Northstar stalls, bucks and snorts

[deansridge]

I have had several Eldorados over the years, but this is my first Northstar. I have very little experience with the modern systems, so I`m hoping this old dog can learn some new tricks! I bought this 94 with 120 thou on it pretty cheap. I was told that it needed some work, but the problems the guy described didn`t scare me, as I`m somewhat of a wrench. I knew it had an oil leak, and a local self-proclaimed expert told me that the Northstar was famous for cam cover seal leaks. Well, eighty bucks worth of seals on the top of the motor later, it still leaks. I have come to the conclusion after some research that I will most likely have to drop the whole thing out to seal up the motor. I`m afraid that is a little over my capacities here, so I`m hoping that I can live with the oil leak for a while. That remains to be seen, because I can`t trust the car enough to drive it anywhere.

After it warms up to 210 to 220 it intermittantly shuts down like the little gremlins under the hood are messing with the ignition switch. Going down the highway at speeds over 50mph are no problem so far. After I slow down in town it will shut down briefly, catch hold again, or die at a stop sign. I will not want start right back up again, but it has after some cranking and curse words, bucked and snorted out of everybodys way, and then it will smooth out again. I have the GM technical service manuals and a borrowed Tech I analyzer, but I`ll admit I`m more than a little overwhelmed. All the code history is extensive, but the only current code is the right front wheel speed sensor TO23. I replaced the fuel filter..no help. I am currently running down ground points and cleaning them. During this process, I`m hopefull the radio will start working too! On my pension, I can`t afford to throw hundred dollar bills at this old car, so I would really appreciate any tips or clues.

[Cadillac Jim]

You should begin by clearing all the codes and seeing what comes back. History codes are important, but if you have 90 days worth of codes in an old car it can be a problem to identify one particular problem. The thing to do with an old car is to do the obvious maintenance - oil change, fresh coolant, EBR clean-up if necessary, service the transmission, and check all the fuses and fix any obvious issues with the wiring.

Your driveability problem is basically a bad miss or near-stall. As you know, this is going to be either the spark or the fuel, but not both. Since teh whole engine seems to stall, the finger points to the fuel, and you have changed the fuel filter. Another item to look at is the FPR; you can pull the vacuum hose off of it and smell for gas to check that.

Another thing to do might be to shut it down, step out of the car, walk around and smell the exhaust when it cuts out. If it smells like gas, you have a problem with the ignition wiring. If it smells lean, check the fuel injectors or fuel pressure. If it smells like gas, check the FPR. If it smells like coolant...

[dmk9561]

Check the coil packs and the wiring going to them. Unplug each of the plugs and plug it back in to see if that creates a fresher connection. For reasons I still don't understand, bad coil packs never threw a code on my 95. I'm pretty sure that newer ones do get a code for that.

[BodybyFisher]

Connect a fuel pressure gage and tape it to the windshield and see what happens to the pressure when she quits, bad fuel pressure wont set a code

It can be the fuel pump, wiring or the fuel pump relay, if you see fuel pressure problems

[Cadillac Jim]

These aren't contradictory bits of advice. I suggest you inspect the FPR first because it's easy to check (and to change) and just might solve part or all of your problem. Then I would check the coils and wiring as davek suggests. Once the spark is checked out and repaired as appropriate, if you still have a problem, get a fuel pressure gauge and follow BodybyFisher's advice. That should do it.

[BodybyFisher]

We brainstorm here, I find brainstorming to be an effective method to diagnosing problems

We all see things that make us think, no codes, we think hmmm,

We have seen crank sensors do this, BUT.... 1) the engine usually starts right up, and 2) codes can be set

This problem 'seems' to be related to temp and speed based on the description, but this could be multiple problems like a balky ISC motor also

Jim is correct about the FPR, I think it is located IN the plenum in the 94, no?, it could be spewing fuel. Do you notice black smoke out of the exhaust?, do you smell fuel?

[deansridge]

To start with, I hope I`m replying in the correct manner. Any tips along those lines would also be thankfully received. I am glad to have the help here..I need it!

