89 Suburban timing issue

[Clark20ry]

Alright I am at my wits end. I have an 89 GMC Suburban 5.7 K motor with the TBI. Simple truck with a pain in the butt issue. The motor is about a year old and was running ok for a about a year. We started having a sputtering issue. I did a little research and a common issue with this motor is P/U coil in the distributor. I changed that out and seemed to make the truck run better. Here is the problem, these motors have an electronic spark control not vacuum advance. So to time the motor you unplug the Timing Control Wire set the timing and then re-connect the timing control wire. The truck runs great with the wire disconnected almost to good except the timing is all the way advanced so I get a real bad ping/knock under load. If I plug the wire back in the truck runs rough barely idles and dies when you put it in gear. It will stay running with some convincing, but still knocks/pings under load. I don't have any codes. I will put a list of what has been replaced. I am about ready to set it on fire... I love this truck yes its a gasser but its a great Suburban.

New Pick up coil
New Distributor w/module
New coil
New Spark control module

I have checked the fuel pressure and its good. Its timed correctly. I am just not sure and I have had it a garage for week and it stumped the mechanics there.

Any help would be appreciated.

 

[THEFERMANATOR]

Something doesn't sound right here as unplugging the timing wire puts the timing in full retard mode at 0 degrees. When you plug it back in the timing should go back up to around 10-18 BTDC at idle. ECM's do go out in these evry once in awhile as well as coolant temp sensor circuit problems. When you say spark control module, are you talking about the knock module mounted to the intake? Are you sure you put the correct one back on it? Normally the knock module will throw codes for timing circuit. From the sound of things, first thing I would do is take the #1 plug out and make sure the timing marks are correct. With the age of teh truck there is a VERY good chance the balancer may have spun and is throwing your timing off when you do the base timing. And you are setting it to 0 degrees when you do the base timing correct?

 

[Clark20ry]

Yes the timing is set to 0. The spark control module is located on the Manifold and I have read several articles on it I have changed it with 2 units and still the same. As soon as I connect the timing control wire the truck runs like crap and still knocks... I have run the truck with and without the Knock sensor plugged in to see if its getting a false reading with no change. I have no codes. The only thing left is the ECM I just don't want to throw another $100 at it guessing.

 

[WarWagon]

Any codes in the computer? What does the timing 'jump to' when you plug the wire in as observed by the timing light? Did the shop use a scope and check for a sloppy timing chain? How about the EGR as they can cause the sputtering issue just off idle. Back pressure valve fails in them and they go wide open nearly killing the engine rather than opening with exhaust pressure. Watch the valve, have someone drop it in drive and give it a little gas. If the EGR valve slams wide open and the engine starts to run bad - you have a bad EGR. Just off idle gives the EGR a vac signal to work and the exhaust pressure valve takes over from there. They fail intermittently going weeks working well than run bad all of a sudden.

When you time the engine by ear with the wire disconnected where is the timing at? This will tell you if the balancer has slipped as suggested above. (You should have 10 - 18 BTDC as suggested above by ear.)

 

[Clark20ry]

Nope got it solved. I stopped at the garage to talk to the mechanic about the balancer being spun. He was thinking that the valves needed adjusting (which they do) causing the knock sensor to over adjust the engine. I said lets time it with a vacuum gauge, he ok lets just retard it first and see and we moved it a quarter inch and the truck has never run better... So off to get a new balancer...

Thanks for the help...

 

[WarWagon]

The 350, 5.7L engine has hydraulic self adjusting lifters. If she has a lifter tick it is may need the lifters replaced. Never had luck with valve adjustments as a new engine was needed, 4.3 V6...