pinging

1985 w/2.5 carb can't get to stop pinging. retarded the timing, richened the fuel mixture. Any suggestions?

Maybe time to decarbonize. Try GM Top Engine Cleaner (get it at GM dealers). Follow instructions, and it will clean a tremendous amount of crap out of your engine. This was the only way I found to stop the pinging on my 95 4.0. Be aware then when used this stuff will lay down a smoke cloud of prodigious proportions, so if you're in a neighborhood where people get fussy about this, try to do it at night or when your neighbors aren't home.

did you try and hit it with a timing light?
how responsive is it? is it sluggish? try and advance it some
is it right up to beat and has a possibly "slow" start after been running retartd is some. we need more info. but start there and let us know.

I have tried several cleaners, to no avail. I have retarded it some more and still the pinging. Does anyone know if the 2.5 should have alot of vaccum at the advance canister while at idle? I have put a timing gun to it and followed the repair manual to the T. When I put the vaccum line back on the advance canister it seems to advance way too far atleast it seems. Thanks in advance(no pun intended)

if you run it in base timming does it ping?

not sure what you mean base timing, but I have set it to factory 12btdc pings under load or under light throttle at hwy. speed.

buckwing0 said:

I have tried several cleaners, to no avail. I have retarded it some more and still the pinging. Does anyone know if the 2.5 should have alot of vacuum at the advance canister while at idle? I have put a timing gun to it and followed the repair manual to the T. When I put the vacuum line back on the advance canister it seems to advance way too far at least it seems. Thanks in advance(no pun intended)

Click to expand...

All engines have the same vacuum pressure, are you sure it's pinging and not Main bearings? Bad Main bearing tend to knock under load or acceleration the best way to describe the sound is it sounds like someone throwing a handful of marbles in a bath tub.

The line to the vacuum advance should not have vacuum at an idle...check your vacuum lines...something may be out of whack..My XJ is also an 85 model...when it was stock it pinged like crazy too (stock compression ratio is 9.2 to 1)...it came down to running high test gas or pulling and capping the vacuum advance..and i reworked the mechanical advance to get back some of the lost advance...at higher rpm where I need it. Make sure the choke is fully opening once the engine warms up...rich engines detonate easier. And don't lug that little buzzer...they do not like to be lugged...

First, the feedback carb on these thing sucks! Next, there is a knock sensor (unplugged or gone bad) that controlls timing no matter where you put the dist. (you can adjust it a little, but not much as the computer over rides it)
What plugs are you running? I decarburize with water trickled down the carb. Obviously, the EGR valve isn't working. (mine went out and I bought a replacement EGR that I didn't use, then found I a new knock sensor and colder plugs that got me by till I sold it 50,000 miles later)