Guest radiotradio Posted March 30, 2007 Share Posted March 30, 2007 This may be a clue to other problems posters are having. My number 1 injector signal goes away during the miss. The pulse measures about 13 volts and is almost 6 mSec wide. The red injector wires appear common as they are hooked together. All of the injectors have a pulse except number one when the problem appears. It is now necessary to figure out where the injector signals originate. I think it is the engine control computer, but not sure at this point. The ground of the oscilloscope probe is connected to the red wire of number one injector plug and as the signal is measured at each of the other injectors black wire, it appears OK, so now it is off to find a different box. Can anyone help with locating one? I have a U-pick junk yard near by.....which ones will work? I believe the EPROM must be changed from my box to the new one, but not sure. The Reatta is a 1990 with a rebuilt engine. I think, at this point, this will fix my haunting problem. Where is the ECM located and how do I get to it? thanks Jack Link to comment Share on other sites More sharing options...
padgett Posted March 30, 2007 Share Posted March 30, 2007 The ECM is mounted on the side of the passenger footwell. You remove the black plastic cover with the courtesy light in it and it is mounted vertically on the side (should see the three wire bundles coming down).Since the injectors are individually driven by the ECM, it and the wiring harness are likely culprits. With an intermittant, I would suspect wiring first particularly if the engine had been removed/replaced. Link to comment Share on other sites More sharing options...
Guest radiotradio Posted March 30, 2007 Share Posted March 30, 2007 Thanks, I wondered if anything else may turn off just the number one injector. My knock count is high and thought maybe it may cause the computer to do something wierd. I will check the computer connector. I do have a wiring diagram showing the ECM and the module wiring. It comes and goes, just like a switch. I have a can of freeze mist spotter, to use on the computer when I find it. I will ring out the wiring for that injector. Compression is 130 pounds. Vacuum does not change. Thanks for your help! jack Link to comment Share on other sites More sharing options...
2seater Posted March 31, 2007 Share Posted March 31, 2007 No event would cause one injector to stop operating. Constant B+ to all injectors with switched individual grounds in the ECM. Only wiring, harness connection or the ECM itself would cause loss of injector pulse. The wiring is nothing special. You could run an external bypass wire from the #1 ECM connection around to the injector itself. There are a multitude of grounds used in the ECM and I imagine you could simply probe the correct connection at the ECM to see if the ground is turning on and off. The injector and other harness connection is at the right rear of the engine, sort of behind the power steering pump. If it is okay cold but acts up as it warms up, it does sound like the ECM is getting warm enough to have the injector driver fail. The other point Padgett made about the connection and harness being disturbed in an engine change is certainly something to look at too. It shouldn't happen but the engine comes out toward that side of the car so something could get pinched or crunched. Link to comment Share on other sites More sharing options...
Guest radiotradio Posted March 31, 2007 Share Posted March 31, 2007 Thanks for the information, guess when I referenced the common wires, the pulse appeared positive on the scope, but would have thought a sinking ground connection would be a much better idea than supply a hot. The injectors all read 15.1 ohms. As I remember, the common connections all read about 200 ohms to ground. The pulse was measured with the injector connected so as to load the circuit properly. I will rig a jumper this weekend as the physical wiring is ruled out. I hate to think chassis wiring is a problem as most would assume it to be OK and the problem would lie elsewhere. Hot on the trail.........thanks........jack Link to comment Share on other sites More sharing options...
2seater Posted March 31, 2007 Share Posted March 31, 2007 You probably know more about how the actual circuit works than I do <img src="http://forums.aaca.org/images/graemlins/grin.gif" alt="" /> The impedance sounds right, used in what they call a saturated circuit. Current draw about 1 amp or so to operate the injector. Good enough response time for most street engines. Low impedance in the 2-4 ohm range are used also, useually in the high performance/high flow types, although not a universal rule there. Quicker response but a lot higher current draw and as far as I know, the hot side is switched using different drivers in the ECM. Link to comment Share on other sites More sharing options...
Guest radiotradio Posted March 31, 2007 Share Posted March 31, 2007 If I can find the individual driver circuits within the computer, I will spray them and the associated circuitry with freeze mist (-40 degrees). I would expect the pulse to to be shown (returned) as the circuit cools. From all indications, at this point, it will be the ECM. It may even have replaceable drivers. jack Link to comment Share on other sites More sharing options...
ikesleeping Posted March 31, 2007 Share Posted March 31, 2007 My 90 had an miss that came and went sometimes to the point of shutting off the engine. Finally got a tech to hook up analyzer as I drove it and could clearly see injector pulse not being triggered replaced ecm and problem went away never to return. I think most gm techs or dealers have this tool. just my 2 Link to comment Share on other sites More sharing options...
2seater Posted March 31, 2007 Share Posted March 31, 2007 You can operate the car with the ECM laying on the floor, which will allow it stay cooler. I have seen sites that describe modifications to the ECM's to operate low impedance injectors, but can't find the link <img src="http://forums.aaca.org/images/graemlins/frown.gif" alt="" /> It sounds like you know about the workings of the electronics, so maybe something will be apparent? Bad solder joint or somehing physical? ECM's aren't terribly expensive and Jim Finn could probably help you with a good takeout. I would bet on the ECM at this point also. Link to comment Share on other sites More sharing options...
Guest radiotradio Posted April 1, 2007 Share Posted April 1, 2007 Pulled the ECM today and have it running with the cover off on the passenger floor. It does not act up. Probably not getting hot enough although the garage ia 80 degrees. Ran it with the scope hooked up for 1/2 hour without fail. It always failed much sooner than this. It has the following numbers: Serv. # 01228253, 868064 and M010572145. I will try to get a another unit. New or Used? I don't think I will assume a bad connector connection. It was a bear to get the front of the ECM free from the bracket. I used muscles that haven't been used in awhile. Probably will have a few pains tomorrow. I'm 6 foot and 240 pounds, much too big for the Reatta floor. <img src="http://forums.aaca.org/images/graemlins/grin.gif" alt="" /> jack Link to comment Share on other sites More sharing options...
2seater Posted April 2, 2007 Share Posted April 2, 2007 It does sound like a good clue it may be heat inside the ECM or very slight chance the wiring/connectors are now in a different position. The connection is pretty tight, as I am sure you know, so I would think that is unlikely. Link to comment Share on other sites More sharing options...
Guest radiotradio Posted April 2, 2007 Share Posted April 2, 2007 <img src="http://forums.aaca.org/images/graemlins/smile.gif" alt="" /> Fixed, at last. Replaced the ECM with one from a 1990 Big Buick, swapped the Mem-Cal EPROM (personality module)and it fixed the number one cylinder problem. I think the Reatta is still a very cheap 2 seater too own and repair. The brakes and engine problem were repaired for less than $100.00. I did spend another couple hundred changing the ICM/coil pack ($40.00) and accumulator ($125.00) and an injector ($10.00) that I did not need, but now I have some spare parts. I spent some time on it (20 hours), but I now understand the brakes and engine quite well. It will be in Traverse City this time next week, as it is running like new now. The availability of parts has not been a problem thanks to forum members, junk yards and Ebay. I think, I too, will now be happy driving a 17 year old Buick. <img src="http://forums.aaca.org/images/graemlins/cool.gif" alt="" /> Thanks again for everyones help. Jack Link to comment Share on other sites More sharing options...
2seater Posted April 3, 2007 Share Posted April 3, 2007 Thank you for sharing the fix with us. The sort of funny thing about the ECM failures is it doesn't really seem to matter what the miles are, just the age of the units? Link to comment Share on other sites More sharing options...
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