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Aftermarket veh. speed sensor misery (CA smog/check engine light). Help? 89 K5.

Blue85 said:
So how does torque converter lockup work without a VSS? You can overheat a 4L60 running in 4th gear without lockup.


You shouldn't use a test light one ECM/electronic signals. Use a voltmeter/DMM - they have high impedance.
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it's a 700r4, and it runs normally. . . no idea.

re: the test light, I was just trying to confirm that the bolt I chose was a good ground.
 
buckallred said:
Jesus God in heaven, don't let me jinx this, but I might have gotten it. TL/DR, I connected the aftermarket VSS to the ECM by locating and cutting wires very close to the ECM in the passenger footwell / dash area

As mentioned above, the 2 diagrams of the ECM (above) indicate 2 sections of cavities. One large plug of wires goes into each cavity/receptacle. The one cavity I needed, A10 for circuit 437 (vehicle speed sensor), is located in the cavity section / plug receptacle located toward the forward of the vehicle (and the plug plugs into the outside of the ECM, meaning the passenger side of the vehicle).

So while I'm laying down in the passenger side footwell looking up at it, I could see the larger cavity section / plug receptacle but could not see the smaller cavity section
/ plug receptacle which is located toward the forward of the vehicle and therefore is blocked from vision by the air conditioner fan box etc.

I was able to locate (by feel and sticking my cell phone camera up in the area) the bank of wires that plug into the smaller cavity section / plug receptacle. Based on the diagram, I was pretty sure I had found the brown wire corresponding to the vehicle speed sensor (cavity A10/circuit 437). I therefore cut that wire and spliced in the signal from the aftermarket VSS. The other wire from the aftermarket VSS I spliced into wire 450, identified as "system return." I thought that sounded like a ground.

After that, the vehicle ran fine but the Check Engine Light (CEL) was totally dead and did not even illuminate when the vehicle was started. So that was bad.

I then re-connected wire 450 ("system return") wire and connected the other wire from the aftermarket VSS to what I believe is a ground. It's a bolt that goes through the body of the vehicle and holds the speedometer cable on the underside. I know that this was an awesome time to learn that my automotive test light was non-functional... **** me!!

At any rate, after reconnecting wire 450 and connecting the other aftermarket VSS wire to a ground, the CEL illuminated at startup as it supposed to, and then during a quick test drive the CEL did not pop on. I did not have time to do an extensive test drive, but I'm cautiously, cautiously, very ****ing cautiously optimistic that leaving wire 450 reconnected and simply connecting one wire from the aftermarket VSS to the brown wire/cavity A10/circuit 437 and the other wire from the aftermarket VSS to any ground on the vehicle is the correct solution.

Thank you all for your help and your patience with my idiotic questions. Surprised to note that no matter how hard I looked at the wires behind the speedometer area, I could not find that brown wire for cavity A10/circuit 437. I don't remember what in the world my buddy & I did with it when I installed that dash and autometer gauges. It should be sitting back there, capped off or just unused but I could not find it despite looking for a very, very long time.

So Californians, don't mess with the dash. Don't mess with the speedometer. Whatever you do, don't mess with the vehicle speed sensor!
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UPDATE. The CEL still pops on. It happens when driving, after I back off the throttle, then apply it again. Like clockwork. Like @dyeager535 said, above.

In my previous "fix," I cut wire 450 and attached/clamped the "other" (ground/negative) wire from the aftermarket VSS to the end of wire 450 that goes into the ECM.

Now, I realize that cutting wire 450 was dumb because wire 450 is (I think!) a ground, and thus wire 450 needs to be connected (as the non-ECU end of it is attached to the engine/frame/ground). So wire 450 goes from engine/frame/ground to the ECU. I need to leave it connected ,and TAP IN the aftermarket VSS negative/ground wire to wire 450.

I confirmed that wire 450 is a ground (with my test light).

SO: See photos.

WIRE 437 (brown) is SPEED SENSOR. Aftermarket Speed Sensor (positive/hot wire) is attached to it (BROWN wire).

WIRE 450 (black/white stripe) is "SYSTEM RETURN." I think that means it is a ground. My test light confirms it is a ground.

