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1998 5.7 GMC Van P1351, PO171, PO174
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speed
User
Mar 17, 2012, 11:53 AM
Post #26 of 72
(9212 views)
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Re: 1998 5.7 GMC Van P1351, PO171, PO174
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been watching this thread from afar and i have a question about it. is it possible that the timing is misadjusted causing the high voltage in circuit code beacuse its at the wrong time? if thats ruled out is it possible that there is something wrong with the reluctor ring for CKP sensor?
GM ASEP 26 SCC Milford ASE certified in Brakes and Electrical on Thursday April 5th 2012
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Discretesignals
Ultimate Carjunky
/ Moderator
Mar 17, 2012, 1:34 PM
Post #27 of 72
(9205 views)
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Re: 1998 5.7 GMC Van P1351, PO171, PO174
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It's unlikely that the if the distributor was out of synchronization a P1351 would show up. If the distributor was way off, the engine wouldn't start and if it it is was running and off enough it would set a P1345 code for a correlation fault between the cam sensor and the crank sensor. Turning the distributor doesn't affect base timing, it affects cam sensor angle which affects fuel injection synchronization. Remember this system uses the crank sensor on the timing cover to determine the order of the cylinders and base timing.
The way it works is that the PCM is sending a 5 volt digital square wave signal to the ICM to trigger the transistor that turns the ignition coil's primary circuit on and off. The actual signal is between 1 to 4 volts because of resistance in the circuit. It is built that way, so the PCM can recognize an open, shorted to power, or shorted to ground circuit.
The illustration below is an ignition trigger signal in blue that should be traveling on that IC circuit wire. Even though this waveform is for Toyota, the signal is probably similar to the GM's.
If the PCM sees 5 volts all the time on that circuit while your cranking the engine, the PCM assumes the circuit has an open. That is when the P1351 code appears. The open could be in the PCM, wiring, or the ICM. I'm assuming that since that code is appearing, the PCM isn't able to trigger the ICM and that is why he doesn't have any secondary action going on.
I'm attempting to get the OP to check all the wiring and make sure that the grounds are good for those components. It's possible a high resistance ground for the ICM could cause that code. Just using the process of elimination.
The next thing I am going to ask the OP to do is to disconnect the ICM connector and short the white wire IC trigger circuit to ground and then crank the engine. This should cause the PCM to set a P1361 code, which is IC trigger circuit low voltage. If that code sets, that means the wiring from the IC to the PCM is good and the PCM can recognize a low voltage and high voltage condition in that circuit.
If the PCM can recognize an IC low circuit voltage condition, then the only thing I have left to advise is one of two things:
(1) The signal is going to have to be scoped to see what the signal actually looks like.
(2) Use a signal generator to pump a waveform down the IC circuit to simulate the signal from the PCM and see if the coil fires. This would eliminate everything after the PCM.
If the signal looks funky on a scope or a signal generator can fire the coil, more than likely the PCM is the culprit.
Since we volunteer our time and knowledge, we ask for you to please follow up when a problem is resolved.
(This post was edited by Discretesignals on Mar 17, 2012, 2:10 PM)
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speed
User
Mar 17, 2012, 2:53 PM
Post #28 of 72
(9185 views)
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Re: 1998 5.7 GMC Van P1351, PO171, PO174
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i see, lol im still learning thankyou for clearing all that up though DS
GM ASEP 26 SCC Milford ASE certified in Brakes and Electrical on Thursday April 5th 2012
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b_oneself
User
Mar 17, 2012, 7:54 PM
Post #29 of 72
(9173 views)
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Re: 1998 5.7 GMC Van P1351, PO171, PO174
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Finally, a minor (or maybe even major) breakthrough! This post concerns the confusion arising over the issue of whether or not I was getting 12 volts at the (D) terminal of the ICM. And here's to the value of double-checking -or repetitive validating in the scientific method: OK, so here's the deal. Following all the procedures carefully and by the book I check the (D) terminal on the ICM and get nothing. I repeat the process and now I get 12 volts. I repeat the test many times over, sometimes getting 12 volts, sometimes nothing. I realize eventually that connector on the coil definitely has a way loose connection. (My harness has only 2 wires (A & C) -no (B) because there is no tachometer in the vehicle. Even though the two wires are snugly in the plastic (no movement at all), there is clearly much slop between the male & female when plugged in - meaning either the posts (pins) in the new coil are a slightly smaller dimension, or my female connector plug (receptacle) is worn out, ie., the hole is too big. I'll work on resolving that loose fit next chance I get. I can imagine why this is preventing the engine from getting spark. Is there any chance it could also be the cause of my P1351 trouble code? It would be great to have this van starting again.