I have not had a lot of time to work on the old car, as I have so many irons in the fire right now, but I have done a few things as you all have suggested. I cleared all the codes and then the PO32 popped up again as history. That diagnostic sent me to PO71, and I quit at the point where I have to remove the intake manifold cover and connect a vacuum source to the MAP sensor. Will a bad MAP sensor cause my cut-out problem? I also tried the reconnection at the coil pac/ICM plugs, all four, no help there. I will try to acquire a fuel pressure tester to use in that area of the testing. Whenever the engine shuts down, I have not smelled gas, nor have I seen any smoke, but next time I will go back and take a sniff at a tail pipe. I guess next I will find the FPR (fuel pressure regulator. right?)and check it out. Oh, by the way, the car will stall as described after warm up sitting in the shop, so speed shouldn`t be a factor here. I have to resist the urge to not ask stupid questions...I know so little that I`m sure I will show my ignorance. That said, was that a type error, or does this car have a EBR (engine braking regulator)? Did you mean EGR? I`m easily confused, but I`m learning fast! I hope I have made some sense here, and again, thanks for the help fellas!

You should begin by clearing all the codes and seeing what comes back. History codes are important, but if you have 90 days worth of codes in an old car it can be a problem to identify one particular problem. The thing to do with an old car is to do the obvious maintenance - oil change, fresh coolant, EBR clean-up if necessary, service the transmission, and check all the fuses and fix any obvious issues with the wiring.

Your driveability problem is basically a bad miss or near-stall. As you know, this is going to be either the spark or the fuel, but not both. Since teh whole engine seems to stall, the finger points to the fuel, and you have changed the fuel filter. Another item to look at is the FPR; you can pull the vacuum hose off of it and smell for gas to check that.

Another thing to do might be to shut it down, step out of the car, walk around and smell the exhaust when it cuts out. If it smells like gas, you have a problem with the ignition wiring. If it smells lean, check the fuel injectors or fuel pressure. If it smells like gas, check the FPR. If it smells like coolant...

Check the coil packs and the wiring going to them. Unplug each of the plugs and plug it back in to see if that creates a fresher connection. For reasons I still don't understand, bad coil packs never threw a code on my 95. I'm pretty sure that newer ones do get a code for that.

Connect a fuel pressure gage and tape it to the windshield and see what happens to the pressure when she quits, bad fuel pressure wont set a code

It can be the fuel pump, wiring or the fuel pump relay, if you see fuel pressure problems

These aren't contradictory bits of advice. I suggest you inspect the FPR first because it's easy to check (and to change) and just might solve part or all of your problem. Then I would check the coils and wiring as davek suggests. Once the spark is checked out and repaired as appropriate, if you still have a problem, get a fuel pressure gauge and follow BodybyFisher's advice. That should do it.

We brainstorm here, I find brainstorming to be an effective method to diagnosing problems

We all see things that make us think, no codes, we think hmmm,

We have seen crank sensors do this, BUT.... 1) the engine usually starts right up, and 2) codes can be set

This problem 'seems' to be related to temp and speed based on the description, but this could be multiple problems like a balky ISC motor also

Jim is correct about the FPR, I think it is located IN the plenum in the 94, no?, it could be spewing fuel. Do you notice black smoke out of the exhaust?, do you smell fuel?

[CarlaValentine]

Yes, a bad MAP will cause cut out problems. I experienced that issue with my 94 eldo as well, and a new MAP cured it. Before you replace the MAP however, you should inspect the wiring in the harness that goes to it. Check for any worn or bare spots. A simple wiring problem such as that can cause the MAP codes to set. If you do see a bare spot you can wrap it in high temp electrical tape. MAKE SURE it is high temp though, as it gets really hot under there. The high temp tape is also oil resistant, and I'm sure you have noticed by now it's pretty oily under there. A new MAP sensor is roughly 60$, and is easy to replace. If you do replace it, be sure to put the rubber seal in the plug on the new one, as they don't always come with one.

If you haven't already checked for a leaky FPR, that is done simply by pulling the intake cover, turning the key to the ON position and seeing if gas comes out of the nipple on the FPR. If it does, then it's leaking. Be sure to NEVER start the car with that cover off, as the engine will rev uncontrollably.