I have a 1991 chev 1500 that has now a 91 tpi engine in it.The tranny is the stock truck tranny(700r4) that has been beefed up a little.The problem im having is that when I get off freeways and come to a stop the idle falls low,not stalling but close.Ive been told I need a vehicle speed sensor for the tranny but I am having a hard time finding one.Does anyone know if this will fix the problem and what company offers this product?Thanks.

 

If you're not running a VSS, you should get one. The ECM uses vehicle speed data for decel fuel control, and IAC adders to prevent stalling. Does the current configuration use a cabled speedometer?

 

Your 700r4 already has a vehicle speed sensor in it. The speedometer, cruise control and ABS all depend on the VSS in the tailshaft of your transmission to be operating correctly.

You'll need to take your dash apart, and find the yellow signal conversion module (called a DRAC), find a 2000 pulse per mile signal output, and run it to pin C6 of your `7730 ECM.

You'll then need to have your chip modified to have the bit at 0x18 (Switch 18) Bit 6 (Magnetic Speed Sensor Installed) to be unchecked, so the ECM knows you are supplying it with an optical tyle 2000 pulse per mile signal input.

Stock the two wires from the Magnetic VSS in the transmission run straight to the ECM, which internally converts the different signals, and sends them to the other electronics like Cruise or the Speedometer. However, your truck has ABS, which the Camaro didn't. So, your ECM wouldn't be able to output the correct speed signal to the ABS, which would make them fail to operate. This way you are using the stock VSS system to the truck, and adapting the ECM to work with it.

Good luck!

Russ

 

80Sierra -wow ok that seems confussing....well when i put in my l-98 tpi motor in my 92fullsize....i had the same probelm with the truck wantin to stall when commin to lights or when i had to slam on my brakes fast it would die.....i found out this was due to the IAC motor "idle air control" my idle air counts were way off...they should be around 7-12 at idle...does you intake make a loud suckin noise at idle...mine sure did. as soon as i got the counts down to the 7-12 the truck drove a crap ton better in traffic and commin to stops....im runin the 730 ecm with a 91 "truck" 700r4 and i have to stock truck vss in it....im not gettin lockup in the tcc at all tho....do you have that problem also?

 

Yeah, the IAC can cause similar problems, but the biggest problem without having the VSS hooked up is that it doesn't know when you are decelerating, and it can cause the idle to fall too low, and stall out under certain conditions.

My IAC is infact messed up too. Not entirely sure what the deal is, but I am unable to drop the counts below 50, and it sets its target idle at 925 - 950 RPM instead of the target idle of 750 I gave it in the prom.

 

i have a truck trans with the truck VSS in my car & went though that problem too.

for a time chevy had the DRAC in the instrument cluster in the trucks, im not sure what year they stopped, 89 or 90 i think.

but i do believe he has the external DRAC, if so its in a small white box. pull your glove box out & look either just to the bottom left side or just below the glove box opening. its about 1/2 an inch thick by about 2 1/2 X 2 1/2 inches.

there was a wire going from it to your old ECM & i think it should have the right speed pulse per mile, though you will need to make the change in the 730 chip & have it on the pin 80Sierra mentioned.

 

sorry been out of the country.Still have not solved the problem.The truck tranny sends 2 pulses and needs to be changed to a 4 pulse tpi output signal.Found a company calledDakota Digital - digital instrumentation and accessories automotive and motorcycle enthusiasts. that makes signal interface that changes pulse rates.Not sure if the SGI-5 is the right product.

 

if you have a 91 truck tranny, i think it should be a 40 pulse per rev speed sensor.

 

d-mann did you ever figure out your problem? also do you have your cruise control hooked up....if so how does it work? how do you like havin a TPI in your truck? do you have any pics?

 

Wow what a surprise, I thought I was the only one with TPI in a truck. I have a 91' Z71 running an 88' TPI setup I installed a year ago. The VSS in my 91' works perfect. I use an autoxray scanner/monitor and vehicle speed is right on the button. My torque convertor locks up perfectly as well. I used a painless wire harness instead of trying to use a GM junkyard engine/ecm harness. Did the same thing to my 67' Camaro when I converted it to TPI back in 1999.
Noticed a good increase in fuel economy and a tremendous boost in power.
5 years ago I installed a 93' Caprice crate motor in the truck. When I installed the TPI I swapped out the cam to a ZZ4.
It's not pretty, but it works great!
Here's some pics:

 

do you have your cruise control hooked up? what scanner do you use? what kind of MPGs do you get with her? this is mine. i have close to the same cam you do its a comp cams 212-218 487-495lift 110 with 1.52 rrs....i need to get my long tubes put on

 

355tpipickup - Wooh ho ho - show quality - nice!!!
I see your cold air entry and air cleaner on the left side of radiator, did you do away with the belt driven fan to get there?? I changed the right side air conditioning bracket to an 89' camaro to move the dampner and air compressor over enough to turn right with the MAF and air intake.