WIRE 450 is now uncut/put back together. The negative/ground wire from the Aftermarket Speed Sensor is tapped in to WIRE 450.

Do I have that right?

Thanks again for tolerating my idiotic questions!

ECM LIST.jpg

CEL.jpg
 
UPDATE: Fail. CEL still popping on.

I'm done. Calling a pro to try to fix it.
 
Hey Buck,

Russell from FB here. Just read through your thread. You need to take the dash apart to get access to your ECM. Then you need to use a multimeter to check for continuity between pin A10 and the brown wire you've tapped into. I'm willing to bet you've connected to an unrelated brown wire.

The stock VSS is chassis grounded, so you should do the same here. Disregard my original thought about grounding to sensor ground which is where the 5V references are grounded to at A11

Another thing you should do is verify the operation of the sensor as well. You can get cheap oscilloscope on Amazon to make sure it produces a square wave. I'm assuming the ECM provides a 12V output at A10 and watches for that signal being pulled to ground and released with each pulse, so hook the positive side of the scope to the A10 position and the other side to where ever you ground the other lead of the sensor. You should see 12V when the VSS is open, and 0V when it is closed.
 
buckallred said:
UPDATE: Fail. CEL still popping on.

I'm done. Calling a pro to try to fix it.
Click to expand...


Good luck trying to find a "pro" to fix an old OBDI/ECM. You might find someone that claims they can fix it, but after calling the shop 100 times, and them saying it will be ready tomorrow 100 times you will find that there is no such thing as a "pro" on old OBDI/ECM's anymore.
 
Yeah, hate to say it, but an intermittent problem is going to occur infrequently enough to get you out the door and down the road before it happens again.

I'd really invest the time tracking it down yourself. For the cost of a "pro" what else could you do differently? Different setup, tools, etc?
 
What a ”pro” could do is put a relay on the CEL that comes on with the key and goes out when oil pressure comes up… never an issue again for the smog check.
 
bradshawtech said:
What a ”pro” could do is put a relay on the CEL that comes on with the key and goes out when oil pressure comes up… never an issue again for the smog check.
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yeeeeah... that only allows you to initiate the test though... an OBD2 vehicle sometimes just runs at idle for a minute with the emissions computer downloading recent data from the vehicle... but, the the bypassed CEL would get immediately discovered... and fail the test before it started.

an obd1 vehicle might sneak through and initiate testing with a bypassed CEL, but it then needs to have more in depth testing than an OBD2 vehicle:
-here in Californistan, that OBD1 vehicle still needs to get its gas tank and charcoal canister ripped apart by 30-40psi of nitrogen (that the vehicle will never produce during normal operation...) therefore failing the test, same treatment to the fuel cap... fail fail fail...

If the gas tank tank holds together, the vehicle will end up on a dyno with the emission computer's sniffer up its rear end. with the CEL manually turned off and hidden, I would wager the vehicle stands a good chance of failing the tests. they measure pollutants at several speed and RPM ranges. especially if the torque converter is not locking, I would think it could be impossible to maintain the speed and rpm in their designated operating windows? I have a manual trans in my k5, and the 35 inch tires and 373 gearing puts my truck in a weird spot on the dyno... they always try to put the sm456 into 3rd gear for the "cruise at speed" part of the test (with the stock 308 gears on 31 inch tires - they would be looking to keep it 45-55MPH -ish), but with the way the truck is set up now, they are lugging the engine a little too much- rpms are way down at the far bottom of their allowable spectrum, and the speed is up at the high end of the allowable spectrum... I usually ask them to try the test in 2nd gear first. Puts the RPM at the higher end of what's allowable, but easier for them to maintain the speed in the correct range, and the engine seems to run more efficiently in the upper part of the power band...

-if that was all done with an auto trans and torque converter was locking/unlocking... or just stuck in the locked/unlocked position when it was not supposed to be? dunno.
 
