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205 with electric speedo? or.. How much does the ecm need the electric Speedo?

Robert79K5

Robert79K5

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Okay I am contemplating putting my SM465/205 in my 90 Blazer, and the only issue I have is with the electric speedometer since my 205 is old school and dosn't have a toner ring. I was thinking that I could just swap in a old style cable speedometer but I don't want to piss off the ECM.

So how much does the ECM care about knowing the speed of the Blazer? If im swapping in my sm465 then I wont be using cruise control so that dosnt matter. Will it throw a code or anything or is the VSS used only to run the electric speedo and cruise control? Is there a kit out there that I havnt seen to adapt a VSS to a np205?
 
it cares quite a bit. Jags That Run sells adapters from old style to new. Its what I'm going to use for my Ford NP205 when I go TPI.
 
So what does the ecm need to know the speed for on a manual transmissioned truck for anyway? (other than to tell the speedometer what value to register.)
 
Okay it was bugging me so I went outside and unplugged the VSS and went for a drive. Other than a non functioning speedometer I couldnt tell any difference. It didn't throw any codes. If I put in my 465 all I need is for the engine to run right. I got a mechanical speedo and a cable. I figure I can just install it in the dash in place of the electric speedo since they look identical and viola! nobody will ever know. Right? What am I missing here?
 
i dont have a speedo hooked up on my 87 because my 205 is too new, wanna trade? but seriously it doesnt matter if you have it hooked up. think about all the guys here with doublers and crap
 
Ask willyswanter, i think he modified a toner ring for his 205 for his late model rig.
 
4X4HIGH said:
Ask willyswanter, i think he modified a toner ring for his 205 for his late model rig.
Click to expand...

steve fox had it done for the UAV. Look at the doubler article, it is noted in there.
 
Thanks for posting that link... it looks like all I need is a 2prs which appears to screw into the speedo drive and give the 2000 pulse per mile signal I need for a 90 TBI.

For anyone reading this thread......
The article basically said that in addition to your speedometer, torque converter lockup and cruise control, the vss helps control your EGR valve and charcoal canister. Also without it if your coasting in gear making the engine spin when you come to a stop your engine may stall because the ECM wil have the Idle Air Control valve closed because it will be thinking that your trying to sit still and idle since it dosnt know your really going down the road. I didnt experience any of that while driving around unplugged but the blazer also currently has an auto in it so that may be why.
 
Why not do it the easy way?

The TBI want a 2000 pulse per mile signal right? Just get an older dash bezel from a mid 80's truck with the speed sensor on the back of the speedometer. its a little green box with three wires coming out of it.

One wire is power, one is ground, and the last goes to your ECM's VSS pin. Easy as pie! Only issue is that your ABS will no longer work, if that is even considered an issue to you.
 
Absolutely right.

You need to swap the entire gauge cluster, they are entirely different '89- and '90+

Probably won't be TOO hard to rewire the gauge connector (printed circuit boards changed extensively) but it will take some work to do right. Otherwise, the cable drive speedo swap and removing the DRAC will solve your problem.

Do one of us a favor and when you do the swap, don't cut any of the wiring. I'd like to have the wiring from the DRAC to the t-case if you don't mind. DRAC could probably be sold as well. Check for my post on DRAC here, the wiring is all linked to so you can figure out how to wire up the older VSS.
 
You can use your 205 and keep your speedo working,, for about,mmmmm 70 cents . How ? if you got access to a drill and a welder and a little time. I HAD to use the tone ring from the t-case in my 205, I have a 4L60E trannyso it wont shift unless it know how fast it is going. If the speedo is not hooked up it wont shift ! I will try to get some pic's for show and tell.
 
allright guys check it out.. here is a screenshot from the pdf file.

The VSS I think im going to get is #1 in the picture. part # 2PRS. It appears to have the mechanical speedo drive with a built in vss, and it gives the DC 2000 pulse per mile signal that my TBI ECM needs.

The way I understand it is that I can screw it into my NP205s speedometer drive and then splice the wires to a connector that will plug up to my VSS connector. Then the mechanical output drive from this unit will just be there and wont get used because my electric speedometer will now have a VSS input.

Whaddya think?

2prs.jpg
 
SierraClassic said:
That'll work, but I doubt you'll like the 100+ bone price tag :S
Click to expand...

If the Jagsthatrun website pricing guide is up to date I can get it for $70 plus shipping. Which in my opinion is money well spent if it makes my ECM and speedo happy without me having to do any custom machining or jumping through flaming hoops.

now that I think about it I guess your talking canadian bones though which would be 100+ I guess... especially after shipping.
 
Yeah, that much is true -- I priced those out when the Canadian Dollar was far weaker, and it was about 100 bucks before shipping for me.

However, there is still one problem you are gonna have:

Your speedometer uses a 4000 pulse per mile signal, unlike the 2000 ppm ECM. So, by using that little adapter, you will loose your speedometer.

Becuase of that, I'd again reccomend just swapping bezels. I'm not 100% sure, but I am about 90% sure that you will not need to do any re-wiring to your truck's cluster connector. As far as I am aware, all 78+ clusters are wired identically. They all use the same gauges, and the same sending units. All it'd take to hook one up is to run a speedometer cable into your cab, hook up a ground wire, a ignition wire, and the wire to the ECM. Then you'd have a working speedometer, and a happy ECM :)

That said, I just remembered and found a little module that came with my TPI setup. I think I remember the guy telling me that it is a VSS buffer that will convert a 2000 ppm signal to a 4000 ppm signal. I have no idea how it works, if it works or how to hook it up, but it could technically fix your speedometer issue... If you want to give it a shot, I'd be happy to mail it to you, I have no use for it at all.
 
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