MTQuest Posted February 23, 2015 Report Share Posted February 23, 2015 (edited) So awhile back my vac advance went out. Start doing the horrible clackity clack on acceleration. Checked timing, was right on the money. Good vacuum source coming from the first of the three vac ports on the TB. So off to the parts store to buy a new vac advance pot. The noise was still there, if anything it was worse. Checked the timing while raising the idle until the noise started to come back and I noticed the timing was steadily advancing the timing as it saw more vacuum, and off the charts, Like 30-40 degrees ATDC. This was even before the noise which starts about 2000rpms. (I know that the knock sensor will cause it to retard) Not even 15 miles later (limping it home) it wiped out my cam. Full rebuild time. Rebuild completed. The noise came back with my new cams after the cam break in procedure. Decided before I took it out, I would try disconnecting and plugging the vac advance. PROBLEM SOLVED. So the question is then, was I sold a vacuum retard pot instead of the vacuum advance pot, or a faulty one? Is it even possible to install the vac pot wrong, seems pretty dumby proof. Distributer is fairly new, and the throws move freely. Any help would be much appreciated ! Edited February 23, 2015 by MTQuest Link to comment Share on other sites More sharing options...
MTQuest Posted February 23, 2015 Author Report Share Posted February 23, 2015 To my understanding the vacuum advance on our vehicles is supposed to retard timing under boost. Doesn't make much sense to call it a vacuum advance but it seems that mine is doing the opposite of what it should. Advancing under vacuum not retarding. If my previous statement doesn't make any sense. Link to comment Share on other sites More sharing options...
TexasQuest Posted February 23, 2015 Report Share Posted February 23, 2015 Yeah it should be vacuum retard if anything lol. Maybe you got one for a non-turbo engine if that's possible? Link to comment Share on other sites More sharing options...
MTQuest Posted February 23, 2015 Author Report Share Posted February 23, 2015 I gave them my info, but it was 'BautoZone. Everything matches up way to closely if it is possible lol. Link to comment Share on other sites More sharing options...
TexasQuest Posted February 23, 2015 Report Share Posted February 23, 2015 I got the one from Rockauto.com. It's the right one for sure. Link to comment Share on other sites More sharing options...
mikec Posted February 24, 2015 Report Share Posted February 24, 2015 Easy enough to test... with the engine warmed up and idling:1: check ignition timing... it should be 10 deg BTDC (to the left of the "T" mark as you face the front of the engine) assuming you're not at high altitude; around 15 deg BTDC if you are at a higher altitude. 2: unplug the vac hose going to the distributor advancer mechanism. There should be no vacuum on the hose at idle if the hoses are properly connected at the throttle body and if your throttle plate is in the normal position for idle. Plug the hose and leave the distributor vacuum advancer port open to the atmosphere. Verify the timing is identical to what you saw in step #1. 3: Hook a fresh/clean hose to the advancer nipple. Apply vacuum to the hose while watching timing - use a hand vacuum pump (Mity Vac type of tool) or just suck on the hose. The timing should move to more advanced - i.e. even more to the left of the "T" - if the advancer is correct and installed to the distributor properly. The correct setup should have:* no vacuum at idle* vacuum at part-throttle "steady cruise" type of engine loads - i.e. low horsepower conditions or even revved up in neutral in the driveway. Timing should advance in this condition.* under boost pressure the distributor should see boost pressure and retard the timing. This happens only with higher throttle openings when the engine is under load - you can't get boost in the driveway... gotta be on the road accelerating or running up a hill. The only way I could see a "vacuum retard" function is if you have the vac hose hooked to the wrong port at the throttle body - i.e. to a port that sees manifold vacuum even at idle. You would have adjusted your distributor position to set timing to 10 deg with all this vacuum advance... under normal driving loads or even moderate throttle opening there is less manifold vacuum... ergo less vacuum at the advancer so the timing appears to retard as the throttle opens & RPMs build. A proper hose setup will have NO vacuum at the distributor when the engine is idling... removing the advancer hose should NOT alter timing nor change idle RPMs. miike c. 1 Link to comment Share on other sites More sharing options...
BandY Posted February 24, 2015 Report Share Posted February 24, 2015 This all sounds lovely, although some of us aren't completely savvy with this stuff. This is beyond Sonny and Cher. Is it weird that while the engine is running, I can move the distributor about 45 degrees without any change in behavior? I can move it completely one way or the other, and not get a change in timing. What the heck. Call me an idiot, so I can delete these posts. I am SO thinking of a V-8 swap. Damnit. Link to comment Share on other sites More sharing options...
MTQuest Posted February 24, 2015 Author Report Share Posted February 24, 2015 Thanks for the simple break down MikeC. Didn't even think to try and manually pull the vaccume down. That's what ill try out today. All most positive I was sold a defective part. I am correct in saying that the vac port closest to the front of the engine in the row of three is the correct port for the advance pot right? Ive went through and deleted all vac lines except for the advance, aftermarket BOV, and Vac storage can for the heater controls. Link to comment Share on other sites More sharing options...
MTQuest Posted February 24, 2015 Author Report Share Posted February 24, 2015 (edited) I'm sure some one else will pipe in for your concern BandY but while I'm on here... The vac advance has a little arm, that very brittle, possible that it fell off/broke off inside of the distributer and there for is not pulling on the distributer throws. Or, I've heard of the distributer throws/arms/weights, the moving parts that let the distributer advance or retard, , get gunked up and will not move freely when placed under vacuum. Edited February 24, 2015 by MTQuest Link to comment Share on other sites More sharing options...
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