HT 4.X base timing question

[Elwood]

Hi guys, I thought I’d start a new thread due to the new problem. As history, I’m working on an 85’ Eldorado that is supposed to have 86,000 original miles on the HT 4.1. I’ve been fighting a stumble off idle and loss of spark on the #4 & #8 cylinders, only at full operating temperature and only at ~1000 RPM (+-200). The problem was a wobbled out distributor housing so I put a junkyard distributor in it which cured that problem, but my “emissions tag” on the core support is gone and all my books refer to the instructions on that tag to set base timing. I winged it and set the timing just above where it was controlling at 10 degrees BTDC on #1. The car seems to have lost about 30% horse power and now is very difficult to start hot (turns over but coughs and stutters between extended “no fire” cranking until you hold the throttle wide open). As chronicled in my previous thread, everything in the ignition system has now been replaced. Can someone please explain how to properly index a replaced distributor in a 4.X gas motor?

[Sevillian273]

Engine #1 cyl at TDC on compression stroke. Drop in distributor and make sure rotor is pointing at #1 when dist body is seated all the way down. Then set timing to 10deg BTDC.

You may simply have the dist shaft one tooth off which would put your timing at something like 4 deg BTDC. You have to set it down with the rotor pointing slightly before the #1 plug. As you push down it will slowly rotate to #1. This is because the gear is helical in shape.

[carnut]

This is basic engine 101!! As Sevillian says bring #1 piston to top dead center, compression stroke. Confirm this with the timing tab on the front cover and the line on the crank pulley. Then drop in the distributor to anticipate the rotation of the drive gear to line up with #1 terminal inside the cap. Snug up the hold down bolt. Then start engine. On your car there is a green connector wire just behind the distributor close to the firewall. That green connector MUST be unplugged when base timing is set with the timing light. Unplugged, it disconnects the computer from advancing the timing at all. Set the timing to 12 degrees and tighten the bolt. The spec is 10 degrees but they run better at 12 degrees BTDC. You might want to just unplug this green connector first and confirm with the timing light where the timing is BEFORE pulling out the assembly. You might find that rotating the distributor to 12 degrees might cure this coughing as it cranks over.

[carnut]

I should mention that the crank pulley does not have a center retaining bolt to facilitate rotating the crank around to TDC. Cadillac puts a cork in the center!! Its easier to remove the upper fan shroud and use a breaker bar and a socket on one of the 3 bolts holding the pulley assembly on the crank dampner. If the upper shroud has never been off, then it is stapled to the lower shroud on the side flanges. Remove the staples with a large screwdriver. Upon reassembly simply drill 2 small holes on both flanges and secure with 2 metal self tapping screws.

[Sevillian273]

To make sure its on the compression stroke, use a peice of hose to blow into the spark plug hole. If you cant blow, its on the comp. stroke. I had them switched once on another vehicle and I blew up a turbo muffler. It looked like an EasyPop container! KAPOW!!

[Elwood]

Something "Green" on the back of the engine was the clue I needed. I hunted around and found a light purple with black stripe wire ducking out of, and then back into the main harnes with a bright green connector body, the only green thing back there other than the temp sensor wire connected to the left head. I unplugged that connector and timing dropped to ~3-4 ATDC so I cranked the distributor around to 12 BTDC and she now runs better than ever. Thanks again for all the help!! This is my first ECM car, but I figured there had to be something like that somewhere.