86 in dash vss

[jameslleary]

Ok...here goes. I have done plenty o swaps in the past, where clients have had everything ready to install....and i have been through quite a few harnesses, thats why my questions seem newbish.
this is a new one for me, because I have always had inline vss's to work with.
Is there any way to test the speedometer cluster mounted VSS in my 86 burb to see if its working, and, can i use it to provide the required signal to my 7747?
Money is funny as of late....started this swap when i was employed, but need to finish it up. all i have is the 4 pole ac vss that was on my tpi setup.
thanks guys!

[1project2many]

You can test the sensor by spinning the cable or speedo head and measuring the voltage out. Speed sensor is connected to ign and gnd and has signal out wire. Find 86 or 87 truck FSM with diagrams and it will show sensor connections. Speedometer signal out wire connects to ecm directly at B10. Wiring diagram on this site is for later vehicle with magnetic sensor and speed signal buffer.

[jameslleary]

ok. thanks. some more info here. I DO have the signal wire(yellow, from the vss box)that went to the old cruise module, hooked up to the brown wire at b10. i have driven the truck a few miles, and i do not get a ses light comming on, would that also mean its working, or does the 7747 throw a code for vss?I know, I should know this, but in my world, the dumbest question, is the one that you dont ask.
Jim

[EagleMark]

First we have never discouraged newb questions, that has brought about detailed conversations about a certain topic/sensor/circuit that we have all learned from.

7747 will set a code if no VSS is detected, I have veiwed them with scan tool. But I do not remember if it will cause check engine light to come on. HTH!

So did you get CEL before? Usually if you fix the issue or the issue is intermetent the light will go off, but the error code will still be stored and seen on scantool for a certain amount of time, I think it's set to how many startups without the code reocurring on 7747.

[jameslleary]

I have only driven with it hooked up. i do get the cel when i disconnect the spout to set the timing. my trans is not locking up, but i think that i may have hooked the brake switch wire up to the wrong side of the resistor that is inline in the harness. i still have to yank the harness back out to clean it all up, and i need to go find a piece of sheetmetal to make a patch for my throttle cable hole in my firewall, as i had to make it a bigger rectangle for the camaro tpi cable, instead of the small square hole for the truck cable.
Edit:I may want to talk to you about the tune you are running in your Suburban at some point.

[EagleMark]

IIRC the brake switch has to give power all the time and turn off when brake applied to release TCC. Don't remember a resister?

Not much special in my suburban tune, stock motor, used Dave W spark table, did the HiWay lean cruise trick started by RBob years ago, then did WOT with wide band O2 sensor. Changed torque converter lockup to 40 MPH instead of 35 MPH because so many streets near my house are 35MPH and radared regular. So to go 35MPH was impossible, you could go below and stay out of lockup or when it locked up you would be above speed limit, rinse repeat, rinse repeat.. was a pain...

[jameslleary]

IIRC the brake switch has to give power all the time and turn off when brake applied to release TCC. Don't remember a resister?

Not much special in my suburban tune, stock motor, used Dave W spark table, did the HiWay lean cruise trick started by RBob years ago, then did WOT with wide band O2 sensor. Changed torque converter lockup to 40 MPH instead of 35 MPH because so many streets near my house are 35MPH and radared regular. So to go 35MPH was impossible, you could go below and stay out of lockup or when it locked up you would be above speed limit, rinse repeat, rinse repeat.. was a pain... have you had any issues with detonation? you and i pretty much have the same truck, except i have a K and yours is an R.

[Six_Shooter]

I see you're a Ford guy... "SPOUT" :P

There should be no resistors in line with the TCC circuit. Yes the brake wire should provide 12V to the TCC at all times (other than when brake is applied) and the other side goes to the ECM. If this is a vehicle that does not have an option to easily add the proper brake switch that has both an N.C. connection for the brake lights, and a N.O. for the TCC, a relay can be used to mimic the function with the existing brake switch.

[1project2many]

Generally it takes 50 "passes" for the ecm to self-clear a code. It's a configurable variable so I usually set it lower. VSS codes usually set when MAP is low and RPM is high (load indicated) for a certain time. If VSS code is set in $42 / 7747 then idle control suffers dramatically. Generally idle speed is increased and the throttle follower is ineffective for the entire key cycle. Easy way to confirm the ecm will set a code... disconnect the VSS box and go for a drive.

