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Car Forum / Driving, Maintenance, Tuning / Maintenance and Repair / February 2005GM3.1L no spark
As per sublect line.....no spark. Verified crank sensor working (.7v pulses), swapped ignition module with a known good one, and have 12v at the module input. I know from past experience that a bad coil van completely knock out the spark on the rest of the coils....tried using 1 coil at a time with all 3.....no dice. Does the ECM control the generation of coil pulses at cranking or just after it gets out of open loop operation? Haven't checked for the pulse input and output at ECM yet...that's next. BTW...the voltages and grounds at ECM are OK. Need to check for the 5v reference for the sensors that use it to verify the 5v regulator in the ECM is ok. Any thoughts? Travis. Try and get it on a scanner and see if the pcm is getting an rpm signal/ > As per sublect line.....no spark. Verified crank sensor working (.7v > pulses), swapped ignition module with a known good one, and have 12v at [quoted text clipped - 9 lines] > > Travis. > As per sublect line.....no spark. Verified crank sensor working (.7v > pulses), swapped ignition module with a known good one, and have 12v at [quoted text clipped - 9 lines] > > Travis. Perhaps this article will be of help: http://www.motorage.com/motorage/article/articleDetail.jsp?id=20037 That article was a good overview on the theory of how est operates, but it wasn't engine specific. Now I have checked the 5v output on the ECM...its there. When checking for the ref pulse in (ref HI, ref Low) I didn't see much going on. There was some activity, but super low level. Seems to me it should be a little closer to the signal coming off the crank sensor, or even close to logic level for the ECM to use as a digital input. Speaking of the crank sensor, I read on this group someone's post describing the crank sensor "kicking the ignition module in the nuts until it collapses". I ask.....can the output pulse from the crank sensor be too high a voltage and damage the input circuit of the module? Some poster said the output of this type crank sensor should be ~300mv. Mine is putting out 700mv, whick doesn't sound like it should cause problems, but I could be wrong here. Possible for a cr. sensor to take out an ignition module? So here's where I am as of now. If the module is doing its job properly, I assume the ECM has failed. This wouldn't surprise me too much...I've already replaced it twice. Any takers? Travis > Perhaps this article will be of help: > http://www.motorage.com/motorage/article/articleDetail.jsp?id=20037 Some wave forms: (with volts) http://www.picotech.com/auto/waveforms/crankshaft_sensor.html http://www.interro.com/wav.htm#28 > Some wave forms: (with volts) Good job Paul! > http://www.picotech.com/auto/waveforms/crankshaft_sensor.html Inductive crankshaft sensor, 2 volts peak to peak on the AC scale. (there's a clue) > http://www.interro.com/wav.htm#28 Second batch down, under "Channel lab scope", the top wave form again is an inductive crank sensor, shows 8 volts peak to peak AC volts (suspect it's a running engine). 700mv isn't indicative of a good crank sensor. >> Some wave forms: (with volts) > [quoted text clipped - 10 lines] >again is an inductive crank sensor, shows 8 volts peak to peak AC >volts (suspect it's a running engine). 5 volts on a scale of 8 >700mv isn't indicative of a good crank sensor. in a 5 volt logic circuit, 0.7 volts would be considered a logic low Lg > >Second batch down, under "Channel lab scope", the top wave form > >again is an inductive crank sensor, shows 8 volts peak to peak AC > >volts (suspect it's a running engine). > > 5 volts on a scale of 8 Okay, 5 volts, that makes 10 volts AC peak to peak. (waveform tagged "YLO") > >700mv isn't indicative of a good crank sensor. > > in a 5 volt logic circuit, 0.7 volts would be considered a logic low Given the two examples posted, his crank sensor is not capable of achieving the voltage level that is characteristic of that type of crank sensor, IOWs, it's kaput. >> >Second batch down, under "Channel lab scope", the top wave form >> >again is an inductive crank sensor, shows 8 volts peak to peak AC [quoted text clipped - 12 lines] >achieving the voltage level that is characteristic of that type >of crank sensor, IOWs, it's kaput. If he can buy a new one at a dealer and install it himself...that is the magic question. He needs that 5 volt output, or darn close to it. I would call anything less than 3.8 or 4 volts not good enough. Lg > If he can buy a new one at a dealer and install it himself...that is > the magic question. He needs that 5 volt output, or darn close to it. > > I would call anything less than 3.8 or 4 volts not good enough. > > Lg On the other hand, the OP hasn't yet mentioned what model year this 3.1 is, IIRC there are a couple of versions of crank sensor depending on when it was built... >> If he can buy a new one at a dealer and install it himself...that is >> the magic question. He needs that 5 volt output, or darn close to it. [quoted text clipped - 6 lines] >this 3.1 is, IIRC there are a couple of versions of crank sensor >depending on when it was built... This is True. There are many *generations* of logic, too many to mention, that have differing requirements regarding VCC and input signals. That is -a- problem trying to diagnose things via long distance, where you can't be there to see things for yourself. It is a universal problem. I mean, the OP would best be served by going to a dealership or somebody and asking a tech "What is the output voltage for this sensor _supposed_ to be." That is maybe how I would approach it. But if it is an older vehicle, or the dealership isn't going to make any money off you, they might not bother to go to the trouble to look up the