This isn't exactly 3rdgen related but, sort of is.
My friend has an 88 GTA TPI unit/harness that I've somehow managed to sort out make run on his '72 chevy truck.
Over last weekend we were actually able to get everyting together and was able to fire up the motor (to both our amazement on the 1st try).
Aside for a few running quirks (no o2 wired in just yet and a raggedy timing chain, hoses plugged, etc), everything seems to check out.
Tonight, I set the timing and was wanting to put the ECM in diag mode to close the IAC to set the minimum air idle speed. Well, no matter what I did, the ECM will not go into self test mode. I even ran a ground staight to the terminal on the ECM and the SES light did nothing but stay lit.
The ECM apparently works properly because the SES light comes on w/the key in run, go off while the engine is running, comes on if you unplug the wire to the dist & comes on once the engine reaches operating temp (no o2)

What would keep the ECM from going into self test mode ??
I feel somewhat stupid that I can get a TPI to run on a 72 truck but can't get the codes from the ECM.
Any thoughts/ideas are appreciated. Sorry I took so long to get to the point of the question too...
Thanks

 

It's a hail-mary shot in the dark, but did where did you run the ground from? Are all of your system grounds firmly grounded? There should be two or three (black wires with white stripes and any number of others tied in). I would try grounding the diag. request line with something tied to a system ground rather than a convenient bolt or something. But like I said, it's a wild guess and probably highly unlikely.

Some would be quick to point at a failing ECM but I've so rarely encountered an actual "bad" ECM.

Hope you find it.:lala:

 

Hey Jza.. thanks for the extra brainpower.
I thought it may have been a ground problem as well so I checked back over my grounds just incase I had a brainfart. When I wired in the ECM harness, I cut all the ECM grounds and soldered them into one central terminal that is bolted to the trans where it meets the block and the ground to the block is good as well.
When I couldn't get the codes to run using the ALDL terminal, I got a paperclip and poked it into the ECM harness and ran a ground to the battery.. still nothing.
A few weeks back before I had the coil wired up and was checking relays and such for power, the ECM would flash out 12 no problems.. I wouldn't think that wiring power to the coil would fudge anything up would it
Anytime I do any wiring work, I unhook the battery so I'm fairly certain I haven't cooked the ECM plus, the engine runs (realitively) fine and the SES light comes on when you unhook anything vital.
Even grounding the A9 (I think.. white wire black stripe..) terminal at the ECM with a paperclip probe didn't do anything. I guess I screwed up somewhere... or maybe I'm just overlooking something really simple.
I appreciate your input though Jza, or anyone elses if they have a guess.

 

Well if you think you cooked something the quick way to tell obviously, would be to swap in a known good ECM. Of course you run the slight risk of frying that one too if it's a wiring problem.

Is there any voltage at all on the diagnostic request wire? If there isn't, obviously there's nothing to ground so that would indicate that something on that circuit inside the ECM has uh-oh'd.

 

Once again, thanks for some input Jza.
Well.. of all thing not to find.. I have no clue where mu multi-meter is so, off to my bud's garage I went w/o. TO save some reading, I took the coil off to make a mount and to humor myself, I keyed the truck on and jumped the a-b terminal w/o the coil plugged in. Now, for a split second (literally), the SES light flashes as if it were to start running codes and the fan relay clicks on & off. W/o being able to check with my voltmeter I'm sure this means nothing but, to me it was a somewhat hopeful sign I haven't turned the ECM into toast (completely).

As an actual ECM electronics diagnostic moron such as myself, a question... how high of voltage should I be looking for at the request terminal... +12,+5, or just anything above 0 to show signs of life ?

 

IIRC should be +5v.

Which ECM are you using? 165 ?

Sounds like a Fairly odd problem, are you sure your wiring to the diagnostic port on the ALDL is sound ?

I guess the Multimeter will establish that.

It is odd that there is no SES while runing but you can't get into Diagnostic Mode. Never heard of that one before myself.

Good luck, I would bet there is an error somewhere stupid. Usually is.

 

Hmm Something just occured to me.

How are you not getting a SES light, with No 02 Sensor Installed ?

 

Joy of joys !!.. I've found my multi-meter (and not in a place I put it...).. yay

Thank you for the reply Bort.. I'm headed out shortly to go play with the truck some more.
To be honest with you.. I haven't a clue what the ECM.. I'm not very ECM savvy when it comes to that. The best I can tell you is it's a MAF TPI form an 88 350 GTA and my stupid azz ( )putting it in.
The only part of the interior harness I've chopped up is wiring for the headlights & turnsignals (nothing ECM related), everything else was just re-wrapped in tape so it would fit behind the dash more cleanly.
As far as the o2 sensor goes.. should the SES light come on when the engine is first started ? It does lights after the engine reaches temp (160º thermo. ) which I took as normal because I've left the o2 on my bird uplugged by accident more than once and the SES light only comes on after the engine gets in the 160º range.
The SES does light when you unplug any other sensor though TPS and CTS were 2 I yanked last night.