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Tom Greenleaf
Ultimate Carjunky
/ Moderator
Mar 17, 2012, 8:24 PM
Post #30 of 72
(9168 views)
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Re: 1998 5.7 GMC Van P1351, PO171, PO174
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If you found a sloppy connection like that I'd concentrate on that. Your call and I'm not looking at this connection but there are things you can do to make them work dependably depending on just how they are made - things like torquing/twisting the male or a gentle squish on a female or take very small screwdriver and see if it can be persuaded without harming it,
T
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b_oneself
User
Mar 19, 2012, 4:30 PM
Post #31 of 72
(9150 views)
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Re: 1998 5.7 GMC Van P1351, PO171, PO174
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Alas, my adventure with this no spark issue is not over. I did indeed have a very sloppy connector at the coil which I by-passed with alternative wiring (strong 12 volts every time now at terminal (D) on the ICM). I repeated every test on the ICM connector (A,B,C,D) and everything checked out: A (pink wire has 12 volts), B (between 2.9 - 3.4 volts when cranking ) C (good ground .3 ohms on 200 scale), D 12 volts with key in run position. I double checked the two grounds DS suggested. A friend said I should check the ECM fuse. There were two (ECM1-20 AMPS and ECMB-20 AMPS) and both were OK (a little bit coroded so I cleaned them up).
I still get the P1351 code after cranking starter for 30 seconds. I read the previous post that advised OP (orignal poster?) to ground the B wire (the wire that is never supposed to put out 5 volts to the IC trigger in the VCM) ie., "High Voltage" to see if it triggers a P1361 code "Low Voltage" and sure enough, it did exactly that. To be precise the code described "control circuit coil #1 and # 4 Low Voltage".
(P1351 ="control circuit coil #1 and #4 High Voltage) This brings up a point that Hammer Time first mentioned, namely that there is only one coil on this engine and, I presume one control circuit.
I did note that Discretesignals recommended one of two final checks (both of which seem beyond me), before concluding the VCM or PCM or ECM ie., the "computer", is kaput. I've been pricing them (between $110 and $200 plus a "computer set-up" fee. The biggest problem is I've been told they have to ship them off (to Florida or somewhere) in order to do this -if it is possible (according the vehicle ID, the part # and whatever else?) Is this the only way to change out the VCM ? I appreciate all the help I have been getting at CarJunky.com
(This post was edited by b_oneself on Apr 2, 2012, 1:39 PM)
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Discretesignals
Ultimate Carjunky
/ Moderator
Mar 19, 2012, 5:16 PM
Post #32 of 72
(9141 views)
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Re: 1998 5.7 GMC Van P1351, PO171, PO174
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By grounding the IC circuit and getting the P1361, you pretty much confirmed that the circuit between the ICM connector and the PCM is good. It would be really nice to see that waveform on the circuit when you crank the engine to even see if the PCM is generating a signal for confirmation, but I think you pretty much have gone as far as you can with what you have. If it was generating the correct pattern signal, I would say you probably are looking at a defective ICM. It is going to be unlikely that you would have three ICM in row that are faulty, but there is always a possibility.
The VCM does need to be programmed for your vehicle's options. The VIN allows the programmer to select the correct calibration to program the VCM with. You have to understand that the same VCM can be used in other vehicles with different options. The VCMs are physically the same, but its the software that makes them different.
Since we volunteer our time and knowledge, we ask for you to please follow up when a problem is resolved.
(This post was edited by Discretesignals on Mar 19, 2012, 5:25 PM)
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b_oneself
User
Mar 19, 2012, 6:53 PM
Post #33 of 72
(9124 views)
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Re: 1998 5.7 GMC Van P1351, PO171, PO174
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Rats. Could you please confirm where exactly the VCM is located. This is a Savannah 3500 van (box truck). For some reason I thought the computer was accessed inside the cab on the driver's side, inside the fender well just below the spot the brake pedal goes into the master cylinder. Now I'm wondering whether it is inside that black hard plastic case directly below the master and power steering fluid reservoir (that has been leaking onto that plastic case for years- it's very soaked with that fluid) that you get to from the front hood, right next to the fuse box/power distribution station. I can't believe they would put the VCM in such a vulnerable place that looks like it's really difficult to extract. Plus it has 4 distinct harness plugs going into it. The computer harness plug-in connectors I've seen before are always in a long row held by a couple screws -and located in a protected area (inside the vehicle). Is it possible I am looking at the wrong place?
