Tourney3p0

After throwing part after part at my car to get it to "behave" on cold startup, I decided it was time to buy a scanner to see what value, exactly, was messed up. So I invested some money in an Autoxray GM ODBI scanner.

The scanner arrives, and I'm ecstatic.. I take it out, configure it for an 88 with the 8th VIN number being 8, plug it in, and start the car.. I hit the Scan button, and.. nothing. It tries to scan for about a minute, then says "Vehicle is not responding". My "Door Ajar" light flashes and my idle slightly changes, and my dash reads bogus numbers for a second, but that's it. Uh oh, something's up.

First I tried cleaning the male pins on the scanner and the female pins on ODB1 connection. Then I made sure nothing was bent out of place, and that the connections hadn't been "pushed back" over time. Then I tried the obvious.. took it to my buddy's 88 Silverado. It worked beautifully, of course. I'm not trying to fix his Silverado, I'm trying to fix my Corvette.

I removed my ECM and made sure all the connections looked good.. no luck there. It had the 1227165 so I bought a 16198259. Still no luck. As I sit right now, nothing is loose and my ECM is brand new.

Is there any way at all it could be my PROM? I've kept the same one.. the only thing else I can figure is that it'd be a severed connection between my ECM and my connector. I'm not sure how to test this, but I plan on studying up on it extensively.

One other thing that I sometimes wonder about.. it's my understanding that these vehicles came with VATS. Mine doesn't have VATS. My key is a standard gold key (non GM) with no chip on it. If VATS was removed from my car at some point, I'm not sure what would have been done to tell my ECM not to worry about it. If I'm not mistaken, the wiring would have needed to be messed with. Maybe this is a clue as to what may be going on.

Siveck

The previous owner of my '89 actually cut the printed circuit on the back of the center information panel so that the service engine light would not come on with a trouble code. But the real genius part was that he had rigged a gem clip between the seat belt light and the service engine light under the bulb holders so that the light would come on like it is supposed to everytime you crank the car and then go out. :mad It sounds like someone bypassed your VATS system with a resistor. It wopuld be found under the steering column in the end of an unplugged harness. As far as the VATS box, it is under the crashpad or breadloaf on the passenger side. I don't know if this helps, but its my 2 cents.

Tourney3p0

That's awesome! I never would have thought of that!

In any case, my Check Engine light works. I can check it manually using the paper clip trick. From time to time I get some weird MAF codes even though I've replaced my MAF and relays.. so I was thinking it could be ECM related.

Siveck

I've replaced my MAF, relays, and ECM a couple of times each and I still get a MAF code. I don't know how to make it go away. The car runs very strong though and the only annoyance is that the check engine light that won't go away.

Stingraynut

If it helps to know someone has a similar problem……..then please feel ‘helped’ !

I got the free download Win ALDL installed on a laptop, the friend that recommended the program made me a connecting lead and……nothing.

The paper clip codes are working

My laptop reads his 84 fine but won’t read my 88. There’s a different configuration code to be entered but otherwise everything is identical.

The cable uses three connections to the ALDL - the two top right (paperclip) pins and the 2nd from left – orange wire –pin. So we suspected a bad connection to the orange wire.

To test that it was sending data my friend sent me this –“get LED and connect it to your ALDL plug across terminals A and E, the longer leg on the LED will go into E. Turn on the key, the LED should blink slowly, maybe once per sec, not from off to on, just changing brightness ( I think the serial data is 3-5V pulses).. Now to force the ECM into ALDL mode, put a 10kohm resistor across A and B (just insert the black and green wires on the WinALDL cable I made for you, there is a 10k resistor in there)
It should now blink alot quicker.. this is what mine did.. If this works then you don't have to stick your head up under the dash and our problem is elsewhere.. If it fails the test, grab a pin, dive under the dash and spike the orange wire you think is the one that needs to be tee'd to the ALDL conector and perform the same test but connect the LED to the pin instead of terminal E.. This will help you locate the correct wire... This should prevent you from teeing into a full 12V supply wire and killing your CM/dash...”

I did all that and got sort of the same results as him.

At the moment we don’t know what else to do. My car is running OK, sends the occasional O2 code (13) and my MPG is poor so I’m fairly sure the O2 needs changing. I would like to be able to scan though.

Maybe you can see which wires your scanner uses and test them the same way

Good luck, PLEASE post the result if you find out what it is, I’ll keep this post on my email list.


Oh, BTW re the MAF codes…….9 out of ten times it’s the two relays, especially if your engine runs OK, just replace them, they go at about 80,000miles + Thanks to the forum I replaced the relays and not the expensive MAF

S’nut

Tourney3p0

Thanks, I wasn't sure which wires it uses to test.. I think that based on what you wrote, I can do some tests of my own.

I'm really not comfortable trying to fix this myself.. a lot of stuff I'll do, but automobile electrical wiring makes me shiver if I don't have a guide telling me exactly what to do. What I'll most likely do is take it to my mechanic, tell him the symptoms, and see if he can find it with a voltmeter or something. It's been so long since I've had a vehicle at the mechanic that I'm not sure he'll remember me. Whoever I take it to, I'll ask them what the problem was. I try to post on the forum whenever I correct a problem of mine.