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scouthead said:
yeeeeah... that only allows you to initiate the test though... an OBD2 vehicle sometimes just runs at idle for a minute with the emissions computer downloading recent data from the vehicle... but, the the bypassed CEL would get immediately discovered... and fail the test before it started.

an obd1 vehicle might sneak through and initiate testing with a bypassed CEL, but it then needs to have more in depth testing than an OBD2 vehicle:
-here in Californistan, that OBD1 vehicle still needs to get its gas tank and charcoal canister ripped apart by 30-40psi of nitrogen (that the vehicle will never produce during normal operation...) therefore failing the test, same treatment to the fuel cap... fail fail fail...

If the gas tank tank holds together, the vehicle will end up on a dyno with the emission computer's sniffer up its rear end. with the CEL manually turned off and hidden, I would wager the vehicle stands a good chance of failing the tests. they measure pollutants at several speed and RPM ranges. especially if the torque converter is not locking, I would think it could be impossible to maintain the speed and rpm in their designated operating windows? I have a manual trans in my k5, and the 35 inch tires and 373 gearing puts my truck in a weird spot on the dyno... they always try to put the sm456 into 3rd gear for the "cruise at speed" part of the test (with the stock 308 gears on 31 inch tires - they would be looking to keep it 45-55MPH -ish), but with the way the truck is set up now, they are lugging the engine a little too much- rpms are way down at the far bottom of their allowable spectrum, and the speed is up at the high end of the allowable spectrum... I usually ask them to try the test in 2nd gear first. Puts the RPM at the higher end of what's allowable, but easier for them to maintain the speed in the correct range, and the engine seems to run more efficiently in the upper part of the power band...

-if that was all done with an auto trans and torque converter was locking/unlocking... or just stuck in the locked/unlocked position when it was not supposed to be? dunno.
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It was just an idea, the OP said it’s passed a couple of times luckily, that he’s scared the CEL will come on on the next test.
 
UPDATE: Well after I THINK I got the aftermarket VSS hooked up correctly to the VSS, I went for smog.

FAIL: high NOX, means bad EGR valve. I am in the process of replacing it. Comedy! After all the hard stuff, the stupid EGR valve!

NOTE: I am not 100% on this, but: the OEM VSS had a third wire for power. The aftermarket has NO POWER SOURCE, just 2 wires (hot and ground). So the shorter the path to the ECU, the better. I had like 8 feet of extra wire laying in loops . . . electrical dude told me that likely was a problem. Longer path for the power to travel, AND the wire loops were coils that impeded/interfered with the signal to travel thru the wire. So I shortened the positive wire to the ECU and grounded the other (ground) wire from the aftermarket VSS to the body, immediately next to the VSS, like 8 inches from the VSS (I tested the ground with a test light).

SO: After I replace the EGR, I hopefully will pass smog. Will let you all know!
 
While I hope the valve fixes it for you. The egr system has multiple failure points. The control of the vacuum signal, and blocked gas passages in the intake are 2 of the more common.
 
buckallred said:
UPDATE: Well after I THINK I got the aftermarket VSS hooked up correctly to the VSS, I went for smog.

FAIL: high NOX, means bad EGR valve. I am in the process of replacing it. Comedy! After all the hard stuff, the stupid EGR valve!

NOTE: I am not 100% on this, but: the OEM VSS had a third wire for power. The aftermarket has NO POWER SOURCE, just 2 wires (hot and ground). So the shorter the path to the ECU, the better. I had like 8 feet of extra wire laying in loops . . . electrical dude told me that likely was a problem. Longer path for the power to travel, AND the wire loops were coils that impeded/interfered with the signal to travel thru the wire. So I shortened the positive wire to the ECU and grounded the other (ground) wire from the aftermarket VSS to the body, immediately next to the VSS, like 8 inches from the VSS (I tested the ground with a test light).

SO: After I replace the EGR, I hopefully will pass smog. Will let you all know!
Click to expand...
went down a rabbit hole recently when the egr valve i had for years on 2 motors finally started sticking... couple of different types out there
 
UPDATE:

1. Aftermarket speed sensor is attached per the above. I grounded it (all confirmed w/test light) to the body, to the battery, and now to the engine block. The check engine list still pops on and OBD1 system gives "no signal from speed sensor" issue. I tested it with the paperclip trick.
2. Even so, I tried to pass smog. I have passed many times before. The CEL usually takes several minutes to pop on, I have gotten lucky I guess.
3. Since the last time I smogged it, I had the vehicle re-geared (5.38 gears on 37" tires). So the RPMS, etc are different since I last passed smog.

