I had a thread on here last week about the hesitation and stumbling and now I have some trouble codes to work with. On my way back home tonight, my car backfired near the y-pipe and immediately shut down while I was driving. The rpms dropped down to zero and everything was all bad. While I was waiting for the truck, I pulled the codes and got 12, 15, 23, 34 and 45. Prior to getting all of these codes, my car ran pretty crappy, got terrible gas mileage and did not once give me codes. My check engine light came on the moment my car stalled. Does this sound like it could be my computer? Has anyone had something like this happen before? Thanks in advance-

 

DTC - 12 ECM is in diagnostic test mode - active. Normal when A+B are shorted together
DTC - 15 Engine coolant temp sensor error (low temp indicated) signal
voltage high. Check harness for shorts.
DTC - 23 Intake air temp sensor error (low temp indicated)
DTC - 34 MAP sensor circuit error (signal low indicating high vacuum) signal
voltage is low during ignition on
DTC - 45 Oxygen sensor error (rich condition indicated)

Check connectors and sensors for shorts, opens melted wires first....

 

I'm going to get a replacement computer and see if that fixes my problem. When the car was running, I did the check on the CTS and all was in range. The sensor is new as is the pigtail connector. The map sensor was replaced recently as well, and the wires + vacuum hose are all intact. I did ground the coolant fan switch and my car was running at 160 degrees the whole time (25 minutes) but I figure if my car was running too cold, it would trigger a check engine light. Also, my car had been running way rich and was getting 8 mpg combined and I never got the code 45 that I was expecting. My car cranks and cranks and I am not getting it to fire. What are the signs of a bad computer?

 

Just to add an update, I now have a code 54 and a no start condition. I couldnt find the computer that I needed today at the boneyard so I still and unsure if the computer is any good. Also, the local auto parts stores do not stock the computer nor can they check if mine is even any good.

 

Another update, I cleared the codes and I still have a no-start condition. I feel the fuel pump relay clicking with the key on, I also hear the fuel pump priming as well. When the engine is cranking, I can see the fuel spraying out of the injectors. I pulled some of the plugs and they smelled of fuel and were a little wet. The oil pressure gauge moves over to the right as I attempt to start it so I'm guessing that the sending unit is working properly. All of my engine grounds are good and solid. I'm still clueless on what tests to run next. My last year at the University begins in a couple of weeks and I need to get the car going asap. I really could use some help

 

Z28

Get a spark plug tester and verify that you have a spark! You may have a dead ignition coil. Since you are getting injectors to pulse fuel during cranking that is very good news - ie ECM sees reference pulse from dizzy and ignition module is functioning. Check coil, the two wire connector between coil and dizzy, center contact in the dizzy and high voltage wire between dizzy and coil. External coils are known to fail.

I hope this helps

//RF

 

+1

Also check the rotor on the distributor. I had a rotor pop off once on the highway, backfired and shut off, just lik eyou said.

 

Thanks for the replies. I will check my cap and rotor this afternoon. Also, I replaced my coil with an MSD coil a couple of weeks back. If I can find my stocker i am going to replace it and see if it makes a difference. I will report back tonight.

 

I bought and installed an MSD cap and rotor kit but still could not get the car to start. I also bought a spark plug tester to check for spark but it is a two man job and I have no one here to help at the moment. I checked for rotor movement by bumping the starter and the rotor/distributor is doing its job by rotating clockwise. As I crank it I can hear a faint sputter out of the exhaust as if it wants to start but it never does.

 

I think you answer is in the distributor, it sounds like a timing problem. A year ago i thought i would go high voltage and purchased an in-cap 50,000V high output coil and put it in. The car backfired and ran like crap, like it had spark plug wires crossed. I knew i put everything back together right but i just could not figure out why it ran so poorly. It did sound different, more aggressive but it would not run smoothly.

While it was running, i messed with the timing and the car just quit....crank but no turnover/startup. I pulled the ignition module and ran it to the parts store and they tested it, the Coil fried the ignition module. I bought a new one, an AZ cheapie and put the stock coil back in. The car fired right up and ran like a purring tiger ever since. These cars come with an HEI system, high energy ignition and they are powerful. The stock ignition parts, i am told... do not do very well at higher voltages ... i am not sure if that is true or not, but in my experience it was very true.

