88 TBI injectors pulsing after motor dies

[Cadillacmak]

Mine also runs pretty constant (or so fast they naked eye can't see it). I am assuming the frame rate of the camera makes it appear to pulse at a lower rate. I did notice that when I took the video, but forgot to mention the camera caused this effect.

Aim your timing gun at the spray and it will give you a still picture(s) of the pattern. This really helps to spot drips or bad spray patterns.

 

[OLD BLUE 88]

Thanks! Nothing has ever been done to the TBI. I've pondered some type of modification to enhance performance and or effeciency once the restoration begins.

 

[14reamdalton]

Sometimes when 'power' electronics goes bad it will break into oscillation instead
of just suddenly quitting. I have a couple of questions:

Q1: Once the engine stalls and the injector(s) are still chattering, if you turn the
key from ON to OFF and back to ON again, will the chattering continue, or will
it cease?

Q2: Assuming that the chattering in Q1 continues across a power cycle, I would
be interested if you could do the following: Malfunction occurs, engine stops,
injectors still chattering, turn key to OFF, pull the plug to the ICM, turn the
key back ON, and then what happens? Our 2 choices would be:

* Chattering stops. Assumption that ICM was the one that broke into oscillation
and was sending spurious signals up to ECM.

* Chattering continues. Since there's no stimulus from the ICM, this would tell
me that the ECM is the component that is breaking into oscillation?

Disclaimer: The GMT400 in my driveway is a Vortec, which is different than a TBI setup. So
I'm having to rely purely upon the TBI section in the older FSMs for troubleshooting approaches.

But the more we learn about your failure before you replace a part the more info that
others can learn from. (In English, I am living vicariously through your real-world
troubleshooting. :0) Seriously, Schurkey's comment about another member having
a similar issue and it was the Ignition Control Module makes sense to me.

Anyway, I would be interested if cycling the power changes the behavior, or does the
suspect circuit just break into oscillation and stays out of control for some period of
time before recovering? BTW, I appreciate the fact that you are trying to take the time
to understand this instead of just shoveling parts at it.

Sorry it's been a couple weeks. I checked to see if the injectors still chattered after the ignition was turned off then back on again. It took a few tries until the injectors continuously pulsed like in the video, and the chattering DID continue after turning the key off, then back on again. Based on your information form earlier posts, I went straight for the ECM as a replacement. I got a used certified model from Howell EFI, swapped the cal-prom and cal-pack, and it's been running excellent since then! I've been waiting to reply so I could get a good amount of driving done just to make sure that was the fix, and it was!

Thanks again for everyone's input and information on what to check and troubleshoot!!!

 

[Road Trip]

I've been waiting to reply so I could get a good amount of driving done just to make sure that was the fix, and it was!

14reamdalton,

Sincere thanks for coming back and closing the troubleshooting loop with your observations and
sharing the final fix! By doing so this strengthens the value of this thread for future DIYers by
taking it from purely theoretical troubleshooting to adding another real world data point for others that
are troubleshooting similar symptoms. (!)

You have set a great example for others, for few things are more frustrating than to read through a couple
dozen replies to a thread that sounds identical to what you are suffering from...only to have it die out with
no documented solution from the OP. :-(

By the way, your detailed observations are extra helpful, for you clearly described an illegal failure condition -- that
is, that it's possible for the drive circuitry to heat up and fail in such a way that the electronics broke into oscillation
and continued to fire the injectors after the key was turned off. (Good thing the fuel pump powered down and after
a couple of seconds only noise was emanating from the injectors.) Super cool that it takes Reference pulses from a
spinning cam/crank (and/or oil pressure from a spinning oil pump) to keep the fuel pump relay energized. This
way even with spurious injector pulsing no flammable fuel was being delivered to a stationary engine. (ie: Any
single failure, no matter how rare, can't lead to uncontrolled fuel metering. (!)

The bottom line is that no matter how new or old your vehicle is, the closer the driver pays attention to the
normal cadence and sounds of the vehicle the safer for all involved. And stopping to figure out why instead of
just letting it ride. Well played, sir!