My scanner is an Autoxray 5000, bought it 8 years ago and had it upgraded about 4 years ago so it would monitor while driving. All 3 of my TPI cars are setup as 88' TPI with MAF.
Cruise control died many years ago and I've never bothered to fix it. It should work with TPI if I fixed it and hooked it up.
I've driven the truck about 7000 miles since converting it to TPI. Hiway MPG averages around 17.5. Stop and go city driving just under 14 mpg. I expected a little better hiway mileage, but it's a big, heavy, non-wind resistent truck. But the power is incredible!!! Opposite of TBI, never down shifts or unlocks the convertor to go up hills. Actually hard to cruise at 65-70 wants to go 80 with very little throttle. If I could figure out how to make it less wind resistent, it would probably get good mileage at 80 mph. But its a big heavy extended cab high off the ground Z71 4 wheel drive!

 

Here's my little beast in my 1990 Chevy C1500. 383, AFR, HSR, etc.

MPG-12/13 in city and 18/19 on hwy.

 

the truck was a 4.3 5spd and i did a 91z28 5.7 motor swap that i had built and also did a 91 "truck" built 700r4 so the motor never had a fan. im runnin dual electric fans in mine the intake pipin goes under the fan shroud and then out of a hole i cut in the side of it and over to were the emmissions canister was. i need to get the motor tuned again for the bigger can but ill get 13-14 in town...never had it on a road trip so im not sure what the highway mpgs would be...but i do love the power its a fun truck to drive!!
----------
by the way dont pay any attention to yankost truck its just a slow terd....just looks fast no i would love that motor

 

i never could get my lockup in the tcc to work right so i just droped th pan and wired it for a 4th gear lockup...no probelems yet seems to work great! but now im in the mid of pullin the trans do to a front pump leak on the thing not sure if it cus of the 4th gear lock up or not...i dont think it would have anythin to do with that...its always somthin

 

I didn't have a problem with the converter lockup, but then my truck already had a 700r4 with a 350 TBI, the wire hookup was the same with TPI.
Sorry to hear about the tranny problem!!!

YenkoST: My 87' IROC has a 383 with AFR heads (190cc discontinued a couple years ago). I assembled and installed the motor 4 years ago.

 

355tpipickup, do you have your cruise hooked up? i don't see the cable in the pic.

i have a truck cruise control on my car & i love it.

 

Awesome. Nice engine!

 

no i dotn have the cruise hooked up i couldnt get me truck cable to work with the TB ill have to make somethin to allow it to work. i just never messed with it cus i thought i may have a problem with the vss and the 730 ecm havin two diff signals causing me to not have lockup and also the cruise not workin right. i could still have this prob im not sure cus i rewired the trans for lockup in 4th only and i never messed with the cruise.....i will try to fix it this summer tho im sure

 

do you still have the DRAC in your truck?

i don't remember for sure, but on mine where the cable goes into the bracket i may have had to modify the bracket some.
where the cable hooks up to the throttle shaft i added a crimp type electrical eye to the end of my cruise cable to make it work, i think it was a yellow or a blue one.
its not crimped so tight that its locked to the end of the cable, but just enough so it won't slide over the the end of the cable. to keep it on the post on the throttle shaft i used the stock clip that normally retains the cruise.

i see in your picture that your using the cruise post for your throttle, i did that for a few days until my TPI throttle cable came in, it made for a some what thrilling take off from the traffic lights when a cop was right behind me do you have that problem? i believe a factory TPI throttle cable would reach on you truck.
the only other problem i can think of is you may need to move the cruise module closer so the cable will reach.

 

I have a 89 k1500 with a TPI, not much stock except the plenum, Edelbrock runners and lower manifold, vortec heads. Still running the 7747 but soon to supplimented with a new Perfect Power piggyback ecm. A neat trick is to find a 88-98 GM 6.4l diesel air filter housing and make an inlet tube, the housing takes cool air where the original snorkal went very stock looking- no more sucking hot air.

 

Here is a pic of the TPI setup in my 80 3/4 ton 4x4. I've had it installed for almost a year, but haven't put it on the road yet. When I built the engine, I didn't build something that is very EFI friendly, so I am planning on a cam swap, and a set of TBI swirlport heads in the very near future.

Despite the lumpy cam, and the powerband being way too high, the thing still runs very strongly...

