'88 Vulcan injector timing

ddan

New Member
Dec 26, 2018
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My '88 3.0 V6 has been acting like the injector timing is wrong. It will only run while the gas pedal is being pulsed. Any steady position of the throttle from idle on up will kill it.

So I made a test lamp to plug into the no. 1 injector connector. While cranking the engine over with the starter, the light blinks for each revolution. When I hit the gas pedal the light immediately glows until I back off. I thought this would happen. The computer ignores crank position during acceleration and opens all injectors simultaneously. This makes it possible to "meter" the fuel with my foot like an old nitro dragster waiting at the line.

I don't have a dual trace scope, so I decided to use the test light to see at what crank angle the injector turns on. I disconnected the coil primary; turned the key to "run"; and cranked the engine over with a wrench until the light blinked (feebly). I did this multiple times to verify a consistent result. It appears the injector fires just as the intake valve CLOSES? I verified this by removing the distributor cap to see where the rotor was pointing and by replacing the no. 1 spark plug with a compressed air adapter. When the light blinks the crank is roughly 180 from the spark timing mark on the chain cover. Compressed air is coming out the intake (filter snorkel removed), but if I turn the crank just a skosh the air is blocked. (I use less than 50psi and I can't turn it much further into the compression stroke with my little 3/8" drive wrench.)

Is the injector "close" angle fixed and the "open" variable? In other words: Does the injector always close with the intake valve, but opens earlier as more gas is needed? Sounds improbable to me. The number "1" is molded into the distributor cap and that is where my no. 1 plug wire is. The only way I know to change the timing of the injectors WITHOUT changing the spark timing is to move the plug wire positions and rotate the distributor the same amount.

Do any other engines use the same distributor cap, but different plug orientation? On my cap the no. 1 is halfway between the mounting screws. (No. 1 plug is passenger front.)

This problem started after replacing intake gaskets, cap, and rotor. Spark timing is perfect.
 
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ddan

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Dec 26, 2018
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Upon further review: My method for seeing injector timing is bogus. Since I am not turning the engine continuously the computer can't time it. I'll have to repeat the test by just watching the light and the rotor (cap off) while cranking with the starter.
 

ddan

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Dec 26, 2018
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Wisconsin
I recorded a video of the distributor looking straight down, cap off while cranking. The no. 1 injector test light is positioned next to the dist.

When viewing the video at less than half speed it is obvious that the no. 1 injector is firing during the power stroke of the no. 1 cylinder.

To make the injector fire during the intake stroke I would need to put the removable rotor piece on backwards, lift the distributor and rotate the rotor assembly 180. Can't do this. Rotor piece only goes on one way. Alternatively, I could lift the distributor, rotate rotor assembly 180, and rotate the plug connections 180. This would put plug wire no. 1 at the front of the distributor. The cap only goes on one way and the electrode marked "1" is at the rear.

I've heard of injectors timed to begin squirting during the exhaust stroke, but starting and finishing during the power stroke? How can this be?
 

ddan

New Member
Dec 26, 2018
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54
Wisconsin
I'm learning! This engine does not control 6 injectors independently. If you look at the engine control diagram you'll see there are 2 groups of 3 injectors. One side of the engine is one group.