[jameslleary]

I see you're a Ford guy... "SPOUT" :P

There should be no resistors in line with the TCC circuit. Yes the brake wire should provide 12V to the TCC at all times (other than when brake is applied) and the other side goes to the ECM. If this is a vehicle that does not have an option to easily add the proper brake switch that has both an N.C. connection for the brake lights, and a N.O. for the TCC, a relay can be used to mimic the function with the existing brake switch.
Fords are what i started doing conversions on back in 94....but, I definately wouldnt say im a Ford guy!This harness is from an 88 2wd c1500. i traced the wire, and it went back toward the ecm, and there was a diod(sorry, i said resistor)

i do have the proper brake switch, as the Burb came from the factory with cruise control.

[sandrock]

CEL/SES/MIL lamps, from my understanding anyways, only come on when the code set is emissions related. Which means every engine sensor that is under the computers watchful eye will set a code if something is wrong. But anything else outside of that, if the computer sees it, will set code but not throw the light on. A good example of this are misfires...the CEL (at least the PCMs I've dealt with) will flash the corresponding cylinder the PCM picked detonation up on, and will set a code and illuminate the CEL continuously until the engine is restarted, then it goes away.

[jameslleary]

CEL/SES/MIL lamps, from my understanding anyways, only come on when the code set is emissions related. Which means every engine sensor that is under the computers watchful eye will set a code if something is wrong. But anything else outside of that, if the computer sees it, will set code but not throw the light on. A good example of this are misfires...the CEL (at least the PCMs I've dealt with) will flash the corresponding cylinder the PCM picked detonation up on, and will set a code and illuminate the CEL continuously until the engine is restarted, then it goes away.Only on OBD2... the only OBD1 system that I know of that will give you anything with cylinder specific ID is Ford EEC4, when you activate the compression test feature.

[1project2many]

OBDII has to follow specific rules regarding when the light it on and when it's not. Emissions levels 1.5X the vehicle's allowable max will illuminate the light, and anything determined to be catalyst damaging will cause the light to flash. OBDI had no such specific rules so the mfgrs did what they wanted. Early Mopars, Volvos, and a few others had a time interval counter which would illuminate the light for no other reason than "It's time."

Some OBDI GM code will give cylinder specific issues. As OBDII approached, GM started implementing misfire detection and injector voltage monitoring code.

[jameslleary]

I would think that would only be the LT1....its the only obd1 (v8, anyway) that i know of that had cylinder identifying capabilities, as it didnt batch fire the injectors.

Anyways, I just spun the speedo cable by hand, with the volt meter hooked to the yeller wire, and i got some readings from it. must work, pretty good for a 25 year old unit.

[EagleMark]

Early Mopars, Volvos, and a few others had a time interval counter which would illuminate the light for no other reason than "It's time."
That would be a code #1 "Check Engine Light" check engine light! :laugh:

[jameslleary]

ok, so...has anyone figured out what this crank signal wire is for? the truck starts without it.

[1project2many]

Some of the early code used the crank input. Later calibrations don't and the wire is unused.

[Six_Shooter]

ok, so...has anyone figured out what this crank signal wire is for? the truck starts without it.

You mean the wire fused at 3 amps?

That is just a signal to the ECM to tell it that the vehicle is in a starting procedure (ignition key turned to the start position).

IIRC, the ECM uses this for starting parameters, such as retarding the timing.

[jameslleary]

Cool, thanks. I'll go ahead and hook it up. Running ASDU, dont know if it requires it or not. I dont have a PC available to me to look...Is there any way to find out which bins have air injection commands programed into them? TBI truckzs are wuite confusing in Ca.
All of the TBI squarebody trucks 87 to 91 have A.I.R., and then you get to the NBS GMT-400 TBI trucks, and sosme do have A.I.R. and some do not. what gives?

[EagleMark]

Every 1227747 I have worked on has the crank signal wire, I beleive it has to do with fuel as well as spark when starting, I have never tried one without. I even use the crank wire on my test bench when running a rewired conversion system, next time I will try without and see if I can notice anything?

Air pumps are a crap shoot. IIRC the 7747 did and the 8747 did not. But in CA everything is differant?

[jameslleary]

are there any differences in the wire harnesses between the 7747and the 8747, or can i just plug n play?

[EagleMark]

I think the plugs for ECM are the same. But 1227747 is $42 and used on light duty, 1228747 is $4F and used on heavy duty. Plug and play would be a crap shoot. There's a lot of differant ECMs with same plugs and most of the wiring is the same, but until you do it or compare wiring diagrams you never know.


Just looked and I don't have 1227787 wiring diagrams so if anyone has them please post up and I will do a 1227787 info thread.

[jameslleary]

Hmmm..most GMT400 half tons are the ones I se without the air pump. I will have to get an emissions sticker for one without, and show it to the ref when i get it inspected.