Dead ECM fixed

Don W.

Don W.

Stab it and steer it
I'm fairly certain I have a dead ECM. NAPA lists them but does anyone know if anyone can test them?
 
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Slyclone

Slyclone

Well-known member
Re: Dead ECM

Re: Dead ECM

Not sure if this helps you.

I remember testing mine. Jumping out the aldl port it should flash code 12 4x. Anything else should indicate a issue. I'm helping a member on here on/off and we just went through this test a few nights back as he had thought his ecm was dead as well. We isolated the problem after a little talking..

I'm not sure of any other way to test.

My GMC syclone had problems. I ended up jumping out the aldl port and it flashed like a strobe light.
 
Don W.

Don W.

Stab it and steer it
Re: Dead ECM

Re: Dead ECM

Haven't done that one but did go through chart A-1 in the book which indicates the ECM is bad. Problem is it doesn't run the fuel pump with key on. I can crank until the FP does come on and it still won't start. I have ign because it will flash a timing light.

I'll work on it some more tomorrow checking code 12 thanks.
 
Slyclone

Slyclone

Well-known member
Re: Dead ECM

Re: Dead ECM

Just make sure you check you fuses as well I have made that mistake before. I blew a fuse when I upgraded my fuel pump ( before a racetronix kit). Something else to check out for.
 
Don W.

Don W.

Stab it and steer it
Re: Dead ECM

Re: Dead ECM

Ya, thanks. There are 3 12v positive feeds if-you-will to the ECM. 2 are hot all the time and one is switched with the key. Checked all 3 at the ECM plugs and all are good. Ground circuit is good also.
 
Quickstop [UK]

Quickstop [UK]

Combating adversyty.
Re: Dead ECM

Re: Dead ECM

Does DM connect with the hey in and engine off? Should get loads of telemetry even with the engine off?
 
P

Poconojoe

Donating Member
Re: Dead ECM

Re: Dead ECM

There is a emulator out there called a JimStim, it comes from JBPerf.com it's used a lot in the Megasquirt world but I've know of it being used on LS1 style PCM'S. You might be able to it to test your ecm
 
SY-1193

SY-1193

Active member
Re: Dead ECM

Re: Dead ECM

Don W. said:
.... Problem is it doesn't run the fuel pump with key on. I can crank until the FP does come on and it still won't start. I have ign because it will flash a timing light.
Click to expand...

You said the fuel pump isn't running. Check your oil pressure sensor. I have seen a bad oil pressure sensor make these symptoms before.
 
Don W.

Don W.

Stab it and steer it
Re: Dead ECM

Re: Dead ECM

SY-1193 said:
You said the fuel pump isn't running. Check your oil pressure sensor. I have seen a bad oil pressure sensor make these symptoms before.
Click to expand...

Re-read what I said. FP doesn't run with key but -will- run with oil pressure. Maybe I wasn't clear.
 
dgoodhue

dgoodhue

BuSTeD 4.3
Re: Dead ECM

Re: Dead ECM

DaveP said:
I wish I could remember the gentleman's name that used to run these ECM's on his kitchen table. IIRC, he passed away a number of years ago after a long illness. There was a time when there were a lot of people like him involved with these trucks. Not so much any longer.
Click to expand...

I don't know if he had SyTy, but are you thinking about Bruce Pelican?
 
T

turbogray

New member
Re: Dead ECM

Re: Dead ECM

DaveP said:
Back in the mailing list days (I joined in the Fall of 1997), there was a guy that was one of the forerunners of early "figuring out our ECM". I can't remember his name. He would conduct seminars at his house on the ECM. I know dig, Todd, BG and other attended these and kept in touch with him.

I remember him posting about and commenting on things he had learned "from running an ECM on my kitchen table". He had a set up where he could make it "run" without it being in a truck. He would make changes, and log it without getting out of his chair.

There are only a few inputs, and even fewer outputs from the ECM. One of the inputs are the reference pulses, which is a variable frequency square wave at 0-5VDV. This signal can probably be generated by a number of signal generators available for less than $50 at surplus outlets. TPS, MAP, CTS, and MAT can be simulated by variable resistors. (Potentiometers). Hook up datamaster, and have a blast. Use an oscilloscope to read the duration of IPW. Could probably use an additional trace on the same 'scope for EST and measure the offset to the reference pulse to visualize, measure, "timing advance".

So there are probably set ups to test the ECM. Most ECM's operate on the same basic principals. There are inputs, and there are outputs. For fueling, the only output that matters is IPW.

I wish I could remember the gentleman's name that used to run these ECM's on his kitchen table. IIRC, he passed away a number of years ago after a long illness. There was a time when there were a lot of people like him involved with these trucks. Not so much any longer.
Click to expand...

Was it by chance. Bruce Plecan ?
 
dgoodhue

dgoodhue

BuSTeD 4.3
Re: Dead ECM

Re: Dead ECM

I haven't ever looked at the fuel pump circuit before, but I have a question on its operation. I was looking at the fuel pump circuit on page 6e3-a-5 of the 91 Syclone service supplement. Is the ECM just basically priming the fuel pump circuit on power up until the oil pressure switch closes and powers the fuel pump?
 
dgoodhue

dgoodhue

BuSTeD 4.3
Re: Dead ECM

Re: Dead ECM

DaveP said:
That's it. I saw Dave's post and thought "close", then remembered "Plecan", and that I remember he didn't have a SyTy, but did have a GN. He used to call his get together's "EFI pow-wows". Then opened Justin's post, and there it was.
Click to expand...

Obvious that is who I was think of. I started researching DIY ECM tuning in 98. In my research I found Bruce Plecan and it was obvious that he was a guru and he was generous enough to share his knowledge. I never asked him a single question, I search his name and studied what he wrote. I spent a lot of time reading his posts the next few years learning from his posts.
 
dgoodhue

dgoodhue

BuSTeD 4.3
Re: Dead ECM

Re: Dead ECM

DaveP said:
No.

The ECM turns on the fuel pump for 2 seconds, OR UNTIL it receives Reference Pulses from the distributor module. If the 2 seconds passes with no reference pulses, it turns off the fuel pump. As soon as reference pulses are received, it turns on the pump again.

When reference pulses are present (the engine is turning), the ECM is commanding the pump ON.

The oil pressure switch is parallel to the relay. Either one will turn on the pump, but the ECM/relay and the oil pressure switch are completely separate from each other.

I have never come across an explanation for this strategy that makes sense as to why they did it this way. (Oil pressure AND ECM control). But GM has been doing the EFI fuel pump control this way since the mid-80's. My 85 Corvette also has both.
Click to expand...

Thanks. Chart A-5 basically reiterates your functionality above. The last sentence of the Fuel Pump Relay circuit description it says 'Should the fuel pump relay or 12V relay drive from the ECM drive fail, the fuel pump circuit will be run through an oil pressure switch back-up circuit.'
 
dgoodhue

dgoodhue

BuSTeD 4.3
Re: Dead ECM

Re: Dead ECM

Don W. said:
Haven't done that one but did go through chart A-1 in the book which indicates the ECM is bad. Problem is it doesn't run the fuel pump with key on. I can crank until the FP does come on and it still won't start. I have ign because it will flash a timing light.

I'll work on it some more tomorrow checking code 12 thanks.
Click to expand...

Don, is your check engine light not lighting up on when you turn the ignition on with the engine not running?
 
Don W.

Don W.

Stab it and steer it
Re: Dead ECM

Re: Dead ECM

The CEL does not light at all. Unless I test the circuit per the manual then it does so the bulb and wiring are OK.
 
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