Engine ECM Issues

scottrj

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I need some help with issues related to the ECM on my Cobra.

I built a FactoryFive Roadster using a '91 Mustang GT 5.0 as the donor car. I've done some upgrades to the engine: 94 Cobra intake, higher lb injectors, larger TB, oversize rockers, etc. and had a SCT 4-Bank Eliminator Chip programmed with all of the modifications. I put the car in for winter storage and when I was getting it ready for this summer, then it just wouldn't start. The car had been running great for all 7K miles and did not have any issues when I parked it last November. The issue it was having is the fuel pump would just keep running and nothing would happen during cranking. I followed the checklist that JRICHKER outlined in the thread:
https://www.stangnet.com/mustang-forums/threads/cranks-ok-but-no-start-no-injector-pulse.781640/

The first fail in the test was the PIP sensor, so I replaced the distributor (still running a stock distributor) and still no start. Then followed all of the other tests in order and they all passed. Thus, the only thing I could think of next was to replace the ECM with a re-manufactured unit (which is all that is available now) without the SCT Eliminator chip. I let it get up to temperature and set timing to 12deg. The car runs fine at idle, but when trying to drive it, it would surge, die, sputter, surge, die, etc.

I then re-installed the SCT Eliminator Chip into the re-manufactured ECM and once again, the car idles great, with no issues. Then once I try to drive it, I have the same problem of sputtering, dying, surging, etc.

I am not sure what to do next. If there are other solutions to this issue on the forum, I have been unable to locate them, thus any suggestions are appreciated.
 

scottrj

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May 26, 2022
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St Louis, MO
What’s the 3-digit code on the ECU?

Do you have continuity from pin 46 to pin 40/60 on the ECU disconnected from the harness?

Factory wiring or aftermarket harness?
Code on ECU: A9L
During step (H) in Jrichker's test regime, I tested the ground of the ECM (which was good) but I can't remember testing Pin 40/60 continuity

Factory wiring harness
 

Trogdor

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The fuel pump continuously running is what mine did when the ECM caps went out. Open the computer and take a look at the caps. Check for the presence of green fuzz and make sure that the capacitor legs are still attached to the board. I replaced the three capacitors myself, but there are ECM repair companies that can do this job for you as well.
 

Mustang5L5

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I agree.
Code on ECU: A9L
During step (H) in Jrichker's test regime, I tested the ground of the ECM (which was good) but I can't remember testing Pin 40/60 continuity

Factory wiring harness

Can you take a photo of the O2 sensor harness where it plugs into the main engine harness? There should be a small jumper in the harness. Need to see how that's pinned as it's transmission specific.

If you can, disconnect the ECU and check continuity from pin 46 to both pin 40 and pin 60. You should have it.


I also second opening up the ECU to look at the three capacitors
 
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scottrj

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I'll pull the computer again and crack it open to look at the capacitors and report back.

Not sure where the jumper is on the O2 sensors, but I'm not concerned about those as the car was running fine before the computer issues (as I doubt the O2 sensor would create a situation where the car would not start). I also have a line on another computer from a member in my Cobra club who switched his donor over to a carburetor engine.

The Factory Five Roadster is a load of fun to drive.
 
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Mustang5L5

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The o2 sensor pin being incorrect has the potential to fry the ECU. It actually has nothing to do with o2 sensors. It’s where ford routed a specific jumper that needs to be changed that is part of the starting circuit.

However if you got the harness and ECU from the same car, it’s likely not an issue. This is a major concern when folks start mixing and matching ECUs and wiring harnesses.

It’s not unheard of to drive perfectly fine for months/years and then one day the ECU fries from it. If you search “pin 46 voltage” you’ll find this being discussed quote a bit.

But again, same donor for ECU and harness, you are likely ok.
 
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limp

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The Factory Five Roadster is a load of fun to drive.
Thanks for the response....... I and everyone I know has thought of doing a Cobra replica car..... I know me and I would have 911 money into one...
What was Shelbys goal? 0 to 100 to 0......

There are some very helpful, very bright people on here who will be able to help you get your car running....
 
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General karthief

wonder how much it would cost to ship you a pair
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Thanks for the response....... I and everyone I know has thought of doing a Cobra replica car..... I know me and I would have 911 money into one...
What was Shelbys goal? 0 to 100 to 0......

There are some very helpful, very bright people on here who will be able to help you get your car running....
Yeah, he just needs to drop it off at my house, I'll take care of it :nice:
like I need another project :doh:
 
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The fuel pump continuously running is what mine did when the ECM caps went out. Open the computer and take a look at the caps. Check for the presence of green fuzz and make sure that the capacitor legs are still attached to the board. I replaced the three capacitors myself, but there are ECM repair companies that can do this job for you as well.
Where do you get the new capacitor’s?
 

jrichker

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Where do you get the new capacitor’s?

They have a definite life cycle and after 22 or more years, they start to fail. The failure mode is they dry out because the liquid electrolyte leaks out. Then they burn up or blow the top out of the can that they are packaged in. A clue to failure is the top of the can starts to bulge. When you see one bulging it has either failed or is in the process failing.

Many of the automotive computer repair places will replace all of them as a first step in any repair efforts. The capacitors have a voltage rating, a capacitance rating, a tolerance for the capacitance rating, an operating temp rating and a life cycle rating. They also have a specification for package size and lead placement

The higher the voltage rating, the larger physical size of the capacitor when compared to one with the same capacitance and a lower voltage rating. Most of the ones used in automotive electronics have a 16-35 volt rating since they are used in low voltage circuits. Using one with a higher voltage rating doesn't hurt anything, but it usually doesn't have any benefits either. There may be a size limitation because of the way the circuit board is laid out. That means there are sometimes limits on replacing the16 or 20 volt cap with a 35 volt cap because it won't physically fit in the space allocated on the circuit board.

The higher temp rating and longer lifecycle ratings increase the cost of a capacitor. In automotive circuits, those are important factors, and the highest rating stands the best chance of lasting the longest and working the best. Most capacitors used in automotive applications are rated at 105° C The typical capacitor used in most automotive electronics is less than $2.00 each.

Some informative help from YouTube…

View: https://www.youtube.com/watch?v=YCSNWi3UHf4


WWW.digikey.com or www.newark.com are good sources for capacitors, resistors and just about any other quality electronic part. Avoid Radio Shack unless it is a temporary repair or emergency situation. Almost all of their parts are less than top quality stuff and a lot of it is just plain junk.


That's the easy part; now here comes the gotcha... The circuit boards are almost all multilayer construction. That means you have to be able to apply enough heat with a pencil tip soldering tool to melt the solder on at least 4 layers and sometimes more. Then you need to have a solder sucker to suck up the solder once it turns molten but before it burns or damages the PCB (Printed Circuit Board). I have been fixing PCB's in computers for 42 years now and it is still a challenge to do it right and not make a mess of it.
The capacitors have a stripe on the side of the can that indicates polarity. Make sure that you match the polarity markings on the capacitor with the polarity markings on the PCB.

Some more help from YouTube…

View: https://www.youtube.com/watch?v=urGB_IUXSIM
 
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