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Northstar removal at wrecking yard Update


jfreezn

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<<I am about to pull a Northstar at the local pick and pull, $99 complete with accessories, and I have a 50% off coupon. I have a choice of a 93 STS or a 94 ETC, both had the Z rated tire option so should be the high horsepower units. >>

Well, that was two months ago. I took the 94 engine. I welded up a test stand and bolted the stand to the slab of my RV pad/basket ball court. (I figured if I reved it up it might want to precess to an inverted position)

A compression test yielded wonderful figures from 195 to 210 PSI, with no oil added to the cylinders. The oil pressure came up to near 50PSI just cranking the thing!

Here's what I found.

The nose on the starter was broken off. I got the 93's starter before I left the yard.

One fuel injector was free flowing whenever fuel pressure was applied. I got a free replacement because I took it back within the 30 day warranty period.

The coolant system showed signs of overheating, the thermostat rubber was peeling out and the air bleed line was clogged. (I drilled that hole clear and was tempted to make it bigger but figured the engineers had already sized it correctly).

Since I had the intake off, I cleaned all the EGR passages and removed the rodent's nest from the starter valley area.

My guess is the PO was tired of the fuel smell and the overheating, and when the starter broke, he gave up and donated it to charity. The rest of the car was pretty straight but the interior was pretty sad.

I had the complete wiring harness so I cleaned it up, adding lots of silicone to restore some of it's flexibility. I studied the shop manual to figure what signals, grounds and power were required to run the engine with the stock PCM. Plugged in the PCM and wired it up and it ran. Just barely though and the exhaust set fire to some small bushes near the edge of the slab. After a quick trip to get the garden hose, I found the leaky injector, mentioned above.

Note to self: wet down bushes before test firing engine again.

I was careful to bar the engine over before trying to start it again, as hydraulic lock from the excess fuel was very possible, and in fact, the engine did discharge some raw gas from the rear exhaust bank.

With all the errant fuel gone, the engine would not fire. Using carburetor cleaner, or starting fluid, the engine would fire, rev cleanly and then stop when the spray was stopped. The engine sounded great! I am sure the ignition portion is working fine, and think I have narrowed the problem to the fuel cut off signal that is controlled by the Passkey security system. For those following along in their shop manuals, this is the blue wire at A3 on the Passkey module, page 8A-133-0.

THE START of my question:

Here is my technical description of the Pass key function as I understand it. When the proper key is identified by Passkey (one of 15 resistor values) it will enable the fuel by creating a pulse width modulated signal, which will bring the PCM provided 5VDC down to about 2 1/2 volts. the troubleshooting tree just says to look for approximately 2 1/2 volts at A3 with the key inserted and on. It DOES NOT say to look at the signal with a scope. So I tried inserting a 5K pot in the circuit and setting the pot to get the 2/1/2 volts at the PCM. Didn't work! I tried several pot settings in 1/2 volt increments without success. I think the PCM is looking for the switching action of PWM.

A portion of the 5VDC is basically bled to ground by regulating the pulse width. Since I don't have a proper key for my $10 ignition switch, is there a cheap tunable electonic device which I can insert in the A3 circuit that will generate a switching action that will give me a chance. What you see above is about the extent of my electronic knowledge.

I have a Passkey module and I think I can use a pot to simulate the 15 different resistors, but I would prefer not to involve Passkey at all.

I know there are some listers who thrive on electronic puzzles, so give me your best shot.

Thanks for listening, I will try to attach a photo or maybe send it separately.

Jim in Phoenix

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Jim in Phoenix

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I would check the fuel pressure regulator. It will spew gas like a whale when it is bad. It is located under the beauty cover. Do not start the engine with the beauty cover off because it will run at full throttle. If you can just pressurize the system you can tell if it is bad. Just because it does not spew gas though, it still may be bad, so I would just plan on changing it out anyway. Only use GM pressure regulator because my experience with aftermarkets has not been good, only lasted a year. I put my old one back in and it has been working fine ever since. Good luck!

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I would check the fuel pressure regulator. It will spew gas like a whale when it is bad. It is located under the beauty cover. Do not start the engine with the beauty cover off because it will run at full throttle. If you can just pressurize the system you can tell if it is bad. Just because it does not spew gas though, it still may be bad, so I would just plan on changing it out anyway. Only use GM pressure regulator because my experience with aftermarkets has not been good, only lasted a year. I put my old one back in and it has been working fine ever since. Good luck!

Thanks, Paul,

I was able to lift the entire manifold enough to observe the 8 injectors, the manifold, and the pressure regulator. I replaced the leaking injector, as noted above, and no more leaks existed. I have a pressure tester installed in the fuel supply line, at the schrader valve, and pressure is about 44 PSI at cranking speed with some excess fuel returning to my temporary fuel tank. I believe the fuel pressure and regulation are good. I just need to get the proper signal to the PCM to turn on the fuel injection.

Anyone else care to venture an opinion?

Jim in Phoenix

Jim in Phoenix

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