Now the way you diagnose problems with the computer, is you start with the lowest codes and work your way up... in your case the 12 is normal, it means the distributor is sending a signal to the ECM. The 15 is the next highest, that means you are going to want to trouble shoot that one next. Just keep in mind that one sensor failure/bad connection can cause another trouble code to be set because the computer thinks that another sensor is not giving a "normal" reading.

When the computer failed in my TPI, the Service Engine Soon light flashed repeatedly very quickly, like 100 times per second, it flickered...not the flash ..flash...flash.

When the computer in my CC Carb camaro quit, the car would start and then when you took your foot of the gas, it would stall. The only way it would run is if you held the gas down while starting it up. The ECM also flickered very very faintly while it was running.

I hope this helps, post more info and we will try to pin point it better.

 

Lucid, thanks for the detailed reply. I checked for spark today by taking out a plug, attaching the wire to it and grounding the plug on a solid ground. I had my girlfriend crank the car while I checked for spark. I didn't see any signs of spark. The plug was totally wet with gasoline and had a strong fuel odor that would burn the eyes. I got a plug tester and ran it along the wires just to make sure I didn't have any spark and it helped confirm that I wasn't getting any spark. Now I know it is spark related, I am going to look into the coil and the ignition module. If I am getting the injectors to spray as I try to start the car, does that mean the ignition module is working? Is there a way to check a coil? What else could cause a no-spark condition?

 

OK, now we are getting somewhere.

1) Check 2 wire harness from dizzy to coil. Get a low cost DVM from RS or even auto parts store and 'ohm it out. Make sure that there is damaged insulation.

2) Check and make sure that you are getting +12 on a main supply line - 10AWG pink wire.

3) Disconnect a short High Voltage between dizzy and coil at dizzy. Plug in you spark plug tester into the disconnected end. Have GF crank over - if no spark - it is a coil almost 99%. IF and only if you have sparks continue to next step. To verify, you can measure coil windings resistance - these values are approximate:
Gray connector ( pink wire) primary: pink to white ~ 0.3 to 0.5 Ohms
Gray connector ( pink wire) secondary: pink wire to center post ~ 11kOhms
If primary is reading open - coil is history

4) check center post in dizzy and rotor

5) Absolute timing check - cylinder 1 on a compression stroke and dizzy is approaching cyl #1 post.

//RF

 

My digital voltmeter is a few towns over right now so what I did today was use my spark plug tester, checking for spark from the coil. When I saw that I wasn't getting any spark, I figured that my coil was the culprit. I went out and purchased a new OEM coil and I still couldn't get the car started. You can hear a sputter out of the exhaust as if it wants to start. I don't know what else to replace now.
I am going to check my timing when I get my tools from Stockton to make sure I am on tdc on the compression stroke of #1.

 

Could spark plugs make a difference? The previous owner replaced nearly everything on the car and there are some newer bosch supers in there right now. They are pretty fouled up from the car running super rich (8 mpg) ever since I had the car. Now they smell like fuel from the numerous cranking attempts without a start. Could a totally failed TPS cause this? I have a new CTS sensor with pigtail and when I checked it a few days ago the numbers were all in order.

 

Dude

You are pretty close. The only way to get through these electrical gremlins is to systematically eliminate failure points.

1) Verify that you are getting spark from center post of your new coil. Do not change anything else for now. If you are not getting spark check sections 1 and 2 from my earlier post. If you are getting spark now then and only then proceed into checking rotor, cap, center pin, plug wires, plugs....

Got to do it in step by step fashion - shotgunning does not work.

//RF

 

Ignition Control Module.

I noticed that my tach did not move when I was cranking it, which screamed to me that it was the ICM. I got a new one at Kragen and slapped it in. Apparently, all of my symptoms are gone (for now at least). Thanks to everyone who has helped me in this thread, I can now enjoy my car again.

 

 

 

You have to watch out for the pick-up coil also, I would pull the distributor and replace that just for grins, cause it's gonna go out sooner or later.

 

Damn man sorry i havent been on in a while, i coulda told u it was the ICM Mine did that a few weeks back, same exact thing ur car did GJ fixing it thou, !!