Vacuum advance

m4ff3w · #1 (**permalink**) 11-05-2009, 08:36 AM

My newly acquired '87 Gold has experienced her first hiccup.

It started with with hesitation and bucking when accelerating from a stop.

The vacuum advance is working intermittently. I moved the vacuum source from the throttle body to the nipple that goes to the charcoal cannister and it is much better.

Will it hurt having the vacuum source changed? Vacuum is MUCH stronger where I have it now.

My long term solution is for the distributor to disappear and use megaquirt+coilpacks for fuel and spark, but I need to get a trigger wheel on the crank first. That will probably be a few weeks out, at least.

m4ff3w · #2 (**permalink**) 11-05-2009, 12:48 PM

Dang, it is still intermittent. Pretty bad actually.

Travis_k · #3 (**permalink**) 11-05-2009, 01:52 PM

Check the small wire attached to the positive bettery cable, mine had a loose connection there and it had a similar effect, although only at higher rpm.

m4ff3w · #4 (**permalink**) 11-05-2009, 06:49 PM

Ok, it isn't the vacuum advance, it appears to be working correctly.

I spent some time outside to try to isolate the issue. I can't.

Vacuum will drop from 13" to 10" when it is acting funny. RPMs also drop down abit, to about 850. I'm unsure which causes which.

When it is acting weird, it backfires through the intake though.

hugnixfra · #5 (**permalink**) 11-05-2009, 07:41 PM

Quote:

Originally Posted by m4ff3w

Dang, it is still intermittent. Pretty bad actually.

Brendan_LS · #6 (**permalink**) 11-05-2009, 07:58 PM

hi,

You should not move the source of vacuum from the distributor advance, as its normal source is generally a 'ported' vacuum port, which acts to increase the vacuum gradually as the revs/load increases. Moving it may cause funny things to happen.

Also if your car has low vacuum and is backfiring though the intake manifold, the distributor may be off a tooth, sparking while the intake valve is open. This can (i think?) also be caused by (gulp) a slipped timing belt; you should verify the cam timing before proceeding.

regards

Travis_k · #7 (**permalink**) 11-05-2009, 08:46 PM

Quote:

Originally Posted by hugnixfra

I think this is enough .....
I do agree with you. Those are the most effective way

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**alfaparticle** · #8 (**permalink**) 11-06-2009, 04:49 AM

I would check that the vane in your AFM is moving freely. The vane can be distorted by a backfire and touch the housing in one or more places, and that really screws up the FI.