hey guys, got a 91 gta with a 305. I just bought this thing (been sitting in a barn) and I'm about ready to take a match to it. It started out running pretty rough and throwing a few codes. so now I've replaced the cap, rotor, plugs (5th set so far),wires,ignition module, coil, fuel filter, mat sensor, cts, tps, O2 sensor, and knock sensor. I fired it up today after getting the plenum back on from changing the air temp sensor and the d*@n thing started spitting codes left and right. It ran pretty smooth for a couple of minutes then all of a sudden it started running real rough and the SES light came on. I sat and revved it up for a minute to get it warmed up and see how it acted. Then all of a sudden it revs up to about 2000 rpms running nice and smooth but I didn't have my foot on the throttle.

I checked the codes when I turned it off and got a 15, 21, 23, 43, 45, and 53. I've already replaced everything on the damn car and keep getting this crap.

the one that really makes me wonder about the ecu is the 53(excessive voltage to ecu) I checked the alternator and it's charging right at 14.7v .


SOMEBODY HELP!!!!!!!

 

Welcome to thirdgen.org.

Let's back up a bit...you mention "plenum", but describe the car as an 'RS'...do you have TPI or TBI?

TPI will look like a "spider" on top of the intake, TBI will resemble a carb set up with a conventional aircleaner.

 

Sorry, for some reason I thought I read 'RS'...silly wabbit...

Start by disconnecting the battery to reset the ECM of all codes.

 

i tried clearing out all the codes and as soon as I hook the battery back up and start the car it goes right back into throwing these codes. when I first got the car I did the whole tuneup thing and started replacing or testing the areas that were giving me codes. the bad thing is that they're not going away. I work for an auto parts company (O'Reilly's) so I'm buying the good quality stuff to put in it. That's why these codes are wearing me out.

 

15- Low temp @ CTS
21- High voltage @ TPS
23- Low temp @ MAT/ TPS problem
43- Low voltage @ EST circuit
45- O2 sensor rich
53- High voltage @ batt/High voltage @ EGR/voltage reference error

To be totally honest, solid state circuitry (like an ECM) is very reliable and almost never at fault. Im not saying that its not a possibility, but your problem probably lies elsewhere. The first thing Id do is get your hands on an ETM and try to figure out if any of these codes have any common connectors, circuits, or grounds. Its possible that the ECM isnt getting the correct reference voltage to some of the sensors, but that still wouldnt explain the O2 code. Id also pull out the ECM and take a look at the visible parts of the harness, its possible something may have rubbed against some of the wires. Eliminate all other possiblities before you buy an ECM for it! Hope this helps.

 

Yeah, I agree with the possibility of grounds being an issue...so many problems at once. ECM grounds are at the rear of the heads (on the heads) between the firewall.

After checking ground, start one by one on the issues, nost of the listed items can be checked with a DMM. You'll need at least a Chiltons or Haynes (Helms preferred) to get sensor values.

 

Also, maybe O'riely's carries a scantool you can borrow..it'll make your life so much easier checking things, pus you can see what the ECM sees while the engine is running.

 

My problem when my ECM was bad

 

another post i made about the bad ecm

 

i seriously believe its your ecm.

 

i'll check the wiring and the ground on the ecm and see if I can see anything. I've replaced the sensor on every one of those codes and it's still throwing them back up after I clear them all out. I may try and get ahold of scan tool that can read a little more than just codes and try that before I go to the expense of a new computer too.

thanks guys for the input

 

i'll check the wiring and the ground on the ecm and see if I can see anything. I've replaced the sensor on every one of those codes and it's still throwing them back up after I clear them all out. I may try and get ahold of scan tool that can read a little more than just codes and try that before I go to the expense of a new computer too.

thanks guys for the input

 

Did that fix your problem? Mine is doing the exact same thing! Code 21 43 45 53. New knock sensor, new O2 sensor, new plugs, wires, cap, and button. My car is a 92 z with 5.7 mods include headers, no cats, smog delete. Mine will do it periodically! It will run fine for a week then all of a sudden won't hardly run. It just done it again today. I drove 20 miles and used 1/2 tank of fuel. It was spitting raw fuel out the pipes. I can shut it off and a hr later it'll run fine for awile. I'm at my witts end with this car. Somebody please help!

 

ecm is only about $25 at a junkyard

 

Is that the problem though?