The Mighty 258 > Fuel Systems.

Knock and Idle issues

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MIPS:
Over the summer I pulled the head and most of the front off my engine and replaced the timing chain and sprockets, oil seal, water pump, thermostat, lifters, plugs and swapped out the '82 head which turned out to be warped with a shop rebuilt head from an '84. No performance parts were added and both timing and idle adjustments were set to spec.

I've always had knock issues that developed when I dropped 2000 feet to visit people on the coast but that was otherwise it and completely understandable. Now the engine starts to knock really badly as soon as the computer satisfies its temperature sensors and the choke is completely open. Accelerate from a light? knock. Accelerate to pass on the highway? Knock. To me that sounds like it's running lean. The CeC tester doesn't find any faults and the choke adjustment is correct. I retarded my timing an additional three degrees to cut back on just how badly it was knocking when passing on the highway. Still does it but at least I can more gently accelerate without sounding like I'm nuking the cylinders.
Two new faults however have now developed. One is that once warm (CTO opens, coolant and air temp switches satisfy) the engine will occasionally develop a miss. Other times the curb idle drops WAY too low to the point the engine will throw the alternator light or just completely stall. What throws me completely off is that you can't reproduce it. Sometimes I can pull into a parking spot, put it into park and turn the lights off and it will do the above, other times it's a smooth idle. I checked to verify the EGR was working and not sticking open and it seemed fine. I'd buy another because those backpressure ones are a pain to test but someone just bought the last cheap Delco one off RockAuto.

The only really suspect things I can find is the two arms on the throttle are loose and a solenoid kick can get cancelled out by the play. The other is the throttle shaft is loose in the throttle body, so it probably needs to be sleeved.....but it's not loose enough that if I spray starter fluid on it the engine doesn't rev from a vacuum leak.....but it really feels like there's a massive vacuum leak somewhere because even putting your hand over the air horn doesn't stall the engine easily. Manifold vacuum is reading about 19 InHg. Carb was rebuilt about a year ago.

amcfool1:
check your power brake booster. could be a leak there. happened to me once. took forever to diagnose. good luck, gz

MIPS:
It's not a leak in the hose or grommet, at least. You pull that sucker off with the engine running and the catastrophic loss of vacuum stalls the car instantly.

I'm going to pull the carb tomorrow and verify I don't have either a plugged jet or a broken gasket somehow. I already have my other two spares out to make a few comparison checks.

AMC of Houston:
Did whoever rebuilt the carb perform the AMC idle bleed service letter??   Is to drill out the bottom of the idle bleed tubes to 0.032 (I always drill to 0.030 with no problems).  Makes a world of difference on the BBD idle issues.

Do that, and adjust everything to the AMC IS-12e service letter; and see how it does.

MIPS:
Me and the mechanic did not because we did not have the tools or resources to widen the orifice. Everything else however was cleaned and overhauled.

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