"Popping"

Discuss with fans and owners of the most luxurious aircooled sedan/wagon that VW ever made, the VW 411/412. Official forum of Tom's Type 4 Corner.
rich2481
Posts: 1539
Joined: Tue Dec 18, 2001 12:01 am

\"Popping\"

Post by rich2481 »

I agree with Matt, sounds like the cylinders are leaking between the head,
dphdo
Posts: 59
Joined: Sun Mar 10, 2002 12:01 am

\"Popping\"

Post by dphdo »

Hi. 2 Questions: 1. I have a '74 wagon, AFC Fuel Inj. When I turn the key to the #1 posistion (run - not start), shouldn't the fuel pump run for about 2 seconds to pre-pressurize the system? Where is this controlled at? The double relay? the ECU?

#2 I am getting a "popping" sound out of cylinders 2 and 3. It's not a backfire, it's a LOUD popping noise. I have checked all the usual things: plugs, points, Valves, compression - all ore good. At idle, it appears that it is only running on 2 cylinders (1 & 4) as removing the plug wires from 2 & 3 had NO change in the idle. When I rev the engine a little, the other two cylinders kick in, but do that "Popping" noise. This is a recent rebuild to a TOTAL restoration. Any thoughts? BTW, I checked the injectors for spray while attempting to start the engine and they all sprayed equally and wonderful.
Bulley
Posts: 98
Joined: Thu Mar 21, 2002 12:01 am

\"Popping\"

Post by Bulley »

AFC doesn't pre-pressurize the fuel like the MPC, it stores the fuel pressure from previous run, and the initial air flow past the measuring vane triggers the pump.

AS for the "popping" I'm a bit concerned that the heads may be leaking at the cylinder top. Are you sure the compression is within specs and within 20psi difference on all cylinders?

------------------
Matthew
412@bulley-hewlett.com

Towns can't pave thier way to beauty, or drive their way to prosperity.
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