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

[dyeager535]

I had it all typed up previously about everyone from way back to the original JTR book having truck VSS wrong, but I then ASSumed at this stage vendors would have figured it out and didn't post it. Apparently not. Vendor says it is right and will work in your application, they own the mistake.

 

[Blue85]

dude (I called him) said this will work. It looks similar to what I have. . .

Speed Sensor 2PRS

Two-pulse square wave speed sensor. The two-pulse square wave unit for all passenger car TBI installations, all computer controlled carbureted engines, and 1985–1989 TPI engines. 7/8–18 thread, .104" square drive. Part Number: 2PRSPrice: 120$(Each)Material: Aluminum & BrassWeight: 9ozMade in USA

jagsthatrun.com

It's interesting that the description is basically identical to the TPI Parts description. Did you tell him specifically that it's not a passenger car TBI and it was originally equipped with the VSS adapter on the speedometer? Does it have 2 wires or 3?

 

[buckallred]

It's interesting that the description is basically identical to the TPI Parts description. Did you tell him specifically that it's not a passenger car TBI and it was originally equipped with the VSS adapter on the speedometer? Does it have 2 wires or 3?

Yes, he was aware, I told him 1989 V10/K5 blazer 4x4. He seemed to know his stuff. He said that by losing/deleting my OEM VSS, I "lost my DRAC" and therefore my antilock brakes and cruise control will not work, but this unit will give my ECU the signal it is looking for. . .

I am inclined to buy it and just give it a try. . . what do you think? 2 wires, just looking at the photo.

 

[dyeager535]

Well, given that 1990 was the first year of DRAC...

I believe the only cars that used the same scheme for VSS as the '81-'89 trucks were the CCC (computerized carb) cars. Those still used an optical eye on the speedometer to create the signal like the trucks.

All the TBI/TPI car stuff used buffers of a different sort, and I believe signal generators that were on the transmission.

 

[buckallred]

@dyeager535 and @Blue85

Speed Sensor 2PRS

Two-pulse square wave speed sensor. The two-pulse square wave unit for all passenger car TBI installations, all computer controlled carbureted engines, and 1985–1989 TPI engines. 7/8–18 thread, .104" square drive. Part Number: 2PRSPrice: 120$(Each)Material: Aluminum & BrassWeight: 9ozMade in USA

jagsthatrun.com

I ordered the above unit. Will run it and see. I am concerned that it looks very similar to what I have. . . the dude (at stealth conversions, I talked to him again) assured me that this unit will "give my ECU what it is looking for."

 

[buckallred]

Man... It looks pretty much just like the one I already have. But we shall see.

 

[K85 Octane]

Good luck

 

[Blue85]

It could work. I almost posted earlier that the only way I could think of to get the pulses with only 2 wires would be a reed relay. Basically magnets pass the contacts making them open and close. You just need the right number of contacts for the pulses per revolution. Whether or not you get the right transitions depends on having a pull-up resistor in the ECU, which I'll just assume is there because they are calling out truck TBI with no DRAC specifically.

I don't want to be a downer, but there's some chance the ECU input has been damaged by the VR sensor. If somebody had a schematic of the truck ECU I would be interested to look at it. Probably the VR sensor doesn't produce enough energy to take something out.

 

[buckallred]

I don't want to be a downer, but there's some chance the ECU input has been damaged by the VR sensor. If somebody had a schematic of the truck ECU I would be interested to look at it. Probably the VR sensor doesn't produce enough energy to take something out.

Hi, if this is the case, the solution is a new ECU. I see them on eBay or Amazon for about $100. It says something about you need to get a "chip flashed" in order to make it work. Do you know what that means? I have no idea. Thank you for all of your help.

Of course, I'm going to hook up this new device and see if it might possibly just fix the problem with my existing ECU.

 

[Wes Harden]

Back in the day if gm techs replaced an ecm, we would remove the prom from the old unit and in stall in the new ecm. even in 87 under warranty they reconditioned ecm.

 

[buckallred]

Wait a minute. If the engine is running, transmission in park, and I connect a test light to the VSS input wire on the ECU (plug A10, brown wire, circuit number 437), and then ground the test light, the test light should turn on, correct?

The ECU, if it is functioning correctly, should send at least some small amount of power/positive/hot to that wire, correct?

During the various times I was fiddling around with that wire (plug A10, brown wire, circuit number 437), it's possible (though I honestly don't remember) that I may have connected positive from the vehicle battery io that wire. If I did that, would that fry something in the ECU?

 

[Blue85]

You should not probe an ECU with a test light, with the exception of certain outputs, like the injector drivers. Circuit 437 is a VSS input, so it should not provide more than a few mA (like a pull-up), so it would not light a bulb.

Does shorting VSS to battery damage something? I don't know the input circuit, but it might not be a problem.

 

[Blue85]

It would really help if you had an ALDL cable to scan for speed (http://aldlcable.com/products/aldlobd1u.asp). Maybe you know somebody who does? You could just put that adapter in a drill and test everything before you even drive. Do you at least have some kind of voltmeter? If you can probe circuit 437, with ignition on, there should be a voltage there. Whether is 5V or 12V I don't know. As you turn the adapter, the voltage should switch between that voltage and zero.

 

[buckallred]

With respect to the cable: I can buy the cable, but what software what I need on my laptop to make it work?

Voltmeter: can you let me know which one of these would be the correct one? As you can see, I'm an idiot, and especially an idiot with anything electrical. But even I should be able to hook up the voltmeter wires and turn the aftermarket VSS to see if the voltage toggles between zero and some positive amount.

Amazon.com : voltmeter

 

[frankin5]

GearHead EFI Forums

Fuel Injection Conversion and tuning information and diagnostics GM ECM!

www.gearhead-efi.com

Full tutorial in injection section by eagle mark.

 

[buckallred]

Man... It looks pretty much just like the one I already have. But we shall see.

View attachment 446954View attachment 446955

You all are NOT going to believe this shit . . .

I installed the above item. It looks absolutely completely identical to the existing aftermarket feed sensor I had installed. Same size. Same color. Same two white wires. Same bolts holding it together. Identical. I rolled my eyes, assumed I was wasting my time and money, and installed the new one just like the old one was.

It fixed the ****ing problem. Now how is that possible? The only possibility I can see is that, by extremely unlikely chance, the older aftermarket vehicle speed sensor I was running was somehow defective. As we have discussed, this is an extremely simple device that sends two pulses whenever the transmission / transfer case makes it spin. What are the odds of that thing not working correctly?

At any rate. I've driven the thing easily 40 miles. Have made several short trips and at least one longer trip. No CEL.

And @dyeager is exactly correct about running without a vehicle's speed sensor. After you driven it about 60 to 90 seconds, whenever you take your foot off the throttle the CEL pops on. It was like an abusive relationship. I was driving the thing, and I could look at the CEL and know exactly when it was going to pop on. I would flinch like a dog that's been beat too much, to quote Springsteen, because every time I thought I had the ****ing thing fixed it would pop on again....

Thank you all very much for your helpful info and for tolerating my idiotic questions. I am very grateful and if I ever meet any of you in person I insist on buying you multiple adult beverages of your choice.

Photos of the older ehicle speed sensor, the incorrect one, are attached. The new one looks absolutely identical...

 

[Wes Harden]

Glad that cel light issue is fixed. take that old one apart and see whats inside, unless you can get your money back.

 

[Blue85]

Well it can be easily explained by what I said - the old one is VR and the new one is reed relays, just in the same package. Or it could be what you said - one is broken.

But glad to hear it works. I hate the ones where we expend brain power never to hear back or find we were never given the relevant information to begin with.