I need to diagnose a problem on my Firebird. I'm trying an F-body forum but the responses so far recommend that I just replace parts. Typical GM eh. I'm going to try to avoid doing that. I have a Haynes manual but it's junk for trouble shooting. I would like to determine with reasonable certainty that it is good or bad.

It's an '88, computer controlled ignition. The distributor simply tells the computer where the crank and cam and so on is. No advance mechanisms. It's an external coil setup.



Yep. As soon as I fix one problem, another comes up. To be fair, though, I haven't had to do much to it in 42000 miles. And at 132000, a module going out will be nothing to complain about.


Lawrenceville, GA

I don't know enough about later model GMs to help and the guy I need to talk to isn't at work today. If nobody chimes in by monday, I'll get you some info monday AM when he shows up.

Dan      Kingman Az.      86409

That will help 'cause I'm having no luck with the Firebird people. Here are more complete details about the car. It's a 1988, 5.0 (305), Throttle Body Injected. It's an external coil ignition (as opposed to the in-cap hei).


Lawrenceville, GA

HEI module turns inductive signal from dizzy to +5V or +12V signal.

ECM calculates ignition advance from engine vacuum and RPM and sends it to coil.

Thats how they usually works.



So you put LED lamp to HEI module output and start engine, if LED blinks, HEI module and inductive sensor is fine.

Put LED to coil end, you know is ECM fine.



I dont know is this helping you but I cannot say much without the wiring diagram.



BTW. LED tester is awesome tool for solving out the ignition problems

http://www.megamanual.com/v22manual/ledtester.gif


Hyvinkää, FI

Well, the problem is that it won't start. But I could use the LED trick while cranking. I don't have a wiring diagram for it either. My Haynes manual has a diagram for TPI (tuned port injection) cars but not TBI cars.

The problem is that there is no spark and no fuel. My theory is that something in with the ignition is bad. Since the computer isn't seeing any signal from the ignition, it doesn't know when to tell the injectors to spray.

You know what, I need to find out if tpi uses the same distributor as tbi. If it does then I can use the diagram I have.


Lawrenceville, GA

Charlie,



I don't have any GM experience but I think the old TBI stuff uses a crankshaft position sensor. If you have fuel pressure but no injector pulse or spark, that may be where to look. I would look around the web for a F-Body forum and get some info there. Probably many sources that could get you on the right track quickly. There are diagnostic trouble shooting procedures to determine the fault but are contained in shop manuals from GM or places like AllData. Usually, these tests require a digital volt/ohm meter to diagnose. These step by step tests determine what system isn't working, then tests all the electrical circuitry to the components in question. If the wiring checks out, then a test/or replacement of a component is next. Haynes doesn't get into that stuff. Chilton makes a set of manuals for shops that contain computer ignition diagnostics. If you Google your no start problem on the particular vehicle and engine you most likely will come up with something.



Mark


57 Black Tbird 312/auto

On this, the distributor is the position sensor.



I'm trying an F body forum. So far nothing useful other than a list of parts to replace has come up, despite my repeated requests for information about how to trouble shoot it - not which parts I should replace.


Lawrenceville, GA

Charlie,



Keep trying the F-Body forums as like other forums dealer techs tend to hang out there also. Use their search functions also. Doing all the required step by step tests with the right diagnostic tools carefully, not skipping one or acting on a hunch is why the competent techs these days get paid the big bucks. It takes patience and consistency. I Googled "88 firebird tbi no spark diagnosis" and came up with lots of specific stuff to look at. That may get you where you need to be.



Mark

57 Black Tbird 312/auto

Believe me, I've searched the internet for testing procedures. If it's out there, I can't find it. Perhaps I'll try another F-body forum.


Lawrenceville, GA

Charlie,



I think you could at least come up with a wiring diagram that would show the circuits, relays, and fuses. You could do some simple checking with that. On the Ford distributors from that era we all kept a throw-away distributor with a good TFI module and stator in our toolboxes. If the problem you have came up, we would unplug the module wiring connector from the vehicle and plug it in to the dummy distributor. Then ground the distributor body to the engine block with jumper wire/alligator clips, turn the ignition to "On" and turn the dummy distributor by hand. If the injectors "clicked" and spark would jump from the coil wire which was disconnected a placed near an acceptable grounding surface, the problem was the TFI module and/or stator. I would always replace both as a rule. I don't think the GM stuff was quite that simple but don't know for sure. If you could locate/borrow/cannibalize another dist. for a test, that would narrow it down for you. BTW, if you do this, and your car is a manual transmission make sure it is out of gear, if the spark somehow gets through the cap to the plugs, it will fire a few times and move the car, usually right on top of your foot.



Mark

57 Black Tbird 312/auto