Timing Problem

Hello,

I have an 88 Chevy 5.7 350 c1500 1/2 ton rear wheel drive truck with electronic fuel injection and a Throttle body injection. I have been working on restoring its youth and have run into a couple of problems. One main problem that I have is the timing. I disconnect the Electronic Spark Control wire to bypass the module, (to set initial timing) and time my truck to 0 degrees, but as soon as I plug back the ESC module wire back in, the timing, checked with my timing gun, goes to about 20-30 degrees before (counterclockwise on my vibration damper) 0 degrees. IS THIS NORMAL? or should it remain the same; at 0 degrees? (this is all done at idle speed in park) The strange thing is that the truck runs smooth for most of the time, only during hard acceleration I hear a fast tapping or clicking, but I'm not sure if it is preignition or if it is valve tarin or some other noise. My question is can any of the sensors relay bad information to the ECM and cause it to change the timing incorrectly? I have been assuming yes, and i have changed several sensors (speed sensor, throttle position sensor, EGR Valve and solenoid, the ESC module itself, idle air control valve, distributor, spark plugs and wires, coil, coolant temperature sensor, and even the computer itself) ( I have also changed the timing chain and gears a long time ago) I have not changed the coolant temperature SWITCH, the MAP sensor and the knock sensor, but I do not want to change these sensors without making sure they are faulty. How can I test these items. Before I changed the distributor (which was the first thing I did) the car would misfire like crazy, and my guess is that it could have damaged the knock sensor causing it to relay bad information; is this possible? There is no carbon in the engine as it has been thoroughly cleaned. I understand there are a lot of questions here, but I am sure somebody knows the answer to some of them....

Thank you,
Matthew

Matthew,
The timing won't be at 0 degrees with the bypass connected, but 20-30 degrees BTDC seems a little high to me. The noise under acceleration you describe sounds like timing knock or pinging to me. The ECM is supposed to retard the timing when the knock sensor senses pinging. Don't know if the distributor problem could have caused a problem in the knock sensor but I doubt it. If it is pinging you hear, it could be bad. My book says you can test the sensor by tapping the engine block with a metallic object (breaker bar?) with the engine running and the timing should retard. I've never tried this so I don't know if it works or how easy it would be to do. Good Luck, I hope you find the problem.
Rick

the tapping or clicking sound could be a loose rocker arm.
i tried the knock sensor test, that rpreston mentioned, and if the sensor is working good your engine will shudder a bit when you tap it.

Hello,

I have an 88 Chevy 5.7 350 c1500 1/2 ton rear wheel drive truck with electronic fuel injection and a Throttle body injection. I have been working on restoring its youth and have run into a couple of problems. One main problem that I have is the timing. I disconnect the Electronic Spark Control wire to bypass the module, (to set initial timing) and time my truck to 0 degrees, but as soon as I plug back the ESC module wire back in, the timing, checked with my timing gun, goes to about 20-30 degrees before (counterclockwise on my vibration damper) 0 degrees. IS THIS NORMAL? or should it remain the same; at 0 degrees? (this is all done at idle speed in park) The strange thing is that the truck runs smooth for most of the time, only during hard acceleration I hear a fast tapping or clicking, but I'm not sure if it is preignition or if it is valve tarin or some other noise. My question is can any of the sensors relay bad information to the ECM and cause it to change the timing incorrectly? I have been assuming yes, and i have changed several sensors (speed sensor, throttle position sensor, EGR Valve and solenoid, the ESC module itself, idle air control valve, distributor, spark plugs and wires, coil, coolant temperature sensor, and even the computer itself) ( I have also changed the timing chain and gears a long time ago) I have not changed the coolant temperature SWITCH, the MAP sensor and the knock sensor, but I do not want to change these sensors without making sure they are faulty. How can I test these items. Before I changed the distributor (which was the first thing I did) the car would misfire like crazy, and my guess is that it could have damaged the knock sensor causing it to relay bad information; is this possible? There is no carbon in the engine as it has been thoroughly cleaned. I understand there are a lot of questions here, but I am sure somebody knows the answer to some of them....

Thank you,
Matthew

Matt, the 20-30 deg. is normal for your year . I have the same year truck. the pinging is sparknock, cheap gas has effected mine that way. Also check your throttlebody base gasket, they are prone to suck in at the back passenger side ccausing it to run lean, without showing a code.
Will also cause a sparknock.
Hope this helps!
Roger

i have an 87 chevy p\u and i had the same prob w\the t\b gasket. i took care of it when i put my t\b spacer in.

According to the almighty Chiltons manual, Timeing should be 4 degrees BTDC. At Idle 700rpm.

I would change the knock sensor, this will cause a problem with the timing. If it is sensing a knock when there is not one it will chang the timing to make up for it.

According to my sticker, 88, it is 0'deg initial, when plugged backin on the bypass wire the computor takes over and mine goes up in the 20's.
My neighbors 89 says the same( 0 deg.) when plugged in his goes up also.
Keep us posted on what the cure is!

Ok, here's whats up... I checked with a chevy specialist; he did say that 20-30 degrees before (advance) TDC is normal, so I'm gonna go off of good faith and hope that he's right.

I've got a '93 C1500, 5.7L. Can anyone tell me what it should idle at in drive sitting still. Is 700 rpm in park correct?