 

yea i do still run my drac.....should i not? i didnt know i was using the wrong tb hookup for my throttle cable, i dont have problems with it binding up on take off tho. ill have to look for a tpi throttle cable

 

yes, you want to keep your DRAC.

if you haven't messed with any of the factory parts or wring as far as the DRAC & cruise goes, i believe your cruise should work once you hook it up as long as every thing else is good.

i think i know why you had problems with TCC lockup, the ECM needs a speed signal input to lock the converter. if you do what 80Sierra talked about in his first post, that should give your ECM a good speed signal.


on the throttle cable, i was wrong, there is a modification that needs to be done, you can check out edgez's TPI install into a suburban, its about half way down. one of the pictures shows where the throttle cable goes on the throttle body shaft.
4. Throttle & Cruise Control Cable
http://www.edgesz28.com/edgesZ28/sub...ccessories.htm

 

If you want to have a normal lockup for your transmission without using the ECM to control it, you can go find an 83-86 Chevy / GMC fullsize pickup with a 700r4, and rob it of it's lockup stuff.

It basically consists of a brake switch, and a vaccum switch.

The brake switch has the normal brake light switch in it, which turns the lights on when you push the pedal down, but also has a switch that kills the power when you push the pedal down. This is an old style switch, and won't fit your new body style rigs, but your trucks already have that same style of dual function switch if they are equipped with cruise control, so you can shut the cruise system off by tapping on the brake. Just have that switch run a pair of relays to isolate the two systems.

The vaccum switch is set up to kill power if it has less than 10 - 15 inches of vaccum on it. Since your engine looses vaccum when it is working hard to pull up a hill, it will unlock the converter, and give the engine a few extra RPMs to pull the rest of the way up the hill. You can buy the switches to kill the power at almost any level of vaccum to tailor them to your specific engine.

From these two switches, it runs to the 4th gear pressure switch, then to the lockup solenoid.

Cheap, quick, and easy! No need to fiddle with your ECM's prom, DRACs, or speed sensors.

As far as the cruise control goes, if you didn't change anything to do with the DRAC to get your speedometer working, and didn't cut any wires to the cruise for some reason, it'll already have the signal it needs, you'll just need to get the cruise box hooked up to your throttle body.

For my throttle cable, I am using a stock TPI throttle cable I picked up off ebay, connected to the little throttle nub on the back side of my throttle body bracket. I had to do some dremel work on my firewall to get the cable to fit, but it hooked straight up to my stock pedal. I've got no trouble with the throttle body opening wide open, or closing. No binding problems, but I do find the pedal is a little too easy to push down compared to the throttle body rigs I am used to!



Keep in mind my engine isn't done yet, and the truck is still a project, so give me a break on my wiring and stuff :P I've still gotta replace my camshaft, heads, and cab, so my wiring is not final by any means! Oh, and I had to ditch the headers, had some un-forseen front driveshaft clearance issues

 

my lockup works fine now....i cut the harnss out of the trans and rewired it so that it has to lockup when it shifts into 4th. it works great cus i never shift into 4th unless im on the freeway or on the back roads goin over 50 so im happy!
i have changed the pin out on my DRAC so the speedo reads right for my smaller tires....but to make sure its hooked to the ecm you are sayin i can fallow the wires off the drac and make sure there is one of the wires goin to the ecm, if there is then the vss should be sendin the right signal to the ecm right...as long as the chip has been changed to read it right? i also have a idal speed that "hunts" when the motor is nice and hot. it will hunt and 300-400rpm around 8-900 to 1000-1100, my idle set reads 825 when im data loggin. i got a new IAC and its set right with my IAC counts around 12-16 at idle not perfect but should be fine. also my IAC volts read .56 if i remember right so thats also fine. the prom was last tuned when i bought the motor for a 208-212 cam and i now have a bigger 212-218 110 cam so maybe this has to do with the idle somewhat?
i have done some data loggin but its still very new to me so im not sure how to read it all, maybe ill find that print out at street and perf so i can fill it out and get some info on if im runnin lean or rich....im guessin after i get my LTs on ill be runnin lean?

 

You are probally running pretty rich, and the ECM is probally wildly flinging the timing back and forth in an attempt to stabalize the idle. Need to change a the timing change constant to slow it down, and that should help at least a bit. The ECM might also be opening and closing the IAC to try and do the same... A good cam for an EFI engine should really have an LSA of 112 degrees or more...

 

"Need to change a the timing change constant to slow it down, and that should help at least a bit." im sorry but what....im not sure what your sayin? when i had the motor worked on and had them put a bigger cam in it, i wanted a bigger one but they said they called comp cams to find out what cam would work best for my app but i call bull crap on that, about 2 days later after doin research i found out that the 110 sucks for a ecm motor

 

Try a ZZ4 cam @.050 208/221 lift .474/.510 112 lobe sep. Should pass smog easily, I have a modified version of this cam (TPIS ZZ9) in my 87' IROC and it passed CAL smog with AFR heads!
ZZ9 @.050 212/226 lift .483/.520.

