Ok, I think this is the right place to ask this question, sorry if it's not.

My dad and I are currently working on getting a 1987 IROC (TPI 305) back to running condition. The car's in pretty dang good shape...except for the engine and the wiring. The engine has already been taken care of (assembly will probably be complete late next week). However, the idiot who owned this car before us decided that he'd try, for whatever reason there might be, to run the engine without using the ECM. To this end, not only did he hack up the wiring harness like the Swedish chef of the Muppets, but he also connected a live wire to the ground connection of the ECM. We had wanted to use this car as a learning bed for TPI systems, but now we wonder if maybe we should just go ahead and use a Megasquirt system seeing as we're having to break in a new engine as well? To wrap this up, I basically have 3 questions

1) Is there any way to test the ECM to see if it's cooked or not?
2) Considering the fact that the wiring harness is so butchered, where can we find a replacement wiring harness for a 1987 IROC?
3) All things considered, should we replace the harness (and possibly ECM) or simply switch to the Megasquirt.

Thanks for the help.

 

I cant answer your question for you, but I can tell you that if you go with a megasquirt I have a fuel and spark table that is already tuned to my stock 89 305 TPI. Yours should run very well with no changes to tuning.

 

1. I would think that the ECM is ok. If a hot wire was connected to the ECM ground, the current from the hot wire should go directly to ground and not through the ECM. It could be that something upstream of the connection on the hot wire side is bad or a fuse is blown??? One way to test is to see if any one you know has the same car, engine, options, etc and see if they will let you plug it and see if the car starts. It is unlikley that a dealer would have the people/knowledge to test it, but have you called one and checked? Remanufactured ECMs are available, but I don't know anyone who could test your unit.

2. Look in a junk yard, the for sale boards here on thrid gen (they might have the ECM also) or maybe someone like Painless Wiring may be able to build you a new harness.

3. I don't know which may be the better approach, but if you keep the ECM I would replace the harness. No telling how may problem you may encounter with the hacked harness.

Dave

 

Just go find someone on the for sale boards that is parting out a car that you could use an ECM from. I love the classifieds here!

I actually bought my car here.

 

1987 should be the same C3 type ECM as used in that period on practically all of the GM products of the day, but the number off of the label would help.
If it is the 8746 I suspect, then checking it isn't too tough.
Connect battery + to pins C16 and B1. Connect battery - to pins A12 and B1.
( this assumes he didn't fry the foils on the ECM board itself )
Connect an ohms meter + probe to pin A5, the - probe to battery -.
Now, when you connect battery + to pin A6 you should see the ohms meter swing short for about 1/2 second, open for about 1/2 second, then short and stay there until about 4 or 5 seconds after you remove battery from A6.
You could also connect a dash light bulb between pin A5 and battery + for the same result. It'll flash like the SES light should.
This will tell you that the ECM's little brain ( the CPU ) is alive, and well, it's read the PROM and found no errors. If it swings rapidly from open to short, and doesn't stop doing that, then it can't find the PROM, or it found an internal error.
If it does nothing at all, or goes short and STAYS there, it's probably trash.
This will NOT tell you that the previous owner didn't fry a foil on the board. For that, take the covers off and look. If you don't see anything obviously burnt, it's probably fine. This will also not tell you that he didn't fry any output drivers, or sensor inputs either, but it's a start.
If you accidentally short or hit other pins while battery is connected, you can instantly fry it, so be careful.

Can't help you with the harness.
There are several after-market ECM's available. Personally, I'm using an EBL-Flash from dynamicEFI.com and recommend it highly, but Megasquirt is also an option.
All things considered, I'd look for a harness from a bone yard, or e-bay, or the classifieds on ThirdGen, and probably a stock ECM if you actually need one.
Regardless of which ECM you choose, tuning experience on stock is invaluable.
Check the DIY-PROM forum, and the various EFI tuning threads.

 

Regarding the battery connections to the pins, are those full 12 volt connections or are they stepped down lower, to like 3.3 or something?

 

Full, regular, 13.6 volt car battery. ( standard 12 volt )
Be careful. A car battery can easily duplicate an arc welder if you accidentally short the pins.

 

Ok, so I didn't actually try this method because the ECM number was different (and I don't have the number with me at the moment). We have decided to continue and have patchworked the original harness to the point that we think it'll work. But we're still having doubts regarding the ECM. Is there any other way of testing it before hooking everything up?

 

The first thing to look for is the SES blink. At key-on, engine-off the SES light should turn on, blink off, then turn on solid. The blinking off is important.

If it does that then the ECM is running from the EPROM and is a good sign.

The second step is to use a scan tool at key-on, engine-off. Check the sensor values to make sure they make sense. An example is the CTS. If it is 50 F out and the CTS reports -40, then something is wrong.

If the ECM passes these tests then 98% sure it is OK.

RBob.

 

If you have time and are willing to spend the money, try TPIParts.net for the wiring harness. According to their website, they are assembling new engine harnesses. It will be more expensive than finding a used one on eBay or at a yard, though.

 

RBob, what exactly do you mean by the SES light?

 

I'm not Rbob, but SES is "service engine soon" aka "check engine" and such.