I have a 92 Chevy Silverado Z71 w/ a 5.7 automatic transmission. I've had a hard time getting it to time @ 0° TDC and still run. In fact it will either barely run or not run at all while @ TDC 0°! I disconnected the EST wire and also checked and made sure that at TDC that the distributor points at #1 and it is on the compression stroke. That all checks out. When I try to time it the proper way it won't run hardly at all. Can't seem to find the problem
The symptoms of rough idle, poor mpg, and spark knock can originate in a number of different areas that may require a qualified tech to diagnose properly. I would double check on the exhaust-gas recirculation-valve operation along with closely inspecting the knock sensor. The system should be gone over with a scan tool checking for trouble codes and proper sensor inputs to the electronic control module that manages the system.
Try to disconnect the knock sensor and see if it makes a difference.
Also Remove the distributor cap and slowly move the crankshaft counterclockwise until the distributor starts moving, then move the crankshaft slowly clockwise and observe the distributor until it starts moving, this will check the slack in the timing chain. You should only have just a few degrees if it registers more than 3 to 5 degrees then you may have a timing chain issue. When a timing chain is worn badly, it develops slack and becomes loose and could skip a tooth. When this happens, the engine's valves, are no longer in sync with the pistons, compression will be low and cause the engine to run poorly and you may have a difficult time setting the ignition timing.
Check that the timing mark on the damper is correct, sometimes the outer portion of the crank damper slips and the mark is in the incorrect position.
Another simple test is to do a compression test if compression is low on all cylinders then the timing chain would be an area of concern and should be looked into.
I thought that I would also add that I can set the timing by ear and the truck runs just fine at idle. However when I put it in gear and start to take off it coughs and backfires at times and has a loss of power. I've replaced the fuel pump and filter, replaced the cap, rotor, wires, and plugs. I've also replaced the ESC and cleaned the IAC as well as the temp sensor for the computer. Everything seems to check out except this problem with timing this thing!
Try the suggestions I gave you and get back to me when you can.
How many miles on the engine?
How did all this start? Truck sat for a long time, you were driving along and it started running bad, or this started after work was done?
Before I answer your questions here's a little more information.
I did check egr operation and it seems to be working ok. The compression is good on all cylinders and no cylinder is more than 20 lbs off from any of the other cylinders. I didn't check the dampener to close but if the dampener was bad I shouldn't be able to line everything up ie the timing mark at 0Â° TDC and the rotor at the#1 spark plug terminal and the piston on its compression stroke. The only thing I didn't check was the knock sensor. Correct me if I'm wrong but with the EST trigger wire disconnected it shouldn't do anything to affect the timing should it? Like I stated in my original post, I can set the timing by ear and when I reattach the EST wire it advances quite a bit. I don't have a timing light with a degree dial on it to find out exactly how much it's being advanced but it runs decent up until I start loading up the engine on heavily acceleration. Then it will cough and sputter. So I don't know quite what else to do. Any further help would be appreciated. PS I have bee
n working on cars and trucks many years but this one has got me stumped.
I bought this truck from a used car dealer that took it on trade-in. It had a very weak transmission but seemed to run ok otherwise. I rebuilt the 700r4 trans and after that I took it to a transmission shop for a check as I've never rebuilt an automatic transmission before then. Everything checked out ok with the trans and my son brought it home. It sat for about 6 months and then we moved it to my house but it seemed to have performance issues. That's when I gave it a full tune up including a new fuel pump which seemed to have helped but not to perfection. So here I am with the timing issue.
PS to answer another question the truck has 180k on the odometer
I brought the timing mark up to the 2nd point on the timing tab to the left of 0° TDC and had to turn the dampner approximately 2° past 0° TDC before the rotor moved. So as I understand it if you have to turn the crankshaft any more than 2-4 degrees you need to replace the timing chain!
If the problem started after the truck sat for a period of time I'd be looking closely at fuel pressure and quality. Take a gas sample to be sure it's clear and clean. There's also an easy method for checking for excessive alcohol. You'll need a gauge to test fuel pressure accurately.
You said you replaced the fuel pump so I'm assuming you also replaced the old can filter.
New pump won't help if the regulator in the throttle body is no good and bleeding pressure back to the tank. You can kink the return hose momentarily while it's running bad to see if that improves anything.
Also look closely inside the throttle body while the engine is running. You should have a fine umbrella shaped spray pattern coming out of both injectors. I sloppy pattern, and/or one different than the other may indicate obstructed injectors.
It's possible you could have a clogged catalytic converter. A quick way to check is to just remove the upstream oxygen sensor (the one in front of the cat converter) then drive the truck. Removing the sensor allows the back pressure to escape, if the truck runs better then you have a clogged catalytic converter.