Both my truck and my 67' Camaro have the ZZ4 cam. Works excellent with TPI, however all my vehicles are MAF TPI systems so I don't have to re-tune the ECM just simply raise the fuel pressure upto 50 lbs. That is why GM finally went back to MAF systems after 1992 with the LT1 and LS1. If the motor has been modified in some way to cause more air to pass through the MAF the ECM adjusts the amount of fuel to get the right mixture!!!! It's a proven fact.

 

There is a constant in the prom, which I cannot remember the name of, that can sometimes cause these kind of problems with a bigger camshaft.

Basically, the ECM will adjust the timing a couple of degrees to bump the idle speed up and down a few rpm, from the factory, it changes the timing a couple degrees at a time, which is fine for a stock cam, but can have a radical difference on an engine without a stock cam. Basically it tries to lower the rpm, so it adjusts the timing a certain amount, but way overshoots it, then adjusts it the other way to fix the overshoot, and overshoots again the other direction.

Just need to change the constant to lower the number of degrees of timing it adjusts the timing at a time to try to help it from overshooting it's correction. There is a similar correction factor for the IAC as well.

Just do some scanning of your timing and IAC compared to your idle. See if it is the IAC that is surging up and down and causing the problem, or if it is your timing that is surging up and down. Or even both!

Sorry, not that great at explaining it, but it is outlined in the tuner faq in the prom section

 

in TunerPro with super_8d xdf, down in Tables/Functions find "Idle Spark Advance Vs RPM Error" & "Idle Spark Retard Vs RPM"
GM set them at 5 degrees at all RPM errors stock, i tapered mine from 0 up to 5 degrees. at 0 RPM error im at 0 timing change, at 50 RPM error 1 degree, 100 RPM 2.5 degrees, 150 RPM 3.5 degrees & 200 RPM 5 degrees.

i don't remember where the one for the IAC is at right now.

you may also want to try to raise the "Idle Engine Speed Deadband" RPM in both drive & park, these are in Constants/Scalars.

some info about tuning with a big cam,
https://www.thirdgen.org/forums/diy-...ome-those.html

 

355tpipickup-sweet ride. Hope to have tpi on my '94 z71 in the future.

I have a question about the vss signal. What is the ppm output on the sensor itself?

 

i dont know forsure all i know is that the 730ecm wont read the same as the truck vss.....its somthin like 40ppm or 20ppm i could be way off but i know i have seen it somwhere.....mayeb somone else can help us on this one, fullsizechevyforum.com could help im sure!

 

the output on a truck speed sensor is 40 pulses per revolution.

 

I dont know if this will help you guys. But I will post my experience anyways.

I have a 89 RS with mechanical speedo. I have a 7730 90-92 TPI on there and the way I got the VSS to work is Painless has a adaptor that goes inline with your speedo cable and converts its signal to to electronic pulses. Just need to know how many pulses you need and go from there. Everything worked perfectly.

Second, for my cruise control, it was a vacumn box that when I pushed the button, vacumn sucked in the cable and held the speed steady. VSS had no effect on that.

 

Not sure if you are stating the PPR for the Optical VSS. Don't have any experience with the Optical type.

The "Magnetic" pickup is 4 Pulses Per Rev of the speedo cable.
Jagsthatrun.com has a unit called the "4PAC integral" that is a cable driving "sleeve" that goes into the 700R4 with the magnetic output.
Allows the use of the cable driven speedo and an electronic output compatible with the 730 input.
That's what I'm using currently without a DRAC. Cost is about $100.
The connection to the ECM is on different pins than the Optical input and there is a selection bit in the PROM that must be set to select Optical input or Magnetic input for the VSS.

Found this on the site explains the different types. Of course the signal requirements are for the ECM, not just the vehicle.

 

vwdave, we are using the truck cruise units, they are fully electronic. you can see it in the pictures that 355tpipickup posted, its between the brake booster & the fender. if you ever use one of them, you'll hate the vacuum controlled units


JP86SS, the VSS im talking about is the magnetic one used on the later model trucks, they didn't use a cable.

im thinking about trying one of the other reluctors, say like the 11 tooth, but i don't know if the output shaft on the 6 speed is the same size as on a 700.

a few days ago i went back to using the DRAC for the speed input to my ECM, it reads a little low, but only about 3~4 MPH, but the speed reading isn't jumping all over the place at speeds over 65 now.

i want to stay away from having the plastic gears for the VSS, but i may look into a 4PAC integral later on if the 11 tooth reluctor won't fit.

 

You could always use one that controls the throttle body via the ecu. But you would need a fully electronic throttle body.