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Old 11-04-2018, 07:29 PM   #21
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Default Re: '94 SL2 manual trans, electrical help needed

Well, I hate to admit it, but I forgot about the blue locks! I know what they are, of course, and noted them on that connector when I was removing the scabbed-on wiring a couple of days ago, but forgot about the locks when trying to extract a contact earlier today. I removed the lock and the first contact came out pretty easily...

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Old 11-08-2018, 04:33 PM   #22
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Default Re: '94 SL2 manual trans, electrical help needed

I'm back again, after wandering in the weeds for a while. Please forgive me if my posts are rambling or confusing, I simply am confused! I'm hoping just discussing it with you kind souls will finally help me see the light.

Understand, there is no issue with it cranking; problems will happen at key-on. If I can get a clean key-on cycle, the engine will fire immediately, as normal. In brief, it seems when the engine won't fire it is because the FP doesn't turn on. More specifically, I think the FP relay isn't getting power to its coil.

The problem(s) are quite intermittent, and seem to "heal" after several key-on cycles; so it is difficult to come to any conclusions when probing. The symptoms go away right about the time I think I am on to something. The only thing that seems to bring the symptoms back is to just let it sit for several hours. Understand, this is in a garage at 65F with cold engine, no big temp changes to make something "heal".

I have concluded that the engine fan is acting flaky (when problem is there). It can come on when it isn't supposed to, like at key-on; and not come on when it is supposed to, like with the paper-clip in the ALDL. And these can be on-off-on... cycles, not even a steady-state failure.

Likewise, the FP relay (and pump) may not come on at key-on, or may go on-off-on... cycles well after the 2-sec normal period.

And, likewise, the SES light may go nuts at key-on. None of these seem co-ordinated; sometimes it will be the FP, sometimes the engine fan, sometimes the SES light. I'm still trying to recognize a pattern...

I was pretty much convinced the PCM1 circuit (ignition switch)was a prime suspect, so I installed a sense wire to the PCM1 fuse. It looked like the voltage there was fluctuating more than expected (+/- .5 V), but I wasn't sure how much the meter was dampening that reading. So, I connected a scope. The reading then looked pretty good, and maybe even better on the DMM. So I cranked it and it immediately fired... healed again while I was connecting things!

With no conclusions, I then made provision to plug that sense lead going to the PCM1 fuse into the cig lighter to provide a 12V source that bypassed the ignition switch. I tried a few key-on cycles with that alternate 12V power for PCM1 and all looked good. Yippee, I'm on to it! Then next time we tried to use the car (no alt power to PCM1) it cranked and fired, but soon died and wouldn't re-start. Great, now I connected the alt power to confirm, but no joy. It wouldn't even enable a clean "key-on" cycle, much less fire the engine. Yes, the FP relay has been swapped around (although the relay should be causing the engine fan and SES light to go nuts, anyway). And yes, I realize the power I was getting from the cig lighter still comes through F6 so isn't an ideal test, but it is independent of the ignition switch, correct? And F6 also shouldn't have anything to do with the fan. Besides, the F6 contacts look perfect.

When several electrical gremlins like this appear, I tend to think of either power or grounds. So, I would like to back-probe the PCM connectors. It looks like there are only two power feeds (PCM1 and PCMB), so I will connect sense leads to both of those. But what about the six grounds, which would be the most meaningful to check? I will also connect a sense lead to the FP drive. I would like to attach all the sense leads that I need at one time, so as to avoid how many times I have to rip those PCM connectors out. They should be good for many (50, 500, 5000?) mating cycles, but I hate to push my luck as they come out so hard.

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Old 11-08-2018, 07:02 PM   #23
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Default Re: '94 SL2 manual trans, electrical help needed

I need pin-outs for those two PCM connectors (2 x 12 and 2 x 16).

I can only see numbers on the housings and the info I have shows pin labels like "7C", "1J", "14A", "B10"... and no clue which housing.

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Old 11-08-2018, 08:22 PM   #24
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Default Re: '94 SL2 manual trans, electrical help needed

Look at the drawing section I posted. Note that there is a 6 or 7 digit number at one end or the other of the dotted line that runs either above or below a row of connections, that is the connector NUMBER. Now each pin has both a letter and number for the Multi pin connectors. The top row is the one closest to A or A depending. Lettering starts with A except for split function connectors then you will have a 2 row connector A and B and another with C and D as happens on the PCM connectors.

These are the PCM connectors: http://www.saturnwiki.com/wiki/index...PCM_connectors

The actual connector only has pin numbers, you have to be able to identify top and bottom to properly label the rows.

