Let's see... When we last left off I had replaced the coil on the off chance that it would help the intermittent stumble the engine had. It also gave me a good spare for the future. The engine's symptoms were as follows: when it was warm, at low RPMs there was a stumble on acceleration but it ran fine at higher RPMs. When the engine was cold it ran great. In my mind there were two possibilities, mechanical and electrical. The engine computer never logged any error codes that would have been related to a failure on its part. I had made sure that the spark plug wires were routed better where they couldn't rub and had less likelihood of crosstalk. I had even begun to add extra insulation to critical system wires in case they were getting interference from their proximity to the spark plug wires themselves.
Then, while traipsing around on a Datsun related website I came across something that hadn't crossed my mind. The chap there was experiencing some coolant seeping out between the head and block. Wait.... the head gaskets on my Suburban! I had never bothered to re-torque them! Oh how silly, how simple. Wait, could it really be that simple? Was that why the engine was using more oil than seemed normal, despite its good compression numbers?
So I popped off the valve covers. Its actually not a very easy feat. The passenger side one absolutely does not come off unless the rearmost valve spring is in the compressed position. Otherwise there is not enough clearance between it and the firewall. I proceeded to tighten all of the head bolts to 80 ft-lbs in the sequence listed in my 1989 FSM. The ones on the driver's side turned further than the ones on the passenger side. On a trip to the grocery store and around town that night it seemed to be running better, but I figured a longer test drive was in order.
This past weekend we took a trip into the mountains to find some fall colors. Turns out it was a good thing we did it on Saturday, because this morning there is snow on that same mountain.
Tried to make a gif of the quaking aspens using multiple shots from my DSLR.
The Suburban ran just like it is 'supposed' to the whole time with nary a hint of stumble present anymore. I love it when my mechanical contraptions just plain ol' work right.