1989 GMC Sierra (S15) 4.3L v6
I’m trying to get the engine to last me until March. I have low compression in the #1 cylinder. I’m guessing it’s the rings but it’s hard to tell.
I did a compression check on all of the cylinders Sunday. To test I installed the compression gage and turned the engine for 4 seconds. This typically provided me with 2 full cycles of compression. The #1 cylinder came in at 65 on the first compression and 95 on the second with about a 2-3 second lag before falling back to around 65-70 and holding. All other cylinders came in 95 on the first and 115+ and hold on the second. Over the 2-3 seconds the drop in compression was negligible on cylinders 2-6.
I keep fouling plugs on the #1 cylinder. I have been running 20-50 but I am changing the oil back to 10-40 to hopefully allow the plug to function better and burn the oil completely. I’m also going to step up the plug heat 1 number and put a new anti fouling thingy on the plug. I’m hoping that this will keep the plug from fouling to often.
After changing the fouled plug I took it out on the freeway and ran it for about 10 miles. The smoking stopped after about 5 miles, but on a cold restart the plug was fouled again. I’m hoping the above changes and longer run (40+miles one way) will allow the cylinder to burn clean this time. On the way back from Charlotte to Columbia (maybe 1/2 to 3/4 of that distance one way) on a fouled plug I am sure has caused problems with the oil and possibly the valves. The oil has visibly thinned but did not burn (discoloration) appreciably. The power increase after changing the fouled plug is very good and there is little vibration coming from the engine.
Does anyone have any other thoughts. I know I need an ignition coil, but if I gotta get an engine, that’s first! Any other suggestions would be very greatly appreciated. Also any thoughts on whether this is a head or rings issue. The engine has 201k on it and has always smoked a little on firing up. Literaly just a puff of smoke and then it has run fine. Is it more likely I have a valve sticking open or some carbon on the valve seats? Hmm ?~? New heads would be a lot cheaper.