specs. OTOH, if you tell them you need a new part at the parts counter, -then- you can ask the question and expect a proper answer. At least this is my experience. When you are flashing a *wad* of money in the air at the parts counter, looking eager to hand it over, THEN they go ask the tech for you ;) Lg This is the 1990 version of the 3.1. I read the output pulses of the sensor on the DC scale of my Fluke 79 to see if they were consistant (the 79 has the bar graph on the display and reacts very quickly to the input). Now that I think of it....when troubleshooting another problem a few months back on this vehicle I read the output of the crank sensor and it was the same as it is now. All was well until about a week ago when it just refused to even fire one day after running great the night before. As far as the sensor needing to put out a logic level sine wave, I doubt this was the plan. They are probably amplifying the wave at the module then diode clipping it to get a useable digital pulse. Travis > On the other hand, the OP hasn't yet mentioned what model year > this 3.1 is, IIRC there are a couple of versions of crank sensor > depending on when it was built... >This is the 1990 version of the 3.1. I read the output pulses of the >sensor on the DC scale of my Fluke 79 to see if they were consistant [quoted text clipped - 12 lines] > >Travis That all makes *sense,* but we can come up with 1,000 scenarios that make sense, that have nothing to do with the solution to the problem at hand. This is why I like to build a *library* of engine parameters on my known good engine, so I can see if something is *drifting out of tolerance.* I have the Motorcraft.com data sheets on my engine parameters, but I much rather have the real, than theoretical values they give. IOW, I measure what things are when all is running correctly, and use that as a baseline to which to compare future readings. I am able to do that with my Carchip e/x, which reads engine parameters under -dynamic- conditions, rather than at idle in a shop bay. I build the library, and save it to a database, and in the future, I have -real- data to refer to, rather that the hypotheical *stuff* motorcraft offers up at www.motorcraft.com, although I wouldn't call their publications useless. My car has it's own parameters/tolerances, those are what I want to know about. At 5 second monitoring intervals, I can get 25 hours of driving time on to a chip before I have to download it. But some parameters, like you crankshaft sensor voltage, that would have to be measured with my Fluke 97 50 MHz Scopemeter. I don't envy the day I may have to do it, then, otoh, I may never have to do it, as my powertrain is warranted for the life of the vehicle as long as I am the original owner. At least, that's whay they -say-. I even have it in writing, but their condition is to have ALL routine service done at their shop, at 10x what I can do it for myself, so, there is always the *catch 22.* They'll screw you one way or the other, so it is best to learn how to do some of these things for yourself. Lg > As per sublect line.....no spark. Verified crank sensor working (.7v > pulses), swapped ignition module with a known good one, and have 12v at [quoted text clipped - 9 lines] > > Travis. Here's some answers given you still haven't told the group what model you're working on -- info will be general to the 90 3.1 V-6. Can a crank sensor damage an ICM? - If you throw it hard enough. Not a problem because yours is functioning. 0.7 volts as measured with a RMS DVOM is good at cranking speed. You've done the correct step to verify good CKP input to the ICM. Do I have a decent input from the ICM to the ECM? -Check the Dref high wire (Purple / White) with positive lead and Dref low (Black / Red) with negative lead AT THE ECM. Your RMS Fluke should show maybe about 3 volts (it's a 5 volt square wave). Check signal frequency in Hz if you can for cranking speed reading. For your engine ---> (Hz * 20) = RPM. So perhaps about 15 to 25 Hz would be right. Do I have a spark command from the ECM to the ICM? -Check the EST wire (White) at the ICM for voltage. This is trickier. Under aprox. 400 RPMs it should be a 0.5 volt square wave. Above 400 RPMs it should be a 5 volt square wave. You can check Hz on this wire to verify a pulsing signal. (Hz * 20) = RPM. Whats the deal with 400 RPMs? -Thats the point that the ECM tells the ICM that its taking over spark timing control. It does this with the Bypass Wire (Tan / Black). This wire should read aprox. 0 volts under 400 RPMs and aprox. 5 volts above 400 RPMs. If it stays at 0 volts at high cranking speeds (with battery charger assist) suspect a grounded wire or bad ECM. Of course this is an OBD I GM, so suspect a bad ECM. But test the wire anyway for educational purposes. Essentially, a good EST signal at the ICM would suggest a bad ICM. Check for B+ to your coils (Pink / Black) and ground to both modules (Black / White) if all else fails. Do this while cranking to load the circuits. Toyota MDT in MO Excellent info Comboverfish! That was exactly the response I was looking for. Now I know exactly what to look for and can isolate what is not operating as intended. Sure would be nice to have a scopemeter to check out how all the control pulses look. I have several bench scopes but don't really want to haul one outside to putz with this thing. The meter should let me know what's going on good enough. Thanks again. I'll post my findings when I get it all checked out. Travis > Here's some answers given you still haven't told the group what model > you're working on -- info will be general to the 90 3.1 V-6. [quoted text clipped - 33 lines] > > Toyota MDT in MO Cool! I'm layed up here at home as sick as a dog so all I can do is type right now. Wish I could be doin' the testin' instead! <g> Its good that you