You are correct, only PCM B and PCM I for power. B = battery and I = Ignition and a drop out on either one and you will cycle the PCM. What you describe is a cycling of the PCM.

I doubt that a relatively slow DVM will catch tis dropout as they have measurable sense time and an analog instrument suffers from ballistic delay and lag. Real old fashioned electron beam oscilloscope will usualy do the trick if it is a high bandwidth scope.

I still think the issue is with the trusty Lucas ignition switch.

Have you even looked at the back side of the UHJB?

The black background scans Fetch posted also have the connector number and the pin identifier, either alpha or numeric or for multi-row alpha-numeric.

To be able to read these will require a zoomed view or a large monitor.

I doubt it is grounds as the power ground is attached to the top transmission mounting stud and the others are various signal grounds that have no impact on basic PCM operation which is what is happening.

Any time those dash indicator lights cycle the PCM has lost and regained power. It should be off for 20 seconds or so it reinitialize completely so any time less than that will get you a more random restart.

The 2 second prime cycle failure is a very basic routine and that failure alone points at the ignition switch.

Last edited by OldNuc; 11-08-2018 at 08:31 PM..

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Old 11-08-2018, 08:57 PM   #25
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Default Re: '94 SL2 manual trans, electrical help needed

How do I extract those contacts? I assume they come out the wire-side, but does the ex tool go in from the mating side? It looks like the ex tool would go in the row of holes outboard of the actual contact holes, correct? the flexible tang is on the contact, similar to the IPJB contacts.

No, I have not looked at the back side of the UHJB. I had been waiting to hear if the wheel and splash-shield had to come out, then wandered off chasing F6 in the IPJB. Everything on the top side of the UHJB looks pristine, bright-and-shiny.

I can believe (and hope) that this is *just* an ignition switch problem, but would like to be able to prove that conclusively. I have a 200MHz 4-channel scope, so won't be limited to what the DMM can catch.

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Old 11-09-2018, 01:00 AM   #26
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Default Re: '94 SL2 manual trans, electrical help needed

What you can actually see depends on the processor speed in the PCM. I suspect that the PCM pins are removed by inserting a tool into the pin side and they come out the wire side but I have yet to come up with any logical reason to do that So I have not actually looked into it. I just use a set of Fluke insulation piercing probes instead.

The UHJB comes out from above and the mounting bolts are all on the outer flange of the block. One located towards the front of the car and 2 located to the left side.

Remember, the ignition lock and the ignition switch are 2 completely separate components with entirely different failure mechanisms and the switch is failure prone as is any sliding contact switch.

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Old 11-09-2018, 01:14 PM   #27
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Default Re: '94 SL2 manual trans, electrical help needed

I got the UHJB loose easy enough, but it would only come up about 3/4", not enough to check much underneath. It seemed like the cable bundle was clamped underneath. I asked about that but got no answer; then moved away from there once I realized the suspect F6 was in the IPJB.

I scoped the PCM1, PCMB, FP, and ground pins at the PCM connectors yesterday. The PCM1 and PCMB look clean, but there is some question of the ground. The FP was interesting, it has a ripple on it I wasn't expecting. I'm going to go back now and also scope the 5V ref; it was a big mistake not to add that lead when I was in there before! In all of this I am hampered because the damn thing "heals" itself after a short while. Heating in the PCM circuits once the PCM1 is powered up? I will post a better description of what I am seeing with the scope after I do a few more tests.

I didn't have to extract the contacts or pierce the insulation. I just remove the locking "comb" and put the end of a small wire in that hole, then re-install the lock to hold the wire end against the contact crimp area and retain the wire lead securely. Should be easy to remove later by just popping th locks back out. Yes, I will do a "drag test" on each contact after I am all done to ensure they all have adequate squeeze...

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Old 11-09-2018, 02:28 PM   #28
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Default Re: '94 SL2 manual trans, electrical help needed

Ripple is not a good sign as that is originating external to the car or the alternator has failed. The alternator rectifier is a fullwave bridge 3 phase configuration so expect a high ripple frequency if it is the alternator zenner failure.

The cable clamp for the engine, forward lamp, and I/P has to be opened so you can lift the UHJB and open up the lower cover. That thing is used as an interconnect between the engine and I/P.

When you open up the lower cover of the UHJB just look for dirt-water damage, or corrosion. No need to pull connectors for a look without further evidence.

