Ha! You didn’t know there was going to be a part 3, did ya? Me neither. And what better day than today to post on the red, white, and blue ’Murlequin’s progress?
Somehow my truck’s surging/hunting idle went away for a moment, which after all that work seemed to have been caused by a mere vacuum leak. But the symptoms soon returned, and I decided to tear into the engine.
In the days leading up to this, I put some Sea Foam into the oil for cleaning, and started draining & refilling the cooling system with plain water on a daily basis to rinse it out.
A bunch of gaskets needed attention. There was soot on a couple of spark plugs, a tiny bit of oil pooling along the side of the intake, oil dripping down the front of the block, and a little water weeping from the water pump ports. Whether or not an intake or exhaust leak might be causing idle fluctuations, this was all stuff that needed to be done anyway. So I rounded up intake, exhaust, valve cover, and timing cover gaskets and started wrenching. Who knows, maybe I’d find answers as I dug deeper...
I started by pulling the water pump and timing cover, and found a sloppy timing chain, allowing about 6° of play between the crank and the camshaft. Fortunately, parts for a Chevy 350 are cheap, and for less than $30 I was able to get a nice double-roller set. It wouldn’t slide on right away, because the cam wasn’t in alignment. So I temporarily slid the old cam sprocket back on so that I could hook a flatbar to turn the cam just a little. Now that it was lined up, the new chain & sprockets slid into place, nice and TIGHT.
The snout of the crank damper was slightly grooved from its contact with the front seal, but the price of a whole new balancer was comparable to a “seal-saver” sleeve, so I just replaced it as a unit to go with the new front seal.
Now that the front was reassembled (with fresh gasketry), I tore into the top end. To my surprise, I found a massive EGR blockage:
Oddly, the heads did not have matching ports. I broke through the buildup anyway, without determining if the blockage affected a deeper junction inside the intake. Was that it? No way to tell from here, but cleaning that mess up was satisfying in its own way. I was able to confirm that the heads and intake were all the correct stock parts, so perhaps carbon was just harmlessly collecting in a dead corner...
Before installing the new valve cover gaskets, I scrubbed the sludgy buildup on the underside of the covers. Fortunately, the rockers did not look so nasty and did not need such attention.
I adjusted the valves before putting the covers back on, and reinstalled the intake with its new gaskets. Next, I unbolted the exhaust manifolds, and cleaned up all the bolts before putting them back in with fresh gaskets. I torqued everything to spec, and refilled the cooling system. Before refilling the oil, I changed the filter; might as well make this a complete oil change.
I set the timing, and as excited as I was to test my work, a couple of other items needed my attention first. (But I’ll post about them later to keep this installment on-topic.) After addressing those items, I went for a test-drive.
The engine felt slightly “better” in a way that’s so hard to describe, it’s probably little more than a placebo. As for the idle? To my dismay, it was still surging at idle, and had lost none of its tendency to stall while waiting at stoplights.
During my trips to the parts store, I often spoke with one of the guys at the counter who was having a similar idling problem on his Chevy truck (same year, same engine). I shared my progress, and he shared his.
Soon after doing all this work on my truck, his latest attempt resulted in an overwhelming victory. What did he do? He replaced his distributor. AGAIN.
He had already done so earlier (as had I), but the difference was that this new one was a Delphi unit. Before that, he (and I) were both using store-brand (Carquest) distributors. We both assumed that they were high-quality replacements, partly on account of the lifetime warranty that came with the product. But when I ran the number on the housing to try to identify the real manufacturer, it led me to a company called “WAI Global”. A visit to their website revealed that they had “acquired Dorman Products ignition distributor division” just a few years ago.
Tearing out that Dorman unit (which was passing the shop manual’s tests) and replacing it with a Delphi had solved all his truck’s idle problems. Though my new distributor was testing OK, I did what I told myself I wasn’t going to do: I “threw parts at the problem”, ordering a Delphi unit to see if that would work for me too.
It did. And it does. The idle is SMOOTH. The timing is STEADY (with the old distributor it had a habit of wavering a few degrees when setting the timing, even with the advance circuit disconnected). It finally stopped surging, hunting, and stalling.
OEM parts FTW.