4. I have failed SMOG 3x now for high nox.
5 The smog dude showed me that the engine is running too cool. 165 degrees (yes I drove it for 20-30 mins before the test). Too cool.
6. THEN, I replaced the thermostat (195 degree unit). I believe the old thermostat was stuck open. New thermostat functions, I watched coolant temp rise, then fall when it opened. Vehicle still runs very cool. Of course, temps here in Sacramento have been cool too, maybe mid 60s.
7. The smog dude is not aware of my "no speed sensor/check engine light" issue (and I did not tell him!).

SO: can a "no speed sensor signal to the ECU" problem make the vehicle run too cool?? And/or cause a "high nox" situation? And/or have an effect on the fuel/air mixture (too lean might cause a hot burn, causing "high nox")? The vehicle otherwise runs and shifts perfectly. Someone above asked me about "lockout," but TBH I have no idea what that means. The tranny shifts thru all 4 gears in a normal manner.

IN OTHER WORDS: Could my actual ECU be bad? Could the aftermarket vehicle speed sensor be hooked up correctly, but the ECU is somehow faulty? Is my problem ultimately the ECU???

ALL of that seems unlikely, but WTF do I know? Thanks for any/all help. I would gladly pay a mechanic to solve this, but noone I can find is really familiar with this old OBD1 system. . .
 
No the VSS will not effect your NOX or the engine temperature. Open the plug gap to .060, retard the timing to 0°, make sure the EGR is working. EGR is the biggest contributor to lowering NOX, in fact NOX is sole reason for egr system. Large carbon build up on the pistons can increase compression, higher compression creates higher NOX.

You may have to bite the bullet and get a new cat, I know in Kommiefornia they 3x the $$$ as any where else, but sometimes the cat is need to clean up NOX.

As for the VSS issue I think the DRAC module is giving the computer the wrong information since your gear and tire change.

Don't know if you have seen this or looked into any DRAC module mods, I found this site with a quick search. I couldn't remember if the drac was only for speedo or if the computer used the info to, which it does.

www.tradecraftspecialties.com

Tradecraft Specialties

Specialized repair and troubleshooting
www.tradecraftspecialties.com www.tradecraftspecialties.com
 
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Wes Harden said:
No the VSS will not effect your NOX or the engine temperature. Open the plug gap to .060, retard the timing to 0°, make sure the EGR is working. EGR is the biggest contributor to lowering NOX, in fact NOX is sole reason for egr system. Large carbon build up on the pistons can increase compression, higher compression creates higher NOX.

You may have to bite the bullet and get a new cat, I know in Kommiefornia they 3x the $$$ as any where else, but sometimes the cat is need to clean up NOX.

As for the VSS issue I think the DRAC module is giving the computer the wrong information since your gear and tire change.

Don't know if you have seen this or looked into any DRAC module mods, I found this site with a quick search. I couldn't remember if the drac was only for speedo or if the computer used the info to, which it does.

www.tradecraftspecialties.com

Tradecraft Specialties

Specialized repair and troubleshooting
www.tradecraftspecialties.com www.tradecraftspecialties.com
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is it possible that the "no speed sensor" issue (or the bad ECU idea) could be causing the EGR to not activate/work as it is supposed to? I know the EGR can function because I manually squeezed it, heard the engine stumble. I do not know if it functions as intended (the ECU activating it, etc.).
 
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Sqeezing the egr only part of the test. The valve itself must have exhaust back pressure to vacuum open it. Also the diaphragm may have a hole and leak vacuum, not opening.
The computer supplies a ground to the egr vacuum solenoid, when egr circulation is needed.
Does the computer need the vss signal to decide to open the solenoid? This is a good question. Since the egr is normally only employed at cruise speeds it may be. I will need to investigate more. Since you haven't had any egr codes I think it may not.
 
The service manual will *probably* tell you if VSS is linked to EGR. I'd have to guess yes.

Usually under whatever code is being thrown, the manual will explain symptoms and what that failure will affect. If there is a separate section in the manual for VSS, it will probably give info there about what all it assists with input.
 
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