Th John V's point, I have experienced the effects of installing bad new tune up parts............infuriating, but I assure you it is more than possible.......It happened to me once and drove me nuts. Per John V's suggestion, I swapped each part out with the old one till I found the culpret....
Good luck.

(grumbers to himself "lucky bas&^%d" for owning two GT cars)

 

Gretch not to pick on you BUT I will : ) ......Gretch "I will lose ignition in one of the cylinder banks. " the failure and protection is two cylinders on EACH bank . As I am sure you know the plug wires from each distributer 2 cross over to the other bank . The temp sensor monitors for 89 were on cylinders 4 and 8 1990 > they were moved to 3 and 7 for " better readings " . If number 1 cylinder were not firing ( loose plug wire ?) I seriously doubt that the temperature sensor near the back of the block would pick up on the "failure" . They were concerned with ignition failure which would shut down spark to 4 cylinders and that is what it detects .

 

Very interesting....

And guess what this '89 has on the number 1 cylinder?

Wait for it...

The injector connector spliced by the PO.

So - back to the top of the thread: what's the easiest way to figure out if all of the injectors are properly firing? My new-from-e-bay 'scope is on its way. Can I just hook the test leads to the connectors on each injector?

Are the injector pulses reasonably low voltage/current?

 

Dave ... check out search for " noid light " , a simple flashing light tester for injection pulse

 

Oh, I have no doubt that it is possible. And like I wrote, swapping old stuff back in goes on the list. But, so far, the car has only run better as new parts have been added. (i.e. it really ran badly when I bought it.)

Quote:

(grumbers to himself "lucky bas&^%d" for owning two GT cars)

All things in their proper perspective:

Right now I own maybe 0.95 GTs given the way this '89 runs and the fact that the t-belt on the '91 is currently exposed for the post-t-belt-R&R tensioning.

While you, Mr. Gretch, own - considering that you have a SuperShark- 1.4 GTs (at least)

 

Ah. Very good. Thanks Jim. I knew something like that must exist - just not the term of art!

I am collecting a lot of tools in this almost 7-year Zen and the Art of 928 Maintenance experience.

 

Jim, You know more than I ever will about these cars. Re your comment: "which would shut down spark to 4 cylinders", Without looking at the wiring, I assumed that meant 4 cylinders on the same bank, because (I thought) the idea was to avoid flooding a hot cat with raw fuel. What am I missing in the theory.

In any event I did not mean to convey more than what I know. What I know is that sometimes my car "feels like" it has dropped 4 cylinders. I incorrectly assumed it was 1 bank of 4.......

Always learning.......

 

D-

If you pierce the harness wire with the scope probe, you will get the signal which is being fed to the injector. Of course, if a connector were intermittant / high resistance / defective your symptoms would probably have changed several times, given the number of times you have disconnected them. Use some "Liquid Electrical Tape" to seal the pinholes.

Of course if you find one signal to be out of spec, you would be able to suspect your harness from that point back to the brain. If all injector signals were affected, you might suspect or the brain itself (or brain wiring, ground, etc.).

The signals won't electrocute you and you will find a suitable range on your scope, if that is what you are concerned about. Be careful not to accidentally short anything to ground...

 

Yup. That was the question. Hooking up spark plug wires to a scope would be a baaad thing. I figured though that the injector pulses - since they come straight from the ECU - would be fine for the scope.

Quote:

Be careful not to accidentally short anything to ground...

But then there are no fun stories to tell

Besides, haven't we all shorted something to ground once or twice in our lives? Surely you've put an IC in backwards once or twice and smelled the results? Or perhaps seen a four-inch long arc of static from your finger fry a multi-hundred-dollar chip as you were pointing out how cool it was? (Not me on that one ) Grabbed an electric cattle fence twice because the first time it was kinda cool? (Not me either...) But, from whence would all these stories come if ground didn't always win?

 

Not with the right probes. If that's out of range, put a couple of wraps of thin wire around the spark plug wire and hook your scope to that. Start on the highest vertical scale you can, and work your way down to a workable scale. Or, just put a timing light on any wire to see if it's getting spark.

 

Gretch,

The injectors are wired in two circuits just like the spark plugs -- 1, 4, 6, 7 on one; 2, 3, 5, 8 on the other (I think . . . off the top of my head). If the monitor on cylinder 8 (3 on later cars) is producing less voltage (because it is cooler) than that on cylinder 4 (7 on later cars), the 2-3-5-8 set of injectors will shut down, cutting off fuel (not spark) to those four cylinders. An elegant system, I think.

 

That's an elegant solution.

Quote:

Or, just put a timing light on any wire to see if it's getting spark.

That, however, is what I was planning on doing.

 

dave

i wonder why your idle is at the s4 level.

my gt idles at 800 warm give or take a few. may want to check the p/n on the computer to make sure it's not an s4.

glenn

 

That's a very good question - and if I may say so - indicates that you are paying careful attention.

I'm going to bet the answer is a simple brain fart on my part and that I typed the wrong number in the post on idle speed. I remember checking the idle speed months ago after everything was back together and the idle speed was where it should be according to the spec book. At the time the LH in the '89 was my spare for the '91, however the idle speed is the same and the '91 part number is correct.

I will re-check the warm idle speed once the '89 is back together after the hall sensor R&R. (I spent tonight doing the re-tension on the '91.)

 

Wait - before someone posts...

The proper LH for an '89GT is in the car now.

The behavior was the same with either LH.