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Old 11-09-2018, 03:32 PM   #29
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Default Re: '94 SL2 manual trans, electrical help needed

Understand, the engine is not running during these most recent tests. This morning the scope is showing the PCMB voltage as a steady 13.6-13.8V Even when I had the battery charger on it, the PCMB ripple was only 280mV P-P

So far, it looks like the 5V is the problem. At the first key-on the 5V didn't come up at all until after a few seconds. It was so slow I feared I hadn't made connection with my back-probe wire. Then it started rising slow and jittery. When it got to about 3V the cooling fan came on. As it approached 5V the cooling fan went off and the FP relay went on for its time-out period. After that, all but one key-on cycle the 5V (and all else) worked fine. The one other time when the 5V wasn't quite OK was after I had let it sit for a while. That time, the 5V came up to about 5V right away, but was quite noisy (1V P-P?) for a bit and the fan/FP did their dance. After a few seconds the 5V stabilized and the others behaved. All OK for the next several key-on cycles. I'm letting it cool again! I'm about ready to take the PCM to the bench, open it up and power it up so I can observe these voltages as I heat/cool various parts of the PCB. Hopefully I can identify the VR chip.

As to why no codes are getting set, I can only surmise the CPU isn't capable of determining what the problem is when the 5V is so bad.

Did I mention "ripple" in the FP relay drive? That may be mis-leading. It is actually a full 12V to 0V swing, like a PWM, but it is high duty cycle so essentially 12V when on. I checked this with the FP fuse pulled so the pump isn't running to produce commutator EMI. Just the load of the relay coil is enough "pull-down" to show low pulses on the PCM FP output. I don't think it is a problem at all, just not what I was expecting. In fact, since it briefly turns on fully, then goes into this PWM for the rest of the FP time-out, I'm thinking that is a "P&H" drive similar to used for low-Z injectors.

PS: I will lift the UHJB again, if nothing else is conclusive, but there is essentially no water/dirt anywhere else in that area. We may have crappy politics here, but real fine weather!

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Old 11-09-2018, 05:05 PM   #30
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Default Re: '94 SL2 manual trans, electrical help needed

A 5V failure is quite possible. That would cause all kinds of odd behavior. It is possible the 5V is being excessively loaded externally. Check with all load and attached wiring removed and see if it still shows a slow rise.

A 94 DOHC PCM where the presence or absence matches your car is a drop in replacement unless you have the electric EGR and then that is also required. JY does not track ABS as Hollanders is incorrect in this area. A mismatch on the ABS sets a 80 DTC.

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Old 11-09-2018, 07:12 PM   #31
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Default Re: '94 SL2 manual trans, electrical help needed

Whatever this finally turns out to be, it sure has been "entertaining"!

I disconnected the (electric) EGR to try forcing a code. At key-on that way the 5V had about 1.4V P-P ripple as it came up, the FP and fan behaved. As I walked over to grab my scanner to check for an EGR code, the cooling fan came on. I ran back and saw the 5V now had 3.48V P-P "ripple"! Then... it healed itself so I connected the scanner to look for codes. None set. I tried the paper clip, none but "12".

OK, so maybe an EGR code wouldn't set until the engine was running? I disconnected the MAP sensor and the scanner showed 34, the blinky only 12. The scanner live-data also showed MAP was way low (.02V), of course.

Next, I disconnected the TPS (EGR and MAP still disconnected). The scanner showed 22 and 34, and the blinky now showed 12, 22, and 34. Key-off and back on... scanner now shows only 22 and 54, even though live-data shows low V and % for MAP. Likewise the blinky is now only 12 and 22, even though MAP connector is still dangling. Meanwhile, it seems like the key-on boot has always been clean while the TPS is disconnected. Time to let it rest again for a while and try again with all these still disconnected.

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Old 11-09-2018, 07:22 PM   #32
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Default Re: '94 SL2 manual trans, electrical help needed

It is possible a sensor(TPS) has failed and is overloading the 5V bus. Or there is a low resistance to ground on the wiring. The 5V should come right up to 5V.

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Old 11-09-2018, 09:39 PM   #33
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Default Re: '94 SL2 manual trans, electrical help needed

The last tests above were done with the TPS, MAP, and EGR all disconnected. I recently did retest (all still disconnected and no harness connectors shorting to ground) and the first key-on had the 5V fluctuating for several seconds, from 5.12V to 1.84V. Subsequent key-on cycles the 5V went cleanly up to 5.2 right away. I'm going to let it cool again and test one more time before taking the PCM to the bench for close scrutiny. The way this "heals" after a very short period makes me think it is a semi-conductor or cap in the PCM.

