Getting an 89 gmc suburban from a buddy. Need some help

[Captkaos]

you can, but the you need to figure out the USB interface, never went that far....  http://winaldl.joby.se/aldlcable.htm

[1979C20]

Well I did some research, you have to go from the aldl to an rs232 circuit and then into usb. The usb cable for a nokia ca-45 is an rs232 circuit to usb, so I ordered one of those cables from ebay and will make my cable for about 10 bucks. Ill let you guys know when I get it all put together and get some data. Ill probably be using the datalogging software TunerproRT, as ive heard its a good program for it from my research.

[Captkaos]

I use WinALDL, it was free.

[1979C20]

Ooooooo. My favirite "F" word. Ill try that out.

[Captkaos]

Link if you need it: http://winaldl.joby.se/

[1979C20]

Oooookay....... Im just going to roll with it. I just gave my buddy the first hundred and he gave me the keys. Said I could take it to my house to work on it. he charged the battery up and I had my roomate take me to it. It started up fine and idled rough. Still had the check engine light. I drove it 1\2 mile and it started running great, but seemed like it wasnt shifting. i stopped at my work and tested the alternator and battery. Battery was good but needed charging. The voltage regulator failed in the alt. When I started the truck up the check engine light was off. It drove like a dream. I got home and pulled the alternator off. Took it to my work and bench tested it. It passed with flying colors. So, I got a new serpentine belt, some locktite fof my sloppy tilt wheel, and an alternator pigtail just in case. The old belt was very loose, cracked, and glossy. So, im thinking it was slipping on the alternator. After I got it all put back together, i started it and disconnected the battery. And it stayed running. So I drove it about 10 miles and so far so good. Im just going to take it as it is and not ask questions. The only thing I can assume, low voltage.

[1979C20]

Well, having some more problems with it. The check engine light came back on. But it will randomly turn back off. When the check engine light is on, it runs rich, idles rough, and has little power. When the light is off it idles smooth, seems like the A/F is correct, and has awesome power. But, the check engine light was off, i started it and idled. I popped the hood and watched the injectors. it randomly sprayed a ton of fuel and killed the engine after running for like 45 seconds. Then the check engine light came back on and flickered like mad. When the light is flickering, the IAC is making a slight, fast ticking noise. and I can feel the tick. The relays on the firewall also click on and off with the check engine light. While the truck is running, I can unplug the brand new TPS and IAC with no change in idle. Any ideas.

[slammed79]

ECM?

[1979C20]

Thats what I'm starting to think, but when I unplug the MAP sensor connector the truck dies out. I did find one burnt wire from the O2 sensor, which I repaired. But, When the check engine light is flickering, I can tap the ECM with my flashlight and the light will go solid. So, it seems like the ECM the culprit. Is it as easy as, unplug the 2 main harnesses, unbolt the bolt to the strap and pull the ECM out? Then swap the prom and reverse process for the new one? I unplugged the main harnesses and felt the prongs on the ECM, none of them are sticking out. I'll probably go into work a bit early tomorrow and pull an ECM off the shelf and slap it in there to see if it works. If it does, then I'll buy it and be happy. If not, then I don't know whats next.

[jaredts]

Have you tried running an extra ground to the ecm just to see if that solves it?  Just a long shot guess.  Installing an ecm and then putting it back on the shelf sounds like a no-no!

[1979C20]

I already asked my manager. He said "you break it, you buy it". Where would I run the extra ground? To the case of the ECM or into the harness? Where is the original ground, for that fact?

[1979C20]

Well, I have determined the ECM to be in fact - bad. When using the GM approved "tap" test, the ECM failed the test. I started it up, no check engine light and running awesome. Tapped the bottom of the ECM and the truck stumbled and died. Loose/ bad circuitry has been the culprit. So, ill probably be getting a new ECM tomorrow. With a life time warranty, hopefully.

[1979C20]

Alright, got the new ECM in and all is well. Runs awesome now!

[bake315]

Good deal.  Now, let's see some pics of this beast!

[1979C20]

I'll probably borrow my gf's phone tomorrow. My nice phone broke so I'm using an old blueberry until I get paid so I can do an insurance claim on the phone. I'll hopefully take pics tomorrow if its not dark when I get home from work. I'll start a new post in the members rides section. Hopefully if anyone else has similar problems as me they can find this post and perform the "tap" test.