I've decided however that if I can't figure it out myself and it costs more than 200 bucks to fix, I'm going to sell the car and get a different Corvette. The whole VATS thing makes me uncomfortable.. I'm thinking there's some less than professional wiring going on that I'll never get sorted out. This is my first Corvette, but I'll never be without one again.

Stingraynut

I don’t think the ‘local mechanic’ is a good idea – I don’t know enough about electronics but in the GM manual there are places marked ‘DO NOT TEST WITH DMM’ (digital Multimeter). So there are places that can be damaged.

I’d recommend an Auto Electrician, especially one that knows Corvettes. Electricians seem to know all sorts of handy things.

I’m a newbie Corvette owner (March this year) and it’s amazing the highs and lows I’ve had – no other car has had that effect on me. For me it’s the distance from the experts (I live in the far north of Queensland Australia), the distance from available parts and the cost. Which is one of the reasons I got the scan software and I’m trying to take control, understand and repair my 88 myself.

If your Corvette is a ‘dodgy’ one that’s been mucked around with and you can afford to get a later Corvette that may be the easy option but all C4’s seem to develop their problems from what I can see, you might fix this and suddenly be on a high.

Have you posted about the car running badly ? If not, start a new post, the experts here are brilliant at remote diagnosis, go with whatever the majority say,

S’nut

jman1

I have the exact same thing wrong with my 88... car runs great but just can't shake the maf codes...i finally got annoyed with looking at the ses light enough i bought one of those little plastic corvette logo pieces that go in that spot and put a piece of black paper behind it so i i don't have to look at the light... if you ever figure it out please email me :D

SuperL98

I have an 88 also, and two AutoXrays.
One very old one that always connected to the car fine.
I decided to buy a new one (with ODB1 and 2) and it didn't see the car at all.
After many calls to AutoX no help.
It's them, not you, send it back and buy something else.

The VATS sounds like someone bought a plug in resistor (eklers, mid america, etc. have them) that plugs into the VATS box and dissables it.
It's a cheaper fix than replacing the lock cylinder when the contacts inside wear out. Very common "cheap" fix.

One perminent fix for the MAF light, if you know someone who can program a chip for you.
In the ECM switch tables, you can turn the MAF high diagnostic OFF.
Also can change the MAF diagnostic error threshold from the stock value to 255 gm/sec, so it will never trigger the code 33.
Had to do this with my supercharger install.

Tourney3p0

Thanks for all the responses guys. I'm feeling a little better about the situation.

I've posted about some of the problems I've been having, and have gotten plenty of great replies but they just don't seem to work for me. Basically when I start my car in the morning (or after it's sat for 8 hours at work) it idles really low for about 5 seconds, or until I gas it. If I don't feather the gas, I'll get a code 34. Sometimes the 34 will pop up even when my idle seems fine. It won't do this then either the car is warm, or the temperature outside is high (like in the 90's).

I replaced the IAC, the TPS (and yes, I did the reset procedures correctly), the MAF, MAF relays, ECM, injectors, battery, alternator, thoroughly cleaned the throttle body, etc.

It's very rare that I get a code 34.. maybe once a month. But once I get it, I can expect to get it for a few days in a row. And when I stop the car and restart it within a few minutes, I'll get a code 36 (Burnoff relay). It will do this for a few days, then just vanish. Code 34 causes about a 1 second delay in my acceleration and when I let off the pedal. I can tell no difference at all with code 36. But anyway, I'll leave that for a different thread (after I monitor the progress with the new ECM).

I guess at this point what I need to do is determine if it's my Autoxray scanner or if it's a legitimate problem. I'll take it to someone with a professional scanner and see what happens.. come to think of it, a guy I know around here used to have an 88, and he said he could never get his scan tool to see it. He mentioned something about a couple of the pins being backwards on the 88, but I just kinda laughed it off.

At least I know that my wiring hasn't necessarily been mangled to bypass my key security.

Bluevette85

Some ecm's use pin M for data instead of pin E. You also need a 10K ohm resistor between pins A+B. Call Autoxray and ask if the resistor is installed in the cable and ask them what data pin the cable is connected too.

Here a picture of the ALDL:

Tourney3p0

Excellent information here. I already emailed Autoxray and asked them which pin to use. They haven't responded yet, but it's still the weekend.

I'm sure I have a 10k ohm resistor around here somewhere.

Stingraynut

Bluevette85 - The info re “some vette’s use different pins” is very interesting, do you know any more ? like which years or why etc.

I’m wondering if the checking ‘M’ pin with a LED will work or will I damage something ?

S’nut

SuperL98

Bluevette, you jogged my memory.
The difference between the old OBD1 scanner that worked and the new OBD1&2 scanner that didn't was that the old one would flash 10k across pins A & B when you hit the scan button.
The new one didn't.
I probed the cable end while hitting the scan button to figure that out.
Didn't try to rig up any 10k to the new one.