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Old 11-09-2018, 09:51 PM   #34
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Default Re: '94 SL2 manual trans, electrical help needed

Quote:
Originally Posted by billr View Post
The last tests above were done with the TPS, MAP, and EGR all disconnected. I recently did retest (all still disconnected and no harness connectors shorting to ground) and the first key-on had the 5V fluctuating for several seconds, from 5.12V to 1.84V. Subsequent key-on cycles the 5V went cleanly up to 5.2 right away. I'm going to let it cool again and test one more time before taking the PCM to the bench for close scrutiny. The way this "heals" after a very short period makes me think it is a semi-conductor or cap in the PCM.
Capacitor.

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Old 11-10-2018, 02:01 PM   #35
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Default Re: '94 SL2 manual trans, electrical help needed

Yes, my gut-feeling is that it is a (electrolytic) capacitor; the way it "heals" so fast when power is first applied and then takes an hour or more to go bad again. Do you have any info on that PCM circuit? It is mostly SMD, hard enough to read any kind of logos or values for components, and it has a conformal coating all over. The coating is clear, but still "wets" the devices enough that many of the faint markings are nearly invisible. Even bright sunlight isn't working, I have to shine a bright light at just the right angle to even see that there are markings there. I will probably have to scrape off the conformal coating to really read, but would like to be able to scrape only suspect devices; would like to home in on 5V regulator section. Sorry about that long ramble! Now for the news:

I have it out on the bench now, nothing connected except both main grounds, both 12V power sources (always-hot and switched), and a 220 ohm load on the FP drive pin. And the scope leads, of course, but those are all high (10M?) impedance. Voltage supplied is a regulated 13V.

The "good" news is that it acts exactly the same out on the bench. On the first "key-on" cycle the 5V takes several seconds to come up, and fluctuates as it does that, it isn't even a steady rise. After that, the 5V comes up near-instantly and the FP drive does its normal short on cycle.

I'm trying now to identify the 5V regulator that gets powered up at key-on. I thought I had found it, looked like a standard 3-pin TO-220 device, but the signals I am seeing there aren't correct for something standard like an LM7805.

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Old 11-10-2018, 03:21 PM   #36
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Default Re: '94 SL2 manual trans, electrical help needed

I do not think anyone has ever spent the time to unravel the PCM schematic completely.

If that car is a 94 DOHC with manual trans and ABS then just about any eBay 94 PCM will work out of the mailer. Much easier than trying to trace that circuit out to find some surface mount device that has died. All you can do is work backwards from the 5v ref out pins and see what you run into and that is likely to be a multilayer board which means there are traces you can not see. New to you PCM is a 20-40$ part.

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Old 11-10-2018, 04:06 PM   #37
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Default Re: '94 SL2 manual trans, electrical help needed

Yeah, if it is going to be a bear to track down/fix, and impossible if it is anything other than a component in that 5V supply circuit. I have already looked on ebay, they all seem to be in the $100-200. JYs are not convenient for me, and I fear the '94s are getting scarce there anyway. This is manual trans, but no ABS and it is the CA special emissions (linear EGR). Looking for rebuilds from normal vendors, I am seeing a lot of "no longer available" and all seem to specify "needs flashing".

There is one cap (47u 10V) that seems a likely candidate, but I hate to risk damaging the PCB by ripping it off yet. I am also trying to find data on what I think is the VR. I have the mfg. and number now, but no joy so far.

PS: anybody who may be able to help, that device is an International Rectifier 9347

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Old 11-10-2018, 05:51 PM   #38
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Default Re: '94 SL2 manual trans, electrical help needed

Does it look like the 3rd item down on this MOUSER search? https://www.mouser.com/Semiconductor...d=9347&FS=True I would backup and look for the input filter if any and then any cap in the output side. Be sure to scope the input to verify it is NOT an input voltage issue.

Last edited by OldNuc; 11-10-2018 at 05:56 PM..

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Old 11-10-2018, 06:28 PM   #39
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Default Re: '94 SL2 manual trans, electrical help needed

No, mine is a 3-pin device. Thanks for looking, though.

I have a scope channel dedicated to PCMB, it has been rock-steady both in the car and on the bench. Whenever I have scoped PCM1 it has been clean, too. Now PCM1 is just a switched jumper from PCMB, so is as good as that except for any resistance in the switch and a few inches of wire.

I am circling that suspicious cap like a vulture now...

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Old 11-10-2018, 06:54 PM   #40
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Default Re: '94 SL2 manual trans, electrical help needed

The 3rd item down in the linked search is a DIP package 3 terminal voltage regulator at 4.75v. If the cap is across the output then that could very well be the problem.

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