ok so i have a 1991 camaro rs with the LQ3 and a 700r4 and the speedo didnt work when i purchased it... well upon further inspection the electronic speedo was unplugged so i plugged it back in...

well now if i put it into drive i get to about 5 mph and the vehicle stalls.. it just shuts off.... this doesnt happen at all when its unplugged

2 questions.... 1. does anyone know whats going on i tried searching the site and the web with no dice and 2. if this cant be fixed easily can i just switch to a mechanical gauge cluster from say an 89 as long as i change the applicable sending units and get a bezel???

thanks for any help ive tried using a GPS as a speedo but with all the trees around where i live this has proved very innaccurate as my ticket for 47 in a 35 will attest to lol

 

700-R4, not 4L60-E? Is there a hole in the case, passenger side front area for a TV cable?

Pop the VSS out of the tailhousing and determine if you have a 40 tooth reluctor wheel there. If a speed limiter is in place (somehow, some way; goodness knows when you buy someone else's swap) for 4004 pulse/mile like the stock VSS, a 40 tooth per driveshaft revolution is going to read waaaay higher and hit it earlier.

A cable driver is $300. It boils down to ... you need to fix the problem, not bonglehunt the speedo.

 

yes it is a 700-r4 ...... from an astrovan i think.... and i know it has a TV cable hooked up to the transmission as i adjusted it in pursuit of a solution... and if this is a stupid question im sorry but how do i tell what the VSS is?? and the vss is what the plug goes to correct?? and yes after further reading about how the vss helps pick shift points ETC i agree i need to fix it.... if it was simply for speed calculation it would be a different matter

 

The Vehicle Speed Sensor is installed in the left/drivers side of the bolt-on cast aluminum tailhousing at the rear of the trans.

If it's a third gen F-body VSS, it will have a speedo gear inside on the output and a speedo gear on the end of the VSS. These are 4004 pulse/mile.

If it has a reluctor VSS wheel and pickup like a later model, that could be providing way too many pulses.

In general, the 4004 pulse/mile sine wave signal in a third gen either goes to a small box that translates it to a 2002 pulse/mile signal for early TPI or all TBI ECMs and a 4004 pulse/mile signal to later TPI ECMs and all electronic third gen speedos.

The late TPI ECMs are capable of receiving the VSS signal and outputting to the speedo/cruise also but I don't know if that feature was used in the third gens.

So at this point, knowing which VSS you have is needed. There are a few ways and devices to use to go about getting the PCM, speedo and cruise the signals they need. Knowing how the vehicle wiring is currently modified would be helpful to simplify the next move.

 

well the wiring is unmodified .... and i talked to the previous owner and he said even the stock transmission did it..... so i am completely lost and dont know where to start looking for the problem.... could it be a bad ecm?

 

Welcome to TGO, best 3rd gen tech site on the web. Note that the 305 TBI engine is an L03, no an LQ3.

In your vehicle the VSS is first buffered by a 4-out buffer box. This box then sends pulse streams to the speedometer, cruise control, and ECM. So if the speedometer is reading correctly then the VSS is OK.

To get the speedometer back can unplug the wire that goes to the ECM. Locate the 4-out buffer box, under the dash passenger side. Usually yellow but sometimes white. Has a paper label on it that states "4-OUT BUFFER."

The brown wire on that box goes to the ECM. Pop the terminal out of the connector, re-connect the VSS, and see if the speedometer is correct.

If so, then check the PROM in the ECM. Someone may have 'updated' it by setting the speed limiter low. Can get to the PROM via the small cover at the one end of the ECM. A stock PROM will be in a black plastic carrier and have a silver label on it. On the label will be a 4-letter code, the BCC.

If it doesn't have that silver label and 4-letter code, then it isn't a stock PROM. It may also be that the ECM is bad. But I wouldn't get another one until the above items are checked.

RBob.

 

thanks for the engine designation correction my monitor sometimes makes txt hard to read.....

and thank you so much for the greeting everyone is extremely helpful here and always seems to be extremely courteous even if i ask a stupid question... i also love all the tech articles, i have nothing but praise for this site

and i will try unplugging the ecm like you said (as soon as it stops raining here lol) that seems to be just the information i was looking for.... it will definitely help me narrow down my problem