5.7 L engine ping

i have a 1991 gmc sierra with a 350 ci [5.7L] engine a700 automatic trans, the problem i have is engine ping under load when warm & hot i have set timing at o degrees with timing connector unplugged and replaced detonation sensor and also checked function by tapping on block next to sensor and checking to see if it retards timing with timing light i have removed intake manifold to check for blockage and also checked and replaced EGR valve my O2 sensor is switching from 0-1 volts and i replaced o2 sensor also i must burn premium 91 octane fuel to help but does not eliminate problem does anybody have any ideal or cure for this problem THANK YOU VERY MUCH IN ADVANCE FOR ANY HELP or for taking time to read this

maybe a vacuum leak somewhere

checked al sources of vacum no leaks found engine runs smooth and idle is within specs

Hello
I have a 91 GMC Sierra as well with a 305 engine. My truck has spark knocked for some time untill I found I could wiggle my rotor button around when changing rotor and distributor cap.Too much play in worn shaft and housing causing eratic firing and thus KNOCK!! Once I replaced both the shaft and housing , no more noise. It will still knock with some batches of regular gas but never with supreme now.

i fergot to mention i did replace distributor complete+cap+rotor and no change

i fergot to mention i did replace distributor complete+cap+rotor and no change also replaced fuel pump and sock in tank and filter still pings. Has anyone heard injectors doing this??? i do have extended crank time on start also and eaven if i prime pump makes no difference on start up but if i bump starter 1-2 times helps crank time on start up

I myself have a 91 with a 5.7, I had a similar problem but as well had some severe flat spots through my rpm range, I checked my timing as well which seemed to be ok untill by accident my son hit the gas peddal while I was checking the timing yet once again and found that the mark bounced around like crazy, at well over 100.000 mi. my problem turned out to be timing chain slop.
I guess under load the chain would streach enough to throw my timing off from being set perfectly while checking it sitting in my driveway, this may or may not be your problem as well, I just know that once I got to the chain I was suprised the truck ran at all, it was so sloppy I could almost pull the chain off with the gears in place. $40.00 for a new double roller made a world of difference for my truck, I figured that since I already had things torn down as far as I did I might as well replace the cam as well.
which was another $ 80.00, now there is one less worry since I know my valve train is tight and new.
Hope this helps, good luck.

yes i did check amount of play in chain and from turning damper and checking when rotor moves there is 6 -7 degrees play and the truck has alot of power and no hesitations or flat spots i checked with alot of knowledgeable fellow techs and still no cure availlable

I own a 90 K1500 5.7 with the 700R4 and I bought it new. Are you sure that the harmonic balancer has not shifted? I had to replace mine because the rubber had deteriorated. You might try to see if you can get number 1 at TDC and make sure that the marks line up.

Also, have you tried to back off the timing to where the pinging stops? Move it 2 degrees at a time until the pinging stops and see how it runs.

//2000CAYukon

I
Also, have you tried to back off the timing to where the pinging stops? Move it 2 degrees at a time until the pinging stops and see how it runs.
//2000CAYukon


Can you really adjust the timing on the new trucks? I have a 98 Jimmy 5.7 I thought the computer took care of all that.

The computer will vary your timing with RPM but you still need to set it manually, usually at zero.(check in manual or on top of rad shroud) You must dis-connect a connector on the passenger side firewall first, before you adjust with timing light.Loosen distributor hold down bolt then turn cap each way untill mark lines up on damper on crankshaft. I too tried to retard timing when I had some pinging. It helped, but wasn't the answer till I replaced distributor housing and shaft.

Can you really adjust the timing on the new trucks? I have a 98 Jimmy 5.7 I thought the computer took care of all that.

The 87-95 TBI trucks do not require a scan tool to adjust the timing like the 96-99 Vortec engines. This post is for a 91 TBI 5.7.

This post is for a 91 TBI 5.7.


I know but I though I would ask anyway about the 98 while I was here :grinno:

well everything checked out good but the only thing i cannot check is if the damper has moved a few degrees unless i use a dail indicator. I do know if i back timing a couple of degrees it looses power enough so i think the damper is ok but never 100% sure unless i replace it or purchase a dial indicator
Thanks so much for all suggestions i was hopping i would capture the attention of a senior GM TECH that has encountered this and knows of hidden repairs as i am a senior Dodge tech and know there are things that only experience and hands on can solve these issues sometimes you cannot always go by the book if you know what i mean

Don't underestamate the shade tree gm tech, we have taught the factory boys a thing or two over the years, I have owned a gm of one sort or another since I was 16 yrs old, so for 25 years I have been under around, inside and out of many a gm motor, though some things have changed, "as i have found on my 91" the basics remain constant. untill just receintly 'because of health' reasons I have never let anyone touch my vehicals, and even though after heart surgery the heavier stuff lays me out for a couple of days after, I think I will go back to doing my own repairs since the last two repairs I went ahead and let a so called "tech" work on my truck they were not up to par and I had to end up repairing thier repairs, I found missing/broken bolts and nuts, etc. the last guy I let work on my truck removed my inner fender flaps, and when I went to pick up my truck I noticed they were missing, he played like he could not find them then went on to tell the service manager that I did not have any when I came in, I went over to the trash bin on a hunch and guess what,, there they were, I guess he did not feel like pulling the fasteners so he just ripped them off ripping through the attachment holes. the replacments are still on order but this is just an example of my experience with gm tech's in my area, not to mention that I just noticed today that he did not fully press the powersteering pully back on so now my belt has just started squeeling and is all chewed up on the ends.
anyhow seems you have covered all your base's and not found the problem, tough one, only other idea I could come up with is carbon build up around the top of the cylinder, I only remember this vaguely, many years ago a friend had an impalla he recieved from his grandmother, the thing would ping like crazy after all else he pulled the motor apart and found a ton of carbon around the top of the cylinders and after the thing warmed up the pistons would slap this and make a sound like a ping, he de-carbonized and the thing ran like a dream, probably far fetched in your case but just an example that since you have definatly checked al the reg items, far fretched may be the road to travel.
since you have checked your ignition system completely condition of hard parts would be he next step logicly in my book. check that your computer is giving proper advance under a load and on from there, fortunatly our trucks are far less computer controled than the newer years.
I wish you the best of luck, and must say that I have found some of the more knowledgable people on this board very helpfull, it's always nice to have a few extra brain cells working on a problem.

sorry if i offended you i never doubted any suggestions from anybody at all i just thought there might be a hidden cure or trick that someone has done in this situation you all know that there is always the exception to every rule and i think this is the one that requires this exception i have decarbonized with a motor vac decarbonizer several times but still the same i think it is only 2 or 3 cylinders pinging though as it doesn't sound like marbles in the engine but a distinct ping