(This post was edited by b_oneself on Mar 25, 2012, 7:59 PM)
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Discretesignals
Ultimate Carjunky
/ Moderator
Mar 19, 2012, 7:17 PM
Post #34 of 72
(9121 views)
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Re: 1998 5.7 GMC Van P1351, PO171, PO174
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It is in on the left side of the engine compartment on the fender right underneath the fuse relay center and PS reservoir. It does have four connectors with a lot of wires. PS fluid leaking all over it isn't a good thing.
Since we volunteer our time and knowledge, we ask for you to please follow up when a problem is resolved.
(This post was edited by Discretesignals on Mar 19, 2012, 7:18 PM)
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b_oneself
User
Mar 19, 2012, 7:33 PM
Post #35 of 72
(9113 views)
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Re: 1998 5.7 GMC Van P1351, PO171, PO174
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So then is it necessary to pull the master, the metal brake lines, the power steering fluid reservoir, -more? before one can get at the VCM. Now that you have clarified the location I'm trying to see about finding that particular ground on the unit you mentioned previously. I obviously did not see it before. (as a last ditch effort to avoid this ultimate verdict about the VCM). Thanks, Bob
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b_oneself
User
Mar 25, 2012, 10:44 PM
Post #36 of 72
(9087 views)
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Re: 1998 5.7 GMC Van P1351, PO171, PO174
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Alright dear experts,
As per post #27, #32, & #34 (Disgretesignals), I should like to present my latest activities and findings. I ended up replacing my computer (PCM, VCM), had it reprogrammed-calibrated, and did a number of further tests to diagnose the no start/ no spark problem. I acquired the full wiring schematic for the engine (from every terminal # on the ECM - all the #'s from the 4 connectors), checked the power leads and grounds going from the harness (4 connectors) to the VCM and everything checked out. Replaced the ICM and coil and crankshaft position sensor (CKP) once more. My mechanic buddy noted that the space from the magnetic pick-up of the CKP to corresponding rotating metal inside the timing chain cover was at least a 1/4 inch, more than he has seen before. The book says minimum gap .030 but does not mention maximum space. We definitely have 12 V and ground and good signal wire to VCM from CKP. In addition when my buddy simulates the CKP signal by moving the (removed) CKP in and out of the magnetic zone (metal/ground) we hear the injector signals going off but still no spark from coil secondary. He keeps thinking: the ICM, the coil, the CKP and now the VCM with all the wiring/fuses checking out correctly -what else could there be???? The latest jab is going to be to disconnect the fuel injector connector, and then each subsequent connector, one at a time, and see if there isn't some short causing an incorrect signal to "double-back" to the VCM and preventing the interruption of that 1-4 volts to the trigger in the VCM. This same buddy (who knows way more than me) did get a waveform report on his more sophisticated scanner tool that definitely showed an abnormal pattern. Furthermore, he is beginning to wonder whether the camshaft position sensor (CMP) -which works with the CKP, in some unknown way, within the VCM) is messing up and preventing the spark.
I'm going after it again tomorrow. Any new ideas to help uncover this perplexing puzzle?
(This post was edited by b_oneself on Mar 30, 2012, 5:11 PM)
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Discretesignals
Ultimate Carjunky
/ Moderator
Mar 26, 2012, 4:55 AM
Post #37 of 72
(9078 views)
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Re: 1998 5.7 GMC Van P1351, PO171, PO174
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Can you post a pic of the abnormal waveform?
Back probe the coil connector on the white IC control wire and connect a voltmeter and measure the voltage at that wire with the ignition turned on.
If you show no voltage, take a 12 volt test light and connect it to battery positive. With the ignition turned on take the probe and tap on the back probe. Don't hold the probe on there, tap on it like your doing morse code. See if the coil fires.
Since we volunteer our time and knowledge, we ask for you to please follow up when a problem is resolved.
(This post was edited by Discretesignals on Mar 26, 2012, 5:05 AM)
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b_oneself
User
Mar 26, 2012, 4:01 PM
Post #38 of 72
(9065 views)
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Re: 1998 5.7 GMC Van P1351, PO171, PO174
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D.S.,
No, I cannot, at the moment, send the waveform we saw on my friend's Snap-on diagnostic scanner tool (Vantage MT2400-"Power Graphing Meter"). I am too ignorant -(barely learned how to use the computer and navigate cyberspace). But, I can describe it. The tool demonstrated what the pulse should look like: it looked like 3 tall, skinny, identical, rectangular skyscrapers. The waveform we observed when measuring the signal at the CKP looked like one big fat rectangle -went immediately up the graph, then all along across the top until nearly the end of the screen, -and then down again to the bottom.