have the scope as a backup -- but if you can get RMS voltage and a reliable Hz reading out of your Fluke then thats 50% of the info you would glean from a waveform anyway. Have fun, Toyota MDT in MO >Cool! I'm layed up here at home as sick as a dog I've had bronchitis going on for about 3 weeks now. Nice to have your company. Maybe it will turn into pneumonia? > so all I can do is >type right now. Wish I could be doin' the testin' instead! <g> [quoted text clipped - 5 lines] > >Toyota MDT in MO Ok, just got done with testing....here's what I found. Reference pulse was not there, same for the EST control signal. However, when I looked for the EST bybass, it was stuck at battery voltage. This leads me to believe that the logic IC that is responsible for putting out that signal has shorted to the supply. Now I ask this....is that output that should be at logic level likely to have damaged the ignition module's input? Not knowing if the input is TTL or CMOS makes me wonder. Perhaps if it is cmos powered from 12v it may have survived. If it is TTL it is surely damaged. So I'm off to find a replacement ECM tomorrow and I just may get a replacement module just for good measure. Travis > Cool! I'm layed up here at home as sick as a dog so all I can do is > type right now. Wish I could be doin' the testin' instead! <g> [quoted text clipped - 5 lines] > > Toyota MDT in MO > Ok, just got done with testing....here's what I found. > [quoted text clipped - 12 lines] > > Travis I would suspect that the input is TTL feeding a CMOS output - but I don't know for sure. The last one that burned out on my own car I opened up and looked at the parts. The only things that appeared to be CMOS were the output transistors/ic's. Also, I would think that it's possible that a constant high burned out it's brain. Wow. Dref and EST activity were zero while cranking? I mean, you're only looking for ~0.3 volts on EST below 400 rpms and ~3 volts above 400 rpms on a DVOM. But the 12 volts on the Tan / Black bypass wire seems bad, very bad. There may be a corroded spot between two terminals in the ECM connector. You may have a short to power in the harnass or I guess the ECM could have failed. Maybe you could tell me -- could the ECM have a zener diode in the 5 volt reference circuit that could fail and pass full battery voltage? That seems weird. But if you have an adequate crank sensor input, then during sub 400 rpm operation (or if you pull apart the bypass wire connector in the passenger footboard area) you should get base spark control to the coils. Suspect the ICM if you have proper powers and grounds -and- you fix the 12 volt bypass problem. I still think your crank sensor should be good enough to trigger the ICM. Did you get the 0.7 volt reading previously with your meter in the A/C volts setting? Just checking. Try this article I just found. http://www.asashop.org/autoinc/may97/techtips.htm It's written better than I could dream of writing on this subject. Don't let the title of code 42 detract from its relevance here. Its pretty detailed. Toyota MDT in MO I think you're dead on. Excellent diagnosis. I've got a 95 Lumina with a 3.1 and could possibly do some ref checks, however I think my readings below 400 rpm would be erroneous. With 12vdc on the ignition bypass circuit chances are good that he might of fried his "known good ," control module also. I might be worth disconnecting the wht wire, till it is known that it will be putting out a proper signal before and after the 400 rpm. Let me know if I can't oblidge in taking some ref measurements. JP Found a relacement ECM, had just enough daylight to slap it in and check for spark, no dice. Did not have time to check out what was happening, so the next day went out to do some checking and the hood latch was stuck (frozen) closed. got a couple of warmer days ahead so I'll do some checking when I can get the damn thing open. Gonna verify wiring from the module to the ECM, but I'm convinced both once working modules are now junk from the battery voltage sent to the bypass line. Should fire right up after the module is replaced. I just may pop one of the toasty modules open to see if any of the parts are identifiable, maybe try to repair one just to see if it can be done. Findings will be posted when they're....uh....found. > I think you're dead on. Excellent diagnosis. I've got a 95 Lumina with > a 3.1 and could possibly do some ref checks, however I think my [quoted text clipped - 6 lines] > > JP any luck yet?1 Well kids.....got it fired up today. Kinda lost interest in it for a while but decided to fool with it some more. After taking care of the rest of the problems, a new crank sensor did the trick in bringing it back to life. I already had the sensor, so it didn't really cost me anything. Just the will to wiggle under the damn thing and get it done. Next project.....get the heater blower diverter to do its job. Right now its just stuck....not in any particular position. Service information on this in the Haynes type manuals is, well, non existant. > any luck yet?1 > Well kids.....got it fired up today. Kinda lost interest in it for a > while but decided to fool with it some more. After taking care of the [quoted text clipped - 6 lines] > information on this in the Haynes type manuals is, well, non existant. > > any luck yet?1 Did you find out anything about the 12 volts on the bypass wire? Toyota MDT in MO > Did you find out anything about the 12 volts on the bypass wire? > Toyota MDT in MO That 12v on the est bypass line was due to the ecm gone south. So I ended up replacing that, the ig. module, and the crank sensor. My guess is that the cr sensor tested good by itself, but was actually failing when loaded by the module's input. Maybe a shorted turn in the coil somewhere. |
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