 100% for emissions 100% of the time.

car isnt overheating via temp guage and snapon scan tool...

car isnt overheating via temp guage and snapon scan tool...

your intake manifold egr port is plugged........

egr not plugged, pulled the distributor out and found the shaft was extreamly hard to turn orderd a msd 8366, so maybe thats the problem or at least one other resolved...we'll see. tonight...

Changed the Dist out, pings worse, but going to check timing again with degree wheel....

Changed the Dist out, pings worse, but going to check timing again with degree wheel....

because you replaced the distributor with a good one it now can advance the timing... this causes more pre-ignition......if your engine will run with EGR removed from engine and the EGR ports are open your intake is plugged..

because you replaced the distributor with a good one it now can advance the timing... this causes more pre-ignition......if your engine will run with EGR removed from engine and the EGR ports are open your intake is plugged..

ok rechecked timing all good at 4 deg btdc which is what the manual and emissions tag say.
egr open??? talking capped or just off all together?? I reinstalled egr (took cap out) ran fine no pinging... now warmed up it went from open loop to closed loop per snap on scanner it ran like shit again... pings but not as bad..
when in open loop all was perfect.. throttle response.. idle all great, than it hit...closed loop, stumbles pinging....etc... the meters shows timing is advancing and retarding as it should... it does show on scanner its at 23 degrees advanced but i imagine that total timing not number 1...

Thanks to all for the help and patiance ... this thing is going to get the best of me and my pocket book, I have tried the dealer..they wont touch it because of the performance mods... and the tiny shops here have no ideal...
any way I can force it to stay in " open loop" ?????

-Jason

Forcing it to stay in open loop is not the answer. Your emissions and fuel economy will not be good if you stay in open loop.

When it went into closed loop, what was BLM and INT values? This will tell you if it is running lean or rich. Also what was the MAP reading?

//2000CAYukon

ok rechecked timing all good at 4 deg btdc which is what the manual and emissions tag say.
egr open??? talking capped or just off all together?? I reinstalled egr (took cap out) ran fine no pinging... now warmed up it went from open loop to closed loop per snap on scanner it ran like shit again... pings but not as bad..
when in open loop all was perfect.. throttle response.. idle all great, than it hit...closed loop, stumbles pinging....etc... the meters shows timing is advancing and retarding as it should... it does show on scanner its at 23 degrees advanced but i imagine that total timing not number 1...

Thanks to all for the help and patiance ... this thing is going to get the best of me and my pocket book, I have tried the dealer..they wont touch it because of the performance mods... and the tiny shops here have no ideal...
any way I can force it to stay in " open loop" ?????

-Jason



when i say remove the egr i mean expose the egr holes/ports one is exhaust when engine is runnig exhaust should come out the other is intake port this is the one i believe to be plugged if engine runs with this port open/uncovered then you have to clean this passageway out....this is how exhaust gases are shuttled to engine combustion chambers to reduce pinging.....

Forcing it to stay in open loop is not the answer. Your emissions and fuel economy will not be good if you stay in open loop.

When it went into closed loop, what was BLM and INT values? This will tell you if it is running lean or rich. Also what was the MAP reading?

//2000CAYukon
BLM INT ??? Map cold hot???

Map cold not started 4.30v 90Kpa
cold just started ideling 1.58v 39Kpa
warm 2000 rpm driving 1.72v 41Kpa

BLM INT ??? Map cold hot???

Map cold not started 4.30v 90Kpa
cold just started ideling 1.58v 39Kpa
warm 2000 rpm driving 1.72v 41Kpa

BLM - Block Learn
INT - Integrator

These are basically long term and short term fuel trims.

See http://www.customefis.com/GMEFI.html

What does you scanner show for fuel trims?

//2000CAYukon

BLM - Block Learn
INT - Integrator

These are basically long term and short term fuel trims.

See http://www.customefis.com/GMEFI.html

What does you scanner show for fuel trims?

//2000CAYukon

I have:

cold no start trim cell - 16
cold running idle - lt trim - 122
warm running 2000 rpm - 118

i'll check more stats tonight

BLM INT ??? Map cold hot???

Map cold not started 4.30v 90Kpa
cold just started ideling 1.58v 39Kpa
warm 2000 rpm driving 1.72v 41Kpa

those readings look normal...

well, it seams the stats are normal but things are still a miss, so far what I have dont is retard the timing 16 degrees btdc, seams who ever put the cam in set it advanced... still pings very little but it not fighting the computer to retard since the computer could on retard 8 degrees max....

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.

I put a new msd stock repacement dist. 8633 i think is the num and a new knock sensor..
still the same thing

I put a new msd stock repacement dist. 8633 i think is the num and a new knock sensor..
still the same thing

I RE-READ your original posting...
with the 4 inch exhaust with little to none back pressure ,,,it would be hard to get any egr to shuttle exhaust gases into the intake manifold..

perhaps using a hotter spark plug would eliminate this...