Is my factory ECU dead?

[Fastish]

Try to make this quick,

Car Factory 5 Cobra Roadster
Engine: 2003 Ford 4.6L 32 valve from a Mustang Mach 1
Transmission: Automatic
Tune: Diablo Sport Predator
Story: I bought the car partially complete, and finished the project in 2009. Car has run fine until about a year ago when it would have an occasional miss. this progressed to occasionally the car would not start. Let it set 5 mins and then it would fire no problem. Now it will not start. It gets fuel (Plug damp), but no spark. I have done some basic troubleshooting like the crank position sensor which seems to be fine. Other things that make me think the ECU is a problem... The electric fan was programmed to come on at 180F and now when the car is cold and you flip the switch to run before hitting the starter button the fan is on. This is new.

The tune on the car was put in right when I got it running and has never been changed since that time, so no changes there. I did try and hook up the tuner to see if it would give me a code and the tuner said it could not communicate with the car. I could not get a code, read a VIN, or anything. I bought a code reader from the auto parts store and it also could not communicate with the car.

I want to make sure that my problem is the ECU before I head down this path. Any advice on diagnostics would be greatly appreciated.

Be Safe,

Jeff

[Six_Shooter]

Start with basics, power inputs (both battery and switched), and grounds. If these are not right the PCM will not power up (properly) and could give you the symptoms that it shows.

Swapping in another OEM ECU is also an option, even if it's just to power it up and see if there is communication.

[elutionsdesign]

I always check the 5V output for TPS, MAP, MAF, whatever the car came with to test that the ECU is getting power and ground. No 5V out, no power or ground or both.

[Fastish]

Interesting comment on the ground. I will check that out this week. I did make a change to the under car wiring to install the leads for a battery tender before all this started happening. I guess I could have failed to make a good connection there. I installed the leads behind the main electrical shut off in the car so that even if i have the main electrical shut off it will still charge while it's in the garage.

With respect to the 5 V measurement where are you measuring this voltage?

In terms of measuring grounding, I assume I can use continuity? If I measure from the - end of the battery tender plug to the frame, or block and get continuity then can I assume the ground is good?

Thanks guys I will admit electrical is not my strong suit.

Happy New Year,

Jeff

[kjones6039]

With respect to the 5 V measurement where are you measuring this voltage?

You can test for VRef at any or all (my preference) of the components that elutionsdesign (TPS, MAP, MAF, etc.) referenced in his post.

Hope that helps................

Ken

[Fastish]

Ok, so let me know if this test procedure sounds right. I pulled the connector for TPS (as an example) and measure the voltage at each of the 3 wires on the connector with the ignition switch in the RUN position as you are normally driving correct? If this is the case my findings are as follows...

Idle Air Control Valve 1.5V on one of the 2 wires
TPS 0.0V on any of the 3 wires
Engine coolant temp 0V on any of the 2 wires
MAF 0V on any of the 4 wires
Crank Position 0V on any of the 2 wires

I went under the car and checked the ground i was worried about and it was fine. I cleaned anyway and put a light coat of electrical grease and re tightened the connection. I checked the grounds behind the dash and they all look good. No corrosion, and no sign of arc, and everything is tight. The car is always garaged so everything is pretty clean and tight.

Update: I got a repair manual on line which shows the voltage readings at each sensor based on temp/pressure/position. I chose the TPS as it is easy to get to, and you can change it by moving the throttle right there. So, with the key turned to "run" like when you drive, the plug plugged into the TPS, and measuring the voltage on each of the 3 wires I get no voltage (maybe a few MV) and no change with a change in throttle position.


Anxious to hear your thoughts on this one.

Thanks,

Jeff

[billr]

Those voltages are all relative to engine ground? If so, the lack of 5V anywhere indicates that the ECM is, indeed, dead. This not an MS of any kind, correct? I will say *gently* that this thread should have been in the "Extra Pits" forum.

[Fastish]

Those voltages are all relative to engine ground? CORRECT

If so, the lack of 5V anywhere indicates that the ECM is, indeed, dead. This not an MS of any kind, correct? Correct

I will say *gently* that this thread should have been in the "Extra Pits" forum. Sorry, as you can see from my low post numbers I am new here, and thought this was the place. Maybe a mod should move?

So now the question is what do I do to replace the factory ECM? The car is pretty simple really, I just need to run the engine/transmission, there is no Antilock Brake, no security system, no climate control, no radio, All of the thinks like lights/turn signals are run out of a separate system and they all function normally.

I am interested in the most plug/play option.

Again thoughts would be appreciated.

Jeff

[kjones6039]

If so, the lack of 5V anywhere indicates that the ECM is, indeed, dead.

Well.......... More than likely!

So now the question is what do I do to replace the factory ECM?

Funny thing................... You just happen to be in the right place!!

My suggestion would be to hop on over to http://DIYAutotune.com and have a look!

Ken

[DaveEFI]

Those voltages are all relative to engine ground? CORRECT

If so, the lack of 5V anywhere indicates that the ECM is, indeed, dead. This not an MS of any kind, correct? Correct

I will say *gently* that this thread should have been in the "Extra Pits" forum. Sorry, as you can see from my low post numbers I am new here, and thought this was the place. Maybe a mod should move?

So now the question is what do I do to replace the factory ECM? The car is pretty simple really, I just need to run the engine/transmission, there is no Antilock Brake, no security system, no climate control, no radio, All of the thinks like lights/turn signals are run out of a separate system and they all function normally.

I am interested in the most plug/play option.

Again thoughts would be appreciated.

Jeff

If the original injection worked well and the engine is standard, I'm not sure I'd go MS purely to repair a fault on the factory ECU. Unless you really want a user programmable ECU.

[Fastish]

I guess there are 2 choices here. Go with a factory ECU, or go with afternarket. If I go with Factory then it will need to be modified to not look for things like Antilock Brakes, PATS security, etc that this car does not have. If I go with Aftermarket then I guess I start from scratch (or some base tune) and work from there. My interest is in working with something that I can actually work on versus going to someplace to get the computer "reflashed" and hope it's right. This is why I am interested in the aftermarket approach.

All that being said I would prefer not to have so assemble my own ECU. I am more interested in a PNP solution where I can focus my efforts on getting the correct tune vs. perfecting my soldering skills. I have some experience with the tuning piece from my motorcycle. I used Mastertune in that case for a HD that I changed the cam in so then needed to change the fueling. I that case I got a base tune that was similar to my bike, and then used the laptop and a few rides to get it adjusted for my bike. The process was actually easier than I thought so I was thinking I could do the same here. The main difference is that I still used the factory ECU from HD. The reason I chose Mastertune is that they were the company that actually wrote the tunes for the factory HD settings so I figured they understood the factory ECU better than most.

I appreciate your continued insight, I am sure you guys have way more experience than I do on this one. I guess I have a project for the winter now...

Jeff

[DaveEFI]

With what amounts to a special, it's unlikely you're going to get a true P&P solution. I'd say the engine harness is going to be pretty well a one off - although you can use a stock one as a basis and modify it. It is important to get the hardware correct before concentrating on the software side.

P&P is fine where you are simply replacing like for like. Once you deviate from this, it can be more trouble than its worth.