avilla20

i got a 90 3.1 rs with original engine and 164,xxxmiles on it, two days ago i started it and it started but the rpms didnt come down and stayed above 1500, i put it in gear and they dropped so i drove it but speedo was not reading and missed at wot, so i parked it. today i went to start it and it wouldnt start unless i gave it throttle. and would shut off if i let off with ses light flickering above 1000rpm, i figured i had an iac and speedo problem, so i decided to check codes to double check. but when i turn the key on the ses lights flickers and the vapor canister purge valve clicks on and off.before the ses light would stay solid until i stated the engine when i short a to b the fan cicks on and off, fuel pump relay clicks, iac valve runs on and off,all thre egr valve solinoids click on and off, the ses will start to flash 12,but then every thing will start cycling off and on and it will try again, after trying ten times i finally got code 51. my chilton book only goes up to 48. does any one know code 51?and what it means wrong? what problem do i need to fix, this is my dd and needs to be smogged by nov 1st.
thanks

Maverick H1L

iTrader: (8)

I believe code 51 is a defective/incorrect MEMCAL. Which is expensive new, but can be found on eBay or junkyards (provided you look for an F-body as the FWD cars have different base timing offsets).

It'll be either the MEMCAL, or there is a wire to the ECM that needs to be checked as it switches the ECM between V6 and V8 modes. I'll have to look up which.

avilla20

what wire is it? would you know where i can get the wiring diagram? would this memcal cause no speedo and incorrect iac operation?

Maverick H1L

iTrader: (8)

http://chevythunder.com/fuel%20injec...ecm#1227730%29

Pinout for the 730...

Not sure about the no speedo, but the MEMCAL contains the fuel, ignition, and idle control programs. If there is something wrong with it, which is unlikely but can happen, everything can get messed up. Has anything happened with the ECM recently, that you know of?

cIaRmOaCrZo

pull the passenger side panel above where your legs would be. pull out the ecm (2 bolts), then remove the memcal cover (2 bolts). now check and see if the memcal is seated completely or even installed correctly. highly doubt it would move or change its seating UNLESS someone has been in there tampering with it or tuning it. i remember when i installed my memcal backwards on my 86' and it would flash a code 51 and wouldnt run, BUT it did run for second very very rough though.

but it probably needs replaced anyway. its easier than it sounds

Six_Shooter

iTrader: (2)

There is no wire that changes the ECM from V6 to V8 mode.

The cylinder selection is set by the hardware on the MEMCAL and the BIN programmed to the EPROM, that is also part of the MEMCAL.

Code 51 is "PROM failure"

With all the problems you are describing though, the ECM itself would likely be one of the last places I would look at. I would start by looking at the grounds that are attached to the engine, since it sounds to me, like you have a voltage issue, most likely cause is a rotted ground wire to the ECM. I would also check the voltage at the battery and at the ECM, to make sure it is strong enough, should be above 10V for proper operation of the ECM, since the ECM doesn't like voltage below that. Even if it is that low I would suspect wiring problems, since you should see within about a 1/4 of a volt of what the battery is, at the battery and ignition connections at the ECM.

avilla20

were would i be able to find a diagram that shows the ecm grounds, if power and grounds check ok, do i need the prom or the whole ecm, does the ecm come with the prom?

avilla20

just wanted to update.....replaced pcm with acdelco reman and smoged, it passed all good now.

galletti

Having same problems. Did you get a new Mem/Cal with the ECM or did you use your old one?

RBob

iTrader: (1)

Reman ECMs don't come with a MEMCAL. Need to swap yours over to it.

RBob.

galletti

Thanks for the reply. I know they don't come with the ECM. I'll rephrase. Did you also purchase a new Mem/Cal when you purchased your new ECM in order to get rid of your problem or did reusing your old Mem/Cal with a new ECM do the trick. Thanks.