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cmaje72
05-19-2011, 06:47 AM
I have not had a TBI setup for about 6 years and I'm a little rusty. Trying to help troubleshoot. Looking at the list views in tunerpro (using the $42 I downloaded from here) towards the bottom is "Crank Sensor Pulse". Should that be toggling Yes/No while the engine is running?

Symptoms seem to indicate an ignition problem and I am wondering if the ECM is losing that signal from the ignition module.

EagleMark
05-19-2011, 10:30 PM
I have always been meaning to ask what that is for but never found tiime to look in the right spot. It has done that on all of mine, I don't know what it is? Thought at first it was the crank signal used when stating...

dave w
05-19-2011, 10:34 PM
I have not had a TBI setup for about 6 years and I'm a little rusty. Trying to help troubleshoot. Looking at the list views in tunerpro (using the $42 I downloaded from here) towards the bottom is "Crank Sensor Pulse". Should that be toggling Yes/No while the engine is running?

Symptoms seem to indicate an ignition problem and I am wondering if the ECM is losing that signal from the ignition module.

Welcome cmaje72.

The "Crank Sensor Pulse" that I'm familiar with is only used when the ignition switch is in the "Start Position".

It's my understanding that the ignition module is controlling spark while the engine is cranking. Once the ECM sees 400 RPM (or more) from the module the ECM takes control of the spark.

dave w

cmaje72
05-24-2011, 11:06 AM
Thanks dave. If there was a "crank pulse" being sent to the ECU while the engine was running would it have any effect or just be ignored?

dave w
05-24-2011, 12:16 PM
Thanks dave. If there was a "crank pulse" being sent to the ECU while the engine was running would it have any effect or just be ignored?

Good question, for which I do not have an answer for. I don't have my EFI test bench currently set up for a '7747. Maybe eaglemark might want to experiment with sending the crank pulse once the ECM see's that the engine is running, or the crank input is always on? I personally would not try experimenting with a crank input with a running / driving vehicle.

As a guess, the 12 Volt input from the cranking input could / should tell the computer to switch timing control back to the ignition module if the engine was running? I also think, as a guess, the ECM knows the engine is running and would / should disregard the crank input? I also think, as a guess, that if the crank input was always on, the engine would not start because the engine would run very poorly with only ignition timing control from the ignition module?

The PIC below is for a Buick ECM, not the '7747!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! !!!!!!!!!!!!!!!!!!!!!!!!!!!!!

dave w

EagleMark
05-25-2011, 06:16 AM
Dave, please explain why that picture is Buick and not 7747? You know something I don't? Buick also used the same module as the picture, so did a lot of GM. It's a small cap EST Module used for many ECMs...

I have a note on my test bench to look into the Crank Signal. My understanding of it is to add fuel when engine is cranking. Other than that I can say I have tested and it never throughs a signal unless the key is in crank position.

Why the $42 7747 ECM has it in data stream and it does change I do not know. Maybe our resident datastream definition maker Robert can make sense of it?

dave w
05-25-2011, 12:15 PM
Dave, please explain why that picture is Buick and not 7747? You know something I don't? Buick also used the same module as the picture, so did a lot of GM. It's a small cap EST Module used for many ECMs...

The ECM pin numbers in the picture are from a Buick ECM not a Chevy '7747. The module shown is a coil in the cap type. The schematic shown is also the same for a Chevy coil in the cap type module.

The point I was wanting to make, is when the ignition is in the start position, the module is controlling the timing. The ecm will control timing when the engine is running more than or equal to 400 ~ 500 RPM. What I think might be happening with the crank input, is the ECM is not going to look for the RPM signal until the ignition is in the run position???? I really don't know why the need for a crank input. Maybe the crank input is for the fuel pump to keep runnning when cranking?


dave w

EagleMark
05-25-2011, 02:15 PM
I did it on the bench. The wire does nothing. Just waites for a signal from key in Crank position. Then adds from a fuel table. But I have not located where in the bin. I am guessing choke something vs rpm or?

I have to look up this picture. I have been useing it for reference on 7747 ECM. They all ran...

Six_Shooter
05-25-2011, 08:57 PM
It looks just like every GM ignition module layout I have seen. The shape is specific to the large cap HEI type.

cmaje72
05-26-2011, 07:26 AM
I did it on the bench. The wire does nothing. Just waites for a signal from key in Crank position. Then adds from a fuel table. But I have not located where in the bin. I am guessing choke something vs rpm or?

Are you able to simulate a running engine on the bench? I'm just curious if the output in the tunerpro still flashes yes/no with that wire disconnected.

EagleMark
05-26-2011, 11:03 AM
I did it on the bench. The wire does nothing. Just waites for a signal from key in Crank position. Then adds from a fuel table. But I have not located where in the bin. I am guessing choke something vs rpm or?

Are you able to simulate a running engine on the bench? I'm just curious if the output in the tunerpro still flashes yes/no with that wire disconnected.
Yes I can and yes it does. I can simulate engine running 2 ways. One is with a complete chevy intake manifold in which I turn on, excite crank wire at same time as I turn on a drill hooked to distributor. Get's spark and records data through TunerPro.

Second way is JimStim stimulator made for Megasquirt wired into GM ECM and record data through TunerPro,

cmaje72
05-27-2011, 06:48 AM
Cool! I sense a test bench setup tech article in your future...hint hint

EagleMark
05-27-2011, 08:17 AM
Cool! I sense a test bench setup tech article in your future...hint hintYeah I guess I could... anything I do I try to document for others to use. Never thought of the bench?

cmaje72
05-27-2011, 10:36 AM
Oh, I have and I am sure I could do it without a problem. Maybe I should just start a thread where people could show off their setups.
I picked up two 7747's at the auto swap last week for $3. Plus I have a newer ECM for a 95 lt1. The hardest part would probably be finding all the plugs.

Looking at the jimstim too...that looks like a good investment.

EagleMark
05-27-2011, 10:40 AM
Just add some here:
viewtopic.php?f=13&t=11 (http://www.eagle-mark.com/Forums/viewtopic.php?f=13&t=11)