I guess the multimeter will tell me if I'm a screw up or not. At least the dammed thing runs after 5 months of sitting stag though.. I can't complain too much about small crap like this happening I guess.

Thanks again guys.. I really appreciate the help and info.

In case anyone really cares.. here's a pic of the turd I'm working on..

 

Yeah, thats a 165 Computer then.

Sounds like its setting codes in closed Loop, So thats normal.

I imagine your going to find something with the multimeter, so let us know how that goes

Looks like a pretty nice setup, Not bad for someone as supposedly ecm Unsavvy as you claim to be.

 

Bort.. I've got to tell you.. I really am a twit when it boils down to it but, somehow in the end.. things work as I "plan" (mostly..)which, is what really counts I suppose

The survey says,, the diag. test wire has 4.97v on it with the key in the run position, from there, leaving the tester probe in the back of the ALDL connector and running to any ground (including straight to the battery) will not put the ECM into test mode. It still flashes a brief second like it's going to do it and you can hear the fan realy click on & off but after that split second... nothing.
I probed the diag wire at the interior harness connector & at the ECM to ground with the same results.
I'd says it's pissing me off but, it's more annoying than anything.

Based upon getting voltage from the test wire.. I'm guessing I didn't cook the ECM (completely) but, I'll be dammed if I know why it won't give me any codes. Maybe the ECM is pissed it's not in an F-body

As soon as my bud finds the o2 bung I bought, I'll be getting that welded on the collector, hopefully that will help smoothe out the idle a pinch (a new timing chain and some cut to fit plug wires wouldn't hurt either tho...)

I wish santa would bring be a hand scanner

 

Well, it just goes to show that if we could teach Chimp's to follow directions, we wouldnt have to work on our cars ever again.

Sounds like you might have a cooked ECM, personally.

I normally hate it when people say this as the tell-all end-all of TPI troubleshooting, but See if you can get a known Good ECM to try. Id let you use some of mine but I imagine your a bit far.

Either try to find a member from here, or someone local to you.

the 165 ECM"s can also be found on ebay, but its a shame to Spend money in the Diagnosing process.

And Don't waste your money on the Pocket Scanner... In 20 minutes you can build your own Two Transistor interface, and have winaldl or craig moates up and Running.

I didnt think it was that easy, Untill I did it. And I assure you, Im not eletrical engineer. hahaha

 

:sillylol: :sillylol: .. if only it were so easy...

I'm going to assume (for motivation to do this..) that the ECM is going to pretty much be the same in my 'bird ('87 305 maf tpi). I may just run by my buds house in a little while and grab the ECM out of the truck and swap them around in my car just in case there is a wiring problem w/in the truck.. I'd rather not bake my ECM too (because I just bought it a few months back).

Another question which might be stupid but, would there not be other problems as well if the ECM is toast ?
I would think it would run like crap or not at all or maybe at least the SES light not going off. If it's just a matter of the diag. test part being fried and the rest good.. I don't think that's anything to worry much about do you ?

Maybe santa needs to bring me a nice laptop instead huh ? ... I doubt it.. maybe some coal though..... lol

 

Yes, the ECM in your 87 is the same

As far as weather or not the ECM being bad would cause more problems... who knows.

Anyone who works with eletronics can tell you that things fail in unexpected ways and cause unexpected symptoms. At leasts, thats what I would tell you. Maybe I just don't have enough experiance.

The Important thing is, if you swap ECM's you will instantly know if it was the ECM or not. If its not, you can move on to other areas of troubleshooting. If it is, your done.

Troubleshooting is about eliminating Variables. Here the ECM is a variable, so Eliminate it.

 

Well.. I was finally able (after a slight timing chain problem on my camaro ) to get my friends ECM over to my house today and put it in my 'bird with... :drumroll:.. the same results
The fan relay clicks for a split second along with the SES light breifly flashing then, nothing. So, I guess that part of the ECM circuit is pretty much toast.
Since everthing else about the ECM seems to be operational, I suppose there's no harm in just running it as is for now. The truck really isn't going anywhere soon...

One last question, w/o the ECM closing the IAC, is there another way to get it fully closed to set the min. idle air or would just taking the IAC out (I'd clean it too but I already did that), extending the plunger(?) by hand and screwing it back into the TB be the easiest way ?

Thanks once again for the help up to now Bort

 

Why not just grab another ECM cheap off ebay ?

Your going to need it sooner or later, and who knows what other problems this is causing that you can't identify.