I did back probe the coil connector wire (the same wire that delivered 12 volts to wire (D- white/black) with the key in run position). That wire showed .02 volts with key off, and no volts with key on. Then we did the morse code test on the white IC control wire (the same one that puts out 1-4 volts with the starter cranking) and sure enough we get a strong spark from the coil wire (secondary circuit) that goes to the distributor. The weird thing is when we back probed the voltage on the IC trigger wire on the ICM we got the following: 1.16 volts with the key off, 3.6 volts with key on. I have the scanner tool with me but I'm not sure where to go next.
(This post was edited by b_oneself on Mar 30, 2012, 5:19 PM)
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Discretesignals
Ultimate Carjunky
/ Moderator
Mar 26, 2012, 5:12 PM
Post #39 of 72
(9057 views)
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Re: 1998 5.7 GMC Van P1351, PO171, PO174
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The trigger bypass with the test lamp proved that your ignition module and coil are good.
Channel 1 on the scope has to be back probed into the white IC wire at the ignition module. Connect your ground wire to a back probe on the black/white wire at the ICM. Make sure the back probes don't touch each other. The signal is a 0-5 V signal, so you want to set your scope's voltage range close, but not under 5 volts. It's going to be a fast signal, so you probably want your time base around 5ms/division. Your going to have to play with the time base, so you can see the full wave form. Turn your trigger on repeat and set it for the rising edge of the slope at around 1 volt. You don't need an attenuator connected.
Crank the engine and watch the signal. It should be a continuous square wave signal between .4 to 4.5 volts as long as your cranking the engine.
It's funny, but I just had a 96 Chevy 1500 with a 5.7L in the shop today. I should of scoped the trigger signal and posted it, so you could see what a good one looks like.
If you have a camera, can you film the scope? You can upload a video file into a video hosting site like YouTube and then send us the link, so we can analyze your signal.
Since we volunteer our time and knowledge, we ask for you to please follow up when a problem is resolved.
(This post was edited by Discretesignals on Mar 26, 2012, 5:14 PM)
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Discretesignals
Ultimate Carjunky
/ Moderator
Mar 26, 2012, 5:18 PM
Post #40 of 72
(9053 views)
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Re: 1998 5.7 GMC Van P1351, PO171, PO174
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I just remembered the boss has a 97 Chevy truck 350 Vortec. I'll scope that tomorrow and post the waveform.
This is a guess, but I'm thinking that you have a short to power on that white IC wire somewhere. The reason i'm thinking this is because you stated you had 3 volts sitting on the IC circuit with the key on and you had zero volts on the control side of the coil.
What that is telling me is that some other circuit that has power is shorting to the IC circuit wire and triggering the ignition module transistor to turn on all the time. With the transistor on all the time when the ignition is on or while cranking, the coil is going to be on all the time too. The coil doesn't produce a spark until the transistor is turned off. The waveform would verify this theory. This theory would also explain why the PCM keeps setting the P1351 high volt circuit code. Inspect that white wire really well all the way back to the PCM. Focus on the area you had power steering fluid leaking on to the PCM.
Since we volunteer our time and knowledge, we ask for you to please follow up when a problem is resolved.
(This post was edited by Discretesignals on Mar 26, 2012, 7:48 PM)
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b_oneself
User
Mar 27, 2012, 12:43 PM
Post #41 of 72
(9035 views)
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Re: 1998 5.7 GMC Van P1351, PO171, PO174
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Thanks D.S.,
- for sticking with this, for directing me toward a solution here, and for surmising a little about the real culprit in this mystery. I am going back to the project as soon as it stops raining. I do have a camera, but as I said I'm a definite novice when it comes to uploading, downloading, e.g., - You-Tube, etc. The only thing I'm adept at is sending a picture to an e-mail address. I'll have to study that Vantage scanner tool extensively to even perform the test you suggested, so the first thing on my agenda is to follow the line of logic in your educated guess. This is essentially my mechanic buddy's theory as well. This is why he was suggesting unplugging each connector (all the circuits), one at a time, to see if I can locate a spark from the coil -even if the engine can't start. Then perhaps I can trace how power is shorting to the IC (white) wire on the ICM. Bob
(This post was edited by b_oneself on Mar 27, 2012, 7:42 PM)
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Hammer Time
Ultimate Carjunky
/ Moderator
Mar 27, 2012, 1:10 PM
Post #42 of 72
(9026 views)
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Re: 1998 5.7 GMC Van P1351, PO171, PO174
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If you have a Vantage, that's not a scanner. It's a portable labscope/DVOM meter. It won't read codes or data.
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.
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Discretesignals
Ultimate Carjunky
/ Moderator
Mar 27, 2012, 6:23 PM
Post #43 of 72
(9018 views)
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Re: 1998 5.7 GMC Van P1351, PO171, PO174
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This is what the ignition control module trigger signal should look like on the IC circuit. I applogize for the noise on the signal. I was in a hurry cause the boss needed his truck.
With the ignition on engine off, there should be no voltage whatsoever on that circuit.
Signal at 10ms time base
Since we volunteer our time and knowledge, we ask for you to please follow up when a problem is resolved.
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Discretesignals
Ultimate Carjunky
/ Moderator
Mar 30, 2012, 5:45 PM
Post #44 of 72
(8986 views)
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Re: 1998 5.7 GMC Van P1351, PO171, PO174
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What's the latest and greatest? Curious how this one is turning out.
Since we volunteer our time and knowledge, we ask for you to please follow up when a problem is resolved.
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b_oneself
User
Apr 1, 2012, 11:34 AM
Post #45 of 72
(8944 views)
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Re: 1998 5.7 GMC Van P1351, PO171, PO174
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D.S.,
I'm going after the no spark problem again today. I've already been tracing many of the wires that go to the VCM, checking for continuity, shorts, etc. I will give a more extensive report later in the day. I'll definitely be communicating about this nagging (and expensive!) dilemma until I get to the bottom of the mystery. And, thank-you Discretesignals, for staying with me on this tricky one. You and the rest of the bunch at CarJunky.com are a great asset to the school of automotive diagnosis. Bravo!
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miracleworker
New User
Apr 1, 2012, 4:49 PM
Post #46 of 72
(8926 views)
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Re: 1998 5.7 GMC Van P1351, PO171, PO174
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Have you tried this: Make sure everything is hooked up as it should be on the engine. Take a deep breath. Close your eyes. Say a little prayer. Then see whether the engine will start.
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b_oneself
User
Apr 1, 2012, 6:28 PM
Post #47 of 72
(8915 views)
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Re: 1998 5.7 GMC Van P1351, PO171, PO174
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You won't believe this. After weeks of hair-pulling, convoluted, spending-money-out-of-control frustration with my "no spark" problem - after investing countless hours (my time as well as everybody else's) - after getting past numerous hurdles e.g., bad connectors, inaccurate trouble codes, and replacing the ignition control module (ICM) and coil 3 times, the pick-up in the distributor, the crankshaft position sensor (CKP) twice, and finally the computer (VCM) (along with the reprogramming), after all this desperate inquiry into the "no spark" condition...
...I was left in such a quandary that I followed the advice of the last one to post here, some "miracleworker". I did exactly as this one suggested, and do you know what? It started right up. It is running great -like never before! It doesn't make sense, but it's like it is a miracle. This is unbelievable!
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Hammer Time
Ultimate Carjunky
/ Moderator
Apr 1, 2012, 6:33 PM
Post #48 of 72
(8913 views)
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Re: 1998 5.7 GMC Van P1351, PO171, PO174
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Just a bad case of "overanalyzing"
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.
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Discretesignals
Ultimate Carjunky
/ Moderator
Apr 1, 2012, 7:45 PM
Post #49 of 72
(8906 views)
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Re: 1998 5.7 GMC Van P1351, PO171, PO174
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I guess you exorcised the demons. You guys aren't pulling my chain are ya? It is April 1st
Since we volunteer our time and knowledge, we ask for you to please follow up when a problem is resolved.
(This post was edited by Discretesignals on Apr 1, 2012, 7:46 PM)
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b_oneself
User
Apr 1, 2012, 7:46 PM
Post #50 of 72
(8902 views)
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Re: 1998 5.7 GMC Van P1351, PO171, PO174
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****************************************************************************8
****************************************************************************
************************APRIL FOOLS*****************************************
****************************************************************************
****************************************************************************
Alright, Okay, a little sense of humor, -don't cut me off, it's just a little practical joke!
(thanks to my niece for playing "miracleworker")
No, it wasn't really as simple as that. I wish reality could be so easy. Actually, there was some substantial progress, though, in today's endeavors, i.e., we got spark!, we found the culprit and and the engine starts. However, a new problem has developed- (i.e.; the engine shuts down 15 seconds after it starts up and runs) Because of the unusual way I stumbled into the "clue" that cornered the precise cause for my lack of spark I would like to report, in full detail, the extent of my discovery in a subsequent post where I can list the test results, divulge further critical information, and expose my method so I can ask again your advise on what I did wrong and what perhaps I can do about it. Since that explanation is rather lengthy, I just wanted to send this as a heads up before I expound on what happened in greater detail. Still, after all